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Current Electricity
1. The S.I. unit of power is
(a) henry
(b) coulomb
(c) watt
(d) watt-hour
Ans: c
2. Electric pressure is also called
(a) resistance
(b) power
(c) voltage
(d) energy
Ans: c
3. The substances whfch have a large
number of free electrons and offer a low
resistance are called
(a) insulators
(b) inductors
(c) semi-conductors
(d) conductors
Ans: d
4. Out of the following which is not a poor
conductor ?
(a) Cast iron
(b) Copper
(c) Carbon
(d) Tungsten
Ans: b
5. Out of the following which is an
insulating material ?
(a) Copper
(b) Gold
(c) Silver
(d) Paper
Ans: d
6. The property of a conductor due to which
it passes current is called
(a) resistance
(b) reluctance
(c) conductance
(d) inductance
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Ans: c
7. Conductance is reciprocal of
(a) resistance
(b) inductance
(c) reluctance
(d) capacitance
Ans: a
8. The resistance of a conductor varies
inversely as
(a) length
(6) area of cross-section
(c) temperature
(d) resistivity
Ans: b
9. With rise in temperature the resistance of
pure metals
(a) increases
(b) decreases
(c) first increases and then decreases
(d) remains constant
Ans: a
10. With rise in temperature the resistance of
semi-conductors
(a) decreases
(b) increases
(c) first increases and then decreases
(d) remains constant
Ans: a
11. The resistance of a copper wire 200 m
long is 21 Q. If its thickness (diameter) is
0.44 mm, its specific resistance is
around
(a) 1.2 x 10~8 Q-m
(b) 1.4 x 10~8 Q-m
(c) 1.6 x 10""8 Q-m
(d) 1.8 x 10"8 Q-m
Ans: c
12. Three resistances of 10 ohms, 15 ohms
and 30 ohms are connected in parallel.
The total resistance of the combination is
(a) 5 ohms
(b) 10 ohms
(c) 15 ohms
(d) 55 ohms
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Ans:
13. An instrument which detects electric
current is known as
(a) voltmeter
(b) rheostat
(c) wattmeter
(d) galvanometer
Ans: d
14. In a circuit a 33 Q resistor carries a
current of 2 A. The voltage across the
resistor is
(a) 33 V
(b) 66 v
(c) 80 V
(d) 132 V
Ans: b
15. A light bulb draws 300 mA when the
voltage across it is 240 V. The resistance of
the light bulb is
(a) 400 Q
(b) 600 Q
(c) 800 Q
(d) 1000 Q
Ans: c
16. The resistance of a parallel circuit
consisting of two branches is 12 ohms. If the
resistance of one branch is 18 ohms, what is
the resistance of the other ?
(a) 18 Q
(b) 36 Q
(c) 48 Q
(d) 64 Q
Ans: b
17. Four wires of same material, the same
cross-sectional area and the same length
when connected in parallel give a resistance
of 0.25 Q. If the same four wires are
connected is series the effective resistance
will be
(a) 1 Q
(b) 2 Q
(c) 3 Q
(d) 4 Q
Ans: d
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18. A current of 16 amperes divides between
two branches in parallel of resistances 8
ohms and 12 ohms
respectively. The current in each branch is
(a) 6.4 A, 6.9 A
(b) 6.4 A, 9.6 A
(c) 4.6 A, 6.9 A
(d) 4.6 A, 9.6 A
Ans: b
19. Current velocity through a copper
conductor is
(a) the same as propagation velocity of
electric energy
(b) independent of current strength
(c) of the order of a few ^.s/m
(d) nearly 3 x 108 m/s
Ans: c
20. Which of the following material has
nearly zero temperature co-efficient of
resistance?
(a) Manganin
(b) Porcelain
(c) Carbon
(d) Copper
Ans: a
21. You have to replace 1500 Q resistor in
radio. You have no 1500 Q resistor but have
several 1000 Q ones which you would
connect
(a) two in parallel
(b) two in parallel and one in series
(c) three in parallel
(d) three in series
Ans: b
22. Two resistors are said to be connected in
series when
(a) same current passes in turn through both
(b) both carry the same value of current
(c) total current equals the sum of branch
currents
(d) sum of IR drops equals the applied e.m.f.
Ans: a
23. Which of the following statement is true
both for a series and a parallel D.C. circuit?
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(a) Elements have individual currents
(b) Currents are additive
(c) Voltages are additive
(d) Power are additive
Ans: d
24. Which of the following materials has a
negative temperature co-efficient of
resistance?
(a) Copper
(b) Aluminum
(c) Carbon
(d) Brass
Ans: c
25. Ohm's law is not applicable to
(a) vacuum tubes
(b) carbon resistors
(c) high voltage circuits
(d) circuits with low current densities
Ans: a
26. Which is the best conductor of electricity
?
(a) Iron
(b) Silver
(c) Copper
(d) Carbon
Ans: b
27. For which of the following 'ampere
second' could be the unit ?
(a) Reluctance
(b) Charge
(c) Power
(d) Energy
Ans: b
28. All of the following are equivalent to
watt except
(a) (amperes) ohm
(b) joules/sec.
(c) amperes x volts
(d) amperes/volt
Ans: d
29. A resistance having rating 10 ohms,
10W is likely to be a
(a) metallic resistor
(b) carbon resistor
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(c) wire wound resistor
(d) variable resistor
Ans: c
30. Which one of the following does not
have negative temperature co-efficient ?
(a) Aluminium
(b) Paper
(c) Rubber
(d) Mica
Ans: a
31. Varistors are
(a) insulators
(6) non-linear resistors
(c) carbon resistors
(d) resistors with zero temperature
coefficient
Ans: b
32. Insulating materials have the function of
(a) preventing a short circuit between
conducting wires
(b) preventing an open circuit between the
voltage source and the load
(c) conducting very large currents
(d) storing very high currents
Ans: b
33. The rating of a fuse wire is always
expressed in
(a) ampere-hours
(b) ampere-volts
(c) kWh
(d) amperes
Ans: d
34. The minimum charge on an ion is
(a) equal to the atomic number of the atom
(b) equal to the charge of an electron
(c) equal to the charge of the number of
electrons in an atom (#) zero
Ans: b
35. In a series circuit with unequal
resistances
(a) the highest resistance has the most of the
current through it
(b) the lowest resistance has the highest
voltage drop
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(c) the lowest resistance has the highest
current
(d) the highest resistance has the highest
voltage drop
Ans: d
36. The filament of an electric bulb is made
of
(a) carbon
(b) aluminium
(c) tungsten
(d) nickel
Ans: c
37. A 3 Q resistor having 2 A current will
dissipate the power of
(a) 2 watts
(b) 4 watts
(c) 6 watts
(d) 8 watts
Ans: c
38. Which of the following statement is
true?
(a) A galvanometer with low resistance in
parallel is a voltmeter
(b) A galvanometer with high resis¬tance in
parallel is a voltmeter
(c) A galvanometer with low resistance in
series is an ammeter
(d) A galvanometer with high resis¬tance
in series is an ammeter
Ans: c
39. The resistance of a few metres of wire
conductor in closed electrical circuit is
(a) practically zero
(b) low
(c) high
(d) very high
Ans: a
40. If a parallel circuit is opened in the main
line, the current
(a) increases in the branch of the lowest
resistance
(b) increases in each branch
(c) is zero in all branches
(d) is zero in the highest resistive branch
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Ans: c
41. If a wire conductor of 0.2 ohm resistance
is doubled in length, its resistance becomes
(a) 0.4 ohm
(b) 0.6 ohm
(c) 0.8 ohm
(d) 1.0 ohm
Ans: a
42. Three 60 W bulbs are in parallel across
the 60 V power line. If one bulb burns open
(a) there will be heavy current in the main
line
(b) rest of the two bulbs will not light
(c) all three bulbs will light
(d) the other two bulbs will light
Ans: d
43. The four bulbs of 40 W each are
connected in series wifti a battery across
them, which of the following statement is
true ?
(a) The current through each bulb in same
(b) The voltage across each bulb is not same
(c) The power dissipation in each bulb is not
same
(d) None of the above
Ans: a
44. Two resistances Rl and Ri are connected
in series across the voltage source where
R2>Ri. The largest drop
will be across
(a) R2
(b) Ri
(c) either Rl or Rz
(d) none of them
Ans: a
45. What will be energy used by the battery
if the battery has to drive 6.28 x 1018
electrons with potential difference of 20 V
across the terminal ?
(a) 5 joules
(b) 10 joules
(c) 15 joules
(d) 20 joules
Ans:
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46. A closed switch has a resistance of
(a) zero
(b) about 50 ohms
(c) about 500 ohms
(d) infinity
Ans: a
47. The hot resistance of the bulb's
fila¬ment is higher than its cold resistance
because the temperature co-efficient of the
filament is
(a) zero
(b) negative
(c) positive
(d) about 2 ohms per degree
Ans: c
48. Heat in a conductor is produced on the
passage of electric current due to
(a) reactance
(b) capacitance
(c) impedance
(d) resistance
Ans:
49. The insulation on a current carrying
conductor is provided
(a) to prevent leakage of current
(b) to prevent shock
(c) both of above factors
(d) none of above factors
Ans: c
50. The thickness of insulation provided on
the conductor depends on
(a) the magnitude of voltage on the conductor
(b) the magnitude of current flowing through
it
(c) both (a) and (b)
(d) none of the above
Ans: a
51. Which of the following quantities
remain the same in all parts of a series
circuit ?
(a) Voltage
(b) Current
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(c) Power
(d) Resistance
Ans: b
52. A 40 W bulb is connected in series with
a room heater. If now 40 W bulb is replaced
by 100 W bulb, the heater output will
(a) decrease
(b) increase
(c) remain same
(d) heater will burn out
Ans: b
53. In an electric kettle water boils in 10m
minutes. It is required to boil the boiler in 15
minutes, using same supply mains
(a) length of heating element should be
decreased
(b) length of heating element should be
increased
(c) length of heating element has no effect
on heating if water
(d) none of the above
Ans: a
54. An electric filament bulb can be worked
from
(a) D.C. supply only
(b) A.C. supply only
(c) Battery supply only
(d) All above
Ans: d
55. Resistance of a tungsten lamp as applied
voltage increases
(a) decreases
(b) increases
(c) remains same
(d) none of the above
Ans: b
56. Electric current passing through the
circuit produces
(a) magnetic effect
(b) luminous effect
(c) thermal effect
(d) chemical effect
(e) all above effects
Ans: c
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57. Resistance of a material always
decreases if
(a) temperature of material is decreased
(6) temperature of material is increased
(c) number of free electrons available
become more
(d) none of the above is correct
Ans: c
58. If the efficiency of a machine is to be
high, what should be low ?
(a) Input power
(b) Losses
(c) True component of power
(d) kWh consumed
(e) Ratio of output to input
Ans: b
59. When electric current passes through a
metallic conductor, its temperature rises.
This is due to
(a) collisions between conduction
electrons and atoms
(b) the release of conduction electrons from
parent atoms
(c) mutual collisions between metal atoms
(d) mutual collisions between conducting
electrons
Ans: a
60. Two bulbs of 500 W and 200 W rated at
250 V will have resistance ratio as
(a) 4 : 25
(b) 25 : 4
(c) 2 : 5
(d) 5 : 2
Ans: c
61. A glass rod when rubbed with silk cloth
is charged because
(a) it takes in proton
(b) its atoms are removed
(c) it gives away electrons
(d) it gives away positive charge
Ans: c
62. Whether circuit may be AC. or D.C. one,
following is most effective in reducing the
magnitude of the current.
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(a) Reactor
(b) Capacitor
(c) Inductor
(d) Resistor
Ans: d
63. It becomes more difficult to remove
(a) any electron from the orbit
(6) first electron from the orbit
(c) second electron from the orbit
(d) third electron from the orbit
Ans: d
64. When one leg of parallel circuit is
opened out the total current will
(a) reduce
(b) increase
(c) decrease
(d) become zero
Ans: c
65. In a lamp load when more than one lamp
are switched on the total resistance of the
load
(a) increases
(b) decreases
(c) remains same
(d) none of the above
Ans: b
66. Two lamps 100 W and 40 W are
connected in series across 230 V
(alternating).
Which of the following statement is correct
?
(a) 100 W lamp will glow brighter
(b) 40 W lamp will glow brighter
(c) Both lamps will glow equally bright
(d) 40 W lamp will fuse
Ans: b
67. Resistance of 220 V, 100 W lamp will
be
(a) 4.84 Q
(b) 48.4 Q
(c) 484 ft
(d) 4840 Q
Ans: c
68. In the case of direct current
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(a) magnitude and direction of current
remains constant
(b) magnitude and direction of current
changes with time
(c) magnitude of current changes with time
(d) magnitude of current remains con¬stant
Ans: a
69. When electric current passes through a
bucket full of water, lot of bubbling is
observed. This suggests that the type of
supply is
(a) A.C.
(b) D.C.
(c) any of above two
(d) none of the above
Ans: b
70. Resistance of carbon filament lamp as
the applied voltage increases.
(a) increases
(b) decreases
(c) remains same
(d) none of the above
Ans: b
71. Bulbs in street lighting are all connected
in
(a) parallel
(b) series
(c) series-parallel
(d) end-to-end
Ans: a
72. For testing appliances, the wattage of
test lamp should be
(a) very low
(b) low
(c) high
(d) any value
Ans: c
73. Switching of a lamp in house produces
noise in the radio. This is because switching
operation produces
(a) arcs across separating contacts
(b) mechanical noise of high intensity
(c) both mechanical noise and arc be¬tween
contacts
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(d) none of the above
Ans: a
74. Sparking occurs when a load is switched
off because the circuit has high
(a) resistance
(b) inductance
(c) capacitance
(d) impedance
Ans: b
75. Copper wire of certain length and
resistance is drawn out to three times its
length without change in volume, the new
resistance of wire becomes
(a) 1/9 times
(b) 3 times
(e) 9 times
(d) unchanged
Ans: c
76. When resistance element of a heater
fuses and then we reconnect it after
removing a portion of it, the power of the
heater will
(a) decrease
(b) increase
(c) remain constant
(d) none of the above
Ans: b
77. A field of force can exist only between
(a) two molecules
(b) two ions
(c) two atoms
(d) two metal particles
Ans: b
78. A substance whose molecules consist of
dissimilar atoms is called
(a) semi-conductor
(b) super-conducto
(c) compound
(d) insulator
Ans: c
79. International ohm is defined in terms of
the resistance of
(a) a column of mercury
(b) a cube of carbon
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(c) a cube of copper
(d) the unit length of wire
Ans: a
80. Three identical resistors are first
connected in parallel and then in series.
The resultant resistance of the first
combination to the second will be
(a) 9 times
(b) 1/9 times
(c) 1/3 times
(d) 3 times
Ans: b
91. Which method can be used for absolute
measurement of resistances ?
(a) Lorentz method
(b) Releigh method
(c) Ohm's law method
(d) Wheatstone bridge method
Ans: d
92. Three 6 ohm resistors are connected to
form a triangle. What is the resistance
between any two corners ?
(a) 3/2 Q
(b 6 Q
(c) 4 Q
(d) 8/3 Q
Ans: c
93. Ohm's law is not applicable to
(a) semi-conductors
(b) D.C. circuits
(c) small resistors
(d) high currents
Ans: a
94. Two copper conductors have equal
length. The cross-sectional area of one
conductor is four times that of the other. If
the conductor having smaller cross-sectional
area has a resistance of 40 ohms the
resistance of other conductor will be
(a) 160 ohms
(b) 80 ohms
(c) 20 ohms
(d) 10 ohms
Ans: d
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95. A nichrome wire used as a heater coil
has the resistance of 2 £2/m. For a heater of
1 kW at 200 V, the length of wire required
will be
(a) 80 m
(b) 60 m
(c) 40 m
(d) 20 m
Ans: a
96. Temperature co-efficient of resistance is
expressed in terms of
(a) ohms/°C
(b) mhos/ohm°C
(e) ohms/ohm°C
(d) mhos/°C
Ans: c
97. Which of the following materials has the
least resistivity ?
(a) Zinc
(b) Lead
(c) Mercury
(d) Copper
Ans:
98. When current flows through heater coil
it glows but supply wiring does not glow
because
(a) current through supply line flows at
slower speed
(b) supply wiring is covered with
in¬sulation layer
(c) resistance of heater coil is more than the
supply wires
(d) supply wires are made of superior
material
Ans: c
99. The condition for the validity under
Ohm's law is that
(a) resistance must be uniform
(b) current should be proportional to the size
of the resistance
(c) resistance must be wire wound type
(d) temperature at positive end should be
more than the temperature at negative end
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Ans: a
100. Which of the following statement is
correct ?
(a) A semi-conductor is a material whose
conductivity is same as be¬tween that of a
conductor and an insulator
(b) A semi-conductor is a material which
has conductivity having average value of
conductivity of metal and insulator
(c) A semi-conductor is one which
con¬ducts only half of the applied voltage
(d) A semi-conductor is a material made
of alternate layers of conducting material
and insulator
Ans: a
101. A rheostat differs from potentiometer
in the respect that it
(a) has lower wantage rating
(b) has higher wattage rating
(c) has large number of turns
(d) offers large number of tappings
Ans: b
102. The weight of an aluminium conductor
as compared to a copper conductor of
identical cross-section, for the same
electrical resistance, is
(a) 50%
(b) 60%
(c) 100%
(d) 150%
Ans: a
103. An open resistor, when checked with
an ohm-meter reads
(a) zero
(b) infinite
(c) high but within tolerance
(d) low but not zero
Ans: b
104. are the materials having electrical
conductivity much less than most of the
metals but much greater than that of typical
insulators.
(a) Varistors
(b) Thermistor
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(c) Semi-conductors
(d) Variable resistors
Ans: c
105. All good conductors have high
(a) conductance
(b) resistance
(c) reluctance
(d) thermal conductivity
Ans: a
106. Voltage dependent resistors are usually
made from
(a) charcoal
(b) silicon carbide
(c) nichrome
(d) graphite
Ans: c
107. Voltage dependent resistors are used
(a) for inductive circuits
(6) to supress surges
(c) as heating elements
(d) as current stabilizers
Ans: b
108. The ratio of mass of proton to that of
electron is nearly
(a) 1840
(b) 1840
(c) 30
(d) 4
Ans: a
109. The number of electrons in the outer
most orbit of carbon atom is
(a) 3
(b) 4
(c) 6
(d) 7
Ans: b
110. With three resistances connected in
parallel, if each dissipates 20 W the total
power supplied by the voltage source equals
(a) 10 W
(b) 20 W
(c) 40 W
(d) 60 W
Ans: d
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111. A thermistor has
(a) positive temperature coefficient
(b) negative temperature coefficient
(c) zero temperature coefficient
(d) variable temperature coefficient
Ans: c
112. If/, R and t are the current, resistance
and time respectively, then according to
Joule's law heat produced will be
proportional to
(a) I2Rt
(b) I2Rf
(c) I2R2t
(d) I2R2t*
Ans: a
113. Nichrome wire is an alloy of
(a) lead and zinc
(b) chromium and vanadium
(c) nickel and chromium
(d) copper and silver
Ans: c
114. When a voltage of one volt is applied, a
circuit allows one microampere current to
flow through it. The conductance of the
circuit is
(a) 1 n-mho
(b) 106 mho
(c) 1 milli-mho
(d) none of the above
Ans: a
115. Which of the following can have
negative temperature coefficient ?
(a) Compounds of silver
(6) Liquid metals
(c) Metallic alloys
(d) Electrolytes
Ans: d
116. Conductance : mho ::
(a) resistance : ohm
(b) capacitance : henry
(c) inductance : farad
(d) lumen : steradian
Ans: a
117. 1 angstrom is equal to
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(a) 10-8 mm
(6) 10"6 cm
(c) 10"10 m
(d) 10~14 m
Ans: c
118. One newton metre is same as
(a) one watt
(b) one joule
(c) five joules
(d) one joule second
Ans: b
Network Theorems
1. Kirchhoff s current law states that
(a) net current flow at the junction is
positive
(b) Hebraic sum of the currents meeting at
the junction is zero
(c) no curreht can leave the junction without
some current entering it.
(d) total sum of currents meeting at the
junction is zero
Ans: b
2. According to Kirchhoffs voltage law, the
algebraic sum of all IR drops and e.m.fs. in
any closed loop of a network is always
(a) negative
(b) positive
(c) determined by battery e.m.fs.
(d) zero
Ans: d
3. Kirchhoffs current law is applicable to
only
(a) junction in a network
(b) closed loops in a network
(c) electric circuits
(d) electronic circuits
Ans: a
4. Kirchhoffs voltage law is related to
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(a) junction currents
(b) battery e.m.fs.
(c) IR drops
(d) both (b) and (c)
(e) none of the above
Ans: d
5. Superposition theorem can be applied
only to circuits having
(a) resistive elements
(b) passive elements
(c) non-linear elements
(d) linear bilateral elements
Ans: d
6. The concept on which Superposition
theorem is based is
(a) reciprocity
(b) duality
(c) non-linearity
(d) linearity
Ans: d
7. Thevenin resistance Rth is found
(a) by removing voltage sources along with
their internal resistances
(6) by short-circuiting the given two
terminals
(c) between any two 'open' terminals
(d) between same open terminals as for Etk
Ans: d
8. An ideal voltage source should have
(a) large value of e.m.f.
(b) small value of e.m.f.
(c) zero source resistance
(d) infinite source resistance
Ans: c
9. For a voltage source
(a) terminal voltage is always lower than
source e.m.f.
(b) terminal voltage cannot be higher than
source e.m.f.
(c) the source e.m.f. and terminal voltage are
equal
Ans: b
10. To determine the polarity of the voltage
drop across a resistor, it is necessary to
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know
(a) value of current through the resistor
(b) direction of current through the
resistor
(c) value of resistor
(d) e.m.fs. in the circuit
Ans: b
11. "Maximum power output is obtained
from a network when the load resistance is
equal to the output resistance of the network
as seen from the terminals of the load". The
above statement is associated with
(a) Millman's theorem
(b) Thevenin's theorem
(c) Superposition theorem
(d) Maximum power transfer theorem
Ans: d
12. "Any number of current sources in
parallel may be replaced by a single current
source whose current is the algebraic sum of
individual source currents and source
resistance is the parallel combination of
individual
source resistances".
The above statement is associated with
(a) Thevenin's theorem
(b) Millman's theorem
(c) Maximum power transfer theorem
(d) None of the above
Ans: b
13. "In any linear bilateral network, if a
source of e.m.f. E in any branch produces a
current I in any other
branch, then same e.m.f. acting in the
second branch would produce the same
current / in the first branch".
The above statement is associated with
(a) compensation theorem
(b) superposition theorem
(c) reciprocity theorem
(d) none of the above
Ans: c
14. Which of the following is non-linear
circuit parameter ?
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(a) Inductance
(b) Condenser
(c) Wire wound resistor
(d) Transistor
Ans: a
15. A capacitor is generally a
(a) bilateral and active component
(b) active, passive, linear and nonlinear
component
(c) linear and bilateral component
(d) non-linear and active component
Ans: c
16. "In any network containing more than
one sources of e.m.f. the current in any
branch is the algebraic sum of a number of
individual fictitious currents (the number
being equal to the number of sources of
e.m.f.), each of which is due to separate
action of each source of e.m.f., taken in
order, when the remaining sources of e.m.f.
are replaced by conductors, the resistances
of which are equal to the internal resistances
of the respective sources".
The above statement is associated with
(a) Thevenin's theorem
(b) Norton's theorem
(c) Superposition theorem
(d) None of the above
Ans: c
17. Kirchhoff s law is applicable to
(a) passive networks only
(b) a.c. circuits only
(c) d.c. circuits only
(d) both a.c. as well d.c. circuits
Ans: d
18. Kirchhoff s law is not applicable to
circuits with
(a) lumped parameters
(b) passive elements
(c) distributed parameters
(d) non-linear resistances
Ans: c
19. Kirchhoff s voltage law applies to
circuits with
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(a) nonlinear elements only
(b) linear elements only
(c) linear, non-linear, active and passive
elements
(d) linear, non-linear, active, passive, time
varying as wells as time-in-variant elements
Ans: d
20. The resistance LM will be
(a) 6.66 Q
(b) 12 Q
(c) 18Q
(d) 20Q
Ans: a
21. For high efficiency of transfer of power,
internal resistance of the source should be
(a) equal to the load resistance
(b) less than the load resistance
(c) more than the load resistance
(d) none of the above
Ans: b
22. Efficiency of power transfer when
maximum transfer of power c xurs is
(a) 100%
(b) 80%
(c) 75%
(d) 50%
Ans: d
23. If resistance across LM in Fig. 2.30 is 15
ohms, the value of R is
(a) 10 Q
(6) 20 Q
(c) 30 Q
(d) 40 Q
Ans: c
24. For maximum transfer of power, internal
resistance of the source should be
(a) equal to load resistance
(b) less than the load resistance
(c) greater than the load resistance
(d) none of the above
Ans: a
25. If the energy is supplied from a source,
whose resistance is 1 ohm, to a load of 100
ohms the source will be
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(a) a voltage source
(b) a current source
(c) both of above
(d) none of the above
Ans: a
26. The circuit whose properties are same in
either direction is known as
(a) unilateral circuit
(b) bilateral circuit
(c) irreversible circuit
(d) reversible circuit
Ans: b
27. In a series parallel circuit, any two
resistances in the same current path must be
in
(a) series with each other
(b) parallel with each other
(c) series with the voltage source.'
(d) parallel with the voltage source
Ans: a
28. The circuit has resistors, capacitors and
semi-conductor diodes. The circuit will be
known as
(a) non-linear circuit
(b) linear circuit
(c) bilateral circuit
(d) none of the above
Ans: a
29. A non-linear network does not satisfy
(a) superposition condition
(b) homogeneity condition
(c) both homogeneity as well as
superposition condition
(d) homogeneity, superposition and
associative condition
Ans: c
30. An ideal voltage source has
(a) zero internal resistance
(b) open circuit voltage equal to the voltage
on full load
(c) terminal voltage in proportion to
current
(d) terminal voltage in proportion to load
Ans: a
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31. A network which contains one or more
than one source of e.m.f. is known as
(a) linear network
(b) non-linear network
(c) passive network
(d) active network
Ans: c
32. The superposition theorem is applicable
to
(a) linear, non-linear and time variant
responses
(b) linear and non-linear resistors only
(c) linear responses only
(d) none of the above
Ans: c
33. Which of the following is not a
nonlinear element ?
(a) Gas diode
(b) Heater coil
(c) Tunnel diode
(d) Electric arc
Ans:
34. Application of Norton's theorem to a
circuit yields
(a) equivalent current source and
impedance in series
(6) equivalent current source and
impedance in parallel
(c) equivalent impedance
(d) equivalent current source
Ans: a
35. Millman's theorem yields
(a) equivalent resistance
(6) equivalent impedance
(c) equivalent voltage source
(d) equivalent voltage or current source
Ans: d
36. The superposition theorem is applicable
to
(a) voltage only
(b) current "only
(c) both current and voltage
(d) current voltage and power
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Ans: d
37. Between the branch voltages of a loop
the Kirchhoff s voltage law imposes
(a) non-linear constraints
(b) linear constraints
(c) no constraints
(d) none of the above
Ans: b
38. A passive network is one which contains
(a) only variable resistances
(b) only some sources of e.m.f. in it
(c) only two sources of e.m.f. in it
(d) no source of e.m.f. in it
Ans: d
39. A terminal where three on more
branches meet is known as
(a) node
(b) terminus
(c) combination
(d) anode
Ans: a
40. Which of the following is the passive
element ?
(a) Capacitance
(b) Ideal current source
(c) Ideal voltage source
(d) All of the above
Ans: a
41. Which of the following is a bilateral
element ?
(a) Constant current source
(b) Constant voltage source
(c) Capacitance
(d) None of the above
Ans: c
42. A closed path made by several branches
of the network is known as
(a) branch
(b) loop
(c) circuit
(d) junction
Ans: b
43. A linear resistor having 0 < R < °o is a
(a) current controlled resistor
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(6) voltage controlled resistor
(c) both current controlled and voltage
controlled resistor
(d) none of the above
Ans: c
44. A star circuit has element of resistance
R/2. The equivalent delta elements will be
(a) R/6
(b) fi?
(c) 2R
(d) 4R
Ans: b
45. A delta circuit has each element of value
R/2. The equivalent elements of star circuit
with be
(a) RIG
(b) R/3
(c) 2R
(d) 3R
Ans: a
46. In Thevenin's theorem, to find Z
(a) all independent current sources are short
circuited and independent voltage sources
are open circuited
(b) all independent voltage sources are open
circuited and all independent current sources
are short circuited
(c) all independent voltage and current
sources are short circuited
(d) all independent voltage sources are short
circuited and all independent current sources
are open circuited
Ans: d
47. While calculating Rth in Thevenin's
theorem and Norton equivalent
(a) all independent sources are made dead
(b) only current sources are made dead
(c) only voltage sources are made dead
(d) all voltage and current sources are made
dead
Ans: a
48. The number of independent equations
to solve a network is equal to
(a) the number of chords
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(b) the number of branches
(c) sum of the number of branches and
chords
(d) sum of number of branches, chords and
nodes
Ans: a
49. The superposition theorem requires as
many circuits to be solved as there are
(a) sources, nodes and meshes
(b) sources and nodes
(c) sources
(d) nodes
Ans: c
50. Choose the incorrect statement.
(a) A branch formed by the parallel
connection of any resistor R and open circuit
has the characteristic of an open circuit.
(b) A branch formed by the parallel
connection of any resistor R and a short
circuit has the characteristic of a short
circuit.
(c) A branch formed by the series
connection of any resistor R and an open
circuit has the characteristic of an open
circuit.
(d) A branch formed by the series
connection of any resistor R and a short
circuit has the characteristic of resistor R.
Ans: a
Electrostatics
1. The force between two charges is 120 N.
If the distance between the charges is
doubled, the force will be
(a) 60 N
(b) 30 N
(c) 40 N
(d) 15 N
Ans: b
2. The electric field intensity at a point
situated 4 metres from a point charge is 200
N/C. If the distance is reduced to 2 metres,
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the field intensity will be
(a) 400 N/C
(b) 600 N/C
(c) 800 N/C
(d) 1200 N/C
Ans: c
3. The lines of force due to charged particles
are
(a) always straight
(b) always curved
(c) sometimes curved
(d) none of the above
Ans: b
4. The electric field at a point situated at a
distance d from straight charged conductor
is
(a) proportional to d
(b) inversely proportional to d
(c) inversely proportional to d
(d) none of the above
Ans: b
5. The direction of electric field due +0
positive charge is .
(a) away from the charge
(b) towards the charge
(c) both (a) and (6)
(d) none of the above
Ans: a
6. A field line and an equipotential surface
are
(a) always parallel
(b) always at 90°
(c) inclined at any angle 0
(d) none of the above
Ans: b
7. The ability of charged bodies to exert
force on 6ne another is attributed to the
existence of
(a) electrons
(b) protons
(c) neutrons
(d) electric field
Ans: d
8. If the sheet of a bakelite is inserted
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between the plates of an air capacitor, the
capacitance will
(a) decrease
(b) increase
(c) remains unchanged
(d) become zero
Ans: b
9. A capacitor stores 0.24 coulombs at 10
volts. Its capacitance is
(a) 0.024 F
(b) 0.12 F
(c) 0.6 F
(d) 0.8 F
Ans: a
10. For making a capacitor, it is better to
select a dielectric having
(a) low permittivity
(b) high permittivity
(c) permittivity same as that of air
(d) permittivity slightly more than that of air
Ans: b
11. The units of capacitance are
(a) volts/coulomb
(b) coulombs/volt
(c) ohms
(d) henry/Wb
Ans: b
12. If three 15 uF capacitors are connected
in series, the net capacitance is
(a) 5 uF
(6) 30 uF
(c) 45 uF
(d) 50 uF
Ans: a
13. If three 10 uF capacitors are connected
in parallel, the net cararitance is
(a) 20 uF
(b) 30 uE
(c) 40 uF
(d) 50 uF
Ans: b
14. A dielectric material must be
(a) resistor
(b) insulator
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(c) good conductor
(d) semi conductor
Ans: b
15. An electrolytic capacitor can be used for
(a) D.C. only
(b) AC. only
(c) both D.C. as well as A.C.
Ans: a
16. The capacitance of a capacitor is not
affected by
(a) distance between plates
(6) area of plates
(c) thickness of plates
(d) all of the above
Ans: c
17. Which of the following is not a vector ?
(a) Linear momentum
(b) Angular momentum
(c) Electric field
(d) Electric potential
Ans: b
18. Two plates of a parallel plate capacitor
after being charged from a constant voltage
source are separated apart by means of
insulated handles, then the
(a) Voltage across the plates increases
(b) voltage across the plates decreases
(c) charge on the capacitor decreases
(d) charge on the capacitor increases
Ans: b
19. If A.C. voltage is applied to capacitive
circuit, the alternating current can flow in
the circuit because
(a) varying voltage produces the charg¬ing
and dicharging currents
(b) of high peak value
(c) charging current can flow
(d) discharge current can flow
Ans: a
20. Voltage applied across a ceramic
dielectric produces an electrolytic field 100
times greater than air. What will be the
value of dielectric constant ?
(a) 50
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(6) 100
(c) 150
(d) 200
Ans: b
21. Which of the following statements is
correct ?
(a) Air capacitors have a blackband to
indicate the outside foil
(6) Electrolytic capacitor must be
con¬nected in the correct polarity
(c) Ceramic capacitors must be con¬nected
in the correct polarity
(d) Mica capacitors are available in
capacitance value of 1 to 10 pF
Ans: b
22. The dissipation factor of a good
dielectric is of the order of
(a) 0.0002
(b) 0.002
(c) 0.02
(d) 0.2
Ans: a
23. "The total electric flux through any
closed surface surrounding charges is equal
to the amount oflcharge enclosed".
The above statement is associated with
(a) Coulomb's square law
(b) Gauss's law
(c) Maxwell's first law
(d) Maxwell's second law
Ans: b
24. Three capacitors each of the capacity C
are given. The resultant capacity 2/3 C
can be obtained by using them
(a) all in series
(b) all in parallel
(c) two in parallel and third in series with
this combination
(d) two in series and third in parallel across
this combination
Ans: c
25. For which of the following parameter
variation, the capacitance of the capacitor
remains unaffected ?
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(a) Distance between plates
(b) Area of the plates
(c) Nature of dielectric
(d) Thickness of the plates
Ans: d
26. Which of the following statement is true
?
(a) The current in the discharging capacitor
grows linearly
(b) The current in the dicharging capacitor
grows exponentially
(c) The current in the discharging capacitor
decays exponentially
(d) The current in the discharging capacitor
decreases constantly
Ans: b
27. Which of the following expression is
correct for electric field strength ?
(a) E = D/E
(b) E = D2/t
(c) E = jtD
(d) E= nD2
Ans: a
28. In a capacitor the electric charge is
stored in
(a) metal plates
(b) dielectric
(c) both (a) and (6)
(d) none of the above
Ans: b
29. Which of the following materials has the
highest value of dielectric constant?
(a) Glass
(b) Vacuum
(c) Ceramics
(d) Oil
Ans: c
30. Which of the following capacitors will
have the least variation ?
(a) Paper capacitor
(b) Ceramic capacitor
(c) Silver plated mica capacitor
(d) None of the above
Ans: c
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31. Which of the following statements is
incorrect ?
(a) The leakage resistance of ceramic
capacitors is generally high
(b) The stored energy in a capacitor
decreases with reduction in value of
capacitance
(c) The stored energy in a capacitor
increases with applied voltage
(d) A wire cable has distributed capacitance
between the conductors
Ans: b
32. Which of the following capacitors has
relatively shorter shelf life ?
(a) Mica capacitor
(b) Electrolytic capacitor
(c) Ceramic capacitor
(d) Paper capacitor
Ans: b
33. The sparking between two electrical
contacts can be reduced by inserting a
(a) capacitor in parallel with contacts
(6) capacitor in series with each contact
(c) resistance in line
(d) none of the above
Ans: a
34. In the case of a lossy capacitor, its series
equivalent resistance value will be
(a) small
(b) very small
(c) large
(d) zero
Ans: c
35. The power dissipated in a pure capacitor
is
(a) zero
(6) proportional to applied voltage
(c) proportional to value of capacitance
(d) both (b) and (c) above
Ans: a
36. In a capacitive circuit
(a) a steady value of applied voltage causes
discharge
(b) an increase in applied voltage makes a
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capacitor charge
(c) decrease in applied voltage makes a
capacitor charge
(d) none of the above
Ans: b
37. When a dielectric slab is introduced in a
parallel plate capacitor, the potential
difference between plates will
(a) remain uncharged
(b) decrease
(c) increase
(d) become zero
Ans: b
38. Capacitance increases with
(a) increase in plate area and decrease in
distance between the plates
(b) increase in plate area and distance
between the plates
(c) decrease in plate area and value of
applied voltage
(d) reduction in plate area and distance
between the plates
Ans: a
39. A capacitor consists of
(a) two insulators separated by a con¬ductor
(b) two conductors separated by an
in¬sulator
(c) two insulators only
(d) two conductors only
Ans: b
40. A gang condenser is a
(a) polarised capacitor
(6) variable capacitor
(c) ceramic capacitor
(d) none of the above
Ans:
41. A paper capacitor is usually available in
the form of
(a) tubes
(b) rolled foil
(c) disc
(d) meshed plates
Ans: b
42. Air capacitors are generally available in
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the range
(a) 10 to 400 pF
(b) 1 to 20 pF
(c) 100 to 900 pF
(d) 20 to 100 pF
Ans: a
43. The unit of capacitance is
(a) henry
(b) ohm
(c) farad
(d) farad/m
Ans: c
44. A capacitor charged to 200 V has 2000
(iC of charge. The value of capacitance will
be
(a) 10 F
(6) 10 uF
(c) 100 nF
(d) 1000 uF
Ans: b
45. A capacitor in a circuit became hot and
ultimately exploded due to wrong
con¬nections, which type of capacitor it
could be ?
(a) Paper capacitor
(b) Ceramic capacitor
(c) Electrolytic capacitor
(d) Any-of the above
Ans: c
46. Energy stored in the electric field of a
capacitor C when charged from a D.C
source of voltage V is equal to joules
(a) CV2
(b) C2V
(c) CV2
(d) CV
Ans: a
47. The absolute permittivity of free space is
given by
(a) 8.854 x 1(T9 F/m)
(6) 8.854 x 1(T10 F/m)
(c) 8.854 x KT11 F/m
(d) 8.854 x 10"12 F/m
Ans: b
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48. The relative permittivity of free space is
given by
(a) 1
(b) 10
(c) 100
(d) 1000
Ans: a
49. Electric field intensity is a quantity
(a) scalar
(b) vector
(c) both (a) and (6)
(d) none of the above
Ans: b
50. When 4 volts e.m.f. is applied across a 1
farad capacitor, it will store energy of
(a) 2 joules
(b) 4 joules
(c) 6 joules
(d) 8 joules
Ans: d
51. The capacitor preferred for high
frequency circuits is
(a) air capacitor
(b) mica capacitor
(c) electrolytic capacitor
(d) none of the above
Ans: b
52. The capacity of capacitor bank used in
power factor correction is expressed in terms
of
(a) kW
(b) kVA
(c) kVAR
(d) volts
Ans: c
53. While testing a capacitor with ohmmetre, if the capacitor shows charging, but
the final resistance reading is appreciably
less than normal, it can be concluded that
the capacitor is
(a) short-circuited
(b) open circuited
(c) alright
(d) leaky
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Ans: d
54. If a 6 (iF capacitor is charged to 200 V,
the charge in coulombs will be
(a) 800 uC
(b) 900 uC
(c) 1200 uC
(d) 1600 uC
Ans: c
55. Which capacitor will be physically
smaller for the same ratings ?
(a) Ceramic capacitor
(b) Paper capacitor
(c) Both will be of equal size
(d) None of the above
Ans: a
56. What is the value of capacitance that
must be connected in parallel with 50 pF
condenser to make an equivalent
capacitance of 150 pF ?
(a) 50 pF
(b) 100 pF
(c) 150 pF
(d) 200 pF
Ans: b
57. A mica capacitor and a ceramic
capacitor both have the same physical
dimensions. Which will have more value of
capacitance ?
(a) Ceramic capacitor
(b) Mica capacitor
(c) Both will have identical value of
capacitance
(d) It depends on applied voltage
Ans: a
58. Which of the following material has
least value of dielectric constant ?
(a) Ceramics
(b) Oil
(c) Glass
(d) Paper
Ans: b
59. Which of the following capacitors will
have the least value of breakdown voltage ?
(a) Mica
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(b) Paper
(c) Ceramic
(d) Electrolytic
Ans: d
3.73. The breakdown voltage for paper
capacitors is usually
(a) 20 to 60 volts
(b) 200 to 1600 volts
(c) 2000 to 3000 volts
(d) more than 10000 volts
Ans:
60. Dielectric constant for mica is nearly
(a) 200
(b) 100
(c) 3 to 8
(d) 1 to 2
Ans: c
61. The value of dielectric constant for
vacuum is taken as
(a) zero
(b) 1
(c) 4
(d) 10
Ans: b
62. Which of the following capacitors is
marked for polarity ?
(a) Air
(b) Paper
(c) Mica
(d) Electrolytic
Ans: d
63. Which of the following capacitors can be
used for temperature compensation ?
(a) Air capacitor
(b) Ceramic capacitor
(c) Paper capacitor
(d) None of the above
Ans: b
64. Which of the following statements is
incorrect ?
(a) The thinner the dielectric, the more the
capacitance and the lower the voltage
breakdown rating for a capacitor .
(b) A six dot mica capacitor colour coded
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white, green, black, red and yellow has the
capacitance value of 500 pF
(c) Capacitors in series provide less
capacitance but a higher voltage breakdown
rating for the combina¬tion
(d) A capacitor can store charge be¬cause it
has a dielectric between two conductors
Ans: b
65. Paper capacitors usually have a tolerance
of
(a) ± 5%
(b) ± 10%
(c) ± 15%
(d) ± 20%
Ans: b
66. For closer tolerances which of the
following capacitors is usually preferred ?
(a) Paper capacitor
(b) Mica capacitor
(c) Ceramic disc capacitor
(d) None of the above
Ans: b
67. The electrostatic force between two
charges of one coulomb each and placed at a
distance of 0.5 m will be
(a) 36 x 10fa
(b) 36 x 107 N
(c) 36 x 108 N
(d) 36 x 109 N
Ans: d
68. The units of volume charge density are
(a) Coulomb/metre
(b) Coulomb/metre
(c) Coulomb/metre
(d) Coulomb/metre
Ans: c
69. "The surface integral of the normal
component of the electric displacement D
over any closed surface equals the charge
enclosed by the surface".
The above statement is associated with
(a) Gauss's law
(b) Kirchhoff s law
(c) Faraday's law
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(d) Lenz's law
Ans: a
70. Dielectric strength of mica is
(a) 10 to 20 kV/mm
(6) 30 to 50 kV/mm
(c) 50 to 200 kV/mm
(d) 300 to 500 kV/mm
Ans: c
71. The dielectric constant (relative
permittivity) of glass is given by
(a) 0.1 to 0.4
(b) 0.5 to 1.0
(c) 2.0 to 4.0
(d) 5 to 100
Ans: d
72 capacitors are mainly used for radio
frequency tuning.
(a) Paper
(b) Air
(c) Mica
(d) Electrolytic
Ans: b
73. capacitors can be used only for D.C.
(a) Air
(b) Paper
(e) Mica
(d) Electrolytic
Ans: d
74. capacitors are used in transistor circuits.
(a) Ceramic
(b) Paper
(c) Air
(d) Electrolytic
Ans: a
75. capacitors are used for audio frequency
and radio frequency coupling and tuning.
(a) Air
(b) Mica
(c) Plastic film
(d) Ceramic
Ans: b
76. The inverse of capacitance is called
(a) reluctance
(b) conductance
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(c) susceptance
(d) elastance
Ans: d
77. When the dielectric is homogeneous,the
potential gradient is
(a) uniform
(b) non-uniform
(c) zero
(d) any of the above
Ans: a
78. The potential gradient across the
material of low permittivity is than across
the material of high permittivity.
(a) smaller
(b) greater
(c) both (a) and (b)
(d) none of the above
Ans: b
79. ________field is associated with the
capacitor.
(a) Electric
(b) Magnetic
(c) Both (a) and (b)
(d) None of the above
Ans: a
80. A capacitor having capacitance of 5 uF
is charged to a potential difference of 10,000
V. The energy stored in the capacitor is
(a) 50 joules
(b) 150 joules
(c) 200 joules
(d) 250 joules
Ans: d
81. A single core cable used on 33000 V has
conductor diameter 10 mm and the in¬ternal
diameter of sheath 25 mm. The maximum
electrostatic stress in the cable is
(a) 62 x 105 V/m
(b) 72 x 105 V/m
(c) 82 x 105 V/m
(d) 92 x 105 V/m
Ans: b
82. Two infinite parallel plates 10 mm apart
have maintained between them a potential
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difference of 100 V. The acceleration of an
electron placed between them is
(a) 0.56 x 1015 m/s2
(b) 1.5 x 1015 m/s2
(c) 1.6 x 1015 m/s2
(d) 1.76 x 1015 m/s2
Ans: d
83. The total deficiency or excess of
electrons in a body is known as
(a) current
(b) voltage
(c) potential gradient
(d) charge
Ans: d
84. The relative permittivity has the
following units
(a) F/m
(b) m/F
(c) Wb/m
(d) no units
Ans: c
85. The phenomenon of an uncharged body
getting charged merely by the nearness of a
charged body is known as
(a) pholoelectric effect
(b) chemical effect
(c) magnetic effect
(d) induction
Ans: d
86. A unit tube of flux is known as tube
(a) Newton
(b) Faraday
(c) Michale
(d) None of the above
Ans: b
87. The number of Faraday tubes of flux
passing through a surface in an electric field
is called
(a) electric flux
(6) electric flux density
(c) magnetic flux density
(d) electric charge density
Ans: a
88. The unit of electric instensity is
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(a) N/C2
(b) Wb/m2
(c) N/C
(d) N2/C
Ans:
89. The value of E within the field due to a
point charge can be found with the help of
(a) Faraday's laws
(b) Kirchhoff s laws
(c) Coulomb's laws
(d) none of the above
Ans: c
90. at a point may be defined as equal to the
lines of force passing normally through a
unit cross section at that point.
(a) Electric intensity
(6) Magnetic flux density
(c) Electric flux
(d) None of the above
Ans: a
91. Electric intensity at any point in an
electric field is equal to the at that point.
(a) electric flux
(b) magnetic flux density
(c) potential gradient
(d) none of the above
Ans: c
92. Electric displacement is
a______quantity.
(a) scalar
(b) vector
(c) both of the above
(d) none of the above
Ans: b
93. at a point is equal to the negative
potential gradient at that point.
(a) Electric intensity
(6) Electric flux
(c) Magnetic flux
(d) Magnetic flux density
Ans: a
94. The unit of dielectric strength is given
by
(a) V/m
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(b) V2/m
(c) m/V
(d) m/V2
Ans: a
95. Dielectric strength ______ with
increasing thickness
(a) increases
(b) decreases
(c) remains unaltered
(d) none of the above
Ans: b
96. The property of a capacitor to store
electricity is called its
(a) capacitance
(b) charge
(c) energy
(d) none of the above
Ans: a
97. is that property of a capacitor which
delays any change of voltage across it.
(a) Inductance
(b) Capacitance
(c) Potential gradient
(d) None of the above
Ans: b
98. A capacitance of 100 fiF is connected in
series with a resistance of 8000 £2. The time
constant of the circuit is
(a) 0.2 s
(b) 0.4 s
(c) 0.6 s
(d) 0.8 s
Ans: d
99. In a cable capacitor, voltage gradient
ismaximum at the surface of the
(a) earth
(b) conduction
(c) sheath
(d) insulator
Ans: b
100. The time constant of an R-C circuit is
defined as the time during which capacitor
charging voltage actually rises to ______
percent of its______value.
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(a) 37, initial
(b) 63.2, initial
(c) 63.2, final
(d) 37, final
Ans: c
101. The time constant and R-C circuit may
also be defined as the time during which the
charging current falls to ______ percent of
its initial maximum value,
(a) 37
(b) 42
(c) 63
(d) 73
Ans: a
102. The capacitance of a capacitor is
influenced by
(a) plate area
(b) plate separation
(c) nature of dielectric
(d) none of the above
(e) all of the above
Ans:
103. A capacitor consists of two
(a) ceramic plates and one mica disc
(b) insulators separated by a dielectric
(c) silver-coated insulators
(d) conductors separated by an insulator
Ans: d
104. Permittivity is expressed in
(a) Farad/sq-m
(b) Farad/metre
(c) Weber/metre
(d) Weber/sq-m
Ans: b
105. Dielectric strength of a material
depends on
(a) moisture content
(b) temperature
(c) thickness
(d) all of the above
(e) none of the above
Ans: d
106. What will happen to an insulating
medium if voltage more than the breakdown
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voltage is applied on it ?
(a) It will become magnetic
(b) It will melt
(c) It will get punctured or cracked
(d) Its molecular structure will get changed
Ans: c
107. Which medium has the least dielectric
strength ?
(a) Paraffin wax
(b) Quartz
(c) Glass
(d) Air
Ans: d
108. 1 volt/metre is same as
(a) 1 metre/coulomb
(6) 1 newton metre
(c) 1 newton/metre
(d) 1 joule/coulomb
Ans: c
109. One volt is the same as
(a) one joule/coulomb
(b) one coulomb/joule
(c) one coulomb
(d) one joule
Ans: a
110. The capacitance between two plates
increases with
(a) shorter plate area and higher ap¬plied
voltage
(6) shorter plate area and shorter
dis¬tance between them
(c) larger plate area, longer distance between
plates and higher,applied voltage
(d) larger plate area and shorter distance
between plates
Ans: d
111. The capacitance C is charged through a
resistance R. The time constant of the
charging circuit is given by
(a) CIR
(b) 1/RC
(c) RC
(d) RIC
Ans: c
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112. The bridge used for the measurement of
the value of the capacitance is
(a) Wien's bridge
(b) Wheatstone bridge
(c) Schering bridge
(d) Hay's bridge
Ans: c
113. If an ohmmeter reading immediately
goes practically to zero and stays there,
capacitor is
(a) charged
(b) short-circuited
(c) lossy
(d) satisfactory
Ans: b
114. Out of the following capacitors of
identical rating which one will have the
smallest dimensions ?
(a) Aluminium foil capacitor
(b) Mica capacitor
(c) Ceramic capacitor
(d) Paper capacitor
Ans: c
115. An uncharged conductor is placed near
a charged conductor, then
(a) the uncharged conductor gets charged
by conduction
(6) the uncharged conductor gets charged
by induction and then attracted towards the
charging body
(c) the uncharged conductor is attracted first
and then charged by induction
(d) it remains as such
Ans: b
116. The presence of an uncharged
conductor near a charged one increases the
(a) charge of the charged conductor
(6) capacity of the charged conductor
(c) potential of the charged conductor
(d) all of the above
Ans: b
117. Paper condenser is
(a) always polarised
(6) usually of fixed value
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(c) electrolytic condenser
(d) a variable condenser
Ans: b
118. Mica capacitors are characterised by all
of thte following except
(a) stable operation
(b) accurate value
(c) low leakage reactance
(d) low losses
Ans: c
119. A potential of 400 V is applied to a
capacitor, the plates of which are 4 mm
apart. The strength of electric field is
(a) 100 kV/m
(b) 10 kV/m
(c) 5 kV/m
(d) 2 kV/m
Ans: a
120. For a good 0.05 uF capacitor ohmmeter
reading should
(a) show low resistance momentarily and
back off to a very high resis¬tance
(6) show high resistance momentarily and
then a very low resistance
(c) go quickly to 50 ohm approximately and
remain there
(d) not move at all
Ans: a
121. The ohmmeter reading for a short
circuited capacitor is
(a) infinity
(b) few kilo ohms
(c) few megaahms
(d) zero
Ans: d
122. Which of the following statements is
correct ?
(a) Mica capacitors are available in
capacitance values of 5 to 20 \iF
(b) Air capapitors have a black band to
indicate the outside foil
(c) Electrolytic capacitors must be
connected in correct polarity
(d) Ceramic capacitors must be con¬nected
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in correct polarity
Ans: c
123. Which of the following capacitors
preferred for high frequency circuits ?
(a) Air capacitor
(b) Electrolytic capacitor
(c) Mica capacitor
(d) none of the above
Ans: c
124. An electrolytic capacitor is generally
made to provide
(a) low capacitance
(b) fixed capacitance
(c) variable capacitance
(d) large value of capacitance
Ans: d
125. In order to remove static electricity
from machinery
(a) construct insulated cabins
(b) insulate the machinery
(c) ground the framework
(d) humidify the surroundings
Ans: c
126. If a third equal and similar charge is
placed between two equal and similar
charges, then this third charge will
(a) move out of the field of influence of the
two charges
(b) remain in stable equilibrium
(c) not be in equilibrium
(d) be in unstable equilibrium
Ans: b
127. A region around a stationary electric
charge has
(a) an electric field
(b) a magnetic field
(c) both (a) and (b)
(d) none of the above
Ans: a
128. The minimum value of potential
gradient in a cable occurs in
(a) insulation
(b) conductor
(c) outer sheath
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(d) uniformly all over
Ans: a
129. Dielectric strength of medium
(a) increases with rise in temperature
(b) increases with moisture content
(c) is same for all insulating materials
(d) none of the above
Ans: d
130. Acharge which when placed in vacuum
from an equal and similar charge repels with
a force of 9 x 10 N, is known as
(a) milli-coulomb
(b) micro-coulomb
(c) pico-coulomb
(d) coulomb
Ans: b
131. Dielectric strength of a medium is
usually expressed in
(a) J/mm
(b) C/m2
(c) kV/mm
(d) N/mm
Ans: c
132. A positive and a negative charge are
initially 50 mm apart. When they are moved
close together so that they are now only 10
mm apart, the force between them will be
(a) 5 times smaller than before
(b) 5 times greater than before
(c) 10 times greater than before
(d) 25 times larger than before
Ans: d
133. Which is the most superior dielectric
out of the following ?
(a) Air
(b) Glass
(c) Bakelite
(d) Paper
Ans: c
134. When a dielectric is placed in an
electric field the field strength
(a) decreases
(b) increases
(c) reduces to zero
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(d) remain unchanged
Ans: a
135. To prevent the generation of static
charges on rubber or flat leather
(a) surface is moistened
(b) conductive dressing is done
(c) oil compound dressing is done
(d) talcum powder is sprayed on the surface
Ans: b
136. Which of the following capacitor is
preferred in case of single phase motor ?
(a) Mica capacitor
(b) Paper capacitor
(c) Electrolytic capacitor
(d) Ceramic capacitor
Ans: c
137. A capacitance is a circuit component
that opposes the change in circuit
(a) current
(b) voltage
(c) impedance
(d) none of the above
Ans: a
138. A condenser suitable for D.C. only is
(a) metallic plate variable gang condenser
(b) metallic paper capacitor
(c) oil impregrated paper condenser
(d) poled aluminium electrolytic condenser
Ans: d
139. In a capacitor, the electric charge is
stored in
(a) metal plates
(b) dielectric
(c) dielectric as well as metal plates
(d) none of the above
Ans: b
Magnetism and Electromagnetism
4.1. Tesla is a unit of
(a) field strength
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(b) inductance
(c) flux density
(d) flux
Ans: c
4.2. A permeable substance is one
(a) which is a good conductor
(6) which is a bad conductor
(c) which is a strong magnet
(d) through which the magnetic lines of
force can pass very easily
Ans: d
4.3. The materials having low retentivity are
suitable for making
(a) weak magnets
(b) temporary magnets
(c) permanent magnets
(d) none of the above
Ans: b
4.4. A magnetic field exists around
(a) iron
(b) copper
(c) aluminium
(d) moving charges
Ans: d
4.7. Ferrites are materials.
(a) paramagnetic
(b) diamagnetic
(c) ferromagnetic
(d) none of the above
Ans: c
4.8. Air gap has_______eluctance as
compared to iron or steel path
(a) little
(b) lower
(c) higher
(d) zero
Ans: b
4.9. The direction of magnetic lines of force
is
(a) from south pole to north pole
(b) from north pole to south pole
(c) from one end of the magnet to another
(d) none of the above
Ans: b
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4.10. Which of the following is a vector
quantity ?
(a) Relative permeability
(b) Magnetic field intensity
(c) Flux density
(d) Magnetic potential
Ans: b
4.11. The two conductors of a transmission
line carry equal current I in opposite
directions. The force on each conductor is
(a) proportional to 7
(b) proportional to X
(c) proportional to distance between the
conductors
(d) inversely proportional to I
Ans: b
4.12. A material which is slightly repelled
by a magnetic field is known as
(a) ferromagnetic material
(b) diamagnetic material
(c) paramag>etic material
(d) conducting material
Ans: b
4.13. When an iron piece is placed in a
magnetic field
(a) the magnetic lines of force will bend
away from their usual paths in order to go
away from the piece
(b) the magnetic lines of force will bend
away from their usual paths in order to pass
through the piece
(c) the magnetic field will not be affected
(d) the iron piece will break
Ans: b
4.14. Fleming's left hand rule is used to find
(a) direction of magnetic field due to current
carrying conductor
(b) direction of flux in a solenoid
(c) direction of force on a current car¬rying
conductor in a magnetic field
(d) polarity of a magnetic pole
Ans: c
4.15. The ratio of intensity of magnetisation
to the magnetisation force is known as
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(a) flux density
(b) susceptibility
(c) relative permeability
(d) none of the above
Ans: b
4.16. Magnetising steel is normals difficult
because
(a) it corrodes easily
(6) it has high permeability
(c) it has high specific gravity
(d) it has low permeability
Ans: d
4.17. The left hand rule correlates to
(a) current, induced e.m.f. and direc¬tion of
force on a conductor
(b) magnetic field, electric field and
direction of force on a conductor
(c) self induction, mutual induction and
direction of force on a conductor
(d) current, magnetic field and direc¬tion of
force on a conductor
Ans: d
4.18. The unit of relative permeability is
(a) henry/metre
(b) henry
(c) henry/sq. m
(d) it is dimensionless
Ans: d
4.19. A conductor of length L has current I
passing through it, when it is placed parallel
to a magnetic field. The force experienced
by the conductor will be
(a) zero
(b) BLI
(c) B2LI
(d) BLI2
Ans: a
4.20. The force between two long parallel
conductors is inversely proportional to
(a) radius of conductors
(b) current in one conductor
(c) product of current in two conduc¬tors
(d) distance between the conductors
Ans: d
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4.21. Materials subjected to rapid reversal of
magnetism should have
(a) large area oiB-H loop
(b) high permeability and low hysteresis loss
(c) high co-ercivity and high reten-tivity
(d) high co-ercivity and low density
Ans: b
4.22. Indicate which of the following
material does not retain magnetism
permanently.
(a) Soft iron
(b) Stainless steel
(e) Hardened steel
(d) None of the above
Ans: a
4.23. The main constituent of permalloy is
(a) cobalt
(b) chromium
(c) nickel
(d) tungsten
Ans: c
4.24. The use of permanent magnets is. not
made in
(a) magnetoes
(6) energy meters
(c) transformers
(d) loud-speakers
Ans: c
4.25. Paramagnetic materials have relative
permeability
(a) slightly less than uuity
(b) equal to unity
(c) slightly more than unity
(d) equal to that ferromagnetic mate rials
Ans: c
4.26. Degaussing is the process of
(a) removal of magnetic impurities
(b) removing gases from the materials
(c) remagnetising metallic parts
(d) demagnetising metallic parts
Ans:
4.27. Substances which have permeability
less than the permeability of free space are
known as
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(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) bipolar
Ans: c
4.28. Two infinitely long parallel conductors
in vacuum anf' separated 1 metre between
centres >rhen a current of 1 ampere flows
thn. ugh each conductor, produce on each
otLer a force of
(a) 2 x 1(T2 N/m)
(b) 2 x KT3 N/m
(c) 2 x 10"5 N/m
(d) 2x 1(T7 N/m)
Ans: d
4.29. In the left hand rule, forefinger always
represents
(a) voltage
(b) current
(c) magnetic field
(d) direction of force on the conductor
Ans: c
4.30. Which of the following is a
ferromagnetic material ?
(a) Tungsten
(b) Aluminium
(c) Copper
(d) Nickel
Ans: d
4.31. Ferrites are a sub-group of
(a) non-magnetic materials
(6) ferro-magnetic materials
(c) paramagnetic materials
(d) ferri-magnetic materials
Ans: d
4.32. Gilbert is a unit of
(a) electromotive force
(6) magnetomotive force
(c) conductance
(d) permittivity
Ans: b
4.33. The working of a meter is based on the
use of a permanent magnet. In order to
protect the meter functioning from stray
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magnetic fields
(a) meter is surrounded by strong
magnetic fields
(b) a soft iron shielding is used
(c) a plastic shielding is provided
(d) a shielding of anon-magnetic material is
used
Ans: b
4.34. Reciprocal of permeability is
(a) reluctivity
(b) susceptibility
(c) permittivity
(d) conductance
Ans: a
4.35. The relative permeability is less than
unity is case of
(a) ferromagnetic materials
(b) ferrites
(c) non-ferrous materials
(d) diamagnetic materials
Ans: d
4.36. Which of the following is the unit of
magnetic flux density ?
(a) weber
(b) lumens
(c) tesla
(d) none of the above
Ans: c
4.37. The magnetism left in the iron after
exciting field has been removed is known as
(a) permeance
(b) residual magnetism
(c) susceptance
(d) reluctance
Ans: b
4.38. Which of the following is not a unit of
flux?
(a) Maxwell
(b) Telsa
(c) Weber
(d) All of the above
Ans: b
4.39. Which of the following is expected to
have the maximum permeability ?
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(a) Brass
(b) Copper
(c) Zinc
(d) Ebonite
Ans: d
4.40. One telsa is equal to
(a) 1 Wb/mm2
(b) 1 Wb/m
(c) 1 Wb/m2
(d) 1 mWb/m2
Ans: c
4.42. Out of the following statements,
concerning an electric field, which statement
is not true ?
(a) The electric intensity is a vector
quantity
(b) The electric field intensity at a point is
numerically equal to the force exerted upon
a charge placed at that point
(c) An electric field is defined as a point in
space at which an electric charge would
experienc* a force
(d) Unit field intensity in the exertion of a
force of one newton on a charge of one
coulomb
Ans: b
4.43. When a magnet is in motion relative to
a coil the induced e.m.f. does not depend
upon
(a) resistance of the coil
(b) motion of the magnet
(c) number of turns of the coil
(d) pole strength of the magnet
Ans: a
4.44. One maxwell is equal to
(a) 10 webers
(b) 10 webers
(c) 10 webers
(d) 10 webers
Ans: d
4.46. When two ends of a circular uniform
wire are joined to the terminals of a battery,
the field at the centre of the circle
(a) will be zero
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(b) will be infinite
(c) will depend on the amount of e.m.f.
applied
(d) will depend on the radius of the circle
Ans: d
4.47. Susceptibility is positive for
(a) non-magnetic substances
(b) diamagnetic substances
(c) ferromagnetic substances
(d) none of the above
Ans: c
4.48. Two long parallel conductors carry
100 A. If the conductors are separated by 20
mm, the force per metre of length of each
conductor will be
(a) 100 N
(b) 10 N
(c) 1 N
(d) 0.1 N
Ans: d
4.49. A 300 mm long conductor is carrying a
current of 10 A and is situated at right
angles to a magnetic field having a flux
density of 0.8 T ; the force on the conductor
will be
(a) 240 N
(6) 24 N
(c) 2.4 N
(d) 0.24 N
Ans: c
4.50. A 200 turn coil having an axial length
of 30 mm and a radius of 10 mm is pivoted
in a magnetic field having a flux density of
0.8 T. If the coil carries a current of 0.5 A,
the torque acting on the coil will be
(a) 4.8 N-m
(b) 0.48 N-m
(e) 0.048 N-m
(d) 0.0048 N-m
[Hint. Torque = 2BIlNr N-m]
Ans: c
4.51. The electromagnet has 50 turns and a
current of 1A flows through the coil. If the
length of the magnet circuit is 200 mm, what
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is the magnetic field strength ?
(a) 2500 AT/m
(b) 250 AT/m
(c) 25 AT/m
(d) 2.5 AT/m
Ans: b
4.52. What is the magnitude and the
direction of force per 1.1m length of a pair
of conductors of a direct current linecarrying
10 amperes and spaced 100 mm apart ?
(a) 22 x 10"8 N
(b) 22 x 10"7 N
(c) 22 x 10-6 N
(d) 22 x 10"5 N
Ans: d
453. A square cross-sectional magnet has a
pole strength of 1 x 10 Wb and cross
sectional area of 20 mm x 20 mm. What is
the strength at a distance of 100 mm from
the unit pole in air ?
(a) 63.38 N/Wb
(b) 633.8 N/Wb
(c) 6338 N/Wb
(d) 63380 N/Wb
Ans: c
4.56.. The unit of flux is the same as that of
(a) reluctance
(b) resistance
(c) permeance
(d) pole strength
Ans: d
4.57. Unit for quantity of electricity is
(a) ampere-hour
(b) watt
(c) joule
(d) coulomb
Ans: d
4.58. The Biot-savart's law is a general
modification of
(a) Kirchhoffs law
(b) Lenz's law
(c) Ampere's law
(d) Faraday's laws
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Ans: c
4.61. The most effective and quickest may
of making a magnet from soft iron is by
(a) placing it inside a coil carrying current
(b) induction
(c) the use of permanent magnet
(d) rubbing with another magnet
Ans: a
4.62. The commonly used material for
shielding or screening magnetism is
(a) copper
(b) aluminium
(c) soft iron
(d) brass
Ans: c
4.63. If a copper disc is rotated rapidly
below a freely suspended magnetic needle,
the magnetic needle shall start rotating with
a velocity
(a) less than that of disc but in opposite
direction
(b) equal to that of disc and in the same
direction
(c) equal to that of disc and in the opposite
direction
(d) less than that of disc and in the same
direction
Ans: d
4.64. A permanent magnet
(a) attracts some substances and repels
others
(b) attracts all paramagnetic substan¬ces and
repels others
(c) attracts only ferromagnetic sub¬stances
(d) attracts ferromagnetic substances and
repels all others
Ans: a
4.65. The retentivity (a property) of material
is useful for the construction of
(a) permanent magnets
(b) transformers
(c) non-magnetic substances
(d) electromagnets
Ans: a
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4.66. The relative permeability of materials
is not constant.
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) insulating
Ans: c
4.67. The materials are a bit inferior
conductors of magnetic flux than air.
(a) ferromagnetic
(b) paramagnetic
(c) diamagnetic
(d) dielectric
Ans: c
4.68. Hysteresis loop in case of magnetically
hard materials is more in shape as compared
to magnetically soft materials.
(a) circular
(b) triangular
(c) rectangular
(d) none of the above
Ans: c
4.69. A rectangular magnet of magnetic
moment M is cut into two piece of same
length, the magnetic moment of each piece
will be
(a) M
(6) M/2
(c) 2 M
(d) M/4
Ans: b
4.70. A keeper is used to
(a) change the direction of magnetic lines
(b) amplify flux
(c) restore lost flux
(d) provide a closed path for flux
Ans: d
4.71. Magnetic moment is a
(a) pole strength
(6) universal constant
(c) scalar quantity
(d) vector quantity
Ans: d
4.72. The change of cross-sectional area of
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conductor in magnetic field will affect
(a) reluctance of conductor
(b) resistance of conductor
(c) (a) and (b) b >th in the same way
(d) none of the above
Ans: c
4.73. The uniform magnetic field is
(a) the field of a set of parallel conductors
(b) the field of a single conductor
(c) the field in which all lines of mag¬netic
flux are parallel and equidis¬tant
(d) none of the above
Ans: c
4.74. The magneto-motive force is
(a) the voltage across the two ends of
exciting coil
(b) the flow of an electric current
(c) the sum of all currents embraced by one
line of magnetic field
(d) the passage of magnetic field through an
exciting coil
Ans: c
4.75. What will be the current passing
through the ring shaped air cored coil when
number of turns is 800 and ampere turns are
3200 ?
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b
4.76. What will be the magnetic potential
difference across the air gap of 2 cm length
in magnetic field of 200 AT/m ?
(a) 2 AT
(b) 4 AT
(c) 6 AT
(d) 10 AT
Ans: b
4.77. Which of the following statements is
correct ?
(a) The magnetic flux inside an exciting coil
is lower than its outside surface
(6) The magnetic flux inside an exciting coil
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is zero
(e) The magnetic flux inside the exciting
coil is greater than its outside surface
(d) The magnetic flux inside the exciting
coil is same as on its outside surface
Ans: d
4.78. A certain amount of current flows
through a ring-shaped coil with fixed
number of turns. How does the mag
netic induction B varies inside the coil if an
iron core is threaded into coil without
dimensional change of coil ?
(a) Decreases
(b) Increases
(c) Remains same
(d) First increases and then decreases
depending on the depth of iron in¬sertion
Ans: b
4.79. The magnetic reluctance of a material
(a) decreases with increasing cross
sectional area of material
(6) increases with increasing cross-sectional area of material
(c) does not vary with increasing crosssectional area of material
(d) any of the above
Ans: a
4.80. The initial permeability of an iron rod
is
(a) the highest permeability of the iron rod
(b) the lowest permeability of the iron rod
(c) the permeability at the end of the iron
rod
(d) the permeability almost in nonmagnetised state
Ans: d
4.82. How does the magnetic compass
needle behave in a magnetic field ?
(a) It assures a position right angle to
magnetic field
(b) It starts rotating
(c) It assures a position which follows a line
of magnetic flux
(d) None of the above
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Ans: c
4.83. In a simple magnetic field the strength
of magnet flux
(a) is constant and has same value in
energy part of the magnetic field
(6) increases continuously from initial
value to final value
(c) decreases continuously from initial value
to final value
(d) first increases and then decreases till it
becomes zero
Ans: d
4.84. The stray line of magnetic flux is
defined as
(a) a line vertical to the flux lines
(b) the mean length of a ring shaped coil
(c) a line of magnetic flux in a non-uniform
field
(d) a line of magnetic flux which does not
follow the designed path
Ans: d
4.85. The bar magnet has
(a) the dipole moment
(b) monopole moment
(c) (a) and (b) both
(d) none of the above
Ans: a
4.86. Which of the following materials are
dia-magnetic ?
(a) Silver
(b) Copper
(c) Silver and copper
(d) Iron
Ans: c
4.87. Which of the following type of
materials are not very important for
engineering applications ?
(a) Ferromagnetic
(b) Paramagnetic
(c) Diamagnetic
(d) None of the above
Ans: c
4.88. The susceptibility of paramagnetic
materials generally lies between
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(a) KT3 and 1CT6
(b) 1CT3 and 1CT7
(c) KT4 and KT8
(d) 10"2 and KT5
Ans: a
4.89. For which of the following materials
the saturation value is the highest ?
(a) Ferromagnetic materials
(6) Paramagnetic materials
(c) Diamagnetic materials
(d) Ferrites
Ans: d
4.90. The magnetic materials exhibit the
property of magnetisation because of
(a) orbital motion of electrons
(b) spin of electrons
(c) spin of nucleus
(d) either of these
(e) all of the above
Ans: c
4.91. For which of the following materials
the net magnetic moment should be zero ?
(a) Diamagnetic materials
(b) Ferrimagnetic materials
(c) Antiferromagnetic materials
(d) Antiferrimagnetic materials
Ans: c
4.92. The attraction capacity of
electromagnet will increase if the
(a) core length increases i
(b) core area increases
(c) flux density decreases
(d) flux density increases
Ans: d
4.93. Which of the following statements is
correct ?
(a) The conductivity of ferrites is better
than ferromagnetic materials
(b) The conductivity of ferromagnetic
materials is better than ferrites
(c) The conductivity of ferrites is very high
(d) The conductivity of ferrites is same as
that of ferromagnetic materials
Ans: a
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4.96. Temporary magnets are used in
(a) loud-speakers
(b) generators
(c) motors
(d) all of the above
Ans: d
4.97. Main causes of noisy solenoid are
(a) strong tendency of fan out of laminations at the end caused by repul¬sion
among magnetic lines of force
(b) uneven bearing surface, caused by dirt
or uneven wear between moving and
stationary parts
(c) both of above
(d) none of the above
Ans: c
4.99. Strength of an electromagnet can be
increased by
(a) increasing the cross-sectional area
(b) increasing the number of turns
(c) increasing current supply
(d) all above methods
Ans:
4.100. Core of an electromagnet should have
(a) low coercivity
(6) high susceptibility
(c) both of the above
(d) none of the above
Ans: c
4.101. Magnetism of a magnet can be
destroyed by
(a) heating
(b) hammering
(c) by inductive action of another magnet
(d) by all above methods
Ans: d
Magnetic Circuit
1. An air gap is usually inserted in magnetic
circuits to
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(a) increase m.m.f.
(b) increase the flux
(c) prevent saturation
(d) none of the above
Ans: c
2. The relative permeability of a
ferromagnetic material is
(a) less than one
(b) more than one
(c) more than 10
(d) more than 100 or 1000
Ans: d
3. The unit of magnetic flux is
(a) henry
(b) weber
(c) ampereturn/weber
(d) ampere/metre
Ans: b
4. Permeability in a magnetic circuit
corresponds to______ in an electric circuit.
(a) resistance
(b) resistivity
(c) conductivity
(d) conductance
Ans: c
5. Point out the wrong statement.
Magnetic leakage is undesirable in electric
machines because it
(a) lowers their power efficiency
(b) increases their cost of manufacture
(c) leads to their increased weight
(d) produces fringing
Ans: a
6. Relative permeability of vacuum is
(a) 1
(b) 1 H/m
(c) 1/4JI
(d) 4n x 10-' H/m
Ans: a
7. Permanent magnets are normally made of
(a) alnico alloys
(b) aluminium
(c) cast iron
(d) wrought iron
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Ans: a
8. Energy stored by a coil is doubled when
its current is increased by percent.
(a) 25
(b) 50
(c)41.4
(d) 100
Ans: c
9. Those magnetic materials are best suited
for making armature and transformer cores
which have____permeability
and_______hystersis loss.
(a) high, high
(b) low, high
(c) high, low
(d) low, low
Ans: c
10. The rate of rise of current through an
inductive coil is maximum
(a) at 63.2% of its maximum steady value
(b) at the start of the current flow
(c) after one time constant
(d) near the final maximum value of current
Ans: b
11. When both the inductance and resistance
of a coil are doubled the value of
(a) time constant remains unchanged
(b) initial rate of rise of current is doubled
(c) final steady current is doubled
(d) time constant is halved
Ans: a
12. The initial rate of rise of current through
a coil of inductance 10 H when suddenly
connected to a D.C. supply of 200 V
is_______Vs
(a) 50
(b) 20
(c) 0.05
(d) 500
Ans: b
13. A material for good magnetic memory
should have
(a) low hysteresis loss
(b) high permeability
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(c) low retentivity
(d) high retentivity
Ans: d
14. Conductivity is analogous to
(a) retentivity
(b) resistivity
(c) permeability
(d) inductance
Ans: c
15. In a magnetic material hysteresis loss
takes place primarily due to
(a) rapid reversals of its magnetisation
(b) flux density lagging behind magnetising
force
(c) molecular friction
(d) it high retentivity
Ans: d
16. Those materials are well suited for
making permanent magnets which
have______retentivity and
_______coercivity.
(a) low, high
(b) high, high
(c) high, low
(d) low, low
Ans: b
17. If the area of hysteresis loop of a
material is large, the hysteresis loss in this
material will be
(a) zero
(b) small
(c) large
(d) none of the above
Ans: c
18. Hard steel is suitable for making
permanent magnets because
(a) it has good residual magnetism
(b) its hysteresis loop has large area
(c) its mechanical strength is high
(d) its mechanical strength is low
Ans: a
19. Silicon steel is used in electrical
machines because it has
(a) low co-ercivity
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(b) low retentivity
(c) low hysteresis loss
(d) high co-ercivity
Ans: c
20. Conductance is analogous to
(a) permeance
(b) reluctance
(c) flux
(d) inductance
Ans: a
21. The property of a material which
opposes the creation of magnetic flux in it is
known as
(a) reluctivity
(b) magnetomotive force
(c) permeance
(d) reluctance
Ans: d
22. The unit of retentivity is
(a) weber
(b) weber/sq. m
(c) ampere turn/metre
(d) ampere turn
Ans: b
23. Reciprocal of reluctance is
(a) reluctivity
(b) permeance
(c) permeability
(d) susceptibility
Ans: b
24. While comparing magnetic and electric
circuits, the flux of magnetic circuit is
compared with which parameter of electrical
circuit ?
(a) E.m.f.
(b) Current
(c) Current density
(d) Conductivity
Ans: b
25. The unit of reluctance is
(a) metre/henry
(b) henry/metre
(c) henry
(d) 1/henry
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Ans: d
26. A ferrite core has less eddy current loss
than an iron core because
(a) ferrites have high resistance
(b) ferrites are magnetic
(c) ferrites have low permeability
(d) ferrites have high hysteresis
Ans: d
27. Hysteresis loss least depends on
(a) volume of material
(b) frequency
(c) steinmetz co-efficient of material
(d) ambient temperature
Ans: d
28. Laminated cores, in electrical machines,
are used to reduce
(a) copper loss
(b) eddy current loss
(c) hysteresis loss
(d) all of the above
Ans: b
Electrolysis and Storage of Batteries
1. "The mass of an ion liberated at an
electrode is directly proportional to the
quantity of electricity".
The above statement is associated with
(a) Newton's law
(b) Faraday's law of electromagnetic
(c) Faraday's law of electrolysis
(d) Gauss's law
Ans: c
2. The charge required to liberate one
gram equivalent of any substance is
known as ______ constant
(a) time
(b) Faraday's
(c) Boltzman
Ans: b
3. During the charging of a lead-acid cell
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(a) its voltage increases
(b) it gives out energy
(c) its cathode becomes dark chocolate
brown in colour
(d) specific gravity of H2SO4 decreases
Ans: a
4. The capacity of a lead-acid cell does not
depend on its
(a) temperature
(b) rate of charge
(c) rate of discharge
(d) quantity of active material
Ans: b
5. During charging the specific gravity of
the electrolyte of a lead-acid battery
(a) increases
(b) decreases
(c) remains the same
(d) becomes zero
Ans: a
6. The active materials on the positive and
negative plates of a fully charged lead-acid
battery are
(a) lead and lead peroxide
(b) lead sulphate and lead
(c) lead peroxide and lead
(d) none of the above
Ans: c
7. When a lead-acid battery is in fully
charged condition, the colour of its positive
plate is
(a) dark grey
(b) brown
(c) dark brown
(d) none of above
Ans: c
8. The active materials of a nickel-iron
battery are
(a) nickel hydroxide
(6) powdered iron and its oxide
(c) 21% solution of KOH
(d) all of the above
Ans: d
9. The ratio of ampere-hour efficiency to
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watt-hour efficiency of a lead-acid cell is
(a) just one
(b) always greater than one
(c) always less than one
(d) none of the above.
Ans: b
10. The best indication about the state of
charge on a lead-acid battery is given by
(a) output voltage
(b) temperature of electrolyte
(c) specific gravity of electrolyte
(d) none of the above
Ans: c
11. The storage battery generally used in
electric power station is
(a) nickel-cadmium battery
(b) zinc-carbon battery
(c) lead-acid battery
(d) none of the above
Ans: c
12. The output voltage of a charger is
(a) less than the battery voltage
(b) higher than the battery voltage
(c) the same as the battery voltage
(d) none of the above
Ans: b
13. Cells are connected in series in order to
(a) increase the voltage rating
(6) increase the current rating
(c) increase the life of the cells
(d) none of the above
Ans: a
14. Five 2 V cells are connected in parallel.
The output voltage is
(a) 1 V
(6) 1.5 V
(c) 1.75 V
(d) 2 V
Ans: d
15. The capacity of a battery is expressed in
terms of
(a) current rating
(b) voltage rating
(e) ampere-hour rating
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(d) none of the above
Ans: c
16. Duringthe charging and discharging of a
nickel-iron cell
(a) corrosive fumes are produced
(b) water is neither formed nor absorbed
(c) nickel hydroxide remains unsplit
(d) its e.m.f. remains constant
Ans: b
17. As compared to constant-current system,
the constant-voltage system of charging a
lead acid cell has the advantage of
(a) reducing time of charging
(b) increasing cell capacity
(c) both (a) and (b)
(d) avoiding excessive gassing
Ans: c
18. A dead storage battery can be revived by
(a) adding distilled water
(6) adding so-called battery restorer
(c) a dose of H2SO4
(d) none of the above
Ans: d
19. As compared to a lead-acid cell, the
efficiency of a nickel-iron cell is less due to
its
(a) compactness
(b) lower e.m.f.
(c) small quantity of electrolyte used
(d) higher internal resistance
Ans: d
20. Trickle charging of a storage battery
helps to
(a) maintain proper electrolyte level
(b) increase its reserve capacity
(c) prevent sulphation
(d) keep it fresh and fully charged
Ans: d
21. Those substances of the cell which take
active part in chemical combination and
hence produce electricity during
charging or discharging are known
as______materials.
(a) passive
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(b) active
(c) redundant
(d) inert
Ans: b
22. In a lead-acid cell dilute sulphuric acid
(electrolyte) approximately comprises the
following
(a) one part H2O, three parts H2SO4
(b) two parts H2O, two parts H2SO4
(c) three parts H2O, one part H2SO4
(d) all H2S04
Ans: c
23. It is noticed that durmg charging
(a) there is a rise in voltage
(6) energy is absorbed by the cell
(c) specific gravity of H2SO4 is increased
(d) the anode becomes chocolate brown in
colour (PbCfe) and cathode be¬comes grey
metallic lead (Pb)
(e) all of the above
Ans: e
24. It is noticed that during discharging the
following does not happen
(a) both anode and cathode become
PbS04
(b) specific gravity of H2SO4 decreases
(c) voltage of the cell decreases
(d) the cell absorbs energy
Ans: d
25. The ampere-hour efficiency of a
leadacid cell is normally between
(a) 20 to 30%
(b) 40 to 50%
(c) 60 to 70%
(d) 90 to 95%
Ans: d
26. The watt-hour efficiency of a lead-acid
cell varies between
(a) 25 to 35%
(b) 40 to 60%
(c) 70 to 80%
(d) 90 to 95%
Ans: c
27. The capacity of a lead-acid cell is
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measured in
(a) amperes
(b) ampere-hours
(c) watts
(d) watt-hours
Ans: b
28. The capacity of a lead-acid cell depends
on
(a) rate of discharge
(b) temperature
(c) density of electrolyte
(d) quantity of active materials
(e) all above
Ans: e
29. When the lead-acid cell is fully charged,
the electrolyte assumes _____ appearance
(a) dull
(b) reddish
(c) bright
(d) milky
Ans: d
30. The e.m.f. of an Edison cell, when fully
charged, is nearly
(a) 1.4 V
(b) 1 V
(c) 0.9 V
(d) 0.8 V
Ans: a
31. The internal resistance of an alkali cell is
nearly _____ times that of the lead-acid cell.
(a) two
(b) three
(c) four
(d) five
Ans: d
32. The average charging voltage for alkali
cell is about
(a) 1 V
(b) 1.2 V
(c) 1.7 V
(d) 2.1 V
Ans: c
33. On the average the ampere-hour
efficiency of an Edison cell is about
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(a) 40%
(b) 60%
(c) 70%
(d) 80%
Ans: d
34. The active material of the positive plates
of silver-zinc batteries is
(a) silver oxide
(b) lead oxide
(c) lead
(d) zinc powder
Ans: a
35. Lead-acid cell has a life of nearly
charges and discharges
(a) 500
(b) 700
(c) 1000
(d) 1250
Ans: d
36. Life of the Edison cell is at least
(a) five years
(b) seven years
(c) eight years
(d) ten years
Ans: a
37. The internal resistance of a lead-acid cell
is _____ that of Edison cell
(a) less than
(b) more than
(c) equal to
(d) none of the above
Ans: a
38. Electrolyte used in an Edison cell is
(a) NaOH
(b) KOH
(c) HC1
(d) HN03
Ans: b
39. Electrolyte used in a lead-acid cell is
(a) NaOH
(b) onlyH2S04
(c) only water
(d) dilute H2SO4
Ans: d
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40. Negative plate of an Edison cell is made
of
(a) copper
(b) lead
(c) iron
(d) silver oxide
Ans: c
41. The open circuit voltage of any storage
cell depends wholly upon
(a) its chemical constituents
(b) on the strength of its electrolyte
(c) its temperature
(d) all above
Ans: d
42. The specific gravity of electrolyte is
measured by
(a) manometer
(6) a mechanical gauge
(c) hydrometer
(d) psychrometer
Ans: c
43. When the specific gravity of the
electrolyte of a lead-acid cell is reduced to
1.1 to 1.15 the cell is in
(a) charged state
(b) discharged state
(c) both (a) and (b)
(d) active state
Ans: b
44. In ______ system the charging current is
intermittently controlled at either a
maximum or minimum value
(a) two rate charge control
(b) trickle charge
(c) floating charge
(d) an equalizing charge
Ans: a
45. Over charging
(a) produces excessive gassing
(b) loosens the active material
(e) increases the temperature resulting in
buckling of plates
(d) all above
Ans: d
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46. Undercharging
(a) reduces specific gravity of the
electrolyte
(b) increases specific gravity of the
electrolyte
(c) produces excessive gassing
(d) increases the temperature
Ans: a
47. Internal short circuits are caused by
(a) breakdown of one or more separators
(b) excess accumulation of sediment at
the bottom of the cell
(c) both (a) and (b)
(d) none of the above
Ans: c
48. The effect of sulphation is that the
internal resistance
(a) increases
(b) decreases
(c) remains same
(d) none of the above
Ans: a
49. Excessive formation of lead sulphate on
the surface of the plates happens because of
(a) allowing a battery to stand in
discharged condition for a long time
(b) topping up with electrolyte
(c) persistent undercharging
(d) low level of electrolyte
(e) all above
Ans: e
50. The substances which combine together
to store electrical energy during the charge
are called ______ materials
(a) active
(b) passive
(c) inert
(d) dielectric
Ans: a
51. In a lead-acid cell, lead is called as
(a) positive active material
(b) negative active material
(c) passive material
(d) none of the above
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Ans: b
52. The lead-acid cell should never be
discharged beyond
(a) 1.8 V
(b) 1.9 V
(c) 2 V
(d) 2.1 V
Ans: a
53. On overcharging a battery
(a) it will bring about chemical change in
active materials
(b) it will increase the capacity of the
battery
(c) it will raise the specific gravity of the
electrolyte
(d) none of the above will occur
Ans: d
54. Each cell has a vent cap
(a) to allow gases out when the cell is on
charge
(b) to add water to the cell if needed
(c) to check the level of electrolyte
(d) to do all above functions
Ans: d
55. Following will occur if level of
electrolyte falls below plates
(a) capacity of the cell is reduced
(b) life of the cell is reduced
(c) open plates are converted to lead
sulphate
(d) all above
Ans: d
56. In constant voltage charging method, the
charging current from discharged to fully
charged condition
(a) decreases
(b) increases
(c) remains constant
(d) none of the above
Ans: a
57. 48 ampere-hour capacity would deliver a
current of
(a) 48 amperes for 1 hour
(b) 24 amperes for 2 hours
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(c) 8 amperes for 6 hours
(d) 6 amperes for 8 hours
Ans: d
58. In constant-current charging method, the
supply voltage from discharged to
fully charged condition
(a) decreases
(b) increases
(c) remains constant
(d) none of the above
Ans: b
59. Battery charging equipment is generally
installed
(a) in well ventilated location
(b) in clean and dry place
(c) as near as practical to the battery being
charged
(d) in location having all above features
Ans: d
60. Following will happen if the specific
gravity of electrolyte becomes more than
1.23.
(a) Loss of capacity
(b) Loss of life
(c) Corrosion of the grids of the plate
(d) All above
Ans: d
61. Batteries are charged by
(a) rectifiers
(b) engine generator sets
(c) motor generator sets
(d) any one of the above methods
Ans: d
62. Cell short circuit results in
(a) low sp. gravity electrolyte
(b) abnormal high temperature
(c) reduced gassing on charge
(d) all above
Ans: d
63. Internal resistance of a cell is reduced by
(a) using vent plug to permit gas formed
during discharge
(b) increasing the plate area
(c) putting plates very close together
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(d) all above methods
Ans: d
64. Capacity of dry cells is
(a) more when it is supplying current for
intermittent periods
(b) more when it is supplying current for
continuous periods
(c) unaffected by the type of discharge
(d) none of the above
Ans: a
65. Battery container should be acid
resistance, therefore it is made up of
(a) glass
(b) plastic
(c) wood
(d) all above
Ans: d
66. Sulphated cells are indicated by
(a) the loss of capacity of the cell
(6) the decrease of the specific gravity
(c) the low voltage of the cell on discharge
(d) all above conditions
Ans: d
67. In a lead-acid cell, if the specific gravity
of sulphuric acid is 1.8, it will require
following ratio of acid to water to get
mixture of specific gravity of 1.3
(a) 6 parts of acid to 4 parts of water
(b) 4 parts of acid to 4 parts of water
(c) 4 parts of acid to 6 parts of water
(d) 4 parts of acid to 8 parts of water
Ans: c
68. Local action in a battery is indicated by
(a) excessive gassing under load conditions
(b) excessive drop in the specific gravity of
electrolyte even when the cell is on open
circuit
(c) both (a) and (b)
(d) none of the above
Ans: d
69. Following will happen if battery
charging rate is too high
(a) excessive gassing will occur
(b) temperature rise will occur
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(c) bulging and buckling of plates will occur
(d) all above will occur
Ans: d
70. Internal resistance of a cell is due to
(a) resistance of electrolyte
(b) electrode resistance
(c) surface contact resistance between
electrode and electrolyte
(d) all above
Ans: d
71. If a battery is wrongly connected on
charge following will happen
(a) current delivered by the battery will be
high
(b) current drawing will be nil
(c) current drawing will be very small
(d) current drawing will be very high
Ans: d
72. In order that a hydrometer may float
vertically in electrolyte its C.G. should be
(a) lowered
(b) raised
(c) undisturbed
(d) displaced sideways
Ans: a
73. If a lead-acid cell is discharged below
1.8 V the following will happen.
(a) Capacity of cell will reduce
(b) Sulphation of plates will occur
(c) Internal resistance will increase
(d) All above will occur
Ans: d
74. Life of the batteries is in the following
ascending order.
(a) Lead-acid cell, Edison cell, Nickel
cadmium cell
(b) Lead-acid cell, Nickel-cadmium cell,
Edison cell
(c) Edison cell, Nickel-cadmium cell, leadacid cell
(d) Nickel-cadmium cell, Edison cell, leadacid cell
Ans: a
75. Persons preparing electrolyte should
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wear
(a) goggles or other face shield
(b) rubber
(c) rubber boots and gloves
(d) all above safety devices
Ans: d
76. Excessive charging a battery tends to
(a) produce gassing
(b) increase the internal resistance of the
battery
(c) to corrode the positive plates into lead
peroxide thereby weakening them physically
(d) bring about all above changes
Ans: d
77. Shelf life of a small dry cell is
(a) equal to that of large dry cell
(6) less than that of large dry cell
(c) more than that of large dry cell
(d) none of the above
Ans: b
78. The current flow through electrolyte is
due to the movement of
(a) ions
(b) holes
(c) electrons
(d) none of the above
Ans: a
79. Level of electrolyte in a cell should be
_____ the level of plates
(a) below
(b) equal to
(c) above
(d) none of the above
Ans: c
80. During discharge, the active material of
both the positive and negative plates is
changed to
(a) Pb
(b) Pb02
(c) PbO
(d) PbS04
Ans: d
81 of electrolytelndicates the state of charge
of the battery
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(a) colour
(b) mass
(c) viscosity
(d) specific gravity
Ans: d
82. The following indicate that battery on
charge has attained full charge
(a) colour of electrode
(b) gassing
(c) specific gravity
(d) all above
Ans: d
83. Dry cell is modification of
(a) Deniell cell
(b) Leclanche cell
(e) Lead-acid cell
(d) Edison cell
Ans: b
84. Capacity of a battery.is expressed in
(a) Ah
(b) Vh
(c) Wh
(d) kWh
Ans: a
85. In alkaline cell the electrolyte is
(a) dilute sulphuric acid
(b) concentrated sulphuric acid
(c) NaOH
(d) KOH
Ans: d
86. Self charge of a Ni-Fe cell is _____
Edison cell.
(a) equal to
(b) less than
(c) more than
(d) much more than
Ans: b
87. Ampere hour capacity of an industrial
battery is based on ____ hours discharge
rate.
(a) 8
(b) 12
(c) 16
(d) 24
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Ans: a
88. The body of Edison cell is made of
(a) bakelite
(b) rubber
(c) nickel plated steel
(d) aluminium
Ans: c
89. Specific gravity of electrolyte in Edison
cell is
(a) 0.8
(b) 0.95
(c) 1.1
(d) 1.21
Ans: d
90. All the electrical connections between
the battery and vehicle should be by
(a) thin aluminium wires
(b) thin copper wires
(c) rigid cables
(d) flexible cables
Ans: d
91. A battery of 6 cells will show a drop of
_____ volts from fully charged state to fully
discharged state.
(a) 1.0
(b) 1.5
(c) 2.4
(d) 2.9
Ans: c
92. During the idle period of the battery,
strong electrolyte tends to change the active
material of the cell into
(a) Pb02
(6) PbSC-4
(c) PbO
(d) Pb
Ans: b
93. Chargmg of sulphated battery produces
____ heat.
(a) no
(b) very little
(c) less
(d) more
Ans: d
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94. Hydrogen evolved during charging
produces explosive mixture when it is more
than
(a) 2%
(b) 4%
(c) 6%
(d) 8%
Ans: d
95. Weston standard cell at 20°C has voltage
of ____ volts.
(a) 0.8
(b) 0.9
(c) 1.0187
(d) 1.5
Ans: c
96. Extent of corrosion in the underground
metal work depends upon
(a) amount of moisture
(b) type of metals
(c) type of soil chemicals
(d) all above factors
Ans: d
97. Mercury cell has which of the following
characteristics ?
(a) Flat discharge current-voltage curve
(6) High power to weight ratio
(c) Comparatively longer shelf life under
adverse conditions of high temperature and
humidity
(d) All of the above
Ans: d
98. Charging a sulphated battery at high rate
results in
(a) boiling of electrolyte due to gassing
(b) warping of plates
(c) damage to separators, cell caps covers
and battery case due to ex¬cessive
temperature
(d) all above
Ans: d
99. Short circuiting of a cell may be caused
(a) buckling of plates
(b) faulty separators
(c) lead particles forming circuit between
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positive and negative plates
(d) excessive accumulation of sediment
(e) any one of above
Ans: e
100. In a battery cover is placed over the
element and sealed to the top of the battery
container. This is done
(a) to reduce evaporation of water from
electrolyte
(b) to exclude dirt and foreign matter
from the electrolyte
(c) to discharge both of the above functions
(d) to discharge none of the above functions
Ans: c
101. For a cell to work, which of the
following condition(s) become necessary ?
(a) Two electrodes of different meta's
should be inserted in the electrolyte, not
touching each other
(b) Electrolyte must chemically react with
one of the electrodes
(c) Electrolyte liquid or paste should be
conducting
(d) All above three conditions are necessary
Ans: d
102. Which of the following primary cells
has the lowest voltage ?
(a) Lithium
(b) Zinc-chloride
(c) Mercury
(d) Carbon-zinc
Ans: c
103. Which of the following primary cells
has the highest voltage ?
(a) Manganese-alkaline
(6) Carbon-zinc
(c) Lithium
(d) Mercury
Ans: c
104. While preparing electrolyte for a leadacid battery
(a) water is poured into acid
(b) acid is poured into water
(c) anyone of the two can be added to other
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chemical
Ans: b
105. Which of the following battery is used
for air-craft ?
(a) Lead-acid battery
(b) Nickel-iron battery
(c) Dry cell battery
(d) Silver oxide battery
Ans: b
106. Which of the following cell has a.
reversible chemical reaction ?
(a) Lead-acid
(b) Mercury oxide
(c) Carbon-zinc
(d) Silver-oxide
Ans: a
107. Which of the following is incorrect ?
(a) A storage cell has a reversible chemical
reaction
(b) A lead-acid cell can be recharged
(c) A carbon-zinc cell has unlimited shelf
life
(d) A primary cell has an irreversible
chemical reaction
Ans: c
108. Which of the following has lower sp.
gravity V
(a) Dilute H2S04
(6) Concentrated H2SO4
(c) Water
(d) Any of the above
Ans: c
109. Under normal charging rate, the
charging current should be
(a) 10% of capacity
(b) 20% of capacity
(c) 30% of capacity
(d) 40% of capacity
Ans: a
110. When two batteries are connected in
parallel, it should be ensured that
(a) they have same e.m.f.
(b) they have same make
(c) they have same ampere-hour capa-city
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(d) they have identical internal resistance
Ans: a
111. A typical output of a solar cell is
(a) 0.1V
(b) 0.26 V
(c) 1.1 V
(d) 2 V
Ans: b
112. Petroleum jelly is applied to the
electrical connections to the lead-acid
battery
(a) prevent local heating
(b) prevent short-circuiting
(c) reduce path resistance
(d) prevent corrosion
Ans: d
113. When the load resistance equals the
generator resistance which of the following
will be maximum ?
(a) Current
(b) Efficiency of the circuit
(c) Power in the load resistance
(d) Voltage across the load resistance
Ans: c
114. The common impurity in the electrolyte
of lead-acid battery is
(a) chlorine
(b) dust particles
(c) lead crystals
(d) iron
Ans: d
115. In a lead-acid battery the energy is
stored in the form of
(a) charged ions
(b) chemical energy
(c) electrostatic energy
(d) electromagnetic energy
Ans: b
116. Which among the following constitutes
the major load for an automobile battery ?
(a) Brake light
(b) Self starter
(c) Parking lights
(d) Spark plugs
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Ans: b
17. Which of the following factors adversely
affects the capacity of the leadacid battery ?
(a) Temperature of surroundings
(b) Specific gravity of electrolyte
(c) Rate of discharge
(d) All of the above
Ans: d
118. Cells are connected in parallel to
(a) increase the efficiency
(b) increase the current capacity
(c) increase the voltage output
(d) increase the internal resistance
Ans: b
119. A constant-voltage generator has
(a) minimum efficiency
(b) minimum current capacity
(c) low internal resistance
(d) high internal resistance
Ans: c
120. Satellite power requirement is provided
through
(a) solar cells
(b) dry cells
(c) nickel-cadmium cells
(d) lead-acid batteries
Ans: a
A.C. Fundamentals, Circuits and
Circuit Theory
1. A sine wave has a frequency of 50 Hz.
Its angular frequency is _______
radian/second.
(a) 100 n
(b) 50 jt
(c) 25 jt
(d) 5 n
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Ans: a
2. The reactance offered by a capacitor to
alternating current of frequency 50 Hz is
20 Q. If frequency is increased to 100 Hz,
reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15
Ans: c
3. The period of a wave is
(a) the same as frequency
(6) time required to complete one cycle
(c) expressed in amperes
(d) none of the above
Ans: b
4. The form factor is the ratio of
(a) peak value to r.m.s. value
(6) r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b
5. The period of a sine wave is _____
seconds.
Its frequency is
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz
Ans: d
6. A heater is rated as 230 V, 10 kW, A.C.
The value 230 V refers to
(a) average voltage
(b) r.m.s. voltage
(c) peak voltage
(d) none of the above
Ans: b
7. If two sinusoids of the same frequency
but of different amplitudes and phase angles
are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
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(d) not a sinusoid
Ans: a
8. The peak value of a sine wave is 200 V.
Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a
9. If two sine waves of the same frequency
have a phase difference of JT radians, then
(a) both will reach their minimum values at
the same instant
(b) both will reach their maximum values at
the same instant
(c) when one wave reaches its maximum
value, the other will reach its minimum
value
(d) none of the above
Ans: c
10. The voltage of domestic supply is 220V.
This figure represents
(a) mean value
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a
11. Two waves of the same frequency have
opposite phase when the phase angle
between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b
12. The power consumed in a circuit
element will be least when the phase
difference between the current and
voltage is
(a) 180"
(b) 90°
(c) 60°
(d) 0°
Ans: b
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13. The r.m.s. value and mean value is the
same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c
14. For the same peak value which of the
following wave will 'have the highest r.m.s.
value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a
15. For the same peak value, which of the
following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a
16. For a sine wave with peak value Imax
the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b
17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c
18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c
19. For a sine wave with peak value
Emax______8.30. the average value is
(a) 0.636 Emax
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(b) 0.707 Emax
(c) 0.434 EWc
(d) lAUEmax
Ans: a
20. For a frequency of 200 Hz, the time
period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b
21. The phase difference between voltage
and current wave through a circuit element
is given as 30°. The essential condition is
that
(a) both waves must have same frequency
(b) both waves must have identical peak
values
(c) both waves must have zero value at the
same time
(d) none of the above
Ans: a
22. The r.m.s. value of a sinusoidal A.C.
current is equal to its value at an angle
of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c
23. Capacitive reactance is more when
(a) capacitance is less and frequency of
supply is less
(b) capacitance is less and frequency of
supply is more
(c) capacitance is more and frequency of
supply is less
(d) capacitance is more and frequency of
supply is more
Ans: a
24. In a series resonant circuit, the
impedance of the circuit is
(a) minimum
(b) maximum
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(c) zero
(d) none of the above
Ans: a
25. Power factor of an electrical circuit is
equal to
(a) R/Z
(b) cosine of phase angle difference between
current and voltage
(c) kW/kVA
(d) ratio of useful current to total current
Iw/I
(e) all above
Ans: e
26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the inductive load
(c) far away from the inductive load
(d) any where
Ans: b
27. Poor power factor
(a) reduces load handling capability of
electrical system
(b) results in more power losses in the
electrical system
(c) overloads alternators, transformers and
distribution lines
(d) results in more voltage drop in the line
(e) results in all above
Ans: e
28. Capacitors for power factor correction
are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d
29. In series resonant circuit, increasing
inductance to its twice value and reducing
capacitance to its half value
(a) will change the maximum value of
current at resonance
(6) will change the resonance frequency
(c) will change the impedance at resonance
frequency
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(d) will increase the selectivity of the circuit
Ans: d
30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some
part of the cycle and then returns back to it
during other part of the cycle
(d) none of the above
Ans: c
31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c
32. Inductance of a coil Varies
(a) directly as the cross-sectional area of
magnetic core
(b) directly as square of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e
33. All the rules and laws of D.C. circuit
also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c
34. Time constant of an inductive circuit
(a) increases with increase of inductance and
decrease of resistance
(b) increases with the increase of inductance
and the increase of resistance
(c) increases with decrease of inductance
and decrease of resistance
(d) increases with decrease of inductance
and increase of resistance
Ans: a
35. Power factor of an inductive circuit is
usually improved by connecting capacitor to
it in
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(a) parallel
(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a
36. In a highly capacitive circuit the
(a) apparent power is equal to the actual
power
(b) reactive power is more than the apparent
power
(c) reactive power is more than the actual
powetf
(d) actual power is more than its reactive
power
Ans: c
37. Power factor of the following circuit will
be zero
(a) resistance
(b) inductance
(c) capacitance
(d) both (b) and (c)
Ans: d
38. Power factor of the following circuit will
be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c
39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the
capacities of generators, lines and
transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d
40. The time constant of the capacitance
circuit is defined as the time during which
voltage
(a) falls to 36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
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Ans: c
41. In a loss-free R-L-C circuit the transient
current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c
42. The r.m.s. value of alternating current is
given by steady (D.C.) current which when
flowing through a given circuit for a given
time produces
(a) the more heat than produced by A.C.
when flowing through the same circuit
(b) the same heat as produced by A.C. when
flowing through the same circuit
(c) the less heat than produced by A.C.
flowing through the same circuit
(d) none of the above
Ans: b
43. The square waveform of current has
following relation between r.m.s. value and
average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than
average value
(c) r.m.s. value of current is less than
average value
(d) none of the above
Ans: a
44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d) R-L-C circuit
Ans: d
45. The transient currents are associated
with the
(a) changes in the stored energy in the
inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a
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46. The power factor at resonance in R-L- C
parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d
47. In the case of an unsymmetrical
alternating current the average value must
always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d
48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d) current is in phase with the voltage
Ans: d
49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by
90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b
50. In a circuit containing R, L and C, power
loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c
51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply
frequency
(c) increases with the increase in supply
frequency
(d) becomes zero with the increase in supply
frequency
Ans: c
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52. In any A.C. circuit always
(a) apparent power is more than actual
power
(b) reactive power is more than apparent
power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a
53. Which of the following circuit
component opposes the change in the circuit
voltage ?
(a) Inductance
(b) Capacitance
(c) Conductance
(d) Resistance
Ans:
54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a
55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d
56. Pure inductive circuit takes power from
the A.C. line when
(a) applied voltage decreases but cur¬rent
increases
(b) applied voltage increases but cur¬rent
decreases
(c) both applied voltage and current increase
(d) both applied voltage and current
decrease
Ans: a
57. Time constant of a circuit is the time in
seconds taken after the application of
voltage to each
(a) 25% of maximum value
(b) 50% of maximum value
(c) 63% of maximum value
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(d) 90% of the maximum value
Ans: c
58. Time constant of an inductive circuit
(a) increases with increase of inductance
and decrease of resistance
(b) increases with the increase of
inductance and the increase of resistance
(c) increases with the decrease of inductance
and decrease of resistance
(d) increases with decrease of inductance
and increase of resistance
Ans: a
59. Time constant of a capacitive circuit
(a) increases with the decrease of
capacitance and decrease of resistance
(b) increases with the decrease of
capacitance and increase of resis¬tance
(c) increases with the increase of
capacitance and decrease of resis¬tance
(d) increase with increase of capacitance and
increase of resis¬tance
Ans: d
60. Magnitude of current at resonance in RL-C circuit
(a) depends upon the magnitude of R
(b) depends upon the magnitude of L
(c) depends upon the magnitude of C
(d) depends upon the magnitude of R,
LandC
Ans: a
61. In a R-L-C circuit
(a) power is consumed in resistance and is
equal to I R
(b) exchange of power takes place between
inductor and supply line
(c) exchange of power takes place between
capacitor and supply line
(d) exchange of power does not take place
between resistance and the supply line
(e) all above are correct
Ans: e
62. In R-L-C series resonant circuit
magnitude of resonance frequency can be
changed by changing the value of
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(a) R only
(b) L only
(c) C only
(d) L or C
(e) R,L or C
Ans: d
63. In a series L-C circuit at the resonant
frequency the
(a) current is maximum
(b) current is minimum
(c) impedance is maximum
(d) voltage across C is minimum
Ans: a
64. The time constant of a series R-C circuit
is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c
65. If resistance is 20 Q. and inductance is
27 in a R-L series circuit, then time constant
of this circuit will be
(a) 0.001 s
(b) 0.1 s
(c) 10 s
(d) 100 s
Ans: b
66. Which of the following coil will have
large resonant frequency ?
(a) A coil with large resistance
(b) A coil with low resistance
(c) A coil with large distributed capacitance
(d) A coil with low distributed capacitance
Ans: c
67. If a sinusoidal wave has frequency of 50
Hz with 30 A r.m.s. current which of the
following equation represents this wave ?
(a) 42.42 sin 3141
(b) 60 sin 25 t
(c) 30 sin 50 t
(d) 84.84 sin 25 t
Ans: a
68. The safest value of current the human
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body can carry for more than 3 second is
(a) 4 mA
(b) 9 mA
(c) 15 mA
(d) 25 mA
Ans: b
69. A pure inductance connected across 250
V, 50 Hz supply consumes 100 W.
This consumption can be attributed to
(a) the big size of the inductor
(b) the reactance of the inductor
(c) the current flowing in the inductor
(d) the statement given is false
Ans: d
70. The input of an A.C. circuit having
power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
(a) 12 kW
(b) 22 kW
(c) 32 kW
(d) 64 kW
Ans: c
71. The effective resistance of an iron-cored
choke working on ordinary supply
frequency is more than its true resistance
because of
(a) iron loss in core
(b) skin effect
(c) increase in temperature
(d) capacitive effect between adjacent coil
turns
Ans: a
72. In an AC. circuit, a low value of kVAR
compared with kW indicates
(a) low efficiency
(b) high power factor
(c) unity power factor
(d) maximum load current
Ans: b
73. In AC. circuits, laminated iron is
invariably used in order to
(a) reduce eddy current loss
(b) increase heat radiation
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(c) make assembly cheap and easier
(d) reduce circuit permeability
Ans: a
74. The ratio of active power to apparent
power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c
75. All definitions of power factor of a
series R-L-C circuit are correct except
(a) ratio of net reactance and impedance
(b) ratio of kW and kVA
(c) ratio of J and Z
(d) ratio of W and VA
Ans: a
76. The apparent power drawn by an A.C.
circuit is 10 kVA and active power is 8 kW.
The reactive power in the circuit is
(a) 4 kVAR
(b) 6 kVAR
(c) 8 kVAR
(d) 16 kVAR
Ans: b
77. What will be the phase angle between
two alternating waves of equal frequency,
when one wave attains maximum value the
other is at zero value ?
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Ans: c
78. The purpose of a parallel circuit
resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b
79. In an A.C. circuit power is dissipated in
(a) resistance only
(b) inductance only
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(c) capacitance only
(d) none of the above
Ans: a
80. In a parallel R-C circuit, the current
always______the applied voltage
(a) lags
(b) leads
(c) remains in phase with
(d) none of the above
Ans: b
81. At very low frequencies a series R-C
circuit behaves as almost purely
(a) resistive
(b) inductive
(c) capacitive
(d) none of the above
Ans: c
82. Skin effect occurs when a conductor
carries current at _____ frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d
83. At ______ frequencies the parallel R-L
circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d
84. In a sine wave the slope is constant
(a) between 0° and 90°
(b) between 90° and 180°
(c) between 180° and 270°
(d) no where
Ans: d
85. The power is measured in terms of
decibles in case of
(a) electronic equipment
(b) transformers
(c) current transformers
(d) auto transformers
Ans: a
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86. Capacitive susceptance is a measure of
(a) reactive power in a circuit
(b) the extent of neutralisation of reactive
power in a circuit
(c) a purely capacitive circuit's ability to
pass current
(d) a purely capacitive circuit's ability to
resist the flow of current
Ans: c
87. Which of the following statements
pertains to resistors only ?
(a) can dissipate considerable amount of
power
(6) can act as energy storage devices
(c) connecting them in parallel in¬creases
the total value
(d) oppose sudden changes in voltage
Ans: a
88. Which of the following refers to a
parallel circuit ?
(a) The current through each element is
same
(b) The voltage across element is in
proportion to it's resistance value
(c) The equivalent resistance is greater than
any one of the resistors
(d) The current through any one element is
less than the source current
Ans: d
89. Aphasoris
(a) a line which represents the mag¬nitude
and phase of an alternating quantity
(b) a line representing the magnitude and
direction of an alternating quantity
(c) a coloured tag or band for distinction
between different phases of a 3-phase supply
(d) an instrument used for measuring
phases of an unbalanced 3-phase load
Ans: a
89. A parallel AC. circuit in resonance will
(a) have a high voltage developed across
each inductive and capacitive section
(b) have a high impedance
(c) act like a resistor of low value
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(d) have current in each section equal to the
line current
Ans: b
90. Wire-wound resistors are unsuitable for
use at high frequencies because they
(a) create more electrical noise
(b) are likely to melt under excessive eddy
current heat
(c) consume more power
(d) exhibit unwanted inductive and
capacitive effects
Ans: d
91. The inductance of a coil can be
increased by
(a) increasing core length
(b) decreasing the number of turns
(c) decreasing the diameter of the former
(d) choosing core material having high
relative permeability
Ans: d
92. In a three-phase supply floating neutral
is undesirable because it way give rise to
(a) high voltage across the load
(b) low voltage across the load
(c) unequal line voltages across the load
Ans: c
93. Which of the following waves has the
highest value of peak factor ?
(a) Square wave
(b) Sine wave
(c) Half wave rectified sine wave
(d) Triangular wave
Ans: c
94. The frequency of domestic power supply
in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d
95. The r.m.s. value of half wave rectified
sine wave is 200 V. The r.m.s. value of full
wave rectified AC. will be
(a) 282.8 V
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(b) 141.4 V
(c) 111 V
(d) 100 V
Ans: a
96. The r.m.s. value of pure cosine function
is
(a) 0.5 of peak value
(b) 0.707 of peak value
(c) same as peak value
(d) zero
Ans: b
97. Ohm is unit of all of the following
except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d) capacitance
Ans: d
98. The series ;nd parallel resonance on L-C
circui' differs in that
(a) series resistance needs a low-resistance
ource for sharp rise in current
(b) series resonance needs a high-resistance
source for sharp increase in current
(c) parallel resonance needs a low-resistance
source for a sharp in¬crease in impedance
(d) parallel resonance needs a low-resistance
source for a sharp rise in line current
Ans: a
99. The phasors for which of the following
pair are 180° out of phase for VL, VC and
VR?
(a) Vc and VR
(b) VL and VR
(c) Vc and VL
(d) none of the above
Ans: c
100. The frequency of an alternating
current is
(a) the speed with which the alternator runs
(b) the number of cycles generated in one
minute
(c) the number of waves passing through a
point in one second
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(d) the number of electrons passing through
a point in one second
Ans: c
101. A pure capacitor connected across an
A.C. voltage consumed 50 W. This is due to
(a) the capacitive reactance in ohms
(b) the current flowing in capacitor
(c) the size of the capacitor being quite big
(d) the statement is incorrect
Ans: d
102. The power factor of a D.C. circuit is
always
(a) less than unity
(b) unity
(c) greater than unity
(d) zero
Ans: b
103. The product of apparent power and
cosine of the phase angle between circuit
voltage and current is
(a) true power
(b) reactive power
(c) volt-amperes
(d) instantaneous power
Ans: a
104. The equation of 50 Hz current sine
wave having r.m.s. value of 60 A is
(a) 60 sin 25 t
(b) 60 sin 50 t
(c) 84.84 sin 3141
(d) 42.42 sin 314 t
Ans: c
105. An A.C. voltage is impressed across a
pure resistance of 3.5 ohms in parallel with a
pure inductance of impedance of 3.5 ohms,
(a) the current through the resistance is more
(b) the current through the resistance is less
(c) both resistance and inductance carry
equal currents
(d) none of the above
Ans: c
106. In a pure inductive circuit if the supply
frequency is reduced to 1/2, the current will
(a) be reduced by half
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(b) be doubled
(c) be four times as high
(d) be reduced to one fourth
Ans: b
107. In a pure capacitive circuit if the supply
frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times at high
(d) be reduced to one fourth
Ans: a
108. When an alternating current passes
through an ohmic resistance the electrical
power converted into heat is
(a) apparent power
(b) true power
(c) reactive power
(d) none of the above
Ans: b
109. In each of the three coils of a three
phase generator, an alternating voltage
having an r.m.s. value of 220 V is induced.
Which of the following values is indicated
by the voltmeters ?
(a) 220 V
(b) 220V3V
(c) 220/V3 V
(d) none of the above
Ans: a
A.C. Fundamentals, Circuits and
Circuit Theory
1. A sine wave has a frequency of 50 Hz.
Its angular frequency is _______
radian/second.
(a) 100 n
(b) 50 jt
(c) 25 jt
(d) 5 n
Ans: a
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2. The reactance offered by a capacitor to
alternating current of frequency 50 Hz is
20 Q. If frequency is increased to 100 Hz,
reactance becomes_____ohms.
(a) 2.5
(b) 5
(c) 10
(d) 15
Ans: c
3. The period of a wave is
(a) the same as frequency
(6) time required to complete one cycle
(c) expressed in amperes
(d) none of the above
Ans: b
4. The form factor is the ratio of
(a) peak value to r.m.s. value
(6) r.m.s. value to average value
(c) average value to r.m.s. value
(d) none of the above
Ans: b
5. The period of a sine wave is _____
seconds.
Its frequency is
(a) 20 Hz
(b) 30 Hz
(c) 40 Hz
(d) 50 Hz
Ans: d
6. A heater is rated as 230 V, 10 kW, A.C.
The value 230 V refers to
(a) average voltage
(b) r.m.s. voltage
(c) peak voltage
(d) none of the above
Ans: b
7. If two sinusoids of the same frequency
but of different amplitudes and phase angles
are subtracted, the resultant is
(a) a sinusoid of the same frequency
(b) a sinusoid of half the original frequency
(c) a sinusoid of double the frequency
(d) not a sinusoid
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Ans: a
8. The peak value of a sine wave is 200 V.
Its average value is
(a) 127.4 V
(b) 141.4 V
(c) 282.8 V
(d)200V
Ans: a
9. If two sine waves of the same frequency
have a phase difference of JT radians, then
(a) both will reach their minimum values at
the same instant
(b) both will reach their maximum values at
the same instant
(c) when one wave reaches its maximum
value, the other will reach its minimum
value
(d) none of the above
Ans: c
10. The voltage of domestic supply is 220V.
This figure represents
(a) mean value
(b) r.m.s. value
(c) peak value
(d) average value
Ans: a
11. Two waves of the same frequency have
opposite phase when the phase angle
between them is
(a) 360°
(b) 180°
(c) 90°
(d) 0°
Ans: b
12. The power consumed in a circuit
element will be least when the phase
difference between the current and
voltage is
(a) 180"
(b) 90°
(c) 60°
(d) 0°
Ans: b
13. The r.m.s. value and mean value is the
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same in the case of
(a) triangular wave
(6) sine wave
(c) square wave
(d) half wave rectified sine wave
Ans: c
14. For the same peak value which of the
following wave will 'have the highest r.m.s.
value ?
(a) square wave
(b) half wave rectified sine wave
(c) triangular wave
(d) sine wave
Ans: a
15. For the same peak value, which of the
following wave has the least mean value ?
(a) half wave rectified sine wave
(b) triangular wave
(c) sine wave
(d) square wave
Ans: a
16. For a sine wave with peak value Imax
the r.m.s. value is
(a) 0.5 Imax
(b) 0.707
(c) 0.9
(d) 1.414 Lmax
Ans: b
17. Form Factor is the ratio of
(a) average value/r.m.s. value
(b) average value/peak value
(e) r.m.s. value/average value
(d) r.m.s. value/peak value
Ans: c
18. Form factor for a sine wave is
(a) 1.414
(b) 0.707
(c) 1.11
(d) 0.637
Ans: c
19. For a sine wave with peak value
Emax______8.30. the average value is
(a) 0.636 Emax
(b) 0.707 Emax
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(c) 0.434 EWc
(d) lAUEmax
Ans: a
20. For a frequency of 200 Hz, the time
period will be
(a) 0.05 s
(b) 0.005 s
(c) 0.0005 s
(d) 0.5 s
Ans: b
21. The phase difference between voltage
and current wave through a circuit element
is given as 30°. The essential condition is
that
(a) both waves must have same frequency
(b) both waves must have identical peak
values
(c) both waves must have zero value at the
same time
(d) none of the above
Ans: a
22. The r.m.s. value of a sinusoidal A.C.
current is equal to its value at an angle
of______degrees.
(a) 90
(b) 60
(c) 45
(d) 30
Ans: c
23. Capacitive reactance is more when
(a) capacitance is less and frequency of
supply is less
(b) capacitance is less and frequency of
supply is more
(c) capacitance is more and frequency of
supply is less
(d) capacitance is more and frequency of
supply is more
Ans: a
24. In a series resonant circuit, the
impedance of the circuit is
(a) minimum
(b) maximum
(c) zero
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(d) none of the above
Ans: a
25. Power factor of an electrical circuit is
equal to
(a) R/Z
(b) cosine of phase angle difference between
current and voltage
(c) kW/kVA
(d) ratio of useful current to total current
Iw/I
(e) all above
Ans: e
26. The best place to install a capacitor is
(a) very near to inductive load
(b) across the terminals of the inductive load
(c) far away from the inductive load
(d) any where
Ans: b
27. Poor power factor
(a) reduces load handling capability of
electrical system
(b) results in more power losses in the
electrical system
(c) overloads alternators, transformers and
distribution lines
(d) results in more voltage drop in the line
(e) results in all above
Ans: e
28. Capacitors for power factor correction
are rated in
(a) kW
(b) kVA
(c) kV
(d) kVAR
Ans: d
29. In series resonant circuit, increasing
inductance to its twice value and reducing
capacitance to its half value
(a) will change the maximum value of
current at resonance
(6) will change the resonance frequency
(c) will change the impedance at resonance
frequency
(d) will increase the selectivity of the circuit
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Ans: d
30. Pure inductive circuit
(a) consumes some power on average
(b) does not take power at all from a line
(c) takes power from the line during some
part of the cycle and then returns back to it
during other part of the cycle
(d) none of the above
Ans: c
31. Inductance affects the direct current flow
(a) only at the time of turning off
(b) only at the time of turning on
(c) at the time of turning on and off
(d) at all the time of operation
Ans: c
32. Inductance of a coil Varies
(a) directly as the cross-sectional area of
magnetic core
(b) directly as square of number of turns
(c) directly as the permeability of the core
(d) inversely as the length of the iron path
(e) as (a) to (d)
Ans: e
33. All the rules and laws of D.C. circuit
also apply to A.C. circuit containing
(a) capacitance only
(b) inductance only
(c) resistance only
(d) all above
Ans: c
34. Time constant of an inductive circuit
(a) increases with increase of inductance and
decrease of resistance
(b) increases with the increase of inductance
and the increase of resistance
(c) increases with decrease of inductance
and decrease of resistance
(d) increases with decrease of inductance
and increase of resistance
Ans: a
35. Power factor of an inductive circuit is
usually improved by connecting capacitor to
it in
(a) parallel
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(b) series
(c) either (a) or (b)
(d) none of the above
Ans: a
36. In a highly capacitive circuit the
(a) apparent power is equal to the actual
power
(b) reactive power is more than the apparent
power
(c) reactive power is more than the actual
powetf
(d) actual power is more than its reactive
power
Ans: c
37. Power factor of the following circuit will
be zero
(a) resistance
(b) inductance
(c) capacitance
(d) both (b) and (c)
Ans: d
38. Power factor of the following circuit will
be unity
(a) inductance
(b) capacitance
(c) resistance
(d) both (a) and (b)
Ans: c
39. Power factor of the system is kept high
(a) to reduce line losses
(b) to maximise the utilization of the
capacities of generators, lines and
transformers
(c) to reduce voltage regulation of the line
(d) due to all above reasons
Ans: d
40. The time constant of the capacitance
circuit is defined as the time during which
voltage
(a) falls to 36.8% of its final steady value
(b) rises to 38.6% of its final steady value
(c) rises to 63.2% of its final steady value
(d) none of the above
Ans: c
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41. In a loss-free R-L-C circuit the transient
current is
(a) oscillating
(b) square wave
(c) sinusoidal
(d) non-oscillating
Ans: c
42. The r.m.s. value of alternating current is
given by steady (D.C.) current which when
flowing through a given circuit for a given
time produces
(a) the more heat than produced by A.C.
when flowing through the same circuit
(b) the same heat as produced by A.C. when
flowing through the same circuit
(c) the less heat than produced by A.C.
flowing through the same circuit
(d) none of the above
Ans: b
43. The square waveform of current has
following relation between r.m.s. value and
average value.
(a) r.m.s. value is equal to average value
(b) r.m.s. value of current is greater than
average value
(c) r.m.s. value of current is less than
average value
(d) none of the above
Ans: a
44. The double energy transient occur in the
(a) purely inductive circuit
(b) R-L circuit
(c) R-C circuit
(d) R-L-C circuit
Ans: d
45. The transient currents are associated
with the
(a) changes in the stored energy in the
inductors and capacitors
(b) impedance of the circuit
(c) applied voltage to the circuit
(d) resistance of the circuit
Ans: a
46. The power factor at resonance in R-L- C
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parallel circuit is
(a) zero
(b) 0.08 lagging
(c) 0.8 leading
(d) unity
Ans: d
47. In the case of an unsymmetrical
alternating current the average value must
always be taken over
(a) unsymmetrical part of the wave form
(b) the quarter cycle
(c) the half cycle
(d) the whole cycle
Ans: d
48. In a pure resistive circuit
(a) current lags behind the voltage by 90°
(b) current leads the voltage by 90°
(c) current can lead or lag the voltage by 90°
(d) current is in phase with the voltage
Ans: d
49. In a pure inductive circuit
(a) the current is in phase with the voltage
(b) the current lags behind the voltage by
90°
(c) the current leads the voltage by 90°
(d) the current can lead or lag by 90°
Ans: b
50. In a circuit containing R, L and C, power
loss can take place in
(a) C only
(b) L only
(c) R only
(d) all above
Ans: c
51. Inductance of coil
(a) is unaffected by the supply frequency
(b) decreases with the increase in supply
frequency
(c) increases with the increase in supply
frequency
(d) becomes zero with the increase in supply
frequency
Ans: c
52. In any A.C. circuit always
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(a) apparent power is more than actual
power
(b) reactive power is more than apparent
power
(c) actual power is more than reactive power
(d) reactive power is more than actual power
Ans: a
53. Which of the following circuit
component opposes the change in the circuit
voltage ?
(a) Inductance
(b) Capacitance
(c) Conductance
(d) Resistance
Ans:
54. In a purely inductive circuit
(a) actual power is zero
(b) reactive power is zero
(c) apparent power is zero
(d) none of above is zero
Ans: a
55. Power factor of electric bulb is
(a) zero
(b) lagging
(c) leading
(d) unity
Ans: d
56. Pure inductive circuit takes power from
the A.C. line when
(a) applied voltage decreases but cur¬rent
increases
(b) applied voltage increases but cur¬rent
decreases
(c) both applied voltage and current increase
(d) both applied voltage and current
decrease
Ans: a
57. Time constant of a circuit is the time in
seconds taken after the application of
voltage to each
(a) 25% of maximum value
(b) 50% of maximum value
(c) 63% of maximum value
(d) 90% of the maximum value
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Ans: c
58. Time constant of an inductive circuit
(a) increases with increase of inductance
and decrease of resistance
(b) increases with the increase of
inductance and the increase of resistance
(c) increases with the decrease of inductance
and decrease of resistance
(d) increases with decrease of inductance
and increase of resistance
Ans: a
59. Time constant of a capacitive circuit
(a) increases with the decrease of
capacitance and decrease of resistance
(b) increases with the decrease of
capacitance and increase of resis¬tance
(c) increases with the increase of
capacitance and decrease of resis¬tance
(d) increase with increase of capacitance and
increase of resis¬tance
Ans: d
60. Magnitude of current at resonance in RL-C circuit
(a) depends upon the magnitude of R
(b) depends upon the magnitude of L
(c) depends upon the magnitude of C
(d) depends upon the magnitude of R,
LandC
Ans: a
61. In a R-L-C circuit
(a) power is consumed in resistance and is
equal to I R
(b) exchange of power takes place between
inductor and supply line
(c) exchange of power takes place between
capacitor and supply line
(d) exchange of power does not take place
between resistance and the supply line
(e) all above are correct
Ans: e
62. In R-L-C series resonant circuit
magnitude of resonance frequency can be
changed by changing the value of
(a) R only
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(b) L only
(c) C only
(d) L or C
(e) R,L or C
Ans: d
63. In a series L-C circuit at the resonant
frequency the
(a) current is maximum
(b) current is minimum
(c) impedance is maximum
(d) voltage across C is minimum
Ans: a
64. The time constant of a series R-C circuit
is given by
(a) R/C
(b) RC2
(c) RC
(d) R2C
Ans: c
65. If resistance is 20 Q. and inductance is
27 in a R-L series circuit, then time constant
of this circuit will be
(a) 0.001 s
(b) 0.1 s
(c) 10 s
(d) 100 s
Ans: b
66. Which of the following coil will have
large resonant frequency ?
(a) A coil with large resistance
(b) A coil with low resistance
(c) A coil with large distributed capacitance
(d) A coil with low distributed capacitance
Ans: c
67. If a sinusoidal wave has frequency of 50
Hz with 30 A r.m.s. current which of the
following equation represents this wave ?
(a) 42.42 sin 3141
(b) 60 sin 25 t
(c) 30 sin 50 t
(d) 84.84 sin 25 t
Ans: a
68. The safest value of current the human
body can carry for more than 3 second is
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(a) 4 mA
(b) 9 mA
(c) 15 mA
(d) 25 mA
Ans: b
69. A pure inductance connected across 250
V, 50 Hz supply consumes 100 W.
This consumption can be attributed to
(a) the big size of the inductor
(b) the reactance of the inductor
(c) the current flowing in the inductor
(d) the statement given is false
Ans: d
70. The input of an A.C. circuit having
power factor of 0.8 lagging is 40 kVA
The power drawn by the circuit is
(a) 12 kW
(b) 22 kW
(c) 32 kW
(d) 64 kW
Ans: c
71. The effective resistance of an iron-cored
choke working on ordinary supply
frequency is more than its true resistance
because of
(a) iron loss in core
(b) skin effect
(c) increase in temperature
(d) capacitive effect between adjacent coil
turns
Ans: a
72. In an AC. circuit, a low value of kVAR
compared with kW indicates
(a) low efficiency
(b) high power factor
(c) unity power factor
(d) maximum load current
Ans: b
73. In AC. circuits, laminated iron is
invariably used in order to
(a) reduce eddy current loss
(b) increase heat radiation
(c) make assembly cheap and easier
(d) reduce circuit permeability
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Ans: a
74. The ratio of active power to apparent
power is known as factor.
(a) demand
(b) load
(c) power
(d) form
Ans: c
75. All definitions of power factor of a
series R-L-C circuit are correct except
(a) ratio of net reactance and impedance
(b) ratio of kW and kVA
(c) ratio of J and Z
(d) ratio of W and VA
Ans: a
76. The apparent power drawn by an A.C.
circuit is 10 kVA and active power is 8 kW.
The reactive power in the circuit is
(a) 4 kVAR
(b) 6 kVAR
(c) 8 kVAR
(d) 16 kVAR
Ans: b
77. What will be the phase angle between
two alternating waves of equal frequency,
when one wave attains maximum value the
other is at zero value ?
(a) 0°
(b) 45°
(c) 90°
(d) 180°
Ans: c
78. The purpose of a parallel circuit
resonance is to magnify
(a) current
(b) voltage
(c) power
(d) frequency
Ans: b
79. In an A.C. circuit power is dissipated in
(a) resistance only
(b) inductance only
(c) capacitance only
(d) none of the above
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Ans: a
80. In a parallel R-C circuit, the current
always______the applied voltage
(a) lags
(b) leads
(c) remains in phase with
(d) none of the above
Ans: b
81. At very low frequencies a series R-C
circuit behaves as almost purely
(a) resistive
(b) inductive
(c) capacitive
(d) none of the above
Ans: c
82. Skin effect occurs when a conductor
carries current at _____ frequencies.
(a) very low
(b) low
(c) medium
(d) high
Ans: d
83. At ______ frequencies the parallel R-L
circuit behaves as purely resistive.
(a) low
(b) very low
(c) high
(d) very high
Ans: d
84. In a sine wave the slope is constant
(a) between 0° and 90°
(b) between 90° and 180°
(c) between 180° and 270°
(d) no where
Ans: d
85. The power is measured in terms of
decibles in case of
(a) electronic equipment
(b) transformers
(c) current transformers
(d) auto transformers
Ans: a
86. Capacitive susceptance is a measure of
(a) reactive power in a circuit
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(b) the extent of neutralisation of reactive
power in a circuit
(c) a purely capacitive circuit's ability to
pass current
(d) a purely capacitive circuit's ability to
resist the flow of current
Ans: c
87. Which of the following statements
pertains to resistors only ?
(a) can dissipate considerable amount of
power
(6) can act as energy storage devices
(c) connecting them in parallel in¬creases
the total value
(d) oppose sudden changes in voltage
Ans: a
88. Which of the following refers to a
parallel circuit ?
(a) The current through each element is
same
(b) The voltage across element is in
proportion to it's resistance value
(c) The equivalent resistance is greater than
any one of the resistors
(d) The current through any one element is
less than the source current
Ans: d
89. Aphasoris
(a) a line which represents the mag¬nitude
and phase of an alternating quantity
(b) a line representing the magnitude and
direction of an alternating quantity
(c) a coloured tag or band for distinction
between different phases of a 3-phase supply
(d) an instrument used for measuring
phases of an unbalanced 3-phase load
Ans: a
89. A parallel AC. circuit in resonance will
(a) have a high voltage developed across
each inductive and capacitive section
(b) have a high impedance
(c) act like a resistor of low value
(d) have current in each section equal to the
line current
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Ans: b
90. Wire-wound resistors are unsuitable for
use at high frequencies because they
(a) create more electrical noise
(b) are likely to melt under excessive eddy
current heat
(c) consume more power
(d) exhibit unwanted inductive and
capacitive effects
Ans: d
91. The inductance of a coil can be
increased by
(a) increasing core length
(b) decreasing the number of turns
(c) decreasing the diameter of the former
(d) choosing core material having high
relative permeability
Ans: d
92. In a three-phase supply floating neutral
is undesirable because it way give rise to
(a) high voltage across the load
(b) low voltage across the load
(c) unequal line voltages across the load
Ans: c
93. Which of the following waves has the
highest value of peak factor ?
(a) Square wave
(b) Sine wave
(c) Half wave rectified sine wave
(d) Triangular wave
Ans: c
94. The frequency of domestic power supply
in India is
(a) 200 Hz
(b) 100 Hz
(c) 60 Hz
(d) 50 Hz
Ans: d
95. The r.m.s. value of half wave rectified
sine wave is 200 V. The r.m.s. value of full
wave rectified AC. will be
(a) 282.8 V
(b) 141.4 V
(c) 111 V
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(d) 100 V
Ans: a
96. The r.m.s. value of pure cosine function
is
(a) 0.5 of peak value
(b) 0.707 of peak value
(c) same as peak value
(d) zero
Ans: b
97. Ohm is unit of all of the following
except
(a) inductive reactance
(b) capacitive reactance
(c) resistance
(d) capacitance
Ans: d
98. The series ;nd parallel resonance on L-C
circui' differs in that
(a) series resistance needs a low-resistance
ource for sharp rise in current
(b) series resonance needs a high-resistance
source for sharp increase in current
(c) parallel resonance needs a low-resistance
source for a sharp in¬crease in impedance
(d) parallel resonance needs a low-resistance
source for a sharp rise in line current
Ans: a
99. The phasors for which of the following
pair are 180° out of phase for VL, VC and
VR?
(a) Vc and VR
(b) VL and VR
(c) Vc and VL
(d) none of the above
Ans: c
100. The frequency of an alternating
current is
(a) the speed with which the alternator runs
(b) the number of cycles generated in one
minute
(c) the number of waves passing through a
point in one second
(d) the number of electrons passing through
a point in one second
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Ans: c
101. A pure capacitor connected across an
A.C. voltage consumed 50 W. This is due to
(a) the capacitive reactance in ohms
(b) the current flowing in capacitor
(c) the size of the capacitor being quite big
(d) the statement is incorrect
Ans: d
102. The power factor of a D.C. circuit is
always
(a) less than unity
(b) unity
(c) greater than unity
(d) zero
Ans: b
103. The product of apparent power and
cosine of the phase angle between circuit
voltage and current is
(a) true power
(b) reactive power
(c) volt-amperes
(d) instantaneous power
Ans: a
104. The equation of 50 Hz current sine
wave having r.m.s. value of 60 A is
(a) 60 sin 25 t
(b) 60 sin 50 t
(c) 84.84 sin 3141
(d) 42.42 sin 314 t
Ans: c
105. An A.C. voltage is impressed across a
pure resistance of 3.5 ohms in parallel with a
pure inductance of impedance of 3.5 ohms,
(a) the current through the resistance is more
(b) the current through the resistance is less
(c) both resistance and inductance carry
equal currents
(d) none of the above
Ans: c
106. In a pure inductive circuit if the supply
frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times as high
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(d) be reduced to one fourth
Ans: b
107. In a pure capacitive circuit if the supply
frequency is reduced to 1/2, the current will
(a) be reduced by half
(b) be doubled
(c) be four times at high
(d) be reduced to one fourth
Ans: a
108. When an alternating current passes
through an ohmic resistance the electrical
power converted into heat is
(a) apparent power
(b) true power
(c) reactive power
(d) none of the above
Ans: b
109. In each of the three coils of a three
phase generator, an alternating voltage
having an r.m.s. value of 220 V is induced.
Which of the following values is indicated
by the voltmeters ?
(a) 220 V
(b) 220V3V
(c) 220/V3 V
(d) none of the above
Ans: a
D.C. Generators
1. Laminations of core are generally made
of
(a) case iron
(b) carbon
(c) silicon steel
(d) stainless steel
Ans: c
2. Which of the following could be
lamina-proximately the thickness of
lamina-tions of a D.C. machine ?
(a) 0.005 mm
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(b) 0.05 mm
(c) 0.5 m
(d) 5 m
(c) brazing
(d) welding
Ans: c
9. According to Fleming's right-hand rule
for finding the direction of induced e.m.f.,
when middle finger points in the direction
of induced e.m.f., forefinger will point in
the direction of
(a) motion of conductor
(b) lines of force
(c) either of the above
(d) none of the above
3. The armature of D.C. generator is
laminated to
(a) reduce the bulk
(b) provide the bulk
(c) insulate the core
(d) reduce eddy current loss
Ans: d
4. The resistance of armature winding
depends on
(a) length of conductor
(b) cross-sectional area of the conductor
(c) number of conductors
(d) all of the above
Ans: d
5. The field coils of D.C. generator are
usually made of
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: b
6. The commutator segments are
connected to the armature conductors by
means of
(a) copper lugs
(b) resistance wires
(c) insulation pads
(d) brazing
Ans: a
7. In a commutator
(a) copper is harder than mica
(b) mica and copper are equally hard
(c) mica is harder than copper
(d) none of the above
Ans: c
8. In D.C. generators the pole shoes are
fastened to the pole core by
(a) rivets
(b) counter sunk screws
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Ans: b
Ans: b
10. Fleming's right-hand rule regarding
direction of induced e.m.f., correlates
(a) magnetic flux, direction of current flow
and resultant force
(b) magnetic flux, direction of motion and
the direction of e.m.f. induced
(c) magnetic field strength, induced voltage
and current
(d) magnetic flux, direction of force and
direction of motion of conductor
Ans: b
11. While applying Fleming's right-hand
rule to And the direction of induced
e.m.f., the thumb points towards
(a) direction of induced e.m.f.
(b) direction of flux
(c) direction of motion of the conductor if
forefinger points in the direction of
generated e.m.f.
(d) direction of motion of conductor, if
forefinger points along the lines of flux
Ans: d
12. The bearings used to support the
rotor shafts are generally
(a) ball bearings
(b) bush bearings
(c) magnetic bearmgs
(d) needle bearings
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Ans: a
13. In D.C. generators, the cause of rapid
brush wear may be
(a) severe sparking
(b) rough commutator surface
(c) imperfect contact
(d) any of the above
Ans: d
14. In lap winding, the number of brushes
is always
(a) double the number of poles
(b) same as the number of poles
(c) half the number of poles
(d) two
Ans: b
15. For a D.C. generator when the
number of poles and the number of
armature conductors is fixed, then which
winding will give the higher e.m.f. ?
(a) Lap winding
(b) Wave winding
(c) Either of (a) and (b) above
(d) Depends on other features of design
Ans: b
16. In a four-pole D.C. machine
(a) all the four poles are north poles
(b) alternate poles are north and south
(c) all the four poles are south poles
(d) two north poles follow two south poles
Ans: b
17. Copper brushes in D.C. machine are
used
(a) where low voltage and high currents are
involved
(b) where high voltage and small cur-rents
are involved
(c) in both of the above cases
(d) in none of the above casesAns: a
18. A separately excited generator as
compared to a self-excited generator
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(a) is amenable to better voltage con-trol
(b) is more stable
(c) has exciting current independent of load
current
(d) has all above features
Ans: d
19. In case of D.C. machines, mechanical
losses are primary function of
(a) current
(b) voltage
(c) speed
(d) none of aboveAns: c
20. Iron losses in a D.C. machine are
independent of variations in
(a) speed
(b) load
(c) voltage
(d) speed and voltageans: b
21. In D.C. generators, current to the
external circuit from armature is given
through
(a) commutator
(b) solid connection
(c) slip rings
(d) none of above
Ans: a
23. Brushes of D.C. machines are made of
(a) carbon
(b) soft copper
(c) hard copper
(d) all of above
Ans: a
24. If B is the flux density, I the length of
conductor and v the velocity of conductor,
then induced e.m.f. is given by
(a)Blv
(b)Blv2
(c)Bl2v
(d)Bl2v2
Ans: a
25. In case of a 4-pole D.C. generator
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provided with a two layer lap winding with
sixteen coils, the pole pitch will be
(a) 4
(b) 8
(c) 16
(d) 32
Ans: b
26. The material for commutator brushes is
generally
(a) mica
(b) copper
(c) cast iron
(d) carbon
Ans: d
27. The insulating material used between the
commutator segments is normally
(a) graphite
(b) paper
(c) mica
(d) insulating varnish
Ans: c
28. In D.C. generators, the brushes on
commutator remain in contact with
conductors which
(a) lie under south pole
(b) lie under north pole
(c) lie under interpolar region
(d) are farthest from the poles
Ans: c
29. If brushes of a D.C. generator are moved
in order to bring these brushes in magnetic
neutral axis, there will be
(a) demagnetisation only
(b) cross magnetisation as well as
magnetisation
(c) crossmagnetisation as well as
demagnetising
(d) cross magnetisation only
Ans: c
30. Armature reaction of an unsaturated
D.C. machine is
(a) crossmagnetising
(b) demagnetising
(c) magnetising
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(d) none of above
Ans: a
31. D.C. generators are connected to the
busbars or disconnected from them only
under the floating condition
(a) to avoid sudden loading of the
primemover
(b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
(d) all above
Ans: d
32. Eddy currents are induced in the pole
shoes of a D.C. machine due to
(a) oscillating magnetic field
(b) pulsating magnetic flux
(c) relative rotation between field and
armature
(d) all above
Ans: c
33. In a D.C. machine, short-circuited field
coil will result in
(a) odour of barning insulation
(b) unbalanced magnetic pull producing
vibrations
(c) reduction of generated voltage for
which excitation has to be increased to
maintain the voltage
(d) all above
Ans:
34. Equilizer rings are required in case
armature is
(a) wave wound
(b) lap wound
(c) delta wound
(d) duplex wound
Ans: b
35. Welding generator will have
(a) lap winding
(b) wave winding
(c) delta winding
(d) duplex wave winding
Ans: a
36. In case of D.C. machine winding,
number of commutator segments is equal to
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(a) number of armature coils
(b) number of armature coil sides
(c) number of armature conductors
(d) number of armature turns
Ans: a
37. For a D.C. machines laboratory
following type of D.C. supply will be
suitable
(a) rotary converter
(b) mercury are rectifier
(c) induction motor D.C. generator set
(d) synchronous motor D.C. generator set
Ans: c
38. The function of pole shoes in the case of
D.C. machine is
(a) to reduce the reluctance of the magnetic
path
(b) to spread out the flux to achieve uniform
flux density
(c) to support the field coil
(d) to discharge all the above functions
Ans: d
39. In the case of lap winding resultant pitch
is
(a) multiplication of front and back pitches
(b) division of front pitch by back pitch
(c) sum of front and back pitches
(d) difference of front and back pitches
Ans: d
40. A D.C. welding generator has
(a) lap winding
(b) wave moving
(c) duplex winding
(d) any of the above
Ans: a
41. Which of the following statement about
D.C. generators is false ?
(a) Compensating winding in a D.C.
machine helps in commutation
(b) In a D. C. generator interpoles
winding is connected in series with the
armature winding
(c) Back pitch and front pitch are both odd
and approximately equal to the pole pitch
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(d) Equilizing bus bars are used with
parallel running of D.C. shunt generators
Ans: d
42. The demagnetising component of
armature reaction in a D.C. generator
(a) reduces generator e.m.f.
(b) increases armature speed
(c) reduces interpoles flux density
(d) results in sparking trouble
Ans: a
43. Magnetic field in a D.C. generator is
produced by
(a) electromagnets
(b) permanent magnets
(c) both (a) and (b)
(d) none of the above
Ans: a
44. The number of brushes in a commutator
depends on
(a) speed of armature
(b) type of winding
(c) voltage
(d) amount of current to be collected
Ans: d
45. Compensating windings are used in D.C.
generators
(a) mainly to reduce the eddy currents by
providing local short-circuits
(b) to provide path for the circulation of
cooling air
(c) to neutralise the cross-magnetising effect
of the armature reaction
(d) none of the above
Ans: c
46. Which of the following components of a
D.C, generator plays vital role for providing
direct current of a D.C. generator ?
(a) Dummy coils
(b) Commutator
(c) Eye bolt
(d) Equilizer rings
Ans: b
47. In a D.C. generator the ripples in the
direct e.m.f. generated are reduced by
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(a) using conductor of annealed copper
(b) using commutator with large number of
segments
(c) using carbon brushes of superior quality
(d) using equiliser rings
Ans: c
48. In D.C. generators, lap winding is used
for
(a) high voltage, high current
(b) low voltage, high current
(c) high voltage, low current
(d) low voltage, low current
Ans: b
49. Two generators A and B have 6-poles
each. Generator A has wave wound
armature while generator B has lap wound
armature. The ratio of the induced e.m.f. is
generator A and B will be
(a) 2 : 3
(b) 3 : 1
(c) 3 : 2
(d) 1 : 3
Ans: b
50. The voltage drop for which of the
following types of brush can be expected to
be least ?
(a) Graphite brushes
(b) Carbon brushes
(c) Metal graphite brushes
(d) None of the above
Ans: c
51. The e.m.f. generated by a shunt wound
D.C. generator isE. Now while pole flux
remains constant, if the speed of the
generator is doubled, the e.m.f. generated
will be
(a) E/2
(b) 2E
(c) slightly less than E
(d) E
Ans: b
52. In a D.C. generator the actual flux
distribution depends upon
(a) size of air gap
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(b) shape of the pole shoe
(c) clearance between tips of the ad¬jacent
pole shoes
(d) all of the above
Ans:
53. The armature core of a D.C. generator is
usually made of
(a) silicon steel
(b) copper
(c) non-ferrous material
(d) cast-iron
Ans: a
9.63. Satisfactory commutation of D.C.
machines requires
(a) brushes should be of proper grade and
size
(b) brushes should smoothly run in the
holders
(c) smooth, concentric commutator properly
undercut
(d) all of the above
Ans: d
54. Open circuited armature coil of a D.C.
machine is
(a) identified by the scarring of the
commutator segment to which open
circuited coil is connected
(b) indicated by a spark completely around
the commutator
(c) both (a) and (b)
(d) none of the above
Ans: c
55. In a D.C. machine, fractional pitch
winding is used
(a) to increase the generated voltage
(b) to reduce sparking
(c) to save the copper because of shorter
end connections
(d) due to (b) and (c) above
Ans:
56. For the parallel operation of two or more
D.C. compound generators, we should
ensure that
(a) voltage of the incoming generator should
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be same as that of bus bar
(b) polarity of incoming generator should be
same as that of bus bar
(c) all the series fields should be run in
parallel by means of equilizer connection
(d) series fields of all generators should be
either on positive side or negative side of the
armature
(e) all conditions mentioned above should be
satisfied
Ans: d
57. D.C. series generator is used
(a) to supply traction load
(b) to supply industrial load at constant
voltage
(c) voltage at the toad end of the feeder
(d) for none of the above purpose
Ans: c
58. Following D.C. generator will be in a
position to build up without any residual
magnetism in the poles
(a) series generator
(b) shunt generator
(c) compound generator
(d) self-excited generator
Ans: d
59. Interpole flux should be sufficient to
(a) neutralise the commutating self induced
e.m.f.
(b) neutralise the armature reaction flux
(c) neutralise both the armature reaction flux
as well as commutating e.m.f. induced in the
coil
(d) perform none of the above functions
Ans: c
60. D.C. generator generally preferred for
charging automobile batteries is
(a) series generator
(b) shunt generator
(c) long shunt compound generator
(d) any of'the above
Ans: c
61. In a D.C. generator the number of
mechanical degrees and electrical degrees
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will be the same when
(a) r.p.m. is more than 300
(b) r.p.m. is less than 300
(c) number of poles is 4
(d) number of poles is 2
Ans: d
62. Permeance is the reciprocal of
(a) flux density
(b) reluctance
(c) ampere-turns
(d) resistance
Ans: b
63. In D.C. generators the polarity of the
interpoles
(a) is the same as that of the main pole ahead
(b) is the same as that of the immediately
preceding pole
(c) is opposite to that of the main pole ahead
(d) is neutral as these poles do not play part
in generating e.m.f.
Ans: a
64. The e.m.f. generated in a D.C. generator
is directly proportional to
(a) flux/pole
(b) speed of armature
(c) number of poles
(d) all of the above
Ans: b
65. In a D.C. generator the magnetic neutral
axis coincides with the geometrical neutral
axis, when
(a) there is no load on|he generator
(b) the generator runs on full load
(c) the generator runs on overload
(d) the generator runs on designed speed
Ans: a
66. In a D.C. generator in order to reduce
sparking at brushes, the self-induced e.m.f.
in the coil is neutralised by all of the
following except
(a) interpoles
(b) dummy coils
(c) compensating winding
(d) shifting of axis of brushes
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Ans: b
67. In D.C. generators on no-load, the air
gap flux distribution in space is
(a) sinusoidal
(b) triangular
(c) pulsating
(d) flat topped
Ans: d
68. A shunt generator running at 1000 r.p.m.
has generated e.m.f. as 200 V. If the speed
increases to 1200 r.p.m., the generated e.m.f.
will be nearly
(a) 150 V
(b) 175 V
(c) 240 V
(d) 290 V
Ans: c
69. The purpose of providing dummy coils
in a generator is
(a) to reduce eddy current losses
(b) to enhance flux density
(c) to amplify voltage
(d) to provide mechanical balance for the
rotor
Ans: d
70. In a shunt generator the voltage build up
is generally restricted by
(a) speed limitation
(b) armature heating
(c) insulation restrictions
(d) saturation of iron
Ans:
71. If a D.C. generator fails to build up the
probable cause could not be
(a) imperfect brush contact
(b) field resistance less than the critical
resistance
(c) no residual magnetism in the generator
(d) faulty shunt connections tending to
reduce the residual magnetism
Ans: b
72. Flashing the field of D.C. generator
means
(a) neutralising residual magnetism
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(b) creating residual magnetism by a D.C.
source
(c) making the magnetic losses of forces
parallel
(d) increasing flux density by adding extra
turns of windings on poles
Ans: b
73. The e.m.f. induced in the armature of a
shunt generator is 600 V. The armature
resistance is 0.1 ohm. If the armature current
is 200 A, the terminal voltage will be
(a) 640 V
(b) 620 V
(c) 600 V
(d) 580 V
Ans: d
74. In a D.C. generator the critical resistance
refers to the resistance of
(a) brushes
(b) field
(c) armature
(d) load
Ans: b
75. To achieve sparkless commutation
brushes of a D.C. generator are rockedm
ahead so as to bring them
(a) just ahead of magnetic neutral axis
(b) in magnetic neutral axis
(c) just behind the magnetic neutral axis
Ans: a
76. Armature coil is short circuited by
brushes when it lies
(a) along neutral axis
(b) along field axis
(c) in any of the above positions
(d) in none of the above positions
Ans: a
77. A cumulatively compounded long shunt
generator when operating as a motor would
be
(a) cumulatively compounded long shunt
(b) differentially compounded long shunt
(c) cumulatively compounded short shunt
(d) differentially compounded short shunt
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Ans: b
78. To avoid formation of grooves in the
commutator of a D.C. machine
(a) the brushes of opposite polarity should
track each other
(b) the brushes of same polarity should track
each other
(c) brush position has no effect on the
commutator grooving
Ans: a
79. The following constitute short-circuit in
the armature winding.
(a) Insulation failure between two commutator bars
(6) Insulation failure between two turns of a
coil
(c) Two of more turns of the same coil
getting grounded
(d) All of the above
Ans: d
80. The rapid wear of brushes takes place
due to
(a) abrasion from dust
(b) excessive spring pressure
(c) rough commutator bars
(d) high mica insulation between commutation bars
(e) all of the above factors
Ans: e
81. Number of tappings for each equilizer
ring is equal to
(a) number of pole pairs
(b) number of poles
(c) number of parallel paths
(d) number of commutator segments
Ans: a
82. A D.C. generator can be considered as
(a) rectifier
(b) primemover
(c) rotating amplifier
(d) power pump
Ans: c
83. In any rotating machine that part which
houses the conductors and in which e.m.f.
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induced is to be utilised is called
(a) rotor
(b) stator
(c) field
(d) armature
Ans: d
84. In a D.C. machine stray loss is the sum
of
(a) total copper loss and mechanical loss
(b) armature copper loss and iron loss
(c) shunt field copper loss and mechanical
loss
(d) iron loss and mechanical loss
Ans: d
85. Lap winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple
of poles + 2
(d) that even number which is exact multiple
of poles
Ans: a
86. In a D.C. generator in case the resistance
of the field winding is increased, then output
voltage will
(a) increase
(b) decrease
(c) remain unaffected
(d) fluctuate heavily
Ans: b
87. An exciter for a turbo generator is a
(a) separately excited generator
(b) shunt generator
(c) series generator
(d) compound generator
Ans: b
88. In case of a flat compounded generator
(a) voltage generated is less than the rated
voltage
(b) generated voltage is proportional to the
load on the generator
(c) voltage remains constant irrespec¬tive of
the load
(d) speed varies in proportion to the load on
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the generator
Ans: c
89. Which of the following generator will
have negligible terminal voltage while
running on no-load ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) Separately excited generator
Ans: a
90. Which of the following D.C. generators
will be in a position to build up without any
residual magnetism in the poles ?
(a) Series generator
(b) Shunt generator
(c) Compound generator
(d) None of the above
Ans: d
91. In over compounded generator, full load
terminal voltage is
(a) almost zero
(b) less than noload terminal voltage
(c) more than noload terminal voltage
(d) equal to no-load terminal voltage
Ans: c
92. In a level compounded D.C. generator,
full load terminal voltage is
(a) negligibly low
(b) equal to no-load terminal voltage
(c) more than no-load terminal voltage
(d) less than no-load terminal voltage
Ans: b
93. The terminal voltage of a D.C. shunt
generator drops on load because of all of the
following reasons except
(a) armature reaction
(b) armature resistance drop
(c) field weakening due to armature reaction
and armature
(d) commutation
Ans: d
94. In a D.C. generator
(a) external resistance = internal characteristic - armature reaction
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(b) internal characteristic = magnetisation
characteristic - ohmic drop
(c) external characteristic = magnetisation
characteristic - ohmic drop - armature
reaction
(d) magnetisation characteristic = external
characteristic
Ans: c
95. A sinusoidal voltage of 5 Hz is applied
to the field of a shunt generator. The
armature voltage wave
(a) will be zero
(b) will be of 5 Hz
(c) willbeof5xiVHz
(d) will be of v Hz 5
Ans: b
96. A 220 V D.C. generator is run at full
speed without any excitation. The open
circuit voltage will be
(a) zero
(b) about 2 V
(c) about 50 V
(d) 220 V
Ans: b
97. In a separately excited generator
supplying rated load the armature reaction ,
(a) is always present
(b) is always absent
(c) may be sometimes present
(d) none of the above
Ans: a
98. If residual magnetism is present in a
D.C. generator, the induced e.m.f. at zero
speed will be
(a) zero
(b) small
(c) the same as rated voltage
(d) high
Ans: a
99. Armature reaction in a generator results
in
(a) demagnetisation of leading pole tip and
magnetisation of trailing pole tip
(b) demagnetisation of trailing pole tip and
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magnetisation of leading pole tip
(c) damagnetising the centre of all poles
(d) magnetising the centre of all poles
Ans: a
100. Following energized winding of a D.C.
machine should not be opened as it would
produce high inductive voltage which may
be dangerous to personnel and may cause its
own insulation failure.
(a) Series field
(b) Compensating field
(c) Inter pole field
(d) Shunt field
Ans: d
101. Wave winding is composed of
(a) any even number of conductors
(b) any odd number of conductors
(c) that even number which is exact multiple
of poles + 2
(d) that even number which is exact multiple
of poles
Ans: c
102. The critical resistance of the D.C.
generator is the resistance of
(a) field
(b) brushes
(c) armature
(d) load
Ans: a
103. When two D.C. series generators are
running in parallel, an equilizer bar is used
(a) to increase the speed and hence
generated e.m.f.
(b) to increase the series flux
(c) so that two similar machines will pass
approximately equal currents to the load
(d) to reduce the combined effect of armature reaction of both machines
Ans: c
104. Which of the following generating
machine will offer constant voltage on all
loads ?
(a) Self-excited generator
(b) Separately excited generator
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(c) Level compounded generator .
(d) All of the above
Ans: c
105. Which of the following generators will
be preferred if they are required to be run in
parallel ?
(a) Shunt generators
(b) Series generators
(c) Compound generators
(d) None of the above
Ans: a
106. Two generators are running in parallel.
One of the generators may run as motor for
which of the following reasons ?
(a) The direction of that generator is
reversed
(b) The speed of that generator is increased
(c) The field of that generator is weakened
(d) That generator takes large share of loads
Ans: d
107. A D.C. generator works on the
principle of
(a) Lenz's law
(b) Ohm's law
(c) Faraday's law of electromagnetic
induction
(d) none of the above
Ans: c
108. A series generator can self-excite
(a) only if the load current is zero
(b) only if the load current is not zero
(c) irrespective of the value of load current
(d) none of the above
Ans: b
109. A shunt generator can self-excite
(a) only if the resistance of the field circuit
is less than critical value
(b) only if the resistance of the field circuit
is greater than critical value
(c) irrespective of the value of the resistance in the field circuit
Ans: a
110. The terminal voltage of a series
generator is 150 V when the load current is
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5 A. If the load current is increased to 10 A,
the terminal voltage will be
(a) 150 V
(b) less than 150 V
(c) greater than 150 V
(d) none of the above
Ans: c
111. The open circuit voltage of a compound
generator is 250 V. At full load the terminal
voltage
(a) will be less than 250 V
(b) will always be 250 V
(c) may be greater or less than 250 V
(d) none of the above
Ans: c
112. Two D.C. shunt generators, each with
armature resistance of 0.02 ohm and field
resistance of 50 ohm run in parallel and
supply a total current of 1000 amperes to the
load circuit. If their e.m.fs. are 270 V and
265 V, their bus bar voltage will be
(a) 270 V
(b) 267.5 V
(c) 265 V
(d) 257.4 V
Ans: b
113. The essential condition for parallel
operation of two D.C. generators is that they
have '
(a) same kW rating
(b) the same operation r.p.m.
(c) the same drooping voltage characteristics
(d) same percentage regulation
Ans: c
114. When two D.C. generators are running
in parallel an equilizer bar is used
(a) to increase the series flux
(b) to increase the generated e.m.f.
(c) to reduce the combined effect of armature reaction of both the machines
(d) so that the two identical machines will
pass approximately equal currents to the
load
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Ans: d
115. With a D.C. generator which of the
following regulation is preferred ?
(a) 100% regulation
(b) infinite regulation
(c) 50% regulation
(d) 1% regulation
Ans: d
116. Which generator would you prefer for
feeding long D.C. transmission lines ?
(a) Series generator
(b) Shunt generator
(c) Over compound generator
(d) Flat compound generator
Ans: c
117. In a D.C. generator the critical
resistance can be increased by
(a) increasing its field resistance
(b) decreasing its field resistance
(c) increasing its speed
(d) decreasing its speed
Ans: c
118. The number of armature parallel paths
in a two-pole D.C. generator having duplex
lap winding is
(a) 2
(b) 4
(c) 6
(d) 8
Ans: b
119. For both lap and wave windings, there
are as many commutator bars as the number
of
(a) slots
(b) armature conductors
(c) winding elements
(d) poles
Ans: c
120. The series field of a short-shunt D.C.
generator is excited by
(a) external current
(b) armature current
(c) shunt current
(d) load current
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Ans: d
121. As a result of armature reaction, the
reduction in the total mutual air gap flux in a
D.C. generator is approximately
(a) 40 percent
(b) 25 percent
(c) 10 percent
(d) 5 percent
Ans: d
122. Shunt generators are most suited for
stable parallel operation because of their
(a) rising voltage characteristics
(b) identical voltage characteristics
(c) drooping voltage characteristics
(d) linear voltage characteristics
Ans: c
123. The main factor which leads to unstable
parallel operation of flat and over
compounded generators is
(a) their rising voltage characteristics
(b) unequal number of turns in their series
field windings
(c) unequal speed regulation of their
primemovers
(d) unequal series field resistances
Ans: a
124. If a self excited D.C. generator after
being installed, fails to build up on its first
trial run, the first thing to do is to
(a) reverse the field connections
(b) increase the field resistance
(c) increase the speed of primemover
(d) check armature insulation resis¬tance
Ans: a
Electromagnetic Induction
1. The property of coil by which a counter
e.m.f. is induced in it when the current
through the coil changes is known as
(a) self-inductance
(b) mutual inductance
(c) series aiding inductance
(d) capacitance
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Ans: a
2. As per Faraday's laws of
electromagnetic induction, an e.m.f. is
induced in a conductor whenever it
(a) lies perpendicular to the magnetic flux
(b) lies in a magnetic field
(e) cuts magnetic flux
(d) moves parallel to the direction of the
magnetic field
Ans: c
3. Which of the following circuit element
stores energy in the electromagnetic field
?
(a) Inductance
(b) Condenser
(c) Variable resistor
(d) Resistance
Ans: a
4. The inductance of a coil will increase
under all the following conditions except
(a) when more length for the same number
of turns is provided
(6) when the number of turns of the coil
increase
(c) when more area for each turn is provided
(d) when permeability of the core increases
Ans: a
5. Higher the self-inductance of a coil,
(a) lesser its weber-turns
(b) lower the e.m.f. induced
(c) greater the flux produced by it
(d) longer the delay in establishing steady
current through it
Ans: d
6. In an iron cored coil the iron core is
removed so that the coil becomes an air
cored coil. The inductance of the coil will
(a) increase
(b) decrease
(c) remain the same
(d) initially increase and then decrease
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Ans: b
7. An open coil has
(a) zero resistance and inductance
(b) infinite resistance and zero inductance
(c) infinite resistance and normal inductance
(d) zero resistance and high inductance
Ans: b
8. Both the number of turns and the core
length of an inductive coil are doubled.
Its self-inductance will be
(a) unaffected
(b) doubled
(c) halved
(d) quadrupled
Ans: b
9. If current in a conductor increases then
according to Lenz's law self-induced voltage
will
(a) aid the increasing current
(b) tend to decrease the amount of cur-rent
(c) produce current opposite to the increasing current
(d) aid the applied voltage
Ans: c
10. The direction of incViced e.m.f. can be
found by
(a) Laplace's law
(b) Lenz's law
(c) Fleming's right hand rule
(d) Kirchhoff s voltage law
Ans: b
11. Air-core coils are practically free from
(a) hysteresis losses
(b) eddy current losses
(c) both (a) and (b)
(d) none of the above
Ans: c
12. The magnitude of the induced e.m.f. in a
conductor depends on the
(a) flux density of the magnetic field
(b) amount of flux cut
(c) amount of flux linkages
(d) rate of change of flux-linkages
Ans: d
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13. Mutually inductance between two
magnetically-coupled coils depends on
(a) permeability of the core
(b) the number of their turns
(c) cross-sectional area of their com-mon
core
(d) all of the above
Ans: d
14. A laminated iron core has reduced
eddy-current losses because
(a) more wire can be used with less D.C.
resistance in coil
(b) the laminations are insulated from each
other
(c) the magnetic flux is concentrated in the
air gap of the core
(d) the laminations are stacked vertf-cally
Ans: b
15. The law that the induced e.m.f. and
current always oppose the cause producing
them is due to
(a) Faraday
(b) Lenz
(c) Newton
(d) Coulomb
Ans: b
16. Which of the following is not a unit of
inductance ?
(a) Henry
(b) Coulomb/volt ampere
(c) Volt second per ampere
(d) All of the above
Ans: b
17. In case of an inductance, current is
proportional to
(a) voltage across the inductance
(b) magnetic field
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: b
18. Which of the following circuit elements
will oppose the change in circuit current ?
(a) Capacitance
(b) Inductance
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(c) Resistance
(d) All of the above
Ans: b
19. For a purely inductive circuit which of
the following is true ?
(a) Apparent power is zero
(b) Relative power is.zero
(c) Actual power of the circuit is zero
(d) Any capacitance even if present in the
circuit will not be charged
Ans: c
20. Which of the following is unit of
inductance ?
(a) Ohm
(b) Henry
(c) Ampere turns
(d) Webers/metre
Ans: b
21. An e.m.f. of 16 volts is induced in a coil
of inductance 4H. The rate of change of
current must be
(a) 64 A/s
(b) 32 A/s
(c) 16 A/s
(d) 4 A/s
Ans: d
22. The core of a coil has a length of 200
mm. The inductance of coil is 6 mH. If the
core length is doubled, all other quantities,
remaining the same, the in ductance will be
(a) 3 mH
(b) 12 mH
(c) 24mH
(d)48mH
Ans: a
23. The self inductances of two coils are 8
mH and 18 mH. If the co-efficients of
coupling is 0.5, the mutual inductance of the
coils is
(a) 4 mH
(b) 5 mH
(c) 6 mH
(d) 12 mH
Ans: c
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24. Two coils have inductances of 8 mH and
18 mH and a co-efficient of coupling of 0.5.
If the two coils are connected in series
aiding, the total inductance will be
(a) 32 mH
(b) 38 mH
(c) 40 mH
(d) 48 mH
Ans: b
25. A 200 turn coil has an inductance of 12
mH. If the number of turns is increased to
400 turns, all other quantities (area, length
etc.) remaining the same, the inductance will
be
(a) 6 mH
(b) 14 mH
(c) 24 mH
(d) 48 mH
Ans: d
26. Two coils have self-inductances of 10 H
and 2 H, the mutual inductance being zero.
If the two coils are connected in series, the
total inductance will be
(a) 6 H
(b) 8 H
(c) 12 H
(d) 24 H
Ans: c
27. In case all the flux from the current in
coil 1 links with coil 2, the co-efficient of
coupling will be
(a) 2.0
(b) 1.0
(c) 0.5
(d) zero
Ans: b
28. A coil with negligible resistance has 50V
across it with 10 mA. The inductive
reactance is
(a) 50 ohms
(b) 500 ohms
(c) 1000 ohms
(d) 5000 ohms
Ans: d
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29. A conductor 2 metres long moves at
right angles to a magnetic field of flux
density 1 tesla with a velocity of 12.5 m/s.
The induced e.m.f. in the conductor will be
(a) 10 V
(6) 15 V
(c) 25V
(d) 50V
Ans: c
30. Lenz's law is a consequence of the law
of conservation of
(a) induced current
(b) charge
(c) energy
(d) induced e.m.f.
Ans: c
31. A conductor carries 125 amperes of
current under 60° to a magnetic field of 1.1
tesla. The force on the conductor will be
nearly
(a) 50 N
(b) 120 N
(c) 240 N
(d) 480 N
Ans: b
32. Find the force acting on a conductor 3m
long carrying a current of 50 amperes at
right angles to a magnetic field having a flux
density of 0.67 tesla.
(a) 100 N
(b) 400 N
(c) 600 N
(d) 1000 N
Ans: a
33. The co-efficient of coupling between
two air core coils depends on
(a) self-inductance of two coils only
(b) mutual inductance between two coils
only
(c) mutual inductance and self inductance of
two coils
(d) none of the above
Ans: c
34. An average voltage of 10 V is induced in
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a 250 turns solenoid as a result of a change
in flux which occurs in 0.5 second. The total
flux change is
(a) 20 Wb
(b) 2 Wb
(c) 0.2 Wb
(d) 0.02 Wb
Ans: d
35. A 500 turns solenoid develops an
average induced voltage of 60 V. Over what
time interval must a flux change of 0.06 Wb
occur to produce such a voltage ?
(a) 0.01 s
(b) 0.1 s
(c) 0.5 s
(d) 5 s
Ans: c
36. Which of the fpllowing inductor will
have the least eddy current losses ?
(a) Air core
(b) Laminated iron core
(c) Iron core
(d) Powdered iron core
Ans: a
37. A coil induces 350 mV when the current
changes at the rate of 1 A/s. The value of
inductance is
(a) 3500 mH
(b) 350 mH
(c) 250 mH
(d) 150 mH
Ans: b
38. Two 300 uH coils in series without
mutual coupling have a total inductance
of
(a) 300 uH
(b) 600 uH
(c) 150 uH
(d) 75 uH
Ans: b
39. Current changing from 8 A to 12 A in
one second induced 20 volts in a coil.
The value of inductance is
(a) 5 mH
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(b) 10 mH
(c) 5 H
(d) 10 H
Ans: c
40. Which circuit element(s) will oppose
the change in circuit current ?
(a) Resistance only
(b) Inductance only
(c) Capacitance only
(d) Inductance and capacitance
Ans: b
41. A crack in the magnetic path of an
inductor will result in
(a) unchanged inductance
(b) increased inductance
(c) zero inductance
(d) reduced inductance
Ans: d
42. A coil is wound on iron core which
carries current I. The self-induced voltage
in the coil is not affected by
(a) variation in coil current
(b) variation in voltage to the coil
(c) change of number of turns of coil
(d) the resistance of magnetic path
Ans: b
43. A moving magnetic field will produce
the same effect as a conductor that is
moving.
(a) Yes
(b) No
Ans:
44. The polarity of the induced voltage
can be determined by using the left-hand
generator rule.
(a) Yes
(b) No
Ans: a
45. Increasing the field or increasing the
current will decrease the force on the
conductor.
(a) Yes
(b) No
Ans: b
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46. Reversing the field or the current will
reverse the force on the conductor.
(a) Yes
(b) No
Ans: a
47. When a conductor moves in the field,
so that it makes an angle 8 with the lines
of flux, the force F is given as : F = Bl sin2
0.
(a) Yes
(b) No
Ans: b
48. The self-inductance of the coil may be
defined as equal to the e.m.f. induced in
volts when the current in the circuit
changes at the rate of unit weber turns.
(a) Yes
(b) No
Ans: b
D.C Motors
1. No-load speed of which of the
following motor will be highest ?
(a) Shunt motor
(b) Series motor
(c) Cumulative compound motor
(d) Differentiate compound motor
Ans: b
2. The direction of rotation of a D.C.
series motor can be changed by
(a) interchanging supply terminals
(b) interchanging field terminals
(c) either of (a) and (b) above
(d) None of the above
Ans: b
3. Which of the following application
requires high starting torque ?
(a) Lathe machine
(b) Centrifugal pump
(c) Locomotive
(d) Air blower
Ans: c
4. If a D.C. motor is to be selected for
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conveyors, which rriotor would be preferred
?
(a) Series motor
(b) Shunt motor
(c) Differentially compound motor
(d) Cumulative compound motor
Ans: a
5. Which D.C. motor will be preferred for
machine tools ?
(a) Series motor
(b) Shunt motor
(c) Cumulative compound motor
(d) Differential compound motor
Ans: b
6. Differentially compound D.C. motors
can find applications requiring
(a) high starting torque
(b) low starting torque
(c) variable speed
(d) frequent on-off cycles
Ans: b
7. Which D.C. motor is preferred for
elevators ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
(d) Cumulative compound motor
Ans: d
8. According to Fleming's left-hand rule,
when the forefinger points in the direction of
the field or flux, the middle finger will point
in the direction of
(a) current in the conductor aovtaat of
conductor
(c) resultant force on conductor
(d) none of the above
Ans: a
9. If the field of a D.C. shunt motor gets
opened while motor is running
(a) the speed of motor will be reduced %
(b) the armature current will reduce
(c) the motor will attain dangerously high
speed 1
(d) the motor will continue to nuvat constant
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speed
Ans: c
10. Starters are used with D.C. motors
because
(a) these motors have high starting torque
(b) these motors are not self-starting
(c) back e.m.f. of these motors is zero
initially
(d) to restrict armature current as there is
no back e.m.f. while starting
Ans: d
11. In D.C. shunt motors as load is
reduced
(a) the speed will increase abruptly
(b) the speed will increase in proportion to
reduction in load
(c) the speed will remain almost/constant
(d) the speed will reduce
Ans: c
12. A D.C. series motor is that which
(a) has its field winding consisting of thick
wire and less turns
(b) has a poor torque
(c) can be started easily without load
(d) has almost constant speed
Ans: a
13. For starting a D.C. motor a starter is
required because
(a) it limits the speed of the motor
(b) it limits the starting current to a safe
value
(c) it starts the motor
(d) none of the above
Ans: b
14. The type of D.C. motor used for shears
and punches is
(a) shunt motor
(b) series motor
(c) differential compoutid D.C. motor
(d) cumulative compound D.C. motor
Ans: d
15. If a D.C. motor is connected across the
A.C. supply it will
(a) run at normal speed
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(b) not run
(c) run at lower speed
(d) burn due to heat produced in the field
winding by .eddy currents
Ans: d
16. To get the speed of D.C, motor below
the normal without wastage of electrical
energy is used.
(a) Ward Leonard control
(b) rheostatic control
(c) any of the above method
(d) none of the above method
Ans: a
17. When two D.C. series motors are
connected in parallel, the resultant speed is
(a) more than the normal speed
(b) loss than the normal speed
(c) normal speed
(d) zero
Ans: c
18. The speed of a D.C. shunt motor more
than its full-load speed can be obtained by
(a) decreasing the field current
(b) increasing the field current
(c) decreasing the armature current
(d) increasing the armature current
Ans: a
19. In a D.C. shunt motor, speed is
(a) independent of armature current
(b) directly proportional to the armature
current
(c) proportional to the square of the
current
(d) inversely proportional to the armature
current
Ans: a
20. A direct on line starter is used: for
starting motors
(a) iip to 5 H.P.
(b) up to 10 H.P.
(c) up to 15 H.P.
(d) up to 20 H.P.
Ans: a
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21. What will happen if the back e.m.f. of
a D.C. motor vanishes suddenly?
(a) The motor will stop
(b) The motor will continue to run
(c) The armature may burn
(d) The motor will run noisy
Ans: c
22. In case of D.C. shunt motors the speed
is dependent on back e.m.f. only because
(a) back e.m.f. is equal to armature drop
(b) armature drop is negligible
(c) flux is proportional to armature current
(d) flux is practically constant in D:C.
shunt motors
Ans: d
23. In a D.C. shunt motor, under the
conditions of maximum power, the current
in the armature will be
(a) almost negligible
(b) rated full-load current
(c) less than full-load current
(d) more than full-load current
Ans: d
24. These days D.C. motors are widely
used in
(a) pumping sets
(b) air compressors
(c) electric traction
(d) machine shops
Ans: c
25. By looking at which part of the motor,
it can be easily confirmed that a particular
motor is D.C. motor?
(a) Frame
(b) Shaft
(c) Commutator
(d) Stator
Ans: c
26. In which of the following applications
D.C. series motor is invariably tried?
(a) Starter for a car
(b) Drive for a water pump
(c) Fan motor
(d) Motor operation in A.C. or D.C.
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Ans: a
27. In D.C. machines fractional pitch
winding is used
(a) to improve cooling
(b) to reduce copper losses
(c) to increase the generated e.m.f.
(d) to reduce the sparking
Ans: d
28. A three point starter is considered
suitable for
(a) shunt motors
(b) shunt as well as compound motors
(c) shunt, compound and series motors
(d) all D.C. motors
Ans: b
29. In case-the conditions for maximum
power for a D.C. motor are established, the
efficiency of the motor will be
(a) 100%
(b) around 90%
(c) anywhere between 75% and 90%
(d) less than 50%
Ans: d
30. The ratio of starting torque to full-load
torque is least in case of
(a) series motors
(b) shunt motors
(c) compound motors
(d) none of the above
Ans: b
32. In D.C. motor which of the following
can sustain the maximum temperature rise?
(a) Slip rings
(b) Commutator
(c) Field winding
(d) Armature winding
Ans: c
33. Which of the following law/rule can he
used to determine the direction of rotation of
D.C. motor ?
(a) Lenz's law
(b) Faraday's law
(c) Coloumb's law
(d) Fleming's left-hand rule
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Ans: d
34. Which of the following load normally
needs starting torque more than the rated
torque?
(a) Blowers
(b) Conveyors
(c) Air compressors
(d) Centrifugal pumps
Ans: b
35. The starting resistance of a D.C. motor
is generally
(a) low
(b) around 500 Q
(c) 1000 Q
(d) infinitely large
Ans: a
36. The speed of a D.C. series motor is
(a) proportional to the armature current
(b) proportional to the square of the
armature current
(c) proportional to field current
(d) inversely proportional to the armature
current
Ans: d
37. In a D.C. series motor, if the armature
current is reduced by 50%, the torque of the
motor will be equal
to
(a) 100% of the previous value
(b) 50% of the previous value
(c) 25% of the previous value
(d) 10% of the previous value
(e) none of the above
Ans: c
38. The current drawn by the armature of
D.C. motor is directly proportional to
(a) the torque required
(b) the speed of the motor
(c) the voltage across the terminals
(d) none of the above
Ans: a
39. The power mentioned on the name
plate of an electric motor indicates
(a) the power drawn in kW
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(b) the power drawn in kVA
(c) the gross power
(d) the output power available at the shaft
Ans: d
40. Which D.C. motor has got maximum
self loading property?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded 'motor
(d) Differentially compounded motor
Ans: d
41. Which D.C. motor will be suitable
alongwith flywheel for intermittent light and
heavy loads?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: c
42. If a D.C. shunt motor is working at no
load and if shunt field circuit suddenly
opens
(a) nothing will happen to th£ motor
(b) this will make armature to take heavy
current, possibly burning it
(c) this will result in excessive speed,
possibly destroying armature due to
excessive centrifugal stresses (d) motor will
run at very slow speed
Ans: c
43. D.C. series motors are used
(a) where load is constant
(b) where load changes frequently
(c) where constant operating speed is needed
(d) in none of the above situations.
Ans: d
44. For the same H.P. rating and full load
speed, following motor has poor starting
torque
(a) shunt
(b) series
(c) differentially compounded
(d) cumulativelyc'ompounded
Ans: c
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45. In case of conductively compensated
D.C. series motors, the compensating
winding is provided
(a) as separately wound unit
(6) in parallel with armature winding
(c) in series with armature winding
(d) in parallel with field winding
Ans: c
46. Sparking at the commutator of a D.C.
motor may result in
(a) damage to commutator segments
(b) damage to commutator insulation
(c) increased power consumption
(d) all of the above
Ans: d
47. Which of the following motor is
preferred for operation in highly explosive
atmosphere ?
(a) Series motor
(b) Shunt motor
(c) Air motor
(d) Battery operated motor
Ans: c
48. If the supply voltage for a D.C. motor
is increased, which of the following will
decrease ?
(a) Starting torque
(b) Operating speed
(c) Full-load current
(d) All of the above
Ans: c
49. Which one of the following is not the
function of pole shoes in a D.C. machine ?
(a) To reduce eddy current loss
(b) To support the field coils
(c) To spread out flux for better uniformity
(d) To reduce the reluctance of the magnetic path
Ans: a
50. The mechanical power developed by a
shunt motor will be maximum when the
ratio of back e.m.f. to applied voltage is
(a) 4.0
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(b) 2.0
(c) 1.0
(d) 0.5
Ans: d
51. The condition for maximum power in
case of D.C. motor is
(a) back e.m.f. = 2 x supply voltage
(b) back e.m.f. = | x supply voltage
(c) supply voltage = | x back e.m.f.
(d) supply voltage = back e.m.f.
Ans: b
52. For which of the following
applications a D.C. motor is preferred over
an A.C. motor ?
(a) Low speed operation
(b) High speed operation
(c) Variable speed operation
(d) Fixed speed operation
Ans: c
53. In D.C. machines the residual
magnetism is of the order of
(a) 2 to 3 per cent
(6) 10 to 15 per cent
(c) 20 to 25 per cent
(d) 50 to 75 per cent
Ans: a
54. Which D.C. motor is generally
preferred for cranes and hoists ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a
55. Three point starter can be used for
(a) series motor only
(b) shunt motor only
(c) compound motor only
(d) both shunt and compound motor
Ans: d
56. Sparking, is discouraged in a D.C.
motor because
(a) it increases the input power consumption
(b) commutator gets damaged
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(c) both (a) and (b)
(d) none of the above
Ans: b
57. Speed control by Ward Leonard
method gives uniform speed variation
(a) in one direction
(b) in both directions
(c) below normal speed only
(d) above normal speed only.
Ans: b
58. Flywheel is used with D.C. compound
motor to reduce the peak demand by the
motor, compound motor will have
to be
(a) level compounded
(b) under compounded
(c) cumulatively compounded
(d) differentially compounded
Ans: c
59. Following motor is used where high
starting torque and wide speed range control
is required.
(a) Single phase capacitor start
(b) Induction motor
(c) Synchronous motor
(d) D.C. motor
(e) None of the above
Ans: d
60. In a differentially compounded D.C.
motor, if shunt field suddenly opens
(a) the motor will first stop and then run in
opposite direction as series motor
(b) the motor will work as series motor and
run at slow speed in the same direction
(c) the motor will work as series motor
and run at high speed in the same direction
(d) the motor will not work and come to
stop
Ans: a
61. Which of the following motor has the
poorest speed regulation ?
(a) Shunt motor
(b) Series motor
(c) Differential compound motor
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(d) Cumulative compound motor
Ans: b
62. Buses, trains, trolleys, hoists, cranes
require high starting torque and therefore
make use of
(a) D.C. series motor
(b) D.C. shunt motor
(c) induction motor
(d) all of above motors
Ans: a
63. As -the load is increased the speed of
D.C. shunt motor will
(a) reduce slightly
(b) increase slightly
(c) increase proportionately
(d) remains unchanged
Ans: a
64. The armature torque of the D.C. shunt
motor is proportional to
(a) field flux only
(b) armature current only
(c) both (a) and (b)
(d) none of the above
Ans: b
65. Which of the following method of
speed control of D.C. machine will offer
minimum efficiency ?
(a) Voltage control method
(b) Field control method
(c) Armature control method
(d) All above methods
Ans: c
66. Usually wide and sensitive speed
control is desired in case of
(a) centrifugal pumps
(b) elevators
(c) steel rolling mills
(d) colliery winders
Ans: d
67. The speed of a motor falls from 1100
r.p.m. at no-load to 1050 r.p.m. at rated load.
The speed regulation of the motor is
(a) 2.36%
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(6) 4.76%
(c) 6.77%
(d) 8.84%
Ans: b
68. The armature voltage control of D.C.
motor provides
(a) constant torque drive
(b) constant voltage drive
(c) constant current drive
(d) none of the above
Ans: a
69. As there is no back e.m.f. at the instant
of starting a D.C. motor, in order to prevent
a heavy current from flowing though the
armature circuit
(a) a resistance is connected in series with
armature
(b) a resistance is connected parallel to
the armature
(c) armature is temporarily open circuited
(d) a high value resistor is connected
across the field winding
Ans: a
70. The speed of a D.C. shunt motor can
be increased by
(a) increasing the resistance in armature
circuit
(b) increasing the resistance in field circuit
(c) reducing the resistance in the field
circuit
(d) reducing the resistance in the armature
circuit
Ans: b
71. If I2 be the armature current, then
speed of a D.C. shunt motor is
(a) independent of Ia
(b) proportional to la
(c) varies as (Ia)
(d) varies as la
Ans: a
72. In case the back e.m.f. and the speed of
a D.C. motor are doubled, the torque
developed by the motor will
(a) remain unchanged
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(6) reduce to one-fourth value
(c) increase four folds
(d) be doubled
Ans: a
73. At the instant of starting when a D.C.
motor is put on supply, it behaves like
(a) a highly resistive circuit
(6) a low resistance circuit
(c) a capacitive circuit
(d) none of the above
Ans: b
74. The speed of a D.C. motor can be
varied by varying
(a) field current
(b) applied voltage
(c) resistance in series with armature
(d) any of the above
Ans: d
75. Which one of the following is not
necessarily the advantage of D.C. motors
over A.C. motors ?
(a) Low cost
(b) Wide speed range
(c) Stability
(d) High starting torque.
Ans: a
76. For a D.C. shunt motor if the
excitation is changed
(a) torque will remain constant
(b) torque will change but power will
remain constant
(c) torque and power both will change
(d) torque, power and speed, all will
change
Ans: b
77. Which motor has the poorest speed
control?
(a) Differentially compounded motor
(b) Cumulatively compounded motor
(c) Shunt motor
(d) Series motor
Ans: d
78. The plugging gives the
(a) zero torque braking
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(b) smallest torque braking
(c) highest torque braking
(d) none of the above
Ans: c
79. The armature voltage control of D.C.
motor provides
(a) constant voltage drive
(b) constant current drive
(c) constant torque drive
(d) none of the above
Ans: c
80. If a D.C. motor designed for 40°C
ambient temperature is to be used for 50°C
ambient temperature, then the motor
(a) of lower H.P. should be selected
(6) of higher H.P. should be selected
(c) can be used for 50°C ambient
temperature also
(d) is to be derated by a factor recommended by manufacturer and select the next
higher H.P. motor
Ans: d
81. If the terminals of armature of D.C.
motor are interchanged, this action will offer
following kind of braking
(o) regenerative
(b) plugging
(c) dynamic braking
(d) none of the above
(e) any of the above
Ans: b
82. Which of the following motors one
will choose to drive the rotary compressor ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Universal motor
(d) Synchronous motor
Ans: d
83. If the speed of a D.C. shunt motor is
increased, the back e.m.f. of the motor will
(a) increase
(b) decrease
(c) remain same
(d) become zero
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Ans: a
84. Why are the D.C. motors preferred for
traction applications ?
(a) Torque and speed are inversely
proportional to armature current
(b) Torque is proportional to armature
current
(c) Torque is proportional to square root of
armature current
(d) The speed is inversely proportional to
the torque and the torque is proportional to
square of armature current
Ans: d
85. Which of the following motors is
usually used in house-hold refrigerators ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Single phase induction motor (split
phase start or induction run motor)
(d) Reluctance motor
(e) Synchronous motor
Ans: c
86. Which of the following motors is most
suitable for signalling devices and many
kinds of timers ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) Induction motor
(d) Reluctance motor
Ans: d
87. Which motor should not be started on
no-load ?
(a) Series motor
(b) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor.
Ans: a
88. Ward-Leonard control is basically a
(a) voltage control method
(b) field divertor method
(c) field control method
(d) armature resistance control method
Ans: a
89. For constant torque drive which speed
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control method is preferred ?
(a) Field control
(b) Armature voltage control
(c) Shunt armature control
(d) Mechanical loading system
Ans: b
90. In Ward-Leonard control the lower
limit of speed is imposed by
(a) residual magnetism of the generator
(b) core losses of motor
(c) mechanical losses of motor and
gen¬erator together
(d) all of the above
Ans: a
91. The main disadvantage of the WardLeonard control method is
(a) high initial cost
(b) high maintenance cost
(c) low efficiency at Hght loads
(d) all of the above
Ans: d
92. Regenerative method of braking is
based on that
(a) back e.m.f. is less than the applied
voltage
(b) back e.m.f. is equal to the applied
voltage
(c) back e.m.f. of rotor is more than the
applied voltage
(d) none of the above
Ans: b
93. The hysteresis loss in a D.C. machine
least depends on
(a) Frequency of magnetic reversals
(b) Maximum value of flux density
(c) Volume and grade of iron
(d) Rate of flow of ventilating air
Ans: d
94. In a D.C. generator all of the following
could be the effects of iron losses except
(a) Loss of efficiency
(b) Excessive heating of core
(c) Increase in terminal voltage
(d) Rise in temperature of ventilating air
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Ans: c
95. The losses occurring in a D.C.
generator are given below. Which loss is
likely to have highest proportion at rated
load of the generator ?
(a) hysteresis loss
(b) field copper loss
(c) armature copper loss
(d) eddy current loss
Ans: c
96. Which of the following loss in a D.C.
generator varies significantly with the load
current ?
(a) Field copper loss
(b) Windage loss
(c) Armature copper loss
(d) None of the above
Ans: c
97. Torque developed by a D.C. motor
depends upon
(a) magnetic field
(b) active length of the conductor
(c) current flow through the conductors
(d) number of conductors
(e) radius of armature
(f) all above factors
Ans: f
98. D.C. shunt motors are used for driving
(a) trains
(b) cranes
(c) hoists
(d) machine tools
Ans: d
99. In a manual shunt motor starter
(a) over load relay is connected in series
and no volt relay in parallel with the load
(6) over load relay is connected in
paral¬lel and no volt relay in series with the
load
(c) over load relay and no volt relay are
both connected in series with the load
(d) over load relay and no volt relay are
both connected in parallel with the load
Ans: a
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100. Which of the following steps is likely
to result in reduction of hysteresis loss in a
D.C. generator ?
(a) Providing laminations in armature core
(b) Providing laminations in stator
(c) Using non-magnetic material for frame
(d) Using material of low hysteresis coefficient for armature core material
Ans: d
101. Which of the following loss in a D.C.
generator is dissipated in the form of heat?
(a) Mechanical loss
(b) Core loss
(c) Copper loss
(d) All of the above
Ans: d
102. Which of the following losses are
significantly reduced by laminating the core
of a D.C. generator ?
(a) Hysteresis losses
(b) Eddy current losses
(c) Copper losses
(d) Windage losses
Ans: b
103. The total losses in a well designed
D.C. generator of 10 kW will be nearly
(a) 100 W
(b) 500 W
(c) 1000 W
(d) 1500 W
Ans: b
104. The condition for maximum
efficiency for a D.C. generator is
(a) eddy current losses = stray losses
(b) hysteresis losses = eddy current losses
(c) copper losses = 0
(d) variable losses = constant losses
Ans: d
105. D.C. generators are normally
designed for maximum efficiency around
(a) full-load
(b) rated r.p.m.
(c) rated voltage
(d) all of the above
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Ans: a
106. In a D.C. generator, the iron losses
mainly take place in
(a) yoke
(b) commutator
(c) armature conductors
(d) armature rotor
Ans: d
107. D.C. generators are installed near the
load centres to reduce
(a) iron losses
(b) line losses
(c) sparking
(d) corona losses
Ans: b
108. The purpose of retardation test on
D.C. shunt machines is to find out
(a) stray losses
(b) eddy current losses
(c) field copper losses
(d) windage losses
Ans: a
109. Which of the following tests will be
suitable for testing two similar D.C. series
motors of large capacity ?
(a) Swinburne's test
(b) Hopkinson's test
(c) Field test
(d) Brake test
Ans: c
110. Hopkinson's test on D.C. machines is
conducted at
(a) no-load
(b) part load
(c) full-load
(d) overload
Ans: c
111. During rheostat braking of D.C.
series motors
(a) motor is run as a generator
(b) motor is reversed in direction
(c) motor is run at reduced speed
Ans: a
112. For which types of D.C. motor,
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dynamic braking is generally used ?
(a) Shunt motors
(b) Series motors
(c) Compound motors
(d) All of the above
Ans: d
113. Which method of braking is generally
used in elevators ?
(a) Plugging
(b) Regenerative braking
(c) Rheostatic braking
(d) None of the above
Ans: a
114. In variable speed motor
(a) a stronger commutating field is needed
at low speed than at high speed
(b) a weaker commutating field is needed
at low speed than at high speed
(c) same commutating field is needed at
low speed than at high speed
(d) none of the above is correct
Ans: b
115. When the armature of a D.C. motor
rotates, e.m.f. induced is
(a) self-induced e.m.f.
(b) mutually induced e.m.f.
(c) back e.m.f.
(d) none of the above
Ans: c
116. Where D.C. motor of H.P. 12 or more
requires frequent starting, stopping,
reversing and speed control
(a) drum type controller is used
(b) three point starter is used
(c) four point starter is used
(d) all above can be used
Ans: a
117. If a D.C. shunt motor is working at
full load and if shunt field circuit suddenly
opens
(a) this will make armature to take heavy
current, possibly burning it
(6) this will result in excessive speed,
possibly destroying armature due to
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excessive centrifugal stresses
(c) nothing will happen to motor
(d) motor will come to stop
Ans: a
118. D.C. motor is to drive a load which
has certain minimum value for most of the
time and some peak value for short
duration. We will select the
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: a
119. D.C. motor is to a drive a load which
is almost nil for certain part of the load cycle
and peak value for short duration. We will
select this
(a) series motor
(b) shunt motor
(c) compound motor
(d) any of the above
Ans: c
120. Which D.C. motor has got maximum
self relieving property ?
(a) Series motor
(6) Shunt motor
(c) Cumulatively compounded motor
(d) Differentially compounded motor
Ans: a
121. In the D.C. motor the iron losses
occur in
(a) the field
(b) the armature
(c) the brushes
(d) the commutator
Ans: b
122. The speed of a D.C. shunt motor is
required to be more than full load speed.
This is possible by
(a) reducing the field current
(b) decreasing the armature current
(c) increasing the armature current
(d) increasing the excitation current
(e) none of the above methods
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Ans: a
123. One D.C. motor drives another D.C.
motor. The second D.C. motor when excited
and driven
(a) runs as a generator
(b) does not run as a generator
(c) also runs as a motor comes to stop after
sometime
Ans: a
Polyphase Induction Motors
1. Which of the following component is
usually fabricated out of silicon steel ?
(a) Bearings
(b) Shaft
(c) Statorcore
(d) None of the above
Ans: c
2. The frame of an induction motor is usually
made of
(a) silicon steel
(b) cast iron
(c) aluminium
(d) bronze
Ans: b
3. The shaft of an induction motor is made of
(a) stiff
(b) flexible
(c) hollow
(d) any of the above
Ans: a
4. The shaft of an induction motor is made of
(a) high speed steel
(b) stainless steel
(c) carbon steel
(d) cast iron
Ans: c
5. In an induction motor, no-load the slip is
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generally
(a) less than 1%
(b) 1.5%
(c) 2%
(d) 4%
Ans: a
6. In medium sized induction motors, the slip
is generally around
(a) 0.04%
(b) 0.4%
(c) 4%
(d) 14%
Ans: c
7. In squirrel cage induction motors, the rotor
slots are usually given slight skew in order to
(a) reduce windage losses
(b) reduce eddy currents
(c) reduce accumulation of dirt and dust
(d) reduce magnetic hum
Ans: d
8. In case the air gap in an induction motor is
increased
(a) the magnetising current of the rotor will
decrease
(b) the power factor will decrease
(c) speed of motor will increase
(d) the windage losses will increase
Ans: b
9. Slip rings are usually made of
(a) copper
(b) carbon
(c) phospor bronze
(d) aluminium
Ans: c
10. A 3-phase 440 V, 50 Hz induction motor
has 4% slip. The frequency of rotor e.m.f. will be
(a) 200 Hz
(b) 50 Hz
(c) 2 Hz
(d) 0.2 Hz
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Ans: c
11. In Ns is the synchronous speed and s the
slip, then actual running speed of an induction
motor will be
(a) Ns
(b) s.N,
(c) (l-s)Ns
(d) (Ns-l)s
Ans: c
12. The efficiency of an induction motor can be
expected to be nearly
(a) 60 to 90%
(b) 80 to 90%
(c) 95 to 98%
(d) 99%
Ans: b
13. The number of slip rings on a squirrel cage
induction motor is usually
(a) two
(b) three
(c) four
(d) none
Ans: d
14. The starting torque of a squirrel-cage
induction motor is
(a) low
(b) negligible
(c) same as full-load torque
(d) slightly more than full-load torque
Ans: a
15. A double squirrel-cage induction motor
has
(a) two rotors moving in oppsite direction
(b) two parallel windings in stator
(c) two parallel windings in rotor
(d) two series windings in stator
Ans: c
16. Star-delta starting of motors is not
possible in case of
(a) single phase motors
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(b) variable speed motors
(c) low horse power motors
(d) high speed motors
Ans: a
17. The term 'cogging' is associated with
(a) three phase transformers
(b) compound generators
(c) D.C. series motors
(d) induction motors
Ans: d
18. In case of the induction motors the torque
is
(a) inversely proportional to (Vslip)
(b) directly proportional to (slip)2
(c) inversely proportional to slip
(d) directly proportional to slip
Ans: d
19. An induction motor with 1000 r.p.m.
speed will have
(a) 8 poles
(b) 6 poles
(c) 4 poles
(d) 2 poles
Ans: b
20. The good power factor of an induction
motor can be achieved if the average flux
density in the air gap is
(a) absent
(b) small
(c) large
(d) infinity
Ans: b
21. An induction motor is identical to
(a) D.C. compound motor
(b) D.C. series motor
(c) synchronous motor
(d) asynchronous motor
Ans: d
22. The injected e.m.f. in the rotor of
induction motor must have
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(a) zero frequency
(b) the same frequency as the slip fre-quency
(c) the same phase as the rotor e.m.f.
(d) high value for the satisfactory speed
control
Ans: b
23. Which of the following methods is easily
applicable to control the speed of the squirrelcage induction motor ?
(a) By changing the number of stator poles
(b) Rotor rheostat control
(c) By operating two motors in cascade
(d) By injecting e.m.f. in the rotor circuit
Ans: a
24. The crawling in the induction motor is
caused by
(a) low voltage supply
(b) high loads
(c) harmonics develped in the motor
(d) improper design of the machine
(e) none of the above
Ans: c
25. The auto-starters (using three auto
transformers) can be used to start cage
induction motor of the following type
(a) star connected only
(b) delta connected only
(c) (a) and (b) both
(d) none of the above
Ans: c
26. The torque developed in the cage
induction motor with autostarter is
(a) k/torque with direct switching
(6) K x torque with direct switching
(c) K2 x torque with direct switching
(d) k2/torque with direct switching
Ans: c
27. When the equivalent circuit diagram of
doouble squirrel-cage induction motor is
constructed the two cages can be
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considered
(a) in series
(b) in parallel
(c) in series-parallel
(d) in parallel with stator
Ans: b
28. It is advisable to avoid line-starting of
induction motor and use starter because
(a) motor takes five to seven times its full load
current
(b) it will pick-up very high speed and may go
out of step
(c) it will run in reverse direction
(d) starting torque is very high
Ans: a
29. Stepless speed control of induction motor
is possible by which of the following methods ?
(a) e.m.f. injection in rotor eueuit
(b) Changing the number of poles
(c) Cascade operation
(d) None of the above
Ans: b
30. Rotor rheostat control method of speed
control is used for
(a) squirrel-cage induction motors only
(b) slip ring induction motors only
(c) both (a) and (b)
(d) none of the above
Ans: b
31. In the circle diagram for induction motor,
the diameter of the circle represents
(a) slip
(b) rotor current
(c) running torque
(d) line voltage
Ans: b
32. For which motor the speed can be
controlled from rotor side ?
(a) Squirrel-cage induction motor
(b) Slip-ring induction motor
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(c) Both (a) and (b)
(d) None of the above
Ans: b
33. If any two phases for an induction motor
are interchanged
(a) the motor will run in reverse direction
(b) the motor will run at reduced speed
(c) the motor will not run
(d) the motor will burn
Ans: a
34. An induction motor is
(a) self-starting with zero torque
(b) self-starting with high torque
(c) self-starting with low torque
(d) non-self starting
Ans: c
35. The maximum torque in an induction
motor depends on
(a) frequency
(b) rotor inductive reactance
(c) square of supply voltage
(d) all of the above
Ans: d
36. In three-phase squirrel-cage induction
motors
(a) rotor conductor ends are short-circuited
through slip rings
(b) rotor conductors are short-circuited
through end rings
(c) rotor conductors are kept open
(d) rotor conductors are connected to
insulation
Ans: b
37. In a three-phase induction motor, the
number of poles in the rotor winding is always
(a) zero
(b) more than the number of poles in stator
(c) less than number of poles in stator
(d) equal to number of poles in stator
Ans: d
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38. DOL starting of induction motors is usually
restricted to
(a) low horsepower motors
(b) variable speed motors
(c) high horsepower motors
(d) high speed motors
Ans: a
39. The speed of a squirrel-cage induction
motor can be controlled by all of the following
except
(a) changing supply frequency
(b) changing number of poles
(c) changing winding resistance
(d) reducing supply voltage
Ans: c
40. The 'crawling" in an induction motor is
caused by
(a) high loads
(6) low voltage supply
(c) improper design of machine
(d) harmonics developed in the motor
Ans: d
41. The power factor of an induction motor
under no-load conditions will be closer to
(a) 0.2 lagging
(b) 0.2 leading
(c) 0.5 leading
(d) unity
Ans: a
42. The 'cogging' of an induction motor can be
avoided by
(a) proper ventilation
(b) using DOL starter
(c) auto-transformer starter
(d) having number of rotor slots more or less
than the number of stator slots (not equal)
Ans: d
43. If an induction motor with certain ratio of
rotor to stator slots, runs at 1/7 of the normal
speed, the phenomenon will be termed as
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(a) humming
(b) hunting
(c) crawling
(d) cogging
Ans: c
44. Slip of an induction motor is negative
when
(a) magnetic field and rotor rotate in opposite
direction
(b) rotor speed is less than the syn-chronous
speed of the field and are in the same direction
(c) rotor speed is more than the syn-chronous
speed of the field and are in the same direction
(d) none of the above
Ans: c
45. Size of a high speed motor as compared to
low speed motorfor the same H.P. will be
(a) bigger
(b) smaller
(c) same
(d) any of the above
Ans: b
46. A 3-phase induction motor stator delta
connected, is carrying full load and one of its
fuses blows out. Then the motor
(a) will continue running burning its one phase
(b) will continue running burning its two
phases
(c) will stop and carry heavy current causing
permanent damage to its winding
(d) will continue running without any harm to
the winding
Ans: a
47. A 3-phase induction motor delta
connected is carrying too heavy load and one of
its fuses blows out. Then the
motor
(a) will continue running burning its one phase
(b) will continue running burning its two phase
(c) will stop and carry heavy current causing
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permanent damage to its winding
(d) will continue running without any harm to
the winding
Ans: c
48. Low voltage at motor terminals is due to
(a) inadequate motor wiring
(b) poorely regulated power supply
(c) any one of the above
(d) none of the above
Ans: c
49. In an induction motor the relationship
between stator slots and rotor slots is that
(a) stator slots are equal to rotor slots
(b) stator slots are exact multiple of rotor
slots
(c) stator slots are not exact multiple of rotor
slots
(d) none of the above
Ans: c
50. Slip ring motor is recommended where
(a) speed control is required
(6) frequent starting, stopping and reversing
is required
(c) high starting torque is needed
(d) all above features are required
Ans: d
51. As load on an induction motor goes on
increasing
(a) its power factor goes on decreasing
(b) its power factor remains constant
(c) its power factor goes on increasing even
after full load
(d) its power factor goes on increasing upto
full load and then it falls again
Ans: d
52. If a 3-phase supply is given to the stator
and rotor is short circuited rotor will move
(a) in the opposite direction as the direction of
the rotating field
(b) in the same direction as the direction of the
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field
(c) in any direction depending upon phase
squence of supply
Ans: b
53. It is advisable to avoid line starting of
induction motor and use starter because
(a) it will run in reverse direction
(b) it will pick up very high speed and may go
out of step
(c) motor takes five to seven times its fullload
current
(d) starting torque is very high
Ans: c
54. The speed characteristics of an induction
motor closely resemble the speedload
characteristics of which of the
following machines
(a) D.C. series motor
(b) D.C. shunt motor
(c) universal motor
(d) none of the above
Ans: b
55. Which type of bearing is provided in small
induction motors to support the rotor shaft ?
(a) Ball bearings
(b) Cast iron bearings
(c) Bush bearings
(d) None of the above
Ans: a
56. A pump induction motor is switched on to
a supply 30% lower than its rated voltage. The
pump runs. What will
eventually happen ? It will
(a) stall after sometime
(b) stall immediately
(c) continue to run at lower speed without
damage
(d) get heated and subsequently get damaged
Ans: d
57. 5 H.P., 50-Hz, 3-phase, 440 V, induction
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motors are available for the following r.p.m.
Which motor will be the
costliest ?
(a) 730 r.p.m.
(b) 960 r.p.m.
(c) 1440 r.p.m.
(d) 2880 r.p.m.
Ans: a
58. A 3-phase slip ring motor has
(a) double cage rotor
(6) wound rotor
(c) short-circuited rotor
(d) any of the above
Ans: b
59. The starting torque of a 3-phase squirrel
cage induction motor is
(a) twice the full load torque
(b) 1.5 times the full load torque
(c) equal to full load torque
Ans: b
60. Short-circuit test on an induction motor
cannot be used to determine
(a) windage losses
(b) copper losses
(c) transformation ratio
(d) power scale of circle diagram
Ans: a
61. In a three-phase induction motor
(a) iron losses in stator will be negligible as
compared to that in rotor
(6) iron losses in motor will be neg¬ligible as
compared to that in rotor
(c) iron losses in stator will be less than that in
rotor
(d) iron losses in stator will be more than that
in rotor
Ans: d
62. In case of 3-phase induction motors,
plugging means
(a) pulling the motor directly on line without
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a starter
(b) locking of rotor due to harmonics
(c) starting the motor on load which is more
than the rated load
(d) interchanging two supply phases for quick
stopping
Ans: d
63. Which is of the following data is required
to draw the circle diagram for an induction
motor ?
(a) Block rotor test only
(b) No load test only
(c) Block rotor test and no-load test
(d) Block rotor test, no-load test and stator
resistance test
Ans: d
64. In three-phase induction motors
sometimes copper bars are placed deep in the
rotor to
(a) improve starting torque
(b) reduce copper losses
(c) improve efficiency
(d) improve power factor
Ans: a
65. In a three-phase induction motor
(a) power factor at starting is high as compared
to that while running
(b) power factor at starting is low as compared
to that while running
(c) power factor at starting in the same as that
while running
Ans: b
66. The vafcie of transformation ratio of an
induction motor can be found by
(a) open-circuit test only
(b) short-circuit test only
(c) stator resistance test
(d) none of the above
Ans: b
67. The power scale of circle diagram of an
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induction motor can be found from
(a) stator resistance test
(6) no-load test only
(c) short-circuit test only
(d) noue of the above
Ans: c
68. The shape of the torque/slip curve of
induction motor is
(a) parabola
(b) hyperbola
(c) rectangular parabola
(d) straigth line
Ans: c
69. A change of 4% of supply voltage to an
induction motor will produce a change of
appromimately
(a) 4% in the rotor torque
(b) 8% in the rotor torque
(c) 12% in the rotor torque
(d) 16% in the rotor torque
Ans: d
70. The stating torque of the slip ring
induction motor can be increased by adding
(a) external inductance to the rotor
(b) external resistance to the rotor
(c) external capacitance to the rotor
(d) both resistance and inductance to rotor
Ans: b
71. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C.
induction motor has a speed of 960 r.p.m. on
full load. The machine has 6 poles. The slip of
the machine will be
(a) 0.01
(b) 0.02
(c) 0.03
(d) 0.04
Ans: d
72. The complete circle diagram of induetion
motor can be drawn with the help of data found
from
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(a) noload test
(6) blocked rotor test
(c) stator resistance test
(d) all of the above
Ans: d
73. In the squirrel-cage induction motor the
rotor slots are usually given slight skew
(a) to reduce the magnetic hum and locking
tendency of the rotor
(b) to increase the tensile strength of the
rotor bars
(c) to ensure easy fabrication
(d) none of the above
Ans: a
74. The torque of a rotor in an induction
motor under running condition is maximum
(a) at the unit value of slip
(b) at the zero value of slip
(c) at the value of the slip which makes rotor
reactance per phase equal to the resistance per
phase
(d) at the value of the slip which makes the
rotor reactance half of the rotor
Ans: c
75. What will happen if the relative speed
between the rotating flux of stator and rotor of
the induction motor is zero ?
(a) The slip of the motor will be 5%
(b) The rotor will not run
(c) The rotor will run at very high speed
(d) The torque produced will be very large
Ans: b
76. The circle diagram for an induction motor
cannot be used to determine
(a) efficiency
(b) power factor
(c) frequency
(d) output
Ans: a
77. Blocked rotor test on induction motors is
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used to find out
(a) leakage reactance
(b) power factor on short circuit
(c) short-circuit current under rated voltage
(d) all of the above
Ans: d
78. Lubricant used for ball bearing is usually
(a) graphite
(b) grease
(c) mineral oil
(d) molasses
Ans: b
79. An induction motor can run at synchronous
speed when
(a) it is run on load
(b) it is run in reverse direction
(c) it is run on voltage higher than the rated
voltage
(d) e.m.f. is injected in the rotor circuit
Ans: d
80. Which motor is preferred for use in mines
where explosive gases exist ?
(a) Air motor
(b) Induction motor
(c) D.C. shunt motor
(d) Synchronous motor
Ans: a
81. The torque developed by a 3-phase
induction motor least depends on
(a) rotor current
(b) rotor power factor
(c) rotor e.m.f.
(d) shaft diameter
Ans: d
82. In an induction motor if air-gap is increased
(a) the power factor will be low
(b) windage losses will be more
(c) bearing friction will reduce
(d) copper loss will reduce In an induction
motor
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Ans: a
83. In induction motor, percentage slip depends
on
(a) supply frequency
(b) supply voltage
(c) copper losses in motor
(d) none of the above
Ans: c
84. When /?2 is tne rotor resistance, .X2 the
rotor reactance at supply frequency
and s the slip, then the condition for maximum
torque under running condi-tions will be
(a) sR2X2 = 1 (b) sR2 = X2
(c) R2 = sX2 id) R2 = s2X2
Ans: c
85. In case of a double cage induction motor,
the inner cage has
(a) high inductance arid low resistance
(b) low inductance and high resistance
(c) low inductance and low resistance
(d) high inductance and high resis¬tance
Ans: a
86. The low power factor of induction motor is
due to
(a) rotor leakage reactance
(b) stator reactance
(c) the reactive lagging magnetizing current
necessary to generate the magnetic flux
(d) all of the above
Ans: d
87. Insertion of reactance in the rotor circuit
(a) reduces starting torque as well as
maximum torque
(b) increases starting torque as well as
maximum torque
(c) increases starting torque but maxi-mum
torque remains unchanged
(d) increases starting torque but maxi-mum
torque decreases
Ans: a
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88. Insertion of resistance in the rotcir of an
induction motor to develop a given torque
(a) decreases the rotor current
(b) increases the rotor current
(c) rotor current becomes zero
(d) rotor current rernains same
Ans: d
89. For driving high inertia loods best type of
induction motor suggested is
(a) slip ring type
(b) squirrel cage type
(c) any of the above
(d) none of the above
Ans: a
90. Temperature of the stator winding of a
three phase induction motor is obtained by
(a) resistance rise method
(b) thermometer method
(c) embedded temperature method
(d) all above methods
Ans: d
91. The purpose of using short-circuit gear is
(a) to short circuit the rotor at slip rings
(b) to short circuit the starting resis¬tances in
the starter
(c) to short circuit the stator phase of motor
to form star
(d) none of the above
Ans: a
92. In a squirrel cage motor the induced e.m.f.
is
(a) dependent on the shaft loading
(b) dependent on the number of slots
(c) slip times the stand still e.m.f. induced in
the rotor
(d) none of the above
Ans: c
93. Less maintenance troubles are
experienced in case of
(a) slip ring induction motor
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(6) squirrel cage induction motor
(c) both (a) and (b)
(d) none of the above
Ans: b
94. A squirrel cage induction motor is not
selected when
(a) initial cost is the main consideration
(b) maintenance cost is to be kept low
(c) higher starting torque is the main
consideration
(d) all above considerations are involved
Ans: c
95. Reduced voltage starter can be used with
(a) slip ring motor only but not with squirrel
cage induction motor
(b) squirrel cage induction motor only but not
with slip ring motor
(c) squirrel cage as well as slip ring induction
motor
(d) none of the above
Ans: c
96. Slip ring motor is preferred over squirrel
cage induction motor where
(a) high starting torque is required
(b) load torque is heavy
(c) heavy pull out torque is required
(d) all of the above
Ans: a
97. In a star-delta starter of an induction
motor
(a) resistance is inserted in the stator
(b) reduced voltage is applied to the stator
(c) resistance is inserted in the rotor
(d) applied voltage per1 stator phase is 57.7%
of the line voltage
Ans: d
98. The torque of an induction motor is
(a) directly proportional to slip
(b) inversely proportional to slip
(c) proportional to the square of the slip
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(d) none of the above
Ans: a
99. The rotor of an induction motor runs at
(a) synchronous speed
(b) below synchronous speed
(c) above synchronous speed
(d) any of the above
Ans: b
100. The starting torque of a three phase
induction motor can be increased by
(a) increasing slip
(b) increasing current
(c) both (a) and (b)
(d) none of the above
Ans: c
101. Insertion of resistance in the stator of an
induction motor
(a) increases the load torque
(b) decreases the starting torque
(c) increases the starting torque
(d) none of the above
Ans: b
Single Phase Induction
1. In a split phase motor, the running winding
should have
(a) high resistance and low inductance
(b) low resistance and high inductance
(c) high resistance as well as high inductance
(d) low resistance as well as low inductiance
Ans: b
2. If the capacitor of a single-phase motor is
short-circuited
(a) the motor will not start
(b) the motor will run
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at
reduced r.p.m.
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Ans: a
3. In capacitor start single-phase motors
(a) current in the starting winding leads the
voltage
(b) current in the starting winding lags the
voltage
(c) current in the starting winding is in phase
with voltage in running winding
(d) none of the above
Ans: a
4. In a capacitor start and run motors the
function of the running capacitor in series with
the auxiliary winding is to
(a) improve power factor
(b) increase overload capacity
(c) reduce fluctuations in torque
(d) to improve torque
Ans: a
5. In a capacitor start motor, the phase
displacement between starting and running
winding can be nearly
(a) 10°
(b) 30°
(c) 60°
(d) 90°
Ans: d
6. In a split phase motor
(a) the starting winding is connected through
a centrifugal switch
(b) the running winding is connected through
a centrifugal switch
(c) both starting and running windings are
connected through a centrifugal switch
(d) centrifugal switch is used to control supply
voltage
Ans: a
7. The rotor developed by a single-phase
motor at starting is
(a) more than i.he rated torque
(b) rated torque
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(c) less than the rated torque
(d) zero
Ans: d
8. Which of the following motor will give
relatively high starting torque ?
(a) Capacitor start motor
(b) Capacitor run motor
(c) Split phase motor
(d) Shaded pole motor
Ans: a
9. Which of the following motor will have
relatively higher power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Capacitor start motor
(d) Split phase motor
Ans: a
10. In a shaded pole motor, the shading coil
usually consist of
(a) a single turn of heavy wire which is in
parallel with running winding
(b) a single turn of heavy copper wire which is
short-circuited and carries only induced current
(c) a multilayer fine gauge copper wire in
parallel with running winding
(d) none of the above
Ans: b
11. In a shaded pole single-phase motor, the
revolving field is produced by the use of
(a) inductor
(b) capacitor
(c) resistor
(d) shading coils
Ans: d
12. A centrifugal switch is used to dis- connect
'starting winding when motor has
(a) run for about 1 minute
(b) run for about 5 minutes
(c) picked up about 50 to 70 per cent of rated
speed
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(d) picked up about 10 to 25 per cent of rated
speed
Ans: c
13. If a particular application needs high speed
and high starting torque, then which of the
following motor will be
preferred ?
(a) Universal motor
(b) Shaded pole type motor
(c) Capacitor start motor
(d) Capacitor start and run motor
Ans: a
14. The value of starting capacitor of a
fractional horse power motor will be
(a) 100 uF
(6) 200 uF
(c) 300 uF
(d) 400 uF
Ans: c
15. In repulsion motor direction of rotation of
motor
(a) is opposite to that of brush shift
(b) is the same as that of brush shift
(c) is independent of brush shift
Ans: b
16. In a single phase motor the centrifugal
switch
(a) disconnects auxiliary winding of the motor
(b) disconnects main winding of the motor
(c) reconnects the main winding the motor
(d) reconnects the auxiliary winding of the
motor
Ans: a
17. The running winding of a single phase
motor on testing with meggar is found to be
ground. Most probable location of the ground
will be
(a) at the end connections
(b) at the end terminals
(c) anywhere on the winding inside a slot
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(d) at the slot edge where coil enters or comes
out of the slot
Ans: d
18. A capacitor-start single phase induction
motor is switched on to supply with its
capacitor replaced by an inductor of equivalent
reactance value. It will
(a) start and then stop
(b) start and run slowly
(c) start and run at rated speed
(d) not start at all
Ans: d
19. Which of the following motors is used in
mixies ?
(a) Repulsion motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor
Ans: d
20. Which of the following motors is
inherently self starting ?
(a) Split motor
(b) Shaded-pole motor
(c) Reluctance motor
(d) None of these
Ans: b
21. The direction of rotation of an hysteresis
motor is determined by
(a) interchanging the supply leads
(b) position of shaded pole with respect to main
pole
(c) retentivity of the rotor material
(d) none of these
Ans: b
22. Burning out of windings is due to
(a) short circuited capacitor
(b) capacitor value hiving changed
(c) open circuiting of capacitor
(d) none of the above
Ans: a
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23. Direction of rotation of a split phase motor
can be reversed by reversing the connection of
(a) running winding only
(b) starting winding only
(c) either (a) or (b)
(d) both (a) and (b)
Ans: c
24. Short-circuiter is used in
(a) repulsion induction motor
(b) repulsion motor
(c) repulsion start induction run motor
(d) none of the above
Ans: c
25. The range of efficiency for shaded pole
motors is
(a) 95% to 99%
(b) 80% to 90%
(c) 50% to 75%
(d) 5% to 35%
Ans: d
26. In a capacitor start single-phase motor,
when capacitor is replaced by a resistance
(a) torque will increase
(b) the motor will consume less power
(c) motor will run in reverse direction
(d) motor will continue to run in same
direction
Ans: d
27. The power factor of a single-phase
induction motor is usually
(a) lagging
(b) always leading
(c) unity
(d) unity to 0.8 leading
Ans: a
28. A shaded pole motor can be used for
(a) toys
(b) hair dryers
(c) circulators
(d) any of the above
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Ans: d
29. A hysteresis motor works on the principle
of
(a) hysteresis loss
(b) magnetisation of rotor
(c) eddy current loss
(d) electromagnetic induction
Ans: a
30. Which of the following motor will give the
highest starting torque ?
(a) D.C. shunt motor
(b) Schrage motor
(c) Repulsion start and induction run motor
(d) Universal motor
Ans: b
31. For which of the applications a reluctance
motor is preferred ?
(a) Electric shavers
(b) Refrigerators
(c) Signalling and timing devices
(d) Lifts and hoists
Ans: c
32. The motor used on small lathes is usually
(a) universal motor
(b) D.C. shunt motor
(c) single-phase capacitor run motor
(d) 3-phase synchronous motor
Ans: c
33. Which of the following motors is preferred
for tape-recorders ?
(a) Shaded pole motor
(b) Hysteresis motor
(c) Two value capacitor motor
(d) Universal motor
Ans: b
34. A single-phase induction motor is
(a) inherently self-starting with high torque
(b) inherently self-starting with low torque
(c) inherently non-self-starting with low
torque
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(d) inherently non-self-starting with high
torque
Ans: c
35. A schrage motor can run on
(a) zero slip
(b) negative slip
(c) positive slip
(d) all of the above
Ans: d
36. A universal motor can run on
(a) A.C. only
(6) D.C. only
(c) either A.C. or D.C.
(d) none of the above
Ans: c
37. Which of the following single-phase
motors is suitable for timing and control
purposes ?
(a) Reluctance motor
(b) Series motor
(c) Repulsion motor
(d) Universal motor
Ans: a
38. Single phase induction motor usually
operates on
(a) 0.6 power factor lagging
(b) 0.8 power factor lagging
(c) 0.8 power factor leading
(d) unity power factor
Ans: a
39. In split-phase motor iauxiliary winding is of
(a) thick wire placed at the bottom of the slots
(b) thick wire placed at the top of the slots
(c) thin wire placed at the top of the slots
(d) thin wire placed at the bottom of the slots
Ans: c
40. Which of the following motors will operate
at high power factor ?
(a) Shaped pole motor
(b) Split phase motor
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(c) Capacitor start motor
(d) Capacitor run motor
Ans: d
41. In a two value capacitor motor, the
capacitor used for running purposes is
(a) air capacitor
(b) paper spaced oilfilled type
(c) ceramic type
(d) a.c. electrolytic type
Ans: b
42. Which of the following motors can be run
on AC. as well as D.C. supply ?
(a) Universal motor
(b) Repulsion motor
(c) Synchronous motor
(d) Reluctance motor
Ans: a
43. In A.C. series motor compensating winding
is employed to
(a) reduce the effects of armature reaction
(b) increase the torque
(c) reduce sparking at the brushes
(d) none of the above
Ans: c
44. Which of the following single-phase
induction motors is generally used in time
phonographs ?
(a) Resistance start
(b) Capacitor start capacitor run
(c) Shaded pole
(d) Universal
Ans: c
45. Which of the following motors has highest
starting torque ?
(a) Repulsion motor
(b) Shaped pole motor
(c) Capacitor-start motor
(d) Split-phase motor
Ans: c
46. The repulsion-start induction-run motor is
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used because of
(a) good power factor
(b) high efficiency
(c) minimum cost
(d) high starting torque
Ans: d
47. In case of a shaded pole motor the
direction of rotation of the motor is
(a) from main pole to shaded pole
(b) from shaded pole to main pole
(c) either of the above depending on voltage
(d) either of the above depending on power
factor
Ans: a
48. In case of high speed universal motor
which of the following needs more attention ?
(a) End play
(b) Air gap
(c) Insulation in rotor
(d) Balancing of rotor
Ans: d
49. The wattage rating for a ceiling fan motor
will be in the range
(a) 200 to 250 W
(b) 250 to 500 W
(c) 50 to 150 W
(d) 10 to 20 W
Ans: c
50. The wattage of motor for driving domestic
sewing machine will be around
(a) 100 to 150 W
(b) 40 to 75 W
(c) 10 to 30 W
(d) 5 to 10 W
Ans: a
51. Which of the following single-phase
motors has relatively poor starting torque ?
(a) Universal motor
(b) Repulsion motor
(c) Capacitor motor
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(d) All single phase motors have zero starting
torque
Ans: c
52. Which type of load is offered by cranes
and hoists ?
(a) Gradually varying load
(b) Non-reversing, no-load start
(c) Reversing, light start
(d) Reversing, heavy start
Ans: d
53. The speed of a universal motor is generally
reduced by using
(a) gear trains
(b) V-belts
(c) brakes
(d) chains
Ans: a
54. Which of the following motors can be used
for unity power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Hysteresis motor
(d) Schrage motor
Ans: d
55. When a D.C. series motor is connected to
A.C. supply, the power factor will be low
because of
(a) high inductance of field and armature
circuits
(b) induced current in rotor due to variations
of flux
(c) fine copper wire winding
(d) none of the above
Ans: a
56. The direction of rotation of universal
motor can be reversed the by reversing the flow
of current through
(a) armature winding
(b) field winding
(c) either armature winding or field winding
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(d) none of the above
Ans: c
57. In which single-phase motor, the rotor has
no teeth or winding ?
(a) Split phase motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor
Ans: c
58. Which motor is normally free from
mechanical and magnetic vibrations ?
(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor
Ans: c
59. As hysteresis motors are free from
mechanical and magnetic vibrations therefore
these are considered as suitable for
(a) fans
(b) blowers
(c) sound equipment
(d) mixer grinders
Ans: c
60. A reluctance motor
(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above
Ans: d
61. In a hysteresis motor, the rotor must have
(a) retentivity
(b) resistivity
(c) susceptibility
(d) none of the above
Ans: a
62. The rotor of a hysteresis motor is made of
(a) aluminium
(b) cast iron
(c) chrome steel
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(d) copper
Ans: c
63. The electric motor used in portable drills is
(a) capacitor run motor
(b) hysteresis motor
(c) universal motor
(d) repulsion motor
Ans: c
64. Which of the following applications always
have some load whenever switched on ?
(a) Vacuum cleaners
(b) Fan motors
(c) Pistol drills
(d) All of the above
Ans: c
65. The speed control of universal motor used
for sewing machines is by
(a) friction
(b) varying the resistance
(c) tapping the field
(d) centrifugal mechanism
Ans: b
66. Torque developed by a single phase
induction motor at starting is
(a) pulsating
(b) uniform
(c) none of the above
(d) nil
Ans: d
67. In split phase motor main winding is of
(a) thin wire placed at the top of the slots
(b) thin wire placed at the bottom of the slots
(c) thick wire placed at the bottom of the slots
(d) thick wire placed at the top of the" slots
Ans: c
68. In repulsion motor, maximum torque is
developed when
(a) brush axis is at 45° electrical to the field
axis
(b) brush axis coincides with the field axis
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(c) brush axis is at 90° electrical to the field
axis
(d) none of the above
Ans: a
69. If the centrifugal switch does not open at
70 to 80 percent of synchronous speed of
motor, it would result in
(a) damage to the starting winding
(b) damage to the centrifugal switch
(c) overloading of running winding
(d) none of the above
Ans: a
70. Speed torque characteristic of a repulsion
induction motor is similar to that of a D.C.
(a) shunt motor
(b) series motor
(c) compound motor
(d) separately excited motor
Ans: c
71. In a ceilingfan employing capacitor run
motor
(a) secondary winding surrounds the primary
winding
(b) primary winding surrounds the secondary
winding
(c) both are usual arrangements
(d) none of the above
Ans: a
72. The shaded pole motor is used for
(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque
Ans: b
73. The rotor slots, in an induction motor, are
usually not quite parallel to the shaft because it
(a) improves the efficiency
(b) helps the rotor teeth to remain under the
stator teeth
(c) helps in reducing the tendency of the rotor
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teeth to remain under the stator teeth
(d) improves the power factor
Ans: c
74. The speed/load characteristics of a
universal motor is same as that of
(a) A.C. motor
(b) D.C. shunt motor
(c) D.C. series motor
(d) none of the above
Ans: c
75. The purpose of stator winding in the
compensated repulsion motor is to
(a) provide mechanical balance
(b) improve power factor and provide better
speed regulation
(c) prevent hunting in the motor
(d) eliminate armature reaction
Ans: b
76. Which of the following motors is used for
unity power factor ?
(a) Hysteresis motor
(b) Schrage motor
(c) Universal motor
(d) Reluctance motor
Ans: b
77. The motor used for the compressors is
(a) d.c. series motor
(b) shaded pole motor
(c) capacitor-start capacitor-run motor
(d) reluctance motor
Ans: c
78. Which of the following motors is used in a
situation where load increases with speed ?
(a) Induction motor
(b) Three-phase series motor
(c) Schrage motor
(d) Hysteresis motor
Ans: b
79. In repulsion motor, zero torque is
developed when
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(a) brush axis is 45° electrical to field axis
(b) brush axis coincides with the field axis
(c) brush axis is 90° electrical to field axis
(d) both (b) and (c)
Ans: d
80. Centrifugal switch disconnects the
auxiliary winding of the motor at about ____
percent of synchronous speed
(a) 30 to 40
(b) 70 to 80
(c) 80 to 90
(d) 100
Ans: b
81. Starting winding of a single phase motor of
a refrigerator is disconnected from the circuit
by means of a
(a) magnetic relay
(b) thermal relay
(c) centrifugal switch
(d) none of the above
Ans: a
82. If a single phase induction motor runs
slower than normal, the most likely defect is
(a) worn bearings
(b) short-circuit in the winding
(c) open-circuit in the winding
(d) none of the above
Ans: a
83. Which of the following motors is used in
tape-recorders ?
(a) Hysteresis motor
(b) Reluctance motor
(c) Capacitor-run motor
(d) Universal motor
Ans: a
84. Which of the following statements
regarding two value capacitor motor is incorrect
?
(a) It is a reversing motor
(b) It is preferred to permanent-split single-
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value capacitor motor where frequent reversals
are required
(c) It has low starting as well as rush¬ing
currents
(d) It has high starting torque
Ans: b
85. Two-value capacitor motor finds increased
application as compressor motor in small home
air-conditioners
because
(a) it is comparatively cheaper
(b) it has almost non-destructible capacitor
(c) it has low starting as well as running
currents at relatively high power factor
(d) it is quiet in operation
Ans: c
86. If the centrifugal switch of a two-value
capacitor motor using two capacitors fails to
open then
(a) motor will not come upto speed
(b) motor will not carry the load
(c) current drawn by the motor will be
excessively high
(d) electrolytic capacitor will, in all
probability, suffer break down
Ans: d
87. In a universal motor, the most common
cause of brush sparking is
(a) open armature winding
(b) shorted armature winding
(c) shorted field winding"
(d) high commutator mica
(e) all of the above
Ans: e
88. If starting winding of a single-phase
induction motor is left in the circuit, it will
(a) run faster
(b) spark at light loads
(c) draw excessive current and overheat
(d) run slower
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Ans: c
89. Most of the fractional horsepower motors
have either
(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearings
(d) plain or sleeve bearings
Ans: d
90. Which of the following statements
regarding reluctance-start motor is incorrect ?
(a) It is similar to reluctance motor
(b) It is basically an induction motor and not a
synchronous one
(c) So far as its basic working principle is
concerned, it is similar to shaded pole motor
(d) the air-gap between rotor and salient
poles is non- uniform
Ans: a
91. To reverse the direction of rotation of
acapacitor start motor while it is running we
should
(a) disconnect motor from the supply till it
stops then reconnect it to supply with reversed
connection of main or auxiliary winding
(b) disconnect motor from supply and
immediately reconnect it to supply with
reversed connections of the main winding
(c) reverse the direction of connection of the
auxiliary winding and after motor comes to rest
then connect auxiliary winding to the supply
(d) reverse the direction of connections of the
auxiliary winding and im-mediately connect it to
supply
Ans: a
92. In case of a reluctance motor, when the
load is increased so that it cannot maintain
synchronous speed the motor will
(a) become unstable
(b) draw excessive armature current and may
burn out
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(c) fall out of synchronism and come to stand
still
(d) run as induction motor
Ans: d
93. Which of the following motors has two
separate windings on the motor ?
(a) Repulsion motor
(b) Repulsion induction motor
(c) Repulsion start induction run motor
(d) None of the above
Ans: b
94. A shaded pole motor does not possess
(a) centrifugal switch
(b) capacitor
(c) commutator
(d) all of the above
Ans: d
95. In a A.C. series motor armature coils are
usually connected to commutator
(a) through resistance
(b) through reactances
(c) through capacitors
(d) solidly
Ans: a
96. Which of the following statements
regarding a reluctance motor is incorrect ?
(a) It cannot be reversed, ordinarily
(b) It requires no D.C. field excitation for its
operation
(c) It is nothing else but a single-phase, salient
pole synchronous-induction motor
(d) Its squirrel cage-rotor is of unsym-metrical
magnetic construction in order to vary
reluctance path bet¬ween stator and rotor
Ans: a
97. A universal motor is one which
(a) can be operated either on D.C. or A.C. supply
at approximately the same speed and output
(b) can be marketed internationally
(c) runs at dangerously high speed on no-load
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Ans: a
98. A repulsion motor is equipped with
(a) slip rings
(b) commutator
(c) both (a) and (b)
(d) none of the above
Ans: b
99. The capacitors used in single-phase
capacitor motors have no
(a) voltage rating
(b) dielectric medium
(c) polarity marking
(d) definite value
Ans: c
100. If a D.C. series motor is operated on A.C.
supply, it will
(a) spark excessively
(b) have poor efficiency
(c) have poor power factor
(d) all of the above
Ans: d
101. After the starting winding of a single
phase induction motor is disconnected from
supply, it continues to run only on
(a) running winding
(b) rotor winding
(c) field winding
(d) compensating winding
Ans: a
102. Which of the following statements
regarding repulsion-start induction motor is
incorrect ?
(a) It requires more maintenance of
commutator and other mechanical devices
(b) It makes quite a bit of noise on starting
(c) In fractional horse power motors, it has
replaced the capacitor motors
(d) It is not easily reversed
Ans: c
103. A.C. series motor as compared to D.C.
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series motor has
(a) smaller brush width
(b) less number of field turns
(c) more number of armature turns
(d) less air gap
(e) all of the above
Ans: e
104. Locked rotor current of a shaded pole
motor is
(a) equal to full load current
(b) less than full load current
(c) slightly more than full load current
(d) several times the full load current
Ans: c
105. Speed control of a universal motor is
achieved by
(a) varying field flux with tapped field
windings
(b) connecting rheostat in series
(c) applying variable voltage by means of
silicon controlled rectifier
(d) applying variable voltage by means of
variable auto-transformer
(e) all of the above methods
Ans: e
106. Hysteresis motor is particularly useful for
high-quality record players and tape-recorders
because
(a) it revolves synchronously
(b) it is not subject to any magnetic or
mechanical vibrations
(c) it can be easily manufactured in extremely
small sizes of upto 1 W output
(d) it develops hysteresis torque which is
extremely steady both in amplitude and phase
Ans: d
107. Which of the following statements
regarding hysteresis motor is in incorrect ?
(a) It is extremely sensitive to fluctuations in
supply voltage
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(b) Its high starting torque is due to its high
rotor hysteresis loss
(c) It is extremely quiet in operation
(d) It accelerates from rest to full-speed
almost instantaneously
Ans: a
23.108. Which of the following statements
regarding single-phase induction motoris
correct ?
(a) It requires only one winding
(b) It can rotate in one direction only
(c) It is self-starting
(d) It is not self-starting
Ans: d
109. The starting winding of a single-phase
motor is placed in
(a) armature
(b) field
(c) rotor
(d) stator
Ans: d
110. The speed ofa universal motor is usually
reduced by using
(a) gearing
(b) belts
(c) brakes
(d) chains
Ans: a
Rectifiers and Converters
1. Which of the following are the applications
of D.C. system ?
(a) Battery charging work
(b) Arc welding
(c) Electrolytic and electro-chemical processes
(d) Arc lamps for search lights
(e) All of the above
Ans: e
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2. Which of the following methods may be
used to convert A.C. system to D.C. ?
(a) Rectifiers
(b) Motor converters
(c) Motor-generator sets
(d) Rotary converters
(e) All of the above
Ans: e
3. In a single phase rotary converter the
number of slip rings will be
(a) two
(b) three
(c) four
(d) six
(e) none
Ans: a
4. A synchronous converter can be started
(a) by means of a small auxiliary motor
(b) from AC. side as induction motor
(c) from D.C. side as D.C. motor
(d) any of the above methods
(e) none of the above methods
Ans: d
5. A rotary converter is a single machine with
(a) one armature and one field
(b) two armatures and one field
(c) one armature and two fields
(d) none of the above
Ans: a
6. A rotary converter combines the function of
(a) an induction motor and a D.C. generator
(b) a synchronous motor and a D.C. generator.
(c) a D.C. series motor and a D.C. generator
(d) none of the above
Ans: b
7. Which of the following is reversible in
action ?
(a) Motor generator set
(b) Motor converter
(c) Rotary converter
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(d) Any of the above
(e) None of the above
Ans: c
8. Which of the following metals is generally
manufactured by electrolysis process ?
(a) Load
(b) Aluminium
(c) Copper
(d) Zinc
(e) None of the above
Ans: b
9. With a motor converter it is possible to
obtain D.C. voltage only upto
(a) 200-100 V
(6) 600—800 V
(c) 1000—1200 V
(d) 1700—2000 V
Ans: d
10. Normally, which of the following is used,
when a large-scale conversion from AC. to D.C.
power is required ?
(a) Motor-generator set
(b) Motor converter
(c) Rotary converter
(d) Mercury arc rectifier
Ans: d
11. A rotary converter in general construction
and design, is more or less like
(a) a transformer
(b) an induction motor
(c) an alternator
(d) any D.C. machine
Ans: d
12. A rotary converter operates at a
(a) low power factor
(6) high power factor
(c) zero power factor
(d) none of the above
Ans: b
13. In which of the following appUcations,
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direct current is absolutely essential ?
(a) Illumination
(b) Electrolysis
(c) Variable speed operation
(d) Traction
Ans: b
14. Which of the following AC. motors is
usually used in large motor-generator sets?
(a) Synchronous motor
(b) Squirrel cage induction motor
(c) Slip ring induction motor
(d) Any of the above
Ans: a
15. In a rotary converter armature currents
are
(a) d.c. only
(b) a.c. only
(c) partly a.c. and partly d.c.
Ans: c
16. In which of the following equipment direct
current is needed ?
(a) Telephones
(b) Relays
(c) Time switches
(d) All of the above
Ans: d
17. In a rotary converter I2R losses as
compared to a D.C. generator of the same size
will be
(a) same
(b) less
(c) double
(d) three times
Ans: b
18. In a mercury arc rectifier positive ions are
attracted towards
(a) anode
(b) cathode
(c) shell bottom
(d) mercury pool
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Ans: b
19. Mercury, in arc rectifiers, is chosen for
cathode because
(a) its ionization potential is relatively low
(b) its atomic weight is quite high
(c) its boiling point and specific heat are low
(d) it remains in liquid state at ordi¬nary
temperature
(e) all of the above
Ans: e
20. The ionization potential of mercury is
approximately
(a) 5.4 V
(b) 8.4 V
(c) 10.4 V
(d) 16.4 V
Ans: c
21. The potential drop in the arc, in a mercury
arc rectifier, varies
(a) 0.05 V to 0.2 V per cm length of the arc
(b) 0.5 V to 1.5 V per cm length of the arc
(c) 2 V to 3.5 V per cm length of the arc
(d) none of the above
Ans: d
22. The voltage drop between the anode and
cathode, of a mercury arc rectifier comprises of
the following
(a) anode drop and cathode drop
(b) anode drop and arc drop
(c) cathode drop and arc drop
(d) anode drop, cathode drop and arc drop
Ans: d
23. Glass rectifiers are usually made into units
capable of D.C. output (maximum continuous
rating) of
(a) 100 A at 100 V
(b) 200 A at 200 V
(c) 300 A at 300 V
(d) 400 A at 400 V
(e) 500 A at 500 V
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Ans: e
24. The voltage drop at anode, in a mercury
arc rectifier is due to
(a) self restoring property of mercury
(b) high ionization potential
(c) energy spent in overcoming the electrostatic
field
(d) high temperature inside the rectifier
Ans: c
25. The internal efficiency of a mercury arc
rectifier depends on
(a) voltage only
(b) current only
(c) voltage and current
(d) r.m.s. value of current
(e) none of the above
Ans: a
26. If cathode and anode connections in a
mercury arc rectifier are inter changed
(a) the rectifier will not operate
(b) internal losses will be reduced
(c) both ion and electron streams will move in
the same direction
(d) the rectifier will operate at reduced
efficiency
Ans: a
27. The cathdde voltage drop, in a mercury arc
rectifier, is due to
(a) expenditure of energy in ionization
(b) surface resistance
(c) expenditure of energy in overcoming the
electrostatic field
(d) expenditure of energy in liberating
electrons from the mercury
Ans: d
28. To produce cathode spot in a mercury arc
rectifier
(a) anode is heated
(b) tube is evacuated
(c) an auxiliary electrode is used
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(d) low mercury vapour pressures are used
Ans: c
29. The advantage of mercury arc rectifier is
that
(a) it is light in weight and occupies small
floor space
(b) it has high efficiency
(c) it has high overload capacity
(d) it is comparatively noiseless
(e) all of the above
Ans: e
30. In a mercury pool rectifier, the voltage
drop across its electrodes
(a) is directly proportional to load
(b) is inversely proportional to load
(c) varies exponentially with the load current
(d) is almost independent of load current
Ans: d
31. In a three-phase mercury arc rectifiers
each anode conducts for
(a) one-third of a cycle
(b) one-fourth of a cycle
(c) one-half a cycle
(d) two-third of a cycle
Ans: a
32. In a mercury arc rectifier characteristic
blue luminosity is due to
(a) colour of mercury
(b) ionization
(c) high temperature
(d) electron streams
Ans: b
33. Which of the following mercury arc
rectifier will deliver least undulating current?
(a) Six-phase
(b) Three-phase
(c) Two-phase
(d) Single-phase
Ans: a
34. In a glass bulb mercury arc rectifier the
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maximum current rating is restricted to
(a) 2000 A
(b) 1500 A
(c) 1000 A
(d) 500 A
Ans: d
35. In a mercury arc rectifier______ flow from
anode to cathode
(a) ions
(b) electrons
(c) ions and electrons
(d) any of the above
Ans: a
36. When a rectifier is loaded which of the
following voltage drops take place ?
(a) Voltage drop in transformer reactance
(6) Voltage drop in resistance of transformer
and smoothing chokes
(c) Arc voltage drop
(d) All of the above
Ans: d
37. On which of the following factors the
number of phases for which a rectifier should
be designed depend ?
(a) The voltage regulation of the rec¬tifier
should be low
(b) In the output circuit there should be no
harmonics
(c) The power factor of the system should be
high
(d) The rectifier supply transformer should be
utilized to the best ad-vantage
(e) all of the above
Ans: e
38. A mercury arc rectifier possesses
________ regulation characteristics
(a) straight line
(b) curved line
(c) exponential
(d) none of the above
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Ans: d
39. It is the_______of the transformer on
which the magnitude of angle of overlap
depends.
(a) resistance
(b) capacitance
(c) leakage reactance
(d) any of the above
Ans: c
41. In a grid control of mercury arc rectifiers
when the grid is made positive relative to
cathode, then it the electrons on their may
to anode.
(a) accelerates
(b) decelerates
(c) any of the above
(d) none of the above
Ans: a
42. In mercury arc rectifiers having grid, the
arc can be struck between anode and cathode
only when the grid attains a certain potential,
this potential being known as
(a) maximum grid voltage
(b) critical grid voltage
(c) any of the above
(d) none of the above
Ans: b
43. In phase-shift control method the control
is carried out by varying the of grid voltage.
(a) magnitude
(b) polarity
(c) phase
(d) any of the above
(e) none of the above
Ans: c
16.44. In a phase-shift control method, the
phase shift between anode and grid voltages
can be achieved by means of
(a) shunt motor
(6) synchronous motor
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(c) induction regulator
(d) synchronous generator
Ans: c
45. The metal rectifiers are preferred to valve
rectifiers due to which of the following
advantages ?
(a) They are mechanically strong
(b) They do not require any voltage for
filament heating
(c) Both (a) and (b)
(d) None of the above
Ans: c
46. Which of the following statement is
incorrect ?
(a) Copper oxide rectifier is a linear device
(b) Copper oxide rectifier is not a perfect
rectifier
(c) Copper oxide rectifier has a low efficiency
(d) Copper oxide rectifier finds use in control
circuits
(e) Copper oxide rectifier is not stable during
early life
Ans: a
47. The efficiency of the copper oxide rectifier
seldom exceeds
(a) 90 to 95%
(b) 85 to 90%
(c) 80 to 85%
(d) 65 to 75%
Ans: d
48. Copper oxide rectifier is usually designed
not to operate above
(a) 10°C
(b) 20°C
(c) 30°C
(d) 45°C
Ans: d
49. Selenium rectifier can be operated at
temperatures as high as
(a) 25°C
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(b) 40°C
(c) 60°C
(d) 75°C
Ans: d
50. In selenium rectifiers efficiencies ranging
from ______ to ______ percent are attainable
(a) 25, 35
(b) 40, 50
(c) 60, 70
(d) 75, 85
Ans: d
51. Ageing of a selenium rectifier may change
the output voltage by
(a) 5 to 10 per cent
(b) 15 to 20 per cent
(c) 25 to 30 per cent
(d) none of the above
Ans: a
52. The applications of selenium rectifiers are
usually limited to potential of
(a) 10 V
(b) 30 V
(c) 60 V
(d) 100 V
(e) 200 V
Ans: d
53. Which of the following rectifiers have
been used extensively in supplying direct
current for electroplating ?
(a) Copper oxide rectifiers
(b) Selenium rectifiers
(c) Mercury arc rectifiers
(d) Mechanical rectifiers
(e) None of the above
Ans: b
54. A commutating rectifier consists of
commutator driven by
(a) an induction motor
(b) a synchronous motor
(c) a D.C. series motor
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(d) a D.C. shunt motor
Ans: b
55. Which of the following rectifiers are
primarily used for charging of low voltage
batteries from AC. supply ?
(a) Mechanical rectifiers
(b) Copper oxide rectifiers
(c) Selenium rectifiers
(d) Electrolytic rectifiers
(e) Mercury arc rectifiers
Ans: d
56. The efficiency of an electrolytic rectifier is
nearly
(a) 80%
(b) 70%
(c) 60%
(d) 40%
Ans: c
57. Which of the following is the loss within
the mercury arc rectifier chamber ?
(a) Voltage drop in arc
(6) Voltage drop at the anode
(c) Voltage drop at the cathode
(d) All of the above
Ans: d
58. The metal rectifiers, as compared to
mercury arc rectifiers
(a) operate on low temperatures
(b) can operate on high voltages
(c) can operate on heavy loads
(d) give poor regulation
(e) none of the above
Ans: a
59. In a mercury arc rectifier, the anode is
usually made of
(a) copper
(b) aluminium
(c) silver
(d) graphite
(e) tungsten
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Ans: d
60. The ignited or auxiliary anode in mercury
arc rectifier is made of
(a) graphite
(b) boron carbide
(c) aluminum
(d) copper
Ans: b
Power Systems
1. An industrial consumer hall a daily load
pattern of 2000 KW, 0.8 lag for 12 Hra and
1000 kW UPF for 1J Hr. The load factor i=
_____.
(a) 0.5
(b) 0.75
(c) 0.6
(d) 2.0
Ans: c
2. What is the maximum value of a load
which consume 500 KWh per day at a load
factor of 0.40, if the consumer increases the
load factor of 0.50 without increasing the
maximum demand?
(a) 52.08 kW
(b) 50.8 kW
(c) 4.5 kW
(d) 60 kW
Ans: a
3. A consumer consume. 600 kWh per day at
a load factor of 0.40. If the coneumer increases
the load factor of 0.70 without increasing the
maximum demand, what is the consumption
of energy in kWh
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(a) 950 kWh
(b) 1000 kWh
(c) 1050 kWh
(d) 1100 kWh
(a) 120 MW, 60.8
(b) 90 MW, 50.6
(c) 103.2 MW, 51.61
(d) 100 MW, 0.51
Ans: c
Ans: c
4. The yearly load duration curve of a power
plant is a straight line. The maximum load is
750 MW and the minimum load is 600 Mw.
The capacity of the plant is 900 MW. What is
the capacity factor and utilization factor?
(a) 0.56,0.80
(b) 0.83,0.75
(c) 0.78, 0.9
(d) 0.75, 0.83
7. The load duration curve for a system, is
shown in the figure below. The load factor will
be
Ans: d
5. What is the utilization factor of a power
station which supplies the following loads?
Load A: Motor load of200 kW between 10 AM
to7PM
Load B : Lighting load of 100 kW between 7 PM
to 11 PM
Load C : Pumping load of 110 kW between 3
PM to 10 AM
(a) 1.60
(c) 1.00
(b) 1.32
(d) 2.56
Ans: b
6. A power station supplies the peak load of 60
Mw, 40 MW and 70 MW to three localities.
The annual load factor is 0.50 p.u. and the
diversity factor of the load at the station is
1.55. The maximum demand on the station
and average load respectively will be
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(a) 0.83
(b) 0.96
(c) 0.67
(d) 0.50
Ans: a
8. A generating station has a maximum demand
of 50 Mw, a load factor of 60%, a plant capacity
factor of 45% and if the plant while running as
per schedule, were fully loaded. The daily
energy produced will be
(a) 400 MW
(b) 720 MW
(c) 500 MW
(d) 600 MW
Ans: b
9. A generating st ation has a maximum,
demand of 20 mW, load factor of 60%, a plant
capacity factor of 50% and a plant
Use factor of 72%. What is the reserve capacity
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of the plant, if the plant, while running as per
schedule, were fully loaded?
(a) 10 MW
(b) 15 MW
(c) 2 MW
(d) 5 MW
Ans: d
10. In the above question, the maximum energy
that could be produced daily is
(a) 500 MWhlday
(b) 360 MWhIday
(c) 600 MWhlday
(d) 720 MWhlday
Ans: a
11. In a DC transmission line
(a) it is necessary for the sending end and
receiving end to be operated in synchronism.
(b) the effects of inductive and capacitive
reactances are greater than in an AC
transmission line of the same rating.
(c) there are no effects due to inductive and
capacitive reactances.
(d) power transfer capability is limited by
stability considerations.
Ans: c
12. The impedance of a circuit is given by
z=3+j4. Its conductance will be
(a) 1/3
(b) 3/5
(c) 3/25
(d) 4/5
Ans: c
13. A 100 km transmiesion line ia deaigned for
a nominal voltage of 132 kV and conaiala of one
conductor per phase. The line reactance is
0.726 ohm/km. The static transmission capacity
of the line, in Megawatts, would be
(a) 132
(b) 240
(c) 416
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(d) 720
Ans: c
14. The per unit impedance ofa circuit
element is 0.15. If the base kV and base MVA
are halved, then the new value of the per unit
impedance of the circuit element will be
(a) 0.075
(b) 0.15
(c) 0.30
(d) 0.600
Ans: c
15. The conductor of a 10 km long, single
phase, two wire line are separated by a distance
of 1.5 m. The diameter of each conductor is 1
cm, If the conductors are of copper, the
inductance of the circuit is
(a) 50.0 mH
(b) 45.3 mH
(c) 23.8 mH
(d) 19.6 mH
Ans: c
16. For a single phase overhead line having
solid copper conductors of diameter 1 cm,
spaced 60 cm between centers, the inductance
in mH/km is
(a) 0.05 + 0.2 ln 60
(b) 0.2 ln 60
(c) 0.05 + 0.2 ln (6010.5)
(d) 0.2 ln (60/0.5)
Ans: c
17. A 100 km long transmission line is loaded
at 110 kV.if the loss of line is 5 MW and the load
is 150 MVA, the resistance of the line is
(a) 8.06 ohms per phase
(b) 0.806 ohms per phase
(c) 0.0806 ohms per phase
(d) 80.6 ohms per phase
Ans: a
18. A 3-phase, 11 kv, 50 Hz, 200 kW load has a
power factor of 0.8 lag. A delta connected 3-
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phase capacitor is used to improve the power
factor to unity. The capacitance perphase of the
capacitor in micro-farads is
(a) 3.948
(b) 1.316
(c) 0.439
(d) 11.844
Ans: b
19. For equilateral spacing of conductors of an
untrasposed 3-phase line, we have
(a) balanced receiving end voltage and no
communication interference
(b) unbalanced receiving end voltage and no
communication interference
(c) balanced receiving end voltage and
communication interference
(d) unbalanced receiving end voltage and
communication interference.
Ans: c
20. For a 500 Hz frequency excitation, a 50 #em
long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data insufficient for decision
Ans: c
21. Which one of the following statement. is not
correct for the use of bundled conductors in
transmission lines?
(a) Control of voltage gradient
(b) Reduction in corona 1088
(c) Reduction in radio interference
(d) Increase in interference with communication
lines
Ans: d
22. The main consideration for higher and
higher operating voltage of transmission is to
(a) increase the efficiency of transmission
(b) reduce power losses
(c) increase power transmission capability
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(d) both (a) and (b) above
Ans: c
23. A single phaae transmisson line of
impedance j 0.8 ohm supplies a resistive load of
500 A at 300 V. The sending end
power factor is
(a) unity
(b) 0.8 lagging
(c) 0.8 leading
(d) 0.6 lagging
Ans: d
24. A medium line with parameters A, B, C, D is
extended by connecting a short line of
impedance Z in series The overall ABCD
parameteres of the series combinatton will be
(a) A, AZ, C + D/Z, D
(b) A, AZ + B, C, CZ + D
(c) A + BZ, B, C + DZ, D
(d) AZ, B, C/Z, D
Ans: b
25. When bundle conductors are used in place
of single conductors, the effective inductance
and capacitance will respectively
(a) increase and decrease
(b) decrease and increase
(c) decrease and remain unaffected
(d) remain unaffected and increase
Ans: c
26. To increase the visual critical voltage of
cporona for an overhead line, one solid phaseconductor is replaced by a "bundle" of four
smaller conductors per phase, having an
aggregate cross-sectional area equal to that of
the solid conductor. If the radius of the solid
conductor is 40 mm, then the radius of each of
the bundle conductors would be
(a) 10 mm
(b) 20 mm
(c) 28.2 mm
(d) 30 mm
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Ans: d
27. For an existing ac transmision line, the string
efficiency is 80%, if dc voltage is supplied for the
same set up, the string efficiency will be
(a) < 80%
(b) 80%
(c) 90%
(d) 100%
Ans: b
28. In a string of suspension insulators, the
voltage distribution across the different units of
a string could be made uniform by the use of a
grading ring, because it
(a) forms capacitances with link-pins to carry
the charging current from link pins
(b) forms capacitances which help to cancel the
charging current from link pins
(c) increases the capacitances of lower insulator
units of cause equal voltage drop
(d) decreases the capacitances of upper
insulators units to cause equal voltage drop
Ans: b
29. A three phase over head transmission line
has its conductors horirzontally spaced with
spacing between adjacent conductors equal to
'd'. if now the conductors of the line are
rearranged to form and equilateral triangle of
sides equal to 'd' then
(a) average capacitance and inductance will
increase
(b) average capacitance will decrease and
inductance will increase
(c) average capacitance will increase and
inductance will decrease
(d) surge impedance loading of the line
Increases
Ans: a
30. For a 500 Hz frequency excitation, a 50
km, long power line will be modelled as
(a) short line
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(b) medium line
(c) long line
(d) data insufficiency for decision
Ans: c
31. If in a short transmission line, resistance
and inductance are found to be equal and
regulation appear. to be zero, then the load will
(a) have unity power factor
(b) have zero power factor
(c) be 0.707 lagging
(d) be 0.707 lagging
Ans: c
32. "Expanded ACSR" are conductors
composed of
(a) larger diameter individual strands for a given
cross-section of the aluminium strangs
(b) larger diameter of a central steel strands for
a given overall diameter of the conductor
(c) larger diamter of the aluminium strands only
for a given overall diameter of the conductor
(d) a fillter between the inner steel and the
outer aluminium strands to increase the overall
diameter of the conductor
Ans: d
33. What is the sag for a span of 400m, if the
ultimate tensile strength of conductor is 6000
kgf, and the weight of conductor is 550 kgf/km?
Factor of safety is 2.
(a) 1.016 m
(b) 2.40 m
(c) 3.6 m
(d) 4.2 m
Ans: c
34. A transmission line haB a span of 275 m
between level supporte. The conductor has a
diameter of 19.58 mm, weight 0.844 kgpm and
has an ultimate breaking strength of 7950 kgf.
Each conductor has a radial covering of ice 9.58
mm thick and is subjected to a horizontal wind
pressure of 40 k617m2 of ice covering projected
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area. If the factor of safety is 2, what is the
deflected sag? Ice weight is 913.5 kg/m3
(a) 5.36
(b) 4.1 m
(c) 3.9 m
(d) 3.01 m
Ans: a
35. A transmission line conductor having a
diameter of 19.5 mm, weight 850 kglkm. The
span is 275 m. The wind pressure is 39 kg/m of
projected area with ice coating of 13 mm. The
ultimate strength of the conductor is'8000 kg.
What is the maximum sag, if the factor of safety
is 2 and ice weight 910 kg/m3?
(a) 4.5 m
(b) 6.4 m
(c) 7.0 m
(d) 5 m
Ans: b
36. A transmission line conductor at a river
crossing is supported from two towers at
height. of 30 m and 90m, above water level. The
horizontal distance between the towers is
270m, if the tension in the conductor is 1800 kg
and the conductor weight 1 kg/m. What is the
clearance between the conductor and the water
at a point midway between the towers?
(a) 79.50 m
(b) 54.94 m
(c) 60 m
(d) 51.4 m
Ans: b
37. An overhead transmission line has a span
of 240m between level supports. What is the
maximum sag if the conductor weight 727
kg/km and has a breaking strength of 6880 kg?
Allow the factor of safety of 2. Neglecting wind
and ice loading.
(a) 1.52 m
(b) 1.6 m
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(c) 0.75 m
(d) 1.25 m
Ans: a
38. The line conductor of a transmission line
has an overall diameter of 19.53 mm, weight
0.844 kg/m and an ultimate breaking strength
of 7950 kg. If the factor of safety is to be 2,
when conductor has an ice of 1 kg/m and a
horizontal wind pressure of 1.5 kg/m. What is
the vertical sag, corresponding to this loading
for a 300 m span level supports?
(a) 1.08 m
(b) 5.0 m
(c) 5.22 m
(d) 4.62 m
Ans: c
39. A two conductor 1 - pi line operates at 50
Hz. The diameter of each conductor is 20 mm
and the spacing between conductors is 3m.
What is the inductance of each conductor per
km?
(a) 1.19 kH/km
(b) 1.24 mH/km
(c) 2.38 mH/km
(d) 0.59 mH/km
Ans: a
40. A two conductor 1 - pi line operates at 50
Hz. The diameter of each conductor is 20mm
and the spacing between conductor is 3m.
When the conductor material is steel of relative
permeability 50, the loop inductance per km of
the line will be
(a) 8.2 mHlkm
(b) 7.281 mHlkm
(c) 5.0 mHlkm
(d) 2 mHlkm
Ans: b
41. A 1-pi line two conductors operate at
50Hz. The diameter of each conductor is 15
mm, and the spacing between the conductor is
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3.5 m. The inductive reactance per km will be
(a) 0.43 ClIkm
(b) 0.65 0Jkm
(c) 0.70 O/km
(d) 0.79 nIkm
Ans: d
42. A conductor is composed of seven identical
copper .Iranu, each having a radius r. The self
GMD of the conductors will be
(a) 2.177 r
(b) 2.645 r
(c) 2.141 r
(d) 1.21 r
Ans: a
43. The charging current per kill of the line is
(a) 0.497 Amp
(b) 0.61 Amp
(c) 0.68 Amp
(d) 0.21 Amp
Ans: a
44. What is the time of operation of a relay of
rating 5 amp 2.2 sec, IDMT and having a relay of
setting of 125% Tms = 0.6 It is connected to a
supply circuit through a CT, 400 ratio. The fault
current is 400 amp.
(a) 10.Osec
(b) 1.92sec
(c) 4.5 sec
(d) 2.4 sec
Ans: b
45. A two conductor 1 - pi line operates at 50
Hz. The diameter of each conductor is 2 cm and
are spaced 3m apart. What is the line to line
capacitance
(a) 9.74 x 10-9 F/km
(b) 4.87 x 10-9 F/km
(c) 3.05 x 10-9 F/km
(d) None of these
Ans: b
46. A two conductor 1 - pi line operates at 50
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Hz.
The diameter of each conductor is 4 cm and are
spaced 6 m apart. What is the capacitive
susceptance to neutral per km?
(a) 1.42 x 10-9 s/km
(b) 3.25 x 10-8 s/km
(c) 4.8 x 10-9 s/krn
(d) 3.06 x 10-9 s/km
Ans: d
47. A three phase 50 Hz line consists of three
conductors each of diameter 21 mm, The
spacing between the conductors all follows:
A - B = 3m, B - C = 5m, C - A = 3.6m
If the line operates at 132 k V, the reactive
voltampere generatd by the line per km is
(a) 51.07 kVAr
(b) 51.70 kVAr
(c) 40.0 kVAr
(d) 60.5 kVAr
Ans: b
48. A two conductor 1 - pi line operates at 50
Hz.
The diameter of each conductor is 20 mm and
the spacing between the conductors is 3m, The
height of conductor above the ground is 6 m.
The capacitance of the line to neutral will be
(a) 9.7 pF/m
(b) 10.2 pF/m
(c) 8.7 uF/km
(d) 2.4 uF/m
Ans: a
49. For a 500 Hz frequency excitation, a 50 km
long power line will be modelled as
(a) short line
(b) medium line
(c) long line
(d) data isufficient decision
Ans: c
50. Bundled conductors are employed to
(a) reduce the short circuit current
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(b) improve system stability
(c) decreases system stability
(d) increase the short circuit current
Ans: c
51. Series capacitive compensation in EHV
transmission lines is used to
(a) reduce the line loading
(b) improve the stability of the system
(c) reduce the voltage profile
(d) improve the protection of the line
Ans: b
52. A lossless radial tranemission line with
surge impedance loading
(a) takes negative VAr at sending end and zero
VAr at receiving end
(b) takes positive VAr at sending end and zero
VAr at receiving end
(c) has flat voltage profile and unity power
factor at all points along it
(d) has sending end voltage higher than
receiving end voltage and unity power factor at
sending end
Ans: a
53. The X:R ratio of 220 kV line as compared
to 400 kV line is
(a) greater
(b) smaller
(c) equal
(d) it could be anything
Ans: b
54. If a line is 100 % series compensated it
may result into series resonance at power
frequency of
(a) 50 Hz
(c) 150 Hz
(b) 100 Hz
(d) none of the above
Ans: a
55. A 60 Hz, 320 km loesless line has Bending
end voltage 1.0 p.u, The receiving end voltage
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on no load is
(a) 1.1 p.u.
(b) 1.088 p.u.
(c) 1.116 p.u.
(d) none of the above
Ans: b
56. With 100 % series compensation of line.
(a) the circuit is series resonant at power
frequency
(b) low transient voltage
(c) high transient current
(d) both (a) and (c)
Ans: d
57. For certain geometry and operating
voltage of the uncompensated transmission
line, the ratio of power transfer capability to the
surge inpedance loading with increase in length
(a) increases
(b) remains unchanged
(c) decreases
(d) uncertain
Ans: c
58. The effect of series capacitance
compensation is
(a) to decrease the virtual surge impedance
(b) to decrease the effective length of the line
(c) to increase virtual surge impedance loading
(d) all of the above
Ans: d
59. For a long uncompensatedline the limit to
the line loading ill governed by
(a) thermal limit
(b) voltage drop
(c) stability limit
(d) corona loss
Ans: c
60. For any fixed degree of inductive shunt
compensation, additional series capacitive
compensation
(a) increase the effective length of line
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(b) increase virtual surge impedance line
(c) decrease virtual surge impedance loading of
the line
(d) none of the above
Ans: d
61. With 100 % inductive shunt compensation,
the voltage profile is flat for
(a) 100 % loading of line
(b) 50 % loading of line
(c) zero loading of line
(d) none of the above
Ans: c
62. A loss less line terminated with its surge
impedance has
(a) flat voltage profile
(b) transmission line angle is greater than actual
length of line
(c) transmission line agnle is less than the actual
length
(d) both (a) and (b) above
Ans: a
63. For reducing tower footing resistance it is
better to Use
(a) chemical and ground rods only
(b) chemical and counterpoise only
(c) ground rod and counterpoise only
(d) chemical, ground rods and counterpoise
Ans: c
64. An RLC series. circuit remains
predominantly inductive
(a) at resonance frequency
(b) below resonance frequency
(c) above resonance frequency
(d) at the lower half power frequency
Ans: c
65. The corona loss on a particular system at
50 Hz is 1 kw/phase per km. The corona loss on
the same system with supply frequency 25 Hz
will be
(a) 1 kW/phase/km
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(b) 0.5 kW/phase/km
(c) 0.667 kW/phase/km
(d) none of the above
Ans: c
66. A voltage of 1000 kV is applied to an
overhead line with its receiving end open. If the
surge impedance of the line is 500 ohm, then
the total surge power in the line ill
(a) 2000 MW
(b) 500 MW
(c) 2 MW
(d) 0.5 MW
Ans: a
67. The main criterion for selection of the size
of a distribution for a radial distribution system
is
(a) voltage drop
(b) corona loss
(c) temperature rise
(d) capital cost
Ans: a
68. If an induction machine is run at above
synchromous speed, it acts as
(a) a synchronous motor
(b) an indcution generator
(c) an inductor motor
(d) none of the above
Ans: b
69. The low voltage winding of a 400/230 V, 1phase, 50 Hz transformer is to be connected to
a 25 Hz, the supply voltage should be
(a) 230 V
(b) 460 V
(c) 115 V
(d) 65 V
Ans: c
70. Corona losses are minimized when
(a) conductors size is reduced
(b) smooth conductor is reduced
(c) sharp points are provided in the line
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hardware
(d) current density in conductors is reduced
Ans: b
71. The order of the sub-harmonic during SSR
for 50 Hz nornal frequency is
(a) 25 Hz
(b) 16 2/3 Hz
(c) 10 HZ
(d) none of the above
Ans: d
72. The non-uniform distribution of voltage
across the units in a string of suspention type
insulators is due to
(a) unequal self-capacitance of the units
(b) non-uniform distance of separation of the
units from the tower body
(c) the existence of stray capacitance between
the metallic junctions of the units and the tower
body
(d) non-uniform distance between the crossarm and the units
Ans: c
73. Whenever the conductors are dead-ended
of there is a change in the direction of
transmission line, the insulator. used are of the
(a) pin type
(b) suspension type
(c) strain type
(d) shackle type
Ans: c
74. The time taken for a surge to travel a 600
km long overhead transmission line is
(a) 6s
(b) 1s
(c) 0.02s
(d) 0.002s
Ans: d
75. The function of the earth wire in an extra
high voltage line is to
(a) prevent earth fault
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(b) provide a safety measure for any high-flying
object
(c) provide a shield to the phase con-ductors
from direct lightning stroke
(d) provide mechanical strength to the towers
Ans: c
76. A long overhead transmission line is
terminated by its characteristic impedance.
Under this operating condition, the ratio of the
voltage to the current at different points along
the line will
(a) progressively increase from the sending-end
to the receiving end
(b) progresively increase from the receiving end
to the sending-end
(c) remain the same at the two ends, but be
higher between the two ends being maximumat
the centre of the line
(d) remain the same at all points
Ans: b
77. For a transmission line with negligible
losses, the lagging reactive power (VAR)
delivered at Ihe receiving end, for a given
receiving end voltage, is directly proportional to
the
(a) square of the line voltage drop
(b) line voltage drop
(c) line inductive reactance
(d) line capacitive reactance
Ans: b
78. Corona loss can be reduced by the use of
hollow conductors because
(a) the current density is reduced
(b) the eddy current in the conductor is
eliminated
(c) for a given cross-section, the radius of the
conductor is increased
(d) of better ventilation in the conductor
Ans: d
79. The insulation of modern EHV lines is
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designed based on
(a) the lightning voltage
(b) corona
(c) radio interface
(d) switching voltage
Ans: d
80. Shunt conapenBation in an EHV line is
"Bed
(a) improve stability
(b) reduce fault level
(c) improve the voltage profile
(d) subsitute for synchronous phase modifier
Ans: d
81. In a 3-core extra-high voltage cable, a
metallic screen around each core¬i,..ulation i.
provided to
(a) facilitate heat dissipation
(b) give mechanical strength
(c) obtain radial electric stress
(d) obtain longtiudinal electric stress
Ans: c
82. The aingle pbase line of 280 V and 3 pha.e
line of 400 V which feed different domestic
circuit. And induetrial loade represent
(a) primary distribution
(b) secondary distribution
(c) secondary transmission
(d) none of the above
Ans: b
83. The transmission line feeding power on
either side of the main transmission line i. called
(a) Secondary distribution
(b) Secondary transmission
(c) Primary transmission
(d) Primary distribution
Ans: b
84. Series capacitive compensation on EHV
transmission lines is used to
(a) reduce the line loading
(b) improve the stability of the system
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(c) reduce the voltage profile
(d) improve the protection of the line
Ans: d
85. At a particular unbalanced node, the real
powers specified are Leaving the node : 20 Mw,
25 Mw, Entering the node: 60 Mw, 30 MW. The
balance power will be
(a) 30 MW leaving the node
(b) 45 MW leaving the node
(c) 45 MW entering the node
(d) 22.5MW entering the node and 22.5 MW
leaving the node
Ans: b
86. When a d.c source is switched is purely
inductive, the current response is
(a) an exponentially rising curve
(b) an exponentially decaying curve
(c) a straight line passing through the origin
(d) a straight line off-set from the origin
Ans: c
87. If transformer frequency is changed from
60 Hz, to 60 Hz the ratio of eddy current loss 60
Hz to 50 Hz, at constant voltage will be
(a) 5/6
(b) 25/36
(c) 6/5
(d) 1.0
Ans: d
88. In load flow analysis, the load connected
at a bUs is represented as
(a) constant current drawn from the bus
(b) constant impedance connected at the bus
(c) voltage and frequency dependent source at
the bus
(d) constant real and reactive drawn from the
bus
Ans: d
89. If the reference bUB is changed in two
load flow runs with same Bystena data and
power obtained for reference bur taken a.
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specified P and Q in the latter run
(a) the system losses will be unchanged but
complex bus voltage will change
(b) the system losses will be changed but
complex bus voltages remain unchanged
(c) the system losses as well be as complex bus
voltage will change
(d) the system losses as well be as complex bus
voltage will unchange
Ans: a
90. A square matrix is called singular if its
(a) determina is unity
(b) determinant is zero
(c) determinant is infinity
(d) rank is unity
Ans: b
91. Gauss-Seidel iterative method can be used
for solving a set of
(a) linear differential equations only
(b) linear algebraic equation only
(c) both linear and nonlinear algebraic
equations
(d) both linear and nonlinear differential
equations
Ans: b
92. Pure inductive circuit takes power
(reactive) from the a.c. line when
(a) both applied voltage and current rise
(b) both applied voltage anti current decrease
(c) applied voltage decreases but current
Increases
(d) none of these
Ans: b
93. An alternator has a phase sequence of RYB
for itB phase voltage. In case offield current is
reversed, the phase sequence will become
(a) RBY
(b) RYB
(c) YRB
(d) none of these
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Ans: b
94. An alternator has a phase sequence of RYB
for its phase voltage. In case the direetior of
rotation of alternator is reversed, the phase
sequence will become
(a) RBY
(b) RYB
(c) YRB
(d) none of these
Ans: a
95. A synchronous generator connected to an
infinite bUB delivers power at a lag p.r. If its
excitation is increased
(a) the terminal voltage increases
(b) voltage angle 8 increases
(c) current delivered increases
(d) all of the above
Ans: c
96. A synchronous motor connected to an
infinite bUB takes power at a lag p.f. If its
excitation is increased
(a) the terminal voltage increases
(b) the load angle increases
(c) the p.f. of motor increases
(d) all of the above
Ans: c
97. A star-conneted 440 V, 50 Hz alternator
has per phase synchronous reactance of 10 n. It
supplies a bal anced capacitive load current of
20 A, as shown in per phase equivalent circuit of
the given figure. It is desirable to have zero
voltage regulation. The load power factor
should be
(a) 0.82
(b) 0.47
(c) 0.39
(d) 0.92
Ans: a
98. A 10k VA, 400 V/200 V single phase
transformer with 10 % impedance draws a
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steady short circuit line current of
(a) 50 A
(b) 150 A
(c) 250 A
(d) 350 A
Ans: b
99. The percentage resistance and percentage
reactance of a 10 kVA, 400 V/200 V, 3-phase
transformer are 2% and 10% respectively. If the
constant losses in the machine are 1 %, the
maximum possible percentage efficiency of the
transformer is
(a) 98.32
(b) 97.25
(c) 96.85
(d) 96.12
Ans: c
100. The voltage of CI generator and an
infinite bus are given as O.92LIO 0 and 1.0L'O 0
respectively. The active power will flow from
(a) generator to infinite bus
(b) infinite bus to generator
(c) the data is insufficient to judge
(d) none of the above
Ans: a
101. In case ora 3 phase short circuit in a
system the power fed into the system is
(a) mostly reactive
(b) mostly active
(c) active and reactive both equal
(d) reactive only
Ans: a
102. With the help of a reactive compensator
it is possible to have
(u) constant voltage opei ation only
(b) unity p.f. operation only
(c) both constant voltage and unity p.f.
(d) either constant voltage or unity p.f.
Ans: d
103. For a long uncompensated line the limit
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to the line loading is governed by
(a) thermal limit
(b) voltage drop
(c) stability limit
(d) corona loss
Ans: c
104. A shunt reactor at 100 MVAr is operated
at 98% of its rated voltage and at 96% of its
rated frequency. The reactive power absorbed
by the reactor is
(a) 98 MVAr
(b) 104.02 MVAr
(c) 96.04 MVAr
(d) 100.04 MVAr
Ans: d
105. A 100 kVA transformer has 4%
impedance and 50 k VA transformer has 3%
impedance when they are operated in parallel,
which 6 transformer will reacb full load first
(a) 3%
(b) 4%
(c) data is insufficient
(d) none of the above
Ans: a
Power Plant Engineering
1. The commercial sources of energy are
(a) solar, wind and biomass
(b) fossil fuels, hydropower and nuclear
energy
(c) wood, animal wastes and agriculture
wastes
(d) none of the above
Ans: b
2.
(a) wood, animal wastes and agriculture
wastes
(b) solar, wind and biomass
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(c) either (a) or (b)
(d) neither (a) or (b)
Ans: a
3. In India largest thermal power station is
located at
(a) Kota
(b) Sarni
(c) Chandrapur
(d) Neyveli
Ans: c
4. The percentage O2 by Veight in
atmospheric air is
(a) 18%
(b) 23%
(c) 77%
(d) 79%
Ans: b
5. The percentage 02 by volume in
atmosphere air is
(a) 21%
(b) 23%
(c) 77%
(d) 79%
Ans: a
6. The proper indication of incomplete
combustion is
(a) high CO content in flue gases at exit
(b) high CO2 content in flue gases at exit
(c) high temperature of flue gases
(d) the smoking exhaust from chimney
Ans: a
7. The main source of production of biogas is
(a) human waste
(b) wet cow dung
(c) wet livestock waste
(d) all above
Ans: d
8. India's first nuclear power plant was
installed at
(a) Tarapore
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(b) Kota
(c) Kalpakkam
(d) none of the above
Ans: a
9. In fuel cell, the ______ energy is converted
into electrical energy.
(a) mechanical
(b) chemical
(c) heat
(d) sound
Ans: b
10. Solar thermal power generation can be
achieved by
(a) using focusing collector or heliostates
(b) using flat plate collectors
(c) using a solar pond
(d) any of the above system
Ans: d
11. The energy radiated by sun on a bright
sunny day is approximately
(a) 700 W/m2
(b) 800 W/m2
(c) 1 kW/m2
(d) 2 kW/m2
Ans: c
12. Thorium Breeder Reactors are most
suitable for India because
(a) these develop more power
(b) its technology is simple
(c) abundance of thorium deposits are
available in India
(d) these can be easily designed
Ans: c
13. The overall efficiency of thermal power
plant is equal to
(a) Rankine cycle efficiency
(b) Carnot cycle efficiency
(c) Regenerative cycle efficiency
(d) Boiler efficiency x turbine efficiency x
generator efficiency
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Ans: c
14. Rankine cycle efficiency of a good steam
power plant may be in the range of
(a) 15 to 20 per cent
(6) 35 to 45 per cent
(c) 70 to 80 per cent
(d) 90 to 95 per ceut
Ans: b
15. Rankine cycle operating on low pressure
limit ofpi an 1 high pressure limit of p2
(a) has higher the rnal efficiency than the
carnot cycie operating between same pressure
limits
(b) has lower the"nal efficiency than carnot
cycle operating between same pressure limit?
(c) has same thermal efficiency as carnot cycle
operating between same pressure limits
(d) may be more or less depending upon the
magnitude ofpi and/>2
Ans: a
16. Rankine efficiency of a steam power plant
(a) improves in summer as compared to that
in winter
(6) improves in winter as compared to that in
summer
(c) is unaffected by climatic conditions
(d) none of the above
Ans: b
17. Carnot cycle comprises of
(a) two isentropic processes and two constant
volume processes
(b) two isentropic processes and two constant
pressure processes
(e) two isothermal processes and three
constant pressure processes
(d) none of the above
Ans: b
18. In Rankine cycle the work output from the
turbine is given by
(a) change of internal energy between inlet and
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outlet
(b) change of enthaply between inlet and outlet
(c) change of entropy between inlet and outlet
(d) change of temperature between inlet and
outlet
Ans: b
19. Regenerative cycle thermal efficiency
(a) is always greater than simple Rankine
thermal efficiency
(b) is greater than simple Rankine cycle
thermal efficiency only when steam is bled at
particular pressure
(c) is same as simple Rankine cycle thermal
efficiency
(d) is always less than simple Rankine cycle
thermal efficiency
Ans: a
20. In a regenerative feed heating cycle, the
optimum value of the fraction of steam
extracted for feed heating
(a) decreases with increase in Rankine cycle
efficiency
(b) increases with increase in Rankine cycle
efficiency
(c) is unaffected by increase in Rankine cycle
efficiency
(d) none of the above
Ans: b
21. In a regenerative feed heating cycle, the
greatest economy is affected
(a) when steam is extracted from only one
suitable point of steam turbine
(b) when steam is extracted from several
places in different stages of steam turbine
(c) when steam is extracted only from the last
stage of steam turbine
(d) when steam is extracted only from the first
stage of steam turbine
Ans: b
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22. The maximum percentage gain in
Regenerative feed heating cycle thermal
efficiency
(a) increases with number of feed heaters
increasing
(b) decreases with number of feed heaters
increasing
(c) remains same unaffected by number of
feed heaters
(d) none of the above
Ans: a
23. In regenerative cycle feed water is heated
by
(a) exhaust gases
(b) heaters
(c) draining steam from the turbine
(d) all above
Ans: c
24. Reheat cycle in steam power plant is used
to
(a) utilise heat of flue gases
(b) increase thermal efficiency
(c) improve condenser performance
(d) reduce loss of heat
Ans: b
25. Mercury is a choice with steam in binary
vapour cycle because it has
(a) higher critical temperature and pressure
(b) higher saturation temperature than other
fluids
(c) relatively low vapourisation pressure
(d) all above
Ans: d
26. Binary'vapour cycles are used to
(a) increase the performance of the condenser
(b) increase the efficiency of the plant
(c) increase efficiency of the turbine
Ans: b
27. A steam power station requires space
(a) equal to diesel power station
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(b) more than diesel power station
(c) less than diesel power station
Ans: b
28. Economiser is used to heat
(a) air
(b) feed water
(c) flue gases
(d) all above
Ans: b
29. The modern steam turbines are
(a) impulse turbines
(b) reaction turbines
(c) impulse-reaction turbines
(d) none of the above
Ans: c
30. The draught which a chimney produces is
called
(a) induced draught
(b) natural draught
(c) forced draught
(d) balanced draught
Ans: b
31. The draught produced by steel chimney as
compared to that produced by brick chimney
for the same height is
(a) less
(b) more
(c) same
(d) may be more or less
Ans: b
32. In a boiler installation the natural draught
is produced
(a) due to the fact that furnace gases being
light go through the chimney giving place to
cold air from outside to rush in
(b) due to the fact that pressure at the grate
due to cold column is higher than the pressure
at the chimney base due to hot column
(c) due to the fact that at the chimney top the
pressure is more than its environmental
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pressure
(d) all of the above
Ans: b
33. The draught produced, for a given height
of the chimney and given mean temperature of
chimney gases
(a) decreases with increase in outside air
temperature
(b) increases with increase in outside air
temperature
(c) remains the same irrespective of outside
air temperature
(d) may increase or decrease with increase in
outside air temperature
Ans: a
34. The draught produced by chimney of given
height at given outside temperature
(a) decreases if the chimney gas temperature
increases
(b) increases if the chimney gas temperature
increases
(c) remains same irrespective of chimney gas
temperature
(d) may increase or decrease
Ans: b
35. For forced draught system, the function of
chimney is mainly
(a) to produce draught to accelerate the
combustion of fuel
(b) to discharge gases high up in the
atmosphere to avoid hazard
(c) to reduce the temperature of the hot gases
discharged
(d) none of the above
Ans: b
36. Artificial draught is produced by
(a) induced fan
(b) forced fan
(c) induced and forced fan
(d) all of the above
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Ans: d
37. The draught in locomotive boilers is
produced by
(a) forced fan
(b) chimney
(c) steam jet
(d) only motion of locomotive
Ans: c
38. For the same draught produced the power
of induced draught fan as compared to forced
draught fan is
(a) less
(b) more
(c) same
(d) not predictable
Ans: b
39. Artificial draught is produced by
(a) air fans
(b) steam jet
(c) fan or steam jet
(d) all of the above
Ans: d
40. The artificial draught normally is designed
to produce
(a) less smoke
(b) more draught
(c) less chimney gas temperature
(d) all of the above
Ans: d
41. For the induced draught the fan is located
(a) near bottom of chimney
(b) near bottom of furnace
(c) at the top of the chimney
(D) anywhere permissible
Ans: a
42. The pressure at the furnace is minimum in
case of
(a) forced draught system
(b) induced draught system
(c) balanced draught system
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(d) natural draught system
Ans: c
43. The efficiency of chimney is approximately
(a) 80%
(b) 40%
(c) 20%
(d) 0.25%
Ans: d
44. The isentropic expansion of steam through
nozzle for the steam initially superheated at
inlet is approximated by equation
(a) pvls=C
(b) pv1126 = C
(c) pv1A = C
(d) pv = C
Ans: a
45. The ratio of exit pressure to inlet pressure
for maximum mass flow rate per unit area of
steam through a nozzle when steam is initially
dry saturated is
(a) 0.6
(6) 0.578
(c) 0.555
(d) 0.5457
Ans: b
46. The ratio of exit pressure to inlet pressure
of maximum mass flow rate per area of steam
through a nozzle when steam is initially
superheated is
(a) 0.555
(b) 0.578
(c) 0.5457
(d) 0.6
Ans: c
47. The critical pressure ratio of a convergent
nozzle is defined as
(a) the ratio of outlet pressure to inlet pressure
of nozzle
(b) the ratio of inlet pressure to outlet pressure
of nozzle
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(c) the ratio of outlet pressure to inlet pressure
only when mass flow rate per unit area is
minimum
(d) the ratio of outlet pressure to inlet pressure
only when mass flow rate = c
Ans: d
48. The isentropic expansion of steam through
nozzle for the steam initially dry saturated at
inlet is approximated by equation.
(a)pv = C
(b)pv1A = C
(c)pv1i = C
(d)pv
Ans: d
49. The effect of considering friction losses in
steam nozzle for the same pressure ratio leads
to
(a) increase in exit velocity from the nozzle
(6) decrease in exit velocity from the nozzle
(c) no change in exit velocity from the nozzle
(d) increase or decrease depending upon the
exit quality of steam
Ans: b
50. The effect of considering friction in steam
nozzles for the same pressure ratio leads to
(a) increase in dryness fraction of exit steam
(b) decrease in dryness fraction of exit steam
(c) no change in the quality of exit steam
(d) decrease or increase of dryness frac-tion of
exit steam depending upon inlet quality
Ans: a
51. In case of impulse steam turbine
(a) there is enthalpy drop in fixed and moving
blades
(b) there is enthalpy drop only in moving blades
(c) there is enthalpy drop in nozzles
(d) none of the above
Ans: c
52. The pressure on the two sides of the
impulse wheel of a steam turbine
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(a) is same
(b) is different
(c) increases from one side to the other side
(d) decreases from one side to the other side
Ans: a
53. In De Laval steam turbine
(a) the pressure in the turbine rotor is
approximately same as in con¬denser
(b) the pressure in the turbine rotor is higher
than pressure in the con¬denser
(c) the pressure in the turbine rotor gradually
decreases from inlet to exit from condenser
(d) none from the above
Ans: a
54. Incase of reaction steam turbine
(a) there is enthalpy drop both in fixed and
moving blades
(b) there is enthalpy drop only in fixed blades
(c) there is enthalpy drop only in moving
blades
(d) none of the above
Ans: a
55. Curtis turbine is
(a) reaction steam turbine
(b) pressure velocity compounded steam
turbine
(c) pressure compounded impulse steam
turbme
(d) velocity compounded impulse steam
turbine
Ans: b
56. Rateau steam turbine is
(a) reaction steam turbine
(b) velocity compounded impulse steam
turbine
(c) pressure compounded impulse steam
turbine
(d) pressure velocity compounded steam
turbine
Ans: c
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57. Parson's turbine is
(a) pressure compounded steam turbine
(b) simple single wheel, impulse steam
turbine
(c) simple single wheel reaction steam turbine
(d) multi wheel reaction steam turbine
Ans: d
58. For Parson's reaction steam turbine,
degree of reaction is
(a) 75%
(b) 100%
(c) 50%
(d) 60%
Ans: c
59. Reheat factor in steam turbines depends
on
(a) exit pressure only
(b) stage efficiency only
(c) initial pressures and temperature only
(d) all of the above
Ans: c
60. The value of reheat factor normally varies
from
(a) 0.5 to 0.6
(b) 0.9 to 0.95
(c) 1.02 to 1.06
(d) 1.2 to 1.6
Ans: c
61. Steam turbines are governed by the
following methods
(a) Throttle governing
(b) Nozzle control governing
(c) By-pass governing
(d) all of the above
Ans: d
62. In steam turbines the reheat factor
(a) increases with the increase in number of
stages
(b) decreases with the increase in number of
stages
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(c) remains same irrespective of num¬ber of
stages
(d) none of the above
Ans: a
63. The thermal efficiency of the engine with
condenser as compared to without condenser,
for a given pressure and temperature of steam,
is
(a) higher
(b) lower
(c) same as long as initial pressure and
temperature is unchanged
(d) none of the above
Ans: a
64. In jet type condensers
(a) cooling water passes through tubes and
steam surrounds them
(b) steam passes through tubes and cooling
water surrounds them
(c) steam and cooling water mix
(d) steam and cooling water do not mix
Ans: c
65. In a shell and tube surface condenser
(a) steam and cooling water mix to give the
condensate
(b) cooling water passes through the tubes and
steam surrounds them
(c) steam passes through the cooling tubes and
cooling water surrounds them
(d) all of the above varying with situa¬tion
Ans: b
66. In a surface condenser if air is removed,
there is
(a) fall in absolute pressure maintained in
condenser
(b) rise in absolute pressure maintained in
condenser
(c) no change in absolute pressure in the
condenser
(d) rise in temperature of condensed steam
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Ans: a
67. The cooling section in the surface
condenser
(a) increases the quantity of vapour extracted
along with air
(b) reduces the quantity of vapour extracted
along with air
(c) does not affect vapour quantity extracted
but reduces pump capacity of air extraction
pump
(d) none of the above
Ans: b
68. Edward's air pump
(a) removes air and also vapour from
condenser
(b) removes only air from condenser
(c) removes only un-condensed vapour from
condenser
(d) removes air alongwith vapour and also the
condensed water from condenser
Ans: d
69. In a steam power plant, the function of a
condenser is
(a) to maintain pressure below atmospheric
to increase work output from the primemover
(b) to receive large volumes of steam
exhausted from steam prime mover
(c) to condense large volumes of steam to
water which may be used again in boiler
(d) all of the above
Ans: d
70. In a regenerative surface condenser
(a) there is one pump to remove air and
condensate
(b) there are two pumps to remove air and
condensate
(c) there are three pumps to remove air,
vapour and condensate
(d) there is no pump, the condensate gets
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removed by gravity
Ans: b
71. Evaporative type of condenser has
(a) steam in pipes surrounded by water
(b) water in pipes surrounded by steam
(c) either (a) or (b)
(d) none of the above
Ans: a
72. Pipes carrying steam are generally made
up of
(a) steel
(b) cast iron
(c) copper
(d) aluminium
Ans: a
73. For the safety of a steam boiler the
number of safety valves fitted are
(a) four
(b) three
(c) two
(d) one
Ans: c
74. Steam turbines commonly used in steam
power station are
(a) condensing type
(b) non-condensing type
(c) none of the above
Ans: a
75. Belt conveyer can be used to transport
coal at inclinations upto
(a) 30°
(b) 60°
(c) 80°
(d) 90°
Ans: a
76. The maximum length of a screw conveyer
is about
(a) 30 metres
(b) 40 metres
(c) 60 metres
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(d) 100 metres
Ans: a
77. The efficiency of a modern boiler using
coal and heat recovery equipment is about
(a) 25 to 30%
(b) 40 to 50%
(c) 65 to 70%
(d) 85 to 90%
Ans: d
78. The average ash content in Indian co als is
about
(a) 5%
(b) 10%
(c) 15%
(d) 20%
Ans: d
79. Load centre in a power station is
(a) centre of coal fields
(b) centre of maximum load of equip-ments
(c) centre of gravity of electrical system
Ans: c
80. Steam pressure in a steam power station,
which is usually kept now-a-days is of the order
of
(a) 20 kgf/cm2
(b) 50 kgf/cm2
(c) 100 kgf/cm2
(d) 150 kgf/cm2
Ans: d
81. Economisers improve boiler efficiency by
(a) 1 to 5%
(b) 4 to 10%
(c) 10 to 12%
Ans: b
82. The capacity of large turbo-generators
varies from
(a) 20 to 100 MW
(b) 50 to 300 MW
(c) 70 to 400 MW
(d) 100 to 650 MW
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Ans: b
83. Caking coals are those which
(a) burn completely
(b) burn freely
(c) do not form ash
(d) form lumps or masses of coke
Ans: d
84. Primary air is that air which is used to
(a) reduce the flame length
(b) increase the flame length
(c) transport and dry the coal
(d) provide air around burners for get¬ting
optimum combustion
Ans: c
85. Secondary air is the air used to
(a) reduce the flame length
(b) increase the flame length
(c) transport and dry the coal
(d) provide air round the burners for getting
optimum combustion
Ans: d
86. In coal preparation plant, magnetic
separators are used to remove
(a) dust
(b) clinkers
(c) iron particles
(d) sand
Ans: c
87. Load carrying capacity of belt conveyor is
about
(a) 20 to 40 tonnes/hr
(b) 50 to 100 tonnes/hr
(c) 100 to 150 tonnes/hr
(d) 150 to 200 tonnes/hr
Ans: b
88. Method which is commonly applied for
unloading the coal for small power plant is
(a) lift trucks
(b) coal accelerators
(c) tower cranes
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(d) belt conveyor
Ans: b
89. Bucket elevators are used for
(a) carrying coal in horizontal direction
(b) carrying coal in vertical direction
(c) carrying coal in any direction
Ans: b
90. The amount of air which is supplied for
complete combustion is called
(a) primary air
(b) secondary air
(c) tertiary air
Ans: b
91. In ______ system fuel from a central
pulverizing unit is delivered to a bunker and
then to the various burners
(a) unit
(b) central
(c) none of the above
Ans: b
92. Under-feed stokers work best for _______
coals high in volatile matter and with caking
tendency
(a) anthracite
(b) lignite
(c) semibituminous and bituminous
Ans: c
93. Example of overfeed type stoker is
(a) chain grate
(b) spreader
(c) travelling grate
(d) all of the above
Ans: d
94. Where unpulverised coal has to be used
and boiler capacity is large, the stoker which is
used is
(a) underfeed stoker
(b) overfeed stoker
(c) any
Ans: b
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95. TravelUng grate stoker can burn coals at the
rates of
(a) 50—75 kg/m per hour
(b) 75—100 kg/m per hour
(c) 100—150 kg/m per hour
(d) 150—200 kg/m2 per hour
Ans: d
96. Blowing down of boiler water is the process
(a) to reduce the boiler pressure
(b) to increase the steam temperature
(c) to control the solid concentration in the
boiler water by removing some of the
concentrated saline water
(d) none of the above
Ans: c
97. Deaerative heating is done to
(a) heat the water
(b) heat the air in the water
(c) remove dissolved gases in the water
Ans: c
98. Reheat factor is the ratio of
(a) isentropic heat drop to useful heat drop
(b) adiabatic heat drop to isentropic heat drop
(c) cumulative actual enthalpy drop for the
stages to total is isentropic enthalpy heat drop
Ans: c
99. The value of the reheat factor is of the order
of
(a) 0.8 to 1.0
(b) 1.0 to 1.05
(c) 1.1 to 1.5
(d) above 1.5
Ans: c
100. Compounding of steam turbine is done
for
(a) reducing the work done
(b) increasing the rotor speed
(c) reducing the rotor speed
(d) balancing the turbine
Ans: c
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Electrical Engineering Materials
1. The converse of hardness is known as
(a) malleability
(b) toughness
(c) softness
(d) none of the above
Ans: c
2. On which of the following factors does the
resistivity of a material depend ?
(a) Resistance of the conductor
(b) Area of the conductor section
(c) Length of the conductor
(d) All of the above
Ans: d
3. is a negatively charged particle present in
an atom.
(a) Proton
(b) Neutron
(c) Electron
(d) None of the above
Ans: c
4. The formula ____ determines the number
of electrons that can be accommodated in any
level.
(a) 2n2
(6) 4n2
(c) 2n3
(d) 4ns
Ans: a
5. The tiny block formed by the arrangement
of a small group of atoms is called the
(a) unit cell
(b) space lattice
(c) either (a) or (b)
(d) none of the above
Ans: a
6. The co-ordination number of a simple cubic
structure is
(a) 2
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(b) 4
(c) 6
(d) 8
Ans: c
7. The covalent bond is formed by
(a) transfer of electrons between atoms
(b) sharing of electrons between atoms
(e) sharing of variable number of electrons by
a variable number of atoms
(d) none of the above
Ans: b
8. A perfect conductor has
(a) zero conductivity
(b) unity conductivity
(c) infinite conductivity
(d) none of the above
Ans: c
9. The metal having the lowest temperature
coefficient of resistance is
(a) gold
(b) copper
(c) aluminium
(d) kanthal
Ans: a
10. Commonly used conducting materials are
(a) copper
(b) aluminium
(c) both (a) and (b)
(d) copper and silver
(e) platinum and gold
Ans: c
11. Which of the following materials is
preferred for transmitting electrical energy over
long distance ?
(a) Copper
(b) Aluminium
(c) Steel reinforced copper
(d) Steel reinforced aluminium
Ans: d
12. The kinetic energy of a bounded electron
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is
(a) less than that of unbounded electron
(6) greater than that of unbounded electron
(c) equal to that of unbounded electron
(d) infinite
(e) none of the above
Ans: a
13. A highly conductive material must have
(a) highest conductivity
(b) lowest temperature co-efficient
(c) good mechanical strength
(d) good corrosion resistance
(e) easy solderable and drawable quality
(f) all of the above
Ans: f
14. The conductivity of a conductor can be
increased by
(a) decreasing its temperature
(b) increasing its temperature
(c) decreasing its vibration
(d) increasing its vibration
Ans: a
15. Superconductivity is observed for
(a) infrared frequencies
(b) d.c. and low frequency
(c) a.c. and high frequency
(d) frequencies having no effect
(e) none of the above
Ans: b
16. The superconductivity is due to
(a) the crystal structure having no atomic
vibration at 0°K
(b) all electrons interact in the superconducting state
(c) the electrons jump into nucleus at 0°K
(d) none of the above
Ans: a
17. The value of critical field below the
transition temperature will
(a) increase
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(b) decrease
(c) remain unchanged
(d) any of the above
Ans: a
18. In a superconductor the value of critical
density depends upon
(a) magnetic field strength
(b) temperature
(c) either (a) or (b)
(d) both (a) and (b)
Ans: d
19. Superconductors are becoming popular
for use in
(a) generating very strong magnetic field
(b) manufacture of bubble memories
(c) generating electrostatic field
(d) generating regions free from magnetic
field
Ans: a
20. High resistivity materials are used in
(a) precision instruments
(6) heating elements
(c) motor starters
(d) incandescent lamps
(e) all of the above
Ans: e
21. Mercury as an electric contact material is
(a) a liquid
(b) a metal
(c) a metal liquid
(d) a gas
Ans: c
22. An H.R.C. fuse is
(a) a ceramic body having metal and caps
(b) a wire of platinum
(c) a heavy cross-section of copper or
aluminium
(d) a ceramic tube having carbon rod inside it
Ans: a
23. Which of the following resistive materials
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has the lowest temperature co-efficient of
resistance ?
(a) Nichrome
(b) Constantan
(c) Kanthal
(d) Molybdenum
Ans: a
24. The coils of D.C. motor starter are wound
with wire of
(a) copper
(b) kanthal
(c) manganin
(d) nichrome
Ans: c
25. The conductors have transport
phenomena of electrons due to
(a) electric field
(b) magnetic field
(c) electromagnetic field
(d) none of the above
Ans: a
26. The transition temperature of mercury is
(a) 18.0°K
(6) 9.22°K
(c) 4.12°K
(d) 1.14'K
Ans: c
27. By increasing impurity content in the
metal alloy the residual resistivity always
(a) decreases
(b) increases
(c) remains constant
(d) becomes temperature independent
Ans: b
28. The structure sensitive property of a super
conductor is
(a) critical magnetic field
(b) transition temperature
(c) critical current density
(d) none of the above
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Ans: c
29. At transition temperature the value of
critical field is
(a) zero
(6) negative real value
(c) positive real value
(d) complex value
Ans: a
30. Which of the following variety of copper
has the best conductivity ?
(a) Induction hardened copper
(b) Hard drawn copper
(c) Pure annealed copper
(d) Copper containing traces of silicon
Ans: c
31. Constantan contains
(a) silver and tin
(b) copper and tungsten
(c) tungsten and silver
(d) copper and nickel
Ans: d
32. Which of the following is the poorest
conductor of electricity ?
(a) Carbon
(b) Steel
(c) Silver
(d) Aluminium
Ans: a
33 ______ has zero temperature co-efficient
of resistance.
(a) Aluminium
(b) Carbon
(c) Porcelain
(d) Manganin
Ans: d
34. Piezoelectric materials serve as a source of
_____ .
(a) resonant waves
(b) musical waves
(c) microwaves
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(d) ultrasonic waves
Ans: d
35. In thermocouples which of the following
pairs is commonly used ?
(a) Copper-constantan
(b) Aluminium-tin
(c) Silver-German silver
(d) Iron-steel
Ans: a
36 is viscoelastic.
(a) Cast-iron
(6) Graphite
(c) Rubber
(d) Glass
Ans: c
37. Carbon electrodes are not used in
(a) GLS lamps
(b) electric arc furnace
(c) dry cells
(d) cinema projectors
Ans: a
38. Solder is an alloy of
(a) copper and aluminium
(b) tin and lead
(c) nickel, copper and zinc
(d) silver, copper and lead
Ans: b
39 ______ is most commonly used for making
magnetic recording tape
(a) Silver nitrate
(b) Ferric oxide
(c) Small particles of iron
(d) Silicon-iron
Ans: b
40. Overhead telephone wires are made of
(a) aluminium
(b) steel
(c) ACSR conductors
(d) copper
Ans: b
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41. ______ is an example of piezoelectric
material.
(a) Glass
(b) Quartz
(c) Corrundum
(d) Neoprene
Ans: b
42. _____ is the main constituent of glass
(a) Fe203
(b) Si02
(c) AI2O3
(d) B2O3
Ans: b
43. A good electric contact material should have
all of the following properties excePt
(a) high resistivity
(b) high resistance to corrosion
(c) good thermal conductivity
(d) high melting point
Ans: a
44. Most of the common metals have _____
structure.
(a) linear
(b) hexagonal
(c) orthorhombic
(d) cubic
Ans: d
45. Which of the following affect greatly the
resistivity of electrical conductors ?
(a) Composition
(b) Pressure
(c) Size
(d) Temperature
Ans: a
46. Thermonic emission occurs in
(a) vacuum tubes
(b) copper conductors
(c) ferrite cores
(d) transistors
Ans: a
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47. _____ is a hard solder.
(a) Tin-lead
(6) Tin-silver-lead
(c) Copper-zinc
(d) None of the above
Ans: c
48. Addition of 0.3 to 4.5% silicon to iron _____
the electrical resistivity of iron.
(a) increases
(b) decreases
(c) does not change
Ans: a
49. Super conductivity can be destroyed by
(a) adding impurities
(b) reducing temperatures
(c) application of magnetic field
(d) any of the above
Ans: c
50. Non-linear resistors
(a) produce harmonic distortion
(b) follows Ohm's law at low tempera¬tures
only
(c) result in non-uniform heating
(d) none of the above
Ans: a
51. A carbon resistor contains
(a) carbon crystals
(b) solid carbon granules
(c) pulverized coal
(d) finely divided carbon black.
Ans: d
52. Which of the following materials does not
have covalent bonds ?
(a) Organic polymers
(b) Silicon
(c) Metals
Ans: c
53. In graphite, bonding is
(a) covalent
(b) metallic
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(c) Vander Waals
(d) Vander Waals and covalent
Ans: d
54. Total number of crystal systems is
(a) 2
(b) 4
(c) 7
(d) 12
Ans: c
55. The number of atoms per unit cell in B.C.C.
structure is
(a) 1
(b) 2
(c) 4
(d) 8
Ans: b
56. The conductivity of a metal is determined
by
(a) the electronic concentration and the
mobility of the free electrons
(6) the number of valence electrons per atom
(c) either (a) or (b)
(d) none of the above
Ans: a
57. The resistivity of a metal is a function of
temperature because
(a) the amplitude of vibration of the atoms
varies with temperature
(b) the electron density varies with
temperature
(c) the electron gas density varies with
temperature
Ans: a
58. In a crystal, an atom vibrates at a
frequency determined by
(a) the heat content of the crystal
(b) the temperature of the crystal
(c) the stiffness of the bonds it makes with
neighbours
Ans: c
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59. Due to which of the following reasons
aluminium does not corrode in atmost phere ?
(a) Aluminium is a noble metal
(b) Atmospheric oxygen can only diffuse very
slowly through the oxide layer which is formed
on the surface of aluminium
(c) No reaction with oxygen occurs ft Any of
the above
Ans: b
60. The impurity atoms is semiconductors
(a) inject more charge carriers
(6) reduce the energy gap
(c) increase the kinetic energy of valence
electrons
(d) all of the above
Ans: b
61. Which of the following material is not a
semiconductor ?
(a) Silica
(b) Germanium
(c) Selenium
(d) Gallium-arsenide
Ans: a
62. Carbon resistors are used extensively
because they are
(a) easy to make
(b) compact
(c) inexpensive
(d) all of the above reasons
Ans: d
63. Carbon rods are used in wet and dry cells
because
(a) carbon rod serves as conductor
(b) carbon can resist the attack of bat¬tery
acid
(c) both (a) and (b)
(d) either (a) or (b)
Ans: c
64. Due to which of the following factors the
brush wear rate is altered ?
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(a) Speed of the machine
(b) Contact pressure
(c) Surface conditions of brush and
commutator
(d) Excessive sparking
(e) All of the above
Ans: e
65. Which of the following are non-conductors
of electricity?
(a) Non-metal solids except carbon
(b) Air and most other gases
(c) Pure water and liquids in general except
mercury
(d) All of the above
Ans: d
66. Carbon bearings are used under which of
the following conditions ?
(a) Where lubrication is difficult or im-possible
(b) Where corrosive chemical action exists
(c) Where high temperature exists
(d) All of the above
Ans: d
67. Which of the following high resistance
materials has the highest operating
temperature ?
(a) Kanthal
(b) Manganin
(c) Nichrome
(d) Eureka
Ans: a
68. Steel wire is used as
(a) overhead telephone wire
(b) earth wire
(c) core wire of ACSR
(d) all of the above
Ans: d
69. Low resistivity materials are used in
(a) transformer, motor and generator
windings
(b) transmission and distribution lines
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(c) house wiring
(d) all above applications
Ans: d
70. Platinum is used in
(a) electrical contacts
(b) thermocouple
(c) heating element in high temperature
furnace
(d) grids of special purpose vacuum tubes
(e) all of the above
Ans: e
71. Which of the following is an advantage of
stranded conductor over equivalent single
conductor ?
(a) Less liability to kink
(b) Greater flexibility
(c) Less liability to break
(d) All of the above
Ans: d
72. Due to which of the following reasons
copper and aluminium are not used for heating
elements ?
(a) Both have great tendency for oxidation
(b) Both have low melting point
(c) Very large length of wires will be required
(d) All of the above
Ans: d
73. Copper, even though costly, finds use in
the windings of electrical machines because
(a) copper points offer low contact resistance
(b) copper can be easily soldered and welded
(e) copper windings are less bulky and the
machines become compact
(d) all of the above
Ans: d
74. Which of the following materials is used
for making coils of standard resistances ?
(a) Copper
(b) Nichrome
(c) Platinum
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(d) Manganin
Ans: d
75. Substances whose specific resistance
abruptly decreases at very low temperature are
called
(a) insulators
(b) conductors
(c) semiconductors
(d) superconductors
Ans: d
76. Which of the following materials is the
best conductor of electricity ?
(a) Tungsten
(b) Aluminium
(c) Copper
(d) Carbon
Ans: c
77. is the property of absorbing moisture
from atmosphere.
(a) Solubility
(b) Viscosity
(c) Porosity
(d) Hygroscopicity
Ans: d
78. Thermocouples are mainly used for the
measurement of
(a) temperature
(b) resistance
(c) eddy currents
(d) coupling co-efficient
Ans: a
79. Due to which of the following fact, in
India, aluminium is replacing copper ?
(a) Aluminium is more ductile and malleable
than copper
(6) Aluminium is available in plenty, cheaper
and lighter than copper
(c) Aluminium has lower resistivity than that
of copper
(d) Aluminium has less temperature co
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efficient than copper
Ans: b
80. The conduction of electricity, in
semiconductors, takes place due to movement
of
(a) positive ions only
(b) negative ions only
(c) positive and negative ions
(d) electrons and holes
Ans: d
81. Which of the following is a semiconductor
material ?
(a) Phosphorous
(b) Rubber
(c) Silicon
(d) Aluminium
Ans: c
82. Selenium is _____ semiconductor.
(a) extrnisic
(b) intmisic
(c) N-type
(d) P-type
Ans: b
83. ________ has the best damping
properties.
(a) Diamond
(b) High speed steel
(c) Mild steel
(d) Cast iron
Ans: d
84. The photo-electric effect occurs only when
the incident light has more than a certain
critical
(a) intensity
(b) speed
(c) frequency
(d) wave length
Ans: c
85. If the resistance of a conductor does not
vary in accordance with Ohm's law it is known
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as
(a) non-linear conductor
(b) reverse conductor
(c) bad-conductor
(d) non-conductor
Ans: a
86. Spark plug makes use of which of the
following materials for insulation ?
(a) Porcelain
(b) Slate
(c) Asbestos
(d) Glass
Ans: a
87. The forbidden gap in an insulator is
(a) large
(b) small
(c) nil
(d) any of the above
Ans: a
88. Which of the following factors affect
resistivity of metals ?
(a) Age hardening
(b) Alloying
(c) Temperature
(d) Cold work
(e) All of the above
Ans: e
89. Effect of moisture on the insulating
materials is to
(a) decrease dielectric constant
(b) decrease dielectric strength
(c) decrease insulation resistance
(d) increase dielectric loss
(e) all of the above
Ans: e
90. Surface resistance of an insulating material
is reduced due to the
(a) smoky and dirty atmosphere
(b) humidity in the atmosphere
(c) both (a) and (b)
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(d) neither (a) nor (b)
Ans: c
91. Superconducting metal in super
conducting state has relative permeability of
(a) zero
(b) one
(c) negative
(d) more than one
Ans: a
92. In conductors conduction of electricity
takes place due to movement of
(a) electrons only
(b) positive ions only
(c) negative ions only
(d) positive and negative ions
(e) none of the above
Ans: a
93. The carbon percentage is least in
(a) low carbon steel
(b) wrought iron
(c) cast iron
(d) malleable iron
Ans: b
94. For a particular material the Hall
coefficient was found to be zero. The material is
(a) insulator
(6) metal
(c) intrinsic semiconductor
(d) none of the above
Ans: b
95. The conductivity of an extrinsic
semiconductor with temperature
(a) decreases
(b) increases
(c) remains constant
Ans: c
96. The current due to electron flow in
conduction band is the hole current in valence
band.
(a) equal to
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(b) less than
(c) greater than
(d) any of the above
Ans: c
97. For a hole which of the following
statements is incorrect ?
(a) Holes can exist in certain semicon-ductors
only
(b) Holes can exist in any material in-cluding
conductors
(c) Holes may constitute an electric current
(d) Holes can be considered as a net positive
charge
Ans: b
98. is an element used in semiconductors
whose atoms have three valence electrons.
(a) An acceptor
(b) A donor
(c) Germanium
(d) Silicon
Ans: a
99. The minority carrier concentration is
largely a function of
(a) forward biasing voltage
(b) reverse biasing voltage
(c) temperature
(d) the amount of doping
Ans: c
100. For germanium the forbidden energy gap
is
(a) 0.15 eV
(b) 0.25 eV
(C) 0.5eV
(d) 0.7eV
Ans: d
Transmission and Distribution
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1. By which of the following systems electric
power may be transmitted ?
(a) Overhead system
(b) Underground system
(c) Both (a) and (b)
(d) None of the above
Ans: c
2 are the conductors, which connect the
consumer's terminals to the distribution
(a) Distributors
(b) Service mains
(c) Feeders
(d) None of the above
Ans: b
3. The underground system cannot be
operated above
(a) 440 V
(b) 11 kV
(c) 33 kV
(d) 66 kV
Ans: d
4. Overhead system can be designed for
operation upto
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 400 kV
Ans: c
5. If variable part of annual cost on account of
interest and depreciation on the capital outlay
is equal to the
annual cost of electrical energy wasted in the
conductors, the total annual cost will be
minimum and the corresponding size of
conductor will be most economical. This
statement is known as
(a) Kelvin's law
(b) Ohm's law
(c) Kirchhoffs law
(d) Faraday's law
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(e) none of the above
Ans: a
6. The wooden poles well impregnated with
creosite oil or any preservative compound have
life
(a) from 2 to 5 years
(b) 10 to 15 years
(c) 25 to 30 years
(d) 60 to 70 years
Ans: c
7. Which of the following materials is not used
for transmission and distribution of electrical
power ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Tungsten
Ans: d
8. Galvanised steel wire is generally used as
(a) stay wire
(b) earth wire
(c) structural components
(d) all of the above
Ans: d
9. The usual spans with R.C.C. poles are
(a) 40—50 metres
(b) 60—100 metres
(c) 80—100 metres
(d) 300—500 metres
Ans: c
10. The corona is considerably affected by
which of the following ?
(a) Size of the conductor
(b) Shape of the conductor
(c) Surface condition of the conductor
(d) All of the above
Ans: d
11. Which of the following are the constants
of the transmission lines ?
(a) Resistance
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(b) Inductance
(c) Capacitance
(d) All of the above
Ans: d
12. 310 km line is considered as
(a) a long line
(b) a medium line
(c) a short line
(d) any of the above
Ans: a
13. The phenomenon qf rise in voltage at the
receiving end of the open-circuited or lightly
loaded line is called the
(a) Seeback effect
(b) Ferranti effect
(c) Raman effect
(d) none of the above
Ans: b
14. The square root of the ratio of line
impedance and shunt admittance is called the
(a) surge impedance of the line
(b) conductance of the line
(c) regulation of the line
(d) none of the above
Ans: a
15. Which of the following is the demerit of a
'constant voltage transmission system' ?
(a) Increase of short-circuit current of the
system
(b) Availability of steady voltage at all loads at
the line terminals
(c) Possibility of better protection for the line
due to possible use of higher terminal
reactances
(d) Improvement of power factor at times of
moderate and heavy loads
(e) Possibility of carrying increased power for
a given conductor size in case of long-distance
heavy power transmission
Ans: a
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16. Low voltage cables are meant for use up
to
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: e
17. The operating voltage of high voltage
cables is upto
(a)l.lkV
(b)3.3kV
(c)6.6kV
(d)llkV
Ans: d
18. The operating voltage of supertension
cables is upto
(a) 3.3 kV
(b) 6.6 kV
(c) 11 kV
(d) 33 kV
Ans: d
19. The operating voltage of extra high
tension cables is upto
(a) 6.6 kV
(b) 11 kV
(c) 33 kV
(d) 66 kV
(e) 132 kV
Ans: d
20. Which of the following methods is used
for laying of underground cables ?
(a) Direct laying
(b) Draw-in-system
(c) Solid system
(d) All of the above
Ans: d
21. Which of the following is the source of
heat generation in the cables ?
(a) Dielectric losses in cable insulation
(b) losses in the conductor
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(c) Losses in the metallic sheathings and
armourings
(d) All of the above
Ans:
22. Due to which of the following reasons the
cables should not be operated too hot ?
(a) The oil may loose its viscosity and it may
start drawing off from higher levels
(b) Expansion of the oil may cause the sheath
to burst
(c) Unequal expansion may create voids in the
insulation which will lead to ionization
(d) The thermal instability may rise due to the
rapid increase of dielectric losses with
temperature
(e) All of the above
Ans: e
23. Which of the following D.C. distribution
system is the simplest and lowest in first cost ?
(a) Radial system
(b) Ring system
(c) Inter-connected system
(d) None of the above
Ans: a
24. A booster is a
(a) series wound generator
(b) shunt wound generator
(c) synchronous generator
(d) none of the above
Ans: a
25. Besides a method of trial and error, which
of the following methods is employed for
solution of network problems in
interconnected system ?
(a) Circulating current method
(b) Thevenin's theorem
(c) Superposition of currents
(d) Direct application of Kirehhoffs laws
(e) All of the above
Ans: e
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26. Which of the following faults is most likely
to occur in cables ?
(a) Cross or short-circuit fault
(b) Open circuit fault
(c) Breakdown of cable insulation
(d) All of the above
Ans: d
27. The cause of damage to the lead sheath of
a cable is
(a) crystallisation of the lead through vibration
(b) chemical action on the lead when buried in
the earth
(c) mechanical damage
(d) all of the above
Ans: d
28. The voltage of the single phase supply to
residential consumers is
(a) 110 V
(b) 210 V
(c) 230 V
(d) 400 V
Ans: c
29. Most of the high voltage transmission lines
in India are
(a) underground
(b) overhead
(c) either of the above
(d) none of the above
Ans: b
30. The distributors for residential areas are
(a) single phase
(b) three-phase three wire
(c) three-phase four wire
(d) none of the above
Ans: c
31. The conductors of the overhead lines are
(a) solid
(b) stranded
(c) both solid and stranded
(d) none of the above
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Ans: b
a) suspension insulators
(b) pin insulators
(c) both (a) and (b)
(d) none of the above
Ans: a
33. Multicore cables generally use
(a) square conductors
(b) circular conductors
(c) rectangular conductors
(d) sector-shaped conductors
(e) none of the above
Ans: d
34. Distribution lines in India generally use
(a) wooden poles
(b) R.C.C. poles
(c) steel towers
(d) none of the above
Ans: b
35. The material commonly used for insulation
in high voltage cables is
(a) lead
(b) paper
(c) rubber
(d) none of the above
Ans: b
36. The loads on distributors systems are
generally
(a) balanced
(b) unbalanced
(c) either of the above
(d) none of the above
Ans: b
37. The power factor of industrial loads is
generally
(a) unity
(b) lagging
(c) leading
(d) zero
Ans: b
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38. Overhead lines generally use
(a) copper conductors
(b) all aluminium conductors
(c) A.C.S.R. conductors
(d) none of these
Ans: c
39. In transmission lines the cross-arms are
made of
(a) copper
(b) wood
(c) R.C.C.
(d) steel
Ans: d
40. The material generally used for armour of
high voltage cables is
(a) aluminium
(b) steel
(c) brass
(d) copper
Ans: b
41. Transmission line insulators are made of
(a) glass
(b) porcelain
(c) iron
(d) P.V.C.
Ans: b
42. The material commonly used for sheaths
of underground cables is
(a) lead
(b) rubber
(c) copper
(d) iron
Ans: a
43. The minimum clearance between the
ground and a 220 kV line is about
(a) 4.3 m
(b) 5.5 m
(c) 7.0 m
(d) 10.5 m
Ans: c
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44. The spacing between phase conductors of
a 220 kV line is approximately equal to
(a) 2 m
(b) 3.5 m
(c) 6 m
(d) 8.5 m
Ans: c
45. Large industrial consumers are supplied
electrical energy at
(a) 400 V
(b) 11 kV
(c) 66 kV
(d) 400 kV
Ans: c
46. In a D.C. 3-wire distribution system,
balancer fields are cross-connected in order to
(a) boost the generated voltage
(b) balance loads on both sides of the neutral
(c) make both machine^ run as unloaded
motors
(d) equalize voltages on the positive and
negative outers
Ans: d
47. In a D.C. 3-wire distributor using balancers
and having unequal loads on the two sides
(a) both balancers run as generators
(b) both balancers run as motors
(c) balancer connected to lightly- loaded side
runs as a motor
(d) balancer connected to heavily- loaded side
runs as a motor
Ans: c
48. Transmitted power remaining the same, if
supply voltage of a D.C. 2-wire feeder is
increased 100 percent, saving in copper is
(a) 25 percent
(b) 50 percent
(c) 75 percent
(d) 100 percent
Ans: b
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49. A uniformly-loaded D.C. distributor is fed
at both ends with equal voltages. As compared
to a similar distributor fed at one end only, the
drop at the middle point is
(a) one-fourth
(b) one-third
(c) one-half
(d) twice
(e) none of the above
Ans: a
50. As compared to a 2-wire D.C. distributor, a
3-wire distributor with same maximum voltage
to earth uses only
(a) 31.25 percent of copper
(b) 33.3 percent of copper
(c) 66.7 percent of copper
(d) 125 percent of copper
Ans: a
51. Which of the following is usually not the
generating voltage ?
(a) 6.6 kV
(b) 8.8 kV
(c) 11 kV
(d) 13.2 kV
Ans: b
52. For an overhead line, the surge impedance
is taken as
(a) 20-30 ohms
(b) 70—80 ohms
(c) 100—200 ohms
(d) 500—1000 ohms
(e) none of the above
Ans: c
53. The presence of ozone due to corona is
harmful because it
(a) reduces power factor
(b) corrodes the material
(c) gives odour
(d) transfer energy to the ground
(e) none of the above
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Ans: b
54. A feeder, in a transmission system, feeds
power to
(a) distributors
(b) generating stations
(c) service mains
(d) all of the above
Ans: a
55. The power transmitted will be maximum
when
(a) corona losses are minimum
(b) reactance is high
(c) sending end voltage is more
(d) receiving end voltage is more
Ans: c
56. A 3-phase 4 wire system is commonly used
on
(a) primary transmission
(b) secondary transmission
(c) primary distribution
(d) secondary distribution
Ans: d
57. Which of the following materials is used
for overhead transmission lines ?
(a) Steel cored aluminium
(b) Galvanised steel
(c) Cadmium copper
(d) Any of the above
Ans: d
58. Which of the following is not a constituent
for making porcelain insulators ?
(a) Quartz
(b) Kaolin
(c) Felspar
(d) Silica
Ans: d
59. There is a greater possibility of occurence
of corona during
(a) dry weather
(b) winter
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(c) summer heat
(d) humid weather
(e) none of the above
Ans: d
60. Which of the following relays is used on
long transmission lines ?
(a) Impedance relay
(b) Mho's relay
(c) Reactance relay
(d) None of the above
Ans: b
61. The steel used in steel cored conductors is
usually
(a) alloy steel
(b) stainless steel
(c) mild steel
(d) high speed steel
(e) all of the above
Ans: c
62. Which of the following distribution
systems is more reliable ?
(a) Radial system
(b) Tree system
(c) Ring main system
(d) All are equally reliable
Ans: c
63. Which of the following characteristics
should the line supports for transmission lines
possess ?
(a) Low cost
(b) High mechanical strength
(c) Longer life
(d) All of the above
Ans: d
64. Transmission voltage of llkV is normally
used for distances upto
(a) 20—25 km
(b) 40—50 km
(c) 60—70 km
(d) 80—100 km
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Ans: a
65. Which of the following regulations is
considered best?
(a) 50%
(b) 20%
(c) 10%
(d) 2%
Ans: d
66. Skin effect is proportional to
(a) (conductor diameter)
(b) (conductor diameter)
(c) (conductor diameter)
(d) (conductor diameter)
(e) none of the above
Ans: c
67. A conductor, due to sag between two
supports, takes the form of
(a) semi-circle
(b) triangle
(c) ellipse
(d) catenary
Ans: d
68. In AC.S.R. conductors, the insulation
between aluminium and steel conductors is
(a) insulin
(b) bitumen
(c) varnish
(d) no insulation is required
Ans: d
69. Which of the followingbus-bar schemes
has the lowest cost ?
(a) Ring bus-bar scheme
(b) Single bus-bar scheme
(c) Breaker and a half scheme
(d) Main and transfer scheme
Ans: b
70. Owing to skin effect
(a) current flows through the half cross-section
of the conductor
(b) portion of the conductor near the surface
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carries more current and core of the conductor
carries less current
(c) portion of the conductor near the surface
carries less current and core of the conductor
carries more current
(d) any of the above
(e) none of the above
Ans: b
71. By which of the following methods string
efficiency can be improved ?
(a) Using a guard ring
(b) Grading the insulator
(c) Using long cross arm
(d) Any of the above
(e) None of the above
Ans: d
72. In aluminium conductors, steel core is
provided to
(a) compensate for skin effect
(b) neutralise proximity effect
(c) reduce line inductance
(d) increase the tensile strength
Ans: d
73. By which of the following a bus-bar is
rated ?
(a) Current only
(b) Current and voltage
(c) Current, voltage and frequency
(d) Current, voltage, frequency and short time
current
Ans: d
74. A circuit is disconnected by isolators when
(a) line is energized
(b) there is no current in the line
(c) line is on full load
(d) circuit breaker is not open
Ans: b
75. For which of the following equipment
current rating is not necessary ?
(a) Circuit breakers
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(b) Isolators
(c) Load break switch
(d) Circuit breakers and load break switches
Ans: b
76. In a substation the following equipment is
not installed
(a) exciters
(b) series capacitors
(c) shunt reactors
(d) voltatre transformers
Ans: a
77. jCorona usually occurs when the
electrostatic stress in air around the conductor
exceeds
(a) 6.6 kV (r.m.s. value)/cm
(b) 11 kV (r.m.s. value)/cm
(c) 22 kV (maximum value)/cm
(d) 30 kV (maximum v^lue)/cm
Ans: d
78. The voltage drop, for constant voltage
transmission is compensated by installing
(a) inductors
(b) capacitors
(c) synchronous motors
(d) all of above
(e) none of the above
Ans: c
79. The use of strain type insulators is made
where the conductors are
(a) dead ended
(b) at intermediate anchor towers
(c) any of the above
(d) none of the above
Ans: c
80. The current drawn by the line due to
corona losses is
(a) non-sinusoidal
(b) sinusoidal
(c) triangular
(d) square
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Ans: a
81. Pin type insulators are generally not used
for voltages beyond
(a) 1 kV
(b) 11 kV
(c) 22 kV
(d) 33 kV
Ans: d
82. Aluminium has a specific gravity of
(a) 1.5
(b) 2.7
(c) 4.2
(d) 7.8
Ans: b
83. For transmission of power over a distance
of 200 km, the transmission voltage should be
(a) 132 kV
(b) 66 kV
(c) 33 kV
(d) 11 kV
Ans: a
84. For aluminium, as compared to copper, all
the following factors have higher values except
(a) specific volume
(6) electrical conductivity
(c) co-efficient of linear expansion
(d) resistance per unit length for same crosssection
Ans: b
85. Which of the following equipment, for
regulating the voltage in distribution feeder, will
be most economical ?
(a) Static condenser
(b) Synchronous condenser
(c) Tap changing transformer
(d) Booster transformer
Ans: d
86. In a tap changing transformer, the
tappings are provided on
(a) primary winding
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(b) secondary winding
(c) high voltage winding
(d) any of the above
Ans: b
87. Constant voltage transmission entails the
following disadvantage
(a) large conductor area is required for same
power transmission
(b) short-circuit current of the system is
increased
(c) either of the above
(d) none of the above
Ans: b
88. On which of the following factors skin
effect depends ?
(a) Frequency of the current
(b) Size of the conductor
(c) Resistivity of the conductor material
(d) All of the above
Ans: d
89. The effect of corona can be detected by
(a) presence of zone detected by odour
(b) hissing sound
(c) faint luminous glow of bluish colour
(d) all of the above
Ans: d
90. For transmission of power over a distance
of 500 km, the transmission voltage should be
in the range
(a) 150 to 220 kV
(b) 100 to 120 kV
(c) 60 to 100 kV
(d) 20 to 50 kV
Ans: a
91. In the analysis of which of the following
lines shunt capacitance is neglected ?
(a) Short transmission lines
(b) Medium transmission lines
(c) Long transmission lines
(d) Medium as well as long transmission lines
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Ans: a
92. When the interconnector between two
stations has large reactance
(a) the transfer of power will take place with
voltage fluctuation and noise
(b) the transfer of power will take place with
least loss
(c) the stations will fall out of step because of
large angular displacement between the
stations
(d) none of the above
Ans: c
93. The frequency of voltage generated, in
case of generators, can be increased by
(a) using reactors
(b) increasing the load
(c) adjusting the governor
(d) reducing the terminal voltage
(e) none of the above
Ans: c
94. When an alternator connected to the busbar is shut down the bus-bar voltage will
(a) fall
(b) rise
(c) remain unchanged
(d) none of the above
Ans: c
95. The angular displacement between two
interconnected stations is mainly due to
(a) armature reactance of both alternators
(b) reactance of the interconnector
(c) synchronous reactance of both the
alternators
(d) all of the above
Ans: a
96. Electro-mechanical voltage regulators are
generally used in
(a) reactors
(b) generators
(c) transformers
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(d) all of the above
Ans: b
97. Series capacitors on transmission lines are
of little use when the load VAR requirement is
(a) large
(b) small
(b) fluctuating
(d) any of the above
Ans: b
98. The voltage regulation in magnetic
amplifier type voltage regulator is effected by
(a) electromagnetic induction
(b) varying the resistance
(c) varying the reactance
(d) variable transformer
Ans: c
99. When a conductor carries more current on
the surface as compared to core, it is due to
(a) permeability variation
(b) corona
(c) skin effect
(d) unsymmetrical fault
(e) none of the above
Ans: c
100. The following system is not generally
used
(a) 1-phase 3 wire
(b) 1-phase 4 wire
(c) 3-phase 3 wire
(d) 3-phase 4 wire
Ans: a
101. The skin effect of a conductor will reduce
as the
(a) resistivity of conductor material increases
(b) permeability of conductor material
increases
(c) diameter increases
(d) frequency increases
Ans: a
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102. When a live conductor of public electric
supply breaks down and touches the earth
which of the following will happen ?
(a) Current will flow to earth
(b) Supply voltage will drop
(c) Supply voltage will increase
(d) No current will flow in the conductor
(e) None of the above
Ans: a
Heating and Welding
1. Which of the following is an advantage of
heating by electricity ?
(a) Quicker operation
(b) Higher efficiency
(c) Absence of flue gases
(d) All of the above
Ans: d
2. ________ has the highest value of thermal
conductivity.
(a) Copper
(b) Aluminium
(c) Brass
(d) Steel
Ans: a
3. Which of the following heating methods has
maximum power factor ?
(a) Arc heating
(b) Dielectric heating
(c) Induction heating
(d) Resistance heating
Ans: d
4 method has leading power factor
(a) Resistance heating
(b) Dielectric heating
(c) Arc heating
(d) Induction heating
Ans: b
5 is used for heating non-conducting
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materials.
(a) Eddy current heating
(b) Arc heating
(c) Induction heating
(d) Dielectric heating
Ans: d
6. Which of the following methods of heating
is not dependent on the frequency of supply ?
(a) Induction heating
(b) Dielectric heating
(c) Electric resistance heating
(d) All of the above
Ans: c
7. When a body reflects entire radiation
incident on it, then it is known as
(a) white body
(b) grey body
(c) black body
(d) transparent body
Ans: a
8. For the transmission of heat from one body
to another
(a) temperature of the two bodies must be
different
(b) both bodies must be solids
(c) both bodies must be in contact
(d) at least one of the bodies must have some
source of heating
Ans: a
9. Heat transfer by condition will not occur
when
(a) bodies are kept in vacuum
(b) bodies are immersed in water
(c) bodies are exposed to thermal radiations
(d) temperatures of the two bodies are
identical
Ans: d
10. A perfect black body is one that
(a) transmits all incident radiations
(b) absorbs all incident radiations
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(c) reflects all incident radiations
(d) absorbs, reflects and transmits all incident
radiations
Ans: b
11. Heat is transferred simultaneously by
condition, convection and radiation
(a) inside boiler furnaces
(b) during melting of ice
(c) through the surface of the insulted pipe
carrying steam
(d) from refrigerator coils to freezer of a
refrigerator
Ans: a
12. The process of heat transfer during the
reentry of satellites and missiles, at very high
speeds, into earth's atmosphere is known as
(a) ablation
(b) radiation
(c) viscous dissipation
(d) irradiation
Ans: a
13. Which of the following has the highest
value of thermal conductivity ?
(a) Water
(b) Steam
(c) Solid ice
(d) Melting ice
Ans: c
14. Induction heating process is based on
which of the following principles ?
(a) Thermal ion release principle
(b) Nucleate heating principle
(c) Resistance heating principle
(d) Electro-magnetic induction princi¬ple
Ans: d
15. Which of the following insulating materials
was suitable for low temperature applications ?
(a) Asbestos paper
(b) Diatomaceous earth
(c) 80 percent magnesia
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(d) Cork
Ans: b
16. A non-dimensional number generally
associated with natural convection heat
transfer is
(a) Prandtl number
(b) Grashoff number
(c) Pecelet number
(d) Nusselt number
Ans: b
17. The temperature inside a furnace is
usually measured by which of the following ?
(a) Optical pyrometer
(b) Mercury thermometer
(c) Alcohol thermometer
(d) Any of the above
Ans: a
18. Which of the following will happen if the
thickness of refractory wall of furnace is
increased ?
(a) Heat loss through furnace wall will
increase
(b) Temperature inside the furnace will fall
(c) Temperature on the outer surface of
furnace walls will drop
(d) Energy consumption will increase
Ans: c
19. The material of the heating element for a
furnace should have
(a) lower melting point
(b) higher temperature coefficient
(c) high specific resistance
(d) all of the above
Ans: c
20. In a resistance furnace the atmosphere is
(a) oxidising
(b) deoxidising
(c) reducing
(d) neutral
Ans: a
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21. By which of the following methods the
temperature inside arc nace can be varied ?
(a) By disconnecting some of the heating
elements
(b) By varying the operating voltage
(c) By varying the current through heating
elements
(d) By any of the above method
Ans: d
22. In induction heating ______ is abnormally
high.
(a) phase angle
(b) frequency
(c) current
(d) voltage
Ans: b
23. By the use of which of the following, high
frequency power supply for induction furnaces
can be obtained ?
(a) Coreless transformers
(b) Current transformers
(c) Motor-generator set
(d) Multi-phase transformer
Ans: c
24. Induction furnaces are employed for
which of the following ?
(a) Heat treatment of castings
(b) Heating of insulators
(c) Melting aluminium
(d) None of the above
Ans: a
25. In an electric room heat convector the
method of heating used is
(a) arc heating
(b) resistance heating
(c) induction heating
(d) dielectric heating
Ans: b
26. In a domestic cake baking oven the
temperature is controlled by
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(a) voltage variation
(b) thermostat
(c) auto-transformer
(d) series-parallel operation
Ans: d
27. In an electric press mica is used
(a) as an insulator
(b) as a device for power factor improvement
(c) for dielectric heating
(d) for induction heating
Ans: a
28. Induction heating takes place iitwhich of
the following ?
(a) Insulating materials
(b) Conducting materials which are
magnetic
(c) Conducting materials which are nonmagnetic
(d) Conducting materials which may or may
not be magnetic
Ans: d
29. For heating element high resistivity
material is chosen to
(a) reduce the length of heating element
(b) increase the life of the heating element
(c) reduce the effect of oxidation
(d) produce large amount of heat
Ans: a
30. In resistance heating highest working
temperature is obtained from heating elements
made of
(a) nickel copper
(b) nichrome
(c) silicon carbide
(d) silver
Ans: c
31. For intermittent work which of the
following furnaces is suitable ?
(a) Indirect arc furnace
(b) Core less furnace
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(c) Either of the above
(d) None of the above
Ans: a
32. Due to which of the following reasons it is
desirable to have short arc length ?
(a) To achieve better heating
(b) To increase the life of roof refractory
(c) To have better stirring action
(d) To reduce problem of oxidation
(e) All of the above
Ans: e
33. In the indirect resistance heating method,
maximum heat-transfer takes place by
(a) radiation
(b) convection
(c) conduction
(d) any of the above
Ans: a
34. Properly of low temperature co-eflficient
of heating element is desired due to which of
the following reasons ?
(a) To avoid initial rush of current
(b) To avoid change in kW rating with
temperature
(c) Both (a) and (b)
(d) Either (a) or (b)
Ans: c
35. Which of the following methods is used to
control temperature in resistance furnaces ?
(a) Variation of resistance
(b) Variation of voltage
(c) Periodical switching on and off of the
supply
(d) All of the above methods
Ans: d
36. It is desirable to operate the arc furnaces
at power factor of
(a) zero
(b) 0.707 lagging
(c) unity
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(d) 0.707 leading
Ans: b
37. Radiations from a black body are
proportional to
(a) T1
(b) T2
(c) T3
(d) T*
Ans: d
38. In arc furnace the function of choke is
(a) to stabilize the arc
(b) to imprpve, power factor
(c) to reduce severity of the surge
(d) none of the above
Ans: a
39. Ajax Wyatt furnace is started when
(a) it is filled below core level
(b) it is filled above core level
(c) it is fully empty
(d) none of the above
Ans: b
40. In electric press, mica is used because it is
_______ conductor of heat but/and ________
conductor of electricity.
(a) bad, good
(b) bad, bad
(c) good, bad
(d) good, good
Ans:
41. Resistance variation method of
temperature control is done by connecting
resistance elements in
(a) series
(b) parallel
(c) series-parallel connections
(d) star-delta connections
(e) all of the above ways
Ans: e
42. Hysteresis loss and eddy current loss are
used in
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(a) induction heating of steel
(b) dielectric heating
(c) induction heating of brass
(d) resistance heating
Ans: a
43. In heating the ferromagnetic material by
induction heating, heat is produced due to
(a) induced current flow through the charge
(b) hysteresis loss taking place below curie
temperature
(c) due to hysteresis loss as well as eddy
current loss takingplace in the charge
(d) none of the above factors
Ans: c
44. Radiant heating is used for which of the
following ?
(a) Annealing of metals
(b) Melting of ferrous metals
(c) Heating of liquids in electric kettle
(d) Drying of paints and varnishes
Ans: d
45. Which of the following devices is
necessarily required for automatic temperature
control in a furnace ?
(a) Thermostat
(b) Thermocouple
(c) Auto-transformer
(d) Heating elements of variable resis-tance
material
Ans: b
(a) The amount of heat generated can be
controlled accurately
(b) Heat at very high rate can be gene-rated
(c) The area of the surface over which heat is
produced can be accurately controlled
(d) All of the above
Ans: d
48. The electrode of a direct arc furnace is
made of
(a) tungsten
(b) graphite
(c) silver
(d) copper
Ans: b
49. Direct arc furnaces have which of the
following power factors ?
(a) Unity
(b) Low, lagging
(c) Low, leading
(d) Any of the above
Ans: b
50. In direct arc furnace, which of the
following has high value ?
(a) Current
(b) Voltage
(c) Power factor
(d) All of the above
Ans: a
46. For radiant heating around 2250°C, the
heating elements are made of
(a) copper alloy
(b) carbon
(c) tungsten alloy
(d) stainless steel alloy
Ans: c
47. Which of the following is an advantage of
eddy current heating ?
1. Load factor of a power station is defined as
(a) maximum demand/average load
(b) average load x maximum demand
(c) average load/maximum demand
(d) (average load x maximum demand)172
Ans: c
2. Load factor of a power station is generally
(a) equal to unity
(b) less than unity
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(c) more than unity
(d) equal to zero Diversity factor is always
Ans: b
3. The load factor of domestic load is usually
(a) 10 to 15%
(b) 30 to 40%
(c) 50 to 60%
(d) 60 to 70%
Ans: a
4. Annual depreciation cost is calculated by
(a) sinkingfund method
(b) straight line method
(c) both (a) and (b)
(d) none of the above
Ans: c
5. Depreciation charges are high in case of
(a) thermal plant
(b) diesel plant
(c) hydroelectric plant
Ans: a
6. Demand factor is defined as
(a) average load/maximum load
(b) maximum demand/connected load
(c) connected load/maximum demand
(d) average load x maximum load
Ans: b
7. High load factor indicates
(a) cost of generation per unit power is
increased
(b) total plant capacity is utilised for most of the
time
(c) total plant capacity is not properly utilised
for most of the time
(d) none of the above
Ans: b
8. A load curve indicates
(a) average power used during the period
(b) average kWh (kW) energy consumption
during the period
(c) either of the above
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(d) none of the above
Ans: b
9. Approximate estimation of power demand
can be made by
(a) load survey method
(b) statistical methods
(c) mathematical method
(d) economic parameters
(e) all of the above
Ans: e
10. Annual depreciation as per straight line
method, is calculated by
(a) the capital cost divided by number of year
of life
(b) the capital cost minus the salvage value, is
divided by the number of years of life
(c) increasing a uniform sum of money per
annum at stipulated rate of interest
(d) none of the above
Ans: b
11. A consumer has to pay lesser fixed charges
in
(a) flat rate tariff
(b) two part tariff
(c) maximum demand tariff
(d) any of the above
Ans: c
12. In two part tariff, variation in load factor
will affect
(a) fixed charges
(b) operating or running charges
(c) both (a) and (b)
(d) either (a) or (b)
Ans: b
13. In Hopknison demand rate or two
parttariff the demand rate or fixed charges are
(a) dependent upon the energy consumed
(b) dependent upon the maximum demand of
the consumer
(c) both (a) and (b)
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(d) neither (a) nor (b)
Ans: b
14. Which plant can never have 100 percent
load factor ?
(a) Peak load plant
(b) Base load plant
(c) Nuclear power plant
(d) Hydro electric plant
Ans: a
15. The area under a load curve gives
(a) average demand
(b) energy consumed
(c) maximum demand
(d) none of the above
Ans: b
16. Different generating stations use following
prime movers
(a) diesel engine
(b) hydraulic turbine
(c) gas turbine
(d) steam turbine
(e) any of the above
Ans: e
17. Diversity factor has direct effect on the
(a) fixed cost of unit generated
(b) running cost of unit generated
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: a
18. Following power plant has instant starting
(a) nuclear power plant
(b) hydro power plant
(c) diesel power plant
(d) both (b) and (c)
(e) none of the above
Ans: d
19. Which of the following generating station
has minimum ruining cost ?
(a) Nuclear
(b) Hydro
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(c) Thermal
(d) Diesel
Ans: b
20. Power plant having maximum demand
more than the installed rated capacity will have
utilisation factor
(a) equal to unity
(b) less than unity
(c) more than unity
(d) none of the above
Ans: c
21. Load curve is useful in deciding the
(a) operating schedule of generating units
(b) sizes of generating units
(c) total installed capacity of the plant
(d) all of the above
Ans: d
22. Load curve of a power plant has always
(a) zero slope
(b) positive slope
(c) negative slope
(d) any combination of (a), (b) and (c)
Ans: e
23. Annual operating expenditure of a power
plant consists of
(a) fixed charges
(b) semi-fixed charges
(c) running charges
(d) all of the above
Ans: d
24. Maximum demand on a power plant is
(a) the greatest of all "short time interval
averaged" demand during a period
(b) instantaneous maximum value of kVA
supplied during a period
(e) both (a) or (b)
(d) none of the above
Ans: a
25. Annual instalment towards depreciation
reduces as rate of interest increases with
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(a) sinking fund depreciation
(b) straight line depreciation
(c) reducing balances depreciation
(d) none of the above
Ans: a
26. Annual depreciation of the plant it
proportional to the earning capacity of the
plant vide
(a) sinking fund depreciation
(b) straight line depreciation
(c) reducing balances depreciation
(d) none of the above
Ans: c
27. For high value of diversity factor, a power
station of given installed capacity will be in a
position to supply
(a) less number of consumers
(b) more number of consumers
(c) neither (a) nor (b)
(d) either (a) or (b)
Ans: b
28. Salvage value of the plant is always
(a) positive
(b) negative
(c) zero
(d) any of the above
Ans: d
29. Load curve helps in deciding
(a) total installed capacity of the plant
(b) sizes of the generating units
(c) operating schedule of generating units
(d) all of the above
Ans: d
30 can generate power at unpredictable or
uncontrolled times,
(a) Solar power plant
(b) Tidal power plant
(c) Wind power plant
(d) Any of the above
Ans: d
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31. Direct conversion of heat into electric
power is possible through
(a) fuel cell
(b) batteries
(c) thermionic converter
(d) all of the above
Ans: c
32. A low utilization factor for a plant
indicates that
(a) plant is used for stand by purpose only
(b) plant is under maintenance
(c) plant is used for base load only
(d) plant is used for peak load as well as base
load
Ans: a
33. Which of the following is not a source of
power ?
(a) Thermocouple
(b) Photovoltaic cell
(c) Solar cell
(d) Photoelectric cell
Ans: a
34. Which of the following should be used for
extinguishing electrical fires ?
(a) Water
(b) Carbon tetrachloride fire extinguisher
(c) Foam type fire extinguisher
(d) CO2 fire extinguisher
Ans: b
35. Low power factor is usually not due to
(a) arc lamps
(b) induction motors
(c) fluorescent tubes
(d) incandescent lamp
Ans: d
36. Ships are generally jpowered by
(a) nuclear power plants
(b) hydraulic turbines
(e) diesel engines
(d) steam accumulators
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(e) none of the above
Ans: c
37. Direct conversion of heat into electrical
energy is possible through
(a) fuel cells
(b) solar cells
(c) MHD generators
(d) none of the above
Ans: c
38. Which of the following place is not
associated with nuclear power plants in India ?
(a) Narora
(b) Tarapur
(c) Kota
(d) Benglore
Ans: d
39. During load shedding
(a) system power factor is changed
(b) some loads are switched off
(c) system voltage is reduced
(d) system frequency is reduced Efficiency is the
secondary consideration in
Ans: b
40. which of the following plants ?
(a) Base load plants
(b) Peak load plants
(c) Both (a) and (b)
(d) none of the above
Ans: b
41. Air will not be the working substance in
which of the following ?
(a) Closed cycle gas turbine
(b) Open cycle gas turbine
(c) Diesel engine
(d) Petrol engine
Ans: a
42. A nuclear power plant is invariably used as a
(a) peak load plant
(b) base load plant
(c) stand-by plant
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(d) spinning reserve plant
(e) any of the above
Ans: b
43. power plant is expected to have the longest
life.
(a) Steam
(b) Diesel
(c) Hydroelectric
(d) Any of the above
Ans: c
44. power plant cannot have single unit of
100 MW.
(a) Hydroelectric
(b) Nuclear
(c) Steam
(d) Diesel
(e) Any of the above
Ans: d
45. Which of the following, in a thermal power
plant, is not a fixed cost ?
(a) Fuel cost
(b) Interest on capital
(c) Depreciation
(d) Insurance charges
Ans: a
46. _______ will offer the least load.
(a) Vacuum cleaner
(b) Television
(c) Hair dryer
(d) Electric shaver
Ans: d
47. In ______ fuel transportation cost is least.
(a) nuclear power plants
(b) diesel generating plants
(c) steam power stations
Ans: a
48. Which of the following equipment
provides fluctuating load ?
(a) Exhaust fan
(b) Lathe machine
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(c) Welding transformer
(d) All of the above
Ans: c
49. The increased load during summer months
is due to
(a) increased business activity
(b) increased water supply
(c) increased use of fans and air conditioners
(d) none of the above
Ans: c
50 is the reserved generating capacity
available for service under emergency
conditions which is not kept in operation but in
working order,
(a) Hot reserve
(b) Cold reserve
(c) Spinning reserve
(d) Firm power
Ans: b
51. Generating capacity connected to the bus
bars and ready to take load when switched on is
known as
(a) firm power
(b) cold reserve
(c) hot reserve
(d) spinning reserve
Ans: d
52. offers the highest electric load.
(a) Television set
(b) Toaster
(c) Vacuum cleaner
(d) Washing machine
Ans: b
53. _______ industry has the least power
consumption per tonne of product.
(a) Soap
(b) Sugar
(c) Vegetable oil
(d) Caustic soda
Ans: c
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54. With reference to a power station which of
the following is not a fixed cost ?
(a) Fuel cost
(b) Interest on capital
(c) Insurance charges
(d) Depreciation
Ans: a
55. _______ is invariably used as base load
plant.
(a) Diesel engine plant
(b) Nuclear power plant
(c) Gas turbine plant
(d) Pumped storage plant
Ans: b
56. In a power plant if the maximum demand
on the plant is equal to the plant capacity, then
(a) plant reserve capacity will be zero
(b) diversity factor will be unity
(c) load factor will be unity
(d) load factor will be nearly 60%
Ans: a
57. Incase of ______ fuel transportation is the
major problem.
(a) diesel power plants
(b) nuclear power plants
(c) hydro-electric power plants
(d) thermal power plants
Ans: d
58. Which of the following power plants need
the least period for installation ?
(a) Thermal power plant
(b) Diesel power plant
(c) Nuclear power plant
(d) Hydro-electric power plant
Ans: b
59. For which of the following power plants
highly skilled engineers are required for running
the plants ?
(a) Nuclear power plants
(b) Gas turbine power plants
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(c) Solar power plants
(d) Hydro-electric power plants
Ans: a
60. In which of the following power plants the
maintenance cost is usually high ?
(a) Nuclear power plant
(b) Hydro-electric power plants
(c) Thermal power plants
(d) Diesel engine power plants
Ans: c
61. ________ is invariably used for peak load
(a) Nuclear power plant
(b) Steam turbine plant
(c) Pumped storage plant
(d) None of the above
Ans: c
62. Which of the following is not an operating
cost ?
(a) Maintenance cost
(b) Fuel cost
(c) Salaries of high officials
(d) Salaries of operating staff
Ans:
63. Which of the following is the essential
requirement of peak load plant ?
(a) It should run at high speed
(b) It should produce high voltage
(c) It should be small in size
(d) It should be capable of starting quickly
Ans: d
64. Large capacity generators are invariably
(a) water cooled
(b) natural air cooled
(c) forced air cooled
(d) hydrogen cooled
Ans: d
65. By the use of which of the following power
factor can be improved ?
(a) Phase advancers
(b) Synchronous compensators
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(c) Static capacitors
(d) Any of the above
Ans: d
66. An induction motor has relatively high
power factor at
(a) rated r.p.m.
(b) no load
(c) 20 percent load
(d) near full load
(e) none of the above
Ans: d
67. Which of the following is the disadvantage
due to low power factor ?
(a) Poor voltage regulation
(b) Increased transmission losses
(c) High cost of equipment for a given load
(d) All of the above
Ans: d
68. In a distribution system, in order to
improve power factor, the synchronous
capacitors are installed
(a) at the receiving end
(b) at the sending end
(c) either (a) or (b)
(d) none of the above
Ans: a
69. Satic capacitors are rated in terms of
(a) kW
(b) kWh
(e) kVAR
(d) none of the above
Ans: c
70. Which of the following is the disadvantage
of a synchronous condenser ?
(a) High maintenance cost
(b) Continuous losses in motor
(c) Noise
(d) All of the above
Ans: d
71. For a consumer the most economical
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power factor is generally
(a) 0.5 lagging
(b) 0.5 leading
(c) 0.95 lagging
(d) 0.95 leading
Ans: c
72. A synchronous condenser is virtually which
of the following ?
(a) Induction motor
(b) Under excited synchronous motor
(c) Over excited synchronous motor
(d) D.C. generator
(e) None of the above
Ans: c
73. For a power plant which of the following
constitutes running cost ?
(a) Cost of wages
(b) Cost of fuel
(c) Cost of lubricants
(d) All of the above
Ans: d
74. In an interconnected system, the diversity
factor of the whole system
(a) remains unchanged
(b) decreases
(c) increases
(d) none of the above
Ans: c
75. Generators for peak load plants are
usually designed for maximum efficiency at
(a) 25 to 50 percent full load
(b) 50 to 75 percent full load
(c) full load
(d) 25 percent overload
Ans: b
76. ________ will be least affected due to
charge in supply voltage frequency.
(a) Electric clock
(b) Mixer grinder
(c) Ceiling fan
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(d) Room heater
Ans: d
77. The connected load of a IVMIM uir
consumer is around
(a) 5 kW
(b) 40 k\V
(c) 80 kW
(d) 120 kW
Ans: a
78. Which of the following is not necessarily
an advantage of interconnecting various power
stations ?
(a) Improved frequency of power supplied
(b) Reduction in total installed capacity
(c) Increased reliability
(d) Economy in operation of plants
Ans: a
79. A power transformer is usually rated in
(a) kW
(b) kVAR
(c) kWh
(d) kVA
Ans: d
80. public sector undertaking is associated
with erection and sometimes running of
thermal power plants
(a) NTPC
(b) SAIL
(c) BEL
(d) BHEL
Ans: a
81. Most efficient plants are normally used as
(a) peak load plants
(b) base load plants
(c) either (a) or (b)
(d) none of the above
Ans:
82. For a diesel generating station the useful
life is expected to be around
(a) 15 to 20 years
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(b) 20 to 50 years
(c) 50 to 75 years
(d) 75 to 100 years
Ans: a
83. Which of the following is not a method for
estimating depreciation charges ?
(a) Sinking fund method
(b) Straight line method
(c) Diminishing value method
(d) Halsey's 50—50 formula
Ans: d
84. The expected useful life of an
hydroelectric power station is around
(a) 15 years
(b) 30 years
(c) 60 years
(d) 100 years
Ans: d
85. In a load curve the highest point
represents
(a) peak demand
(b) average demand
(c) diversified demand
(d) none of the above
Ans: a
86. Which of the following source of power is
least reliable ?
(a) Solar energy
(b) Geothermal power
(c) Wind power
(d) iMHD
Ans:
87. In India production and distribution of
electrical energy is confined to
(a) private sector
(b) public sector
(c) government sectors
(d) joint sector
(e) none of the above
Ans: b
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88. A pilot exciter is provided on generators
for which of the following reasons ?
(a) To excite the poles of main exciter
(b) To provide requisite starting torque to
main exciter
(c) To provide requisite starting torque to
generator
(d) None of the above
Ans: a
89. The primary reason for low power factor is
supply system is due to installation of
(a) induction motors
(b) synchronous motors
(c) single phase motors
(d) d.c. motors
Ans: a
90. An over excited synchronous motor on
noload is known as
(a) synchronous condenser
(b) generator
(c) induction motor
(d) alternator
Ans: a
91. Which of the following is an advantage of
static capacitor for power factor improvement ?
(a) Little maintenance cost
(b) Ease in installation
(c) Low losses
(d) All of the above
Ans: d
92. For any type of consumer the ideal tariff is
(a) two part tariff
(b) three part tariff
(c) block rate tariff
(d) any of the above
Ans: b
93. The efficiency of a plant is of least concern
when it is selected as
(a) peak load plant
(b) casual run plant
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(c) either (a) or (b)
(d) base load plant
Ans: c
94. Which of the following plants is almost
inevitably used as base load plant ?
(a) Diesel engine plant
(b) Gas turbine plant
(c) Nuclear power plant
(d) Pumped storage plant
Ans: c
95. Which of the following component, in a
steam power plant, needs maximum
maintenance attention ?
(a) Steam turbine
(b) Condenser
(c) Water treatment plant
(d) Boiler
Ans: d
96. For the same cylinder dimensions and
speed, which of the following engine will
produce least power ?
(a) Supercharged engine
(b) Diesel engine
(c) Petrol engine
(d) All of the above engines will equal power
Ans: c
97. The least share of power is provided in
India, by which of the following power plants ?
(a) Diesel power plants
(b) Thermal power plants
(c) Hydro-electric power plants
(d) Nuclear power plants
Ans: a
98. Submarines for under water movement,
are powered by which of the following ?
(a) Steam accumulators
(b) Air motors
(c) Diesel engines
(d) Batteries
Ans: d
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99. An alternator coupled to a _____ runs at
slow speed, as compared to as compared to
others.
(a) diesel engine
(6) hydraulic turbine
(c) steam turbine
(d) gas turbine
Ans: b
100. The effect of electric shock on human
body depends on which of the following
(a) current
(b) voltage
(c) duration of contact
(d) all of the above
Ans: d
101. Which lightening stroke is most dangerous
?
(a) Direct stroke on line conductor
(b) Indirect stroke on conductor
(c) Direct stroke on tower top
(d) Direct stroke on ground wire
Ans: a
102. Which of the following devices may be
used to provide protection against lightening
over voltages ?
(a) Horn gaps
(b) Rod gaps
(c) Surge absorbers
(d) All of the above
Ans: d
103. When the demand of consumers is not
met by a power plant, it will resort to which of
the following ?
(a) Load shedding
(b) Power factor improvement at the ,
generators
(c) Penalising high load consumers by increasing
the charges for electricity
(d) Efficient plant operation
Ans: a
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104. Load shedding is possible through which
of the following ?
(a) Switching of the loads
(b) Frequency reduction
(c) Voltage reduction
(d) Any of the above
Ans: d
105. In power plants insurance cover is
provided for which of the following ?
(a) Unskilled workers only
(b) Skilled workers only
(c) Equipment only
(d) All of the above
Ans: d
106 A company can raise funds through
(a) fixed deposits
(b) shares
(c) bonds
(d) any of the above
Ans: d
107. Which of the following are not repayable
after a stipulated period ?
(a) Shares
(b) Fixed deposits
(c) Cash certificates
(d) Bonds
Ans: a
108. The knowledge of diversity factor helps in
determining
(a) plant capacity
(b) average load
(c) peak load
(d) kWh generated
(e) none of the above
Ans: a
109. Which of the following is the
disadvantage of static capacitor for power
factor improvement ?
(a) Easily damaged by high voltage
(b) Cannot be repaired
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(c) Short service life
(d) All of the above
Ans: d
Economics of Power Generation
1. Load factor of a power station is defined as
(a) maximum demand/average load
(b) average load x maximum demand
(c) average load/maximum demand
(d) (average load x maximum demand)172
Ans: c
2. Load factor of a power station is generally
(a) equal to unity
(b) less than unity
(c) more than unity
(d) equal to zero Diversity factor is always
Ans: b
3. The load factor of domestic load is usually
(a) 10 to 15%
(b) 30 to 40%
(c) 50 to 60%
(d) 60 to 70%
Ans: a
4. Annual depreciation cost is calculated by
(a) sinkingfund method
(b) straight line method
(c) both (a) and (b)
(d) none of the above
Ans: c
5. Depreciation charges are high in case of
(a) thermal plant
(b) diesel plant
(c) hydroelectric plant
Ans: a
6. Demand factor is defined as
(a) average load/maximum load
(b) maximum demand/connected load
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(c) connected load/maximum demand
(d) average load x maximum load
Ans: b
7. High load factor indicates
(a) cost of generation per unit power is
increased
(b) total plant capacity is utilised for most of the
time
(c) total plant capacity is not properly utilised
for most of the time
(d) none of the above
Ans: b
8. A load curve indicates
(a) average power used during the period
(b) average kWh (kW) energy consumption
during the period
(c) either of the above
(d) none of the above
Ans: b
9. Approximate estimation of power demand
can be made by
(a) load survey method
(b) statistical methods
(c) mathematical method
(d) economic parameters
(e) all of the above
Ans: e
10. Annual depreciation as per straight line
method, is calculated by
(a) the capital cost divided by number of year
of life
(b) the capital cost minus the salvage value, is
divided by the number of years of life
(c) increasing a uniform sum of money per
annum at stipulated rate of interest
(d) none of the above
Ans: b
11. A consumer has to pay lesser fixed charges
in
(a) flat rate tariff
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(b) two part tariff
(c) maximum demand tariff
(d) any of the above
Ans: c
12. In two part tariff, variation in load factor
will affect
(a) fixed charges
(b) operating or running charges
(c) both (a) and (b)
(d) either (a) or (b)
Ans: b
13. In Hopknison demand rate or two
parttariff the demand rate or fixed charges are
(a) dependent upon the energy consumed
(b) dependent upon the maximum demand of
the consumer
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: b
14. Which plant can never have 100 percent
load factor ?
(a) Peak load plant
(b) Base load plant
(c) Nuclear power plant
(d) Hydro electric plant
Ans: a
15. The area under a load curve gives
(a) average demand
(b) energy consumed
(c) maximum demand
(d) none of the above
Ans: b
16. Different generating stations use following
prime movers
(a) diesel engine
(b) hydraulic turbine
(c) gas turbine
(d) steam turbine
(e) any of the above
Ans: e
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17. Diversity factor has direct effect on the
(a) fixed cost of unit generated
(b) running cost of unit generated
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans: a
18. Following power plant has instant starting
(a) nuclear power plant
(b) hydro power plant
(c) diesel power plant
(d) both (b) and (c)
(e) none of the above
Ans: d
19. Which of the following generating station
has minimum ruining cost ?
(a) Nuclear
(b) Hydro
(c) Thermal
(d) Diesel
Ans: b
20. Power plant having maximum demand
more than the installed rated capacity will have
utilisation factor
(a) equal to unity
(b) less than unity
(c) more than unity
(d) none of the above
Ans: c
21. Load curve is useful in deciding the
(a) operating schedule of generating units
(b) sizes of generating units
(c) total installed capacity of the plant
(d) all of the above
Ans: d
22. Load curve of a power plant has always
(a) zero slope
(b) positive slope
(c) negative slope
(d) any combination of (a), (b) and (c)
Ans: e
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23. Annual operating expenditure of a power
plant consists of
(a) fixed charges
(b) semi-fixed charges
(c) running charges
(d) all of the above
Ans: d
24. Maximum demand on a power plant is
(a) the greatest of all "short time interval
averaged" demand during a period
(b) instantaneous maximum value of kVA
supplied during a period
(e) both (a) or (b)
(d) none of the above
Ans: a
25. Annual instalment towards depreciation
reduces as rate of interest increases with
(a) sinking fund depreciation
(b) straight line depreciation
(c) reducing balances depreciation
(d) none of the above
Ans: a
26. Annual depreciation of the plant it
proportional to the earning capacity of the
plant vide
(a) sinking fund depreciation
(b) straight line depreciation
(c) reducing balances depreciation
(d) none of the above
Ans: c
27. For high value of diversity factor, a power
station of given installed capacity will be in a
position to supply
(a) less number of consumers
(b) more number of consumers
(c) neither (a) nor (b)
(d) either (a) or (b)
Ans: b
28. Salvage value of the plant is always
(a) positive
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(b) negative
(c) zero
(d) any of the above
Ans: d
29. Load curve helps in deciding
(a) total installed capacity of the plant
(b) sizes of the generating units
(c) operating schedule of generating units
(d) all of the above
Ans: d
30 can generate power at unpredictable or
uncontrolled times,
(a) Solar power plant
(b) Tidal power plant
(c) Wind power plant
(d) Any of the above
Ans: d
31. Direct conversion of heat into electric
power is possible through
(a) fuel cell
(b) batteries
(c) thermionic converter
(d) all of the above
Ans: c
32. A low utilization factor for a plant
indicates that
(a) plant is used for stand by purpose only
(b) plant is under maintenance
(c) plant is used for base load only
(d) plant is used for peak load as well as base
load
Ans: a
33. Which of the following is not a source of
power ?
(a) Thermocouple
(b) Photovoltaic cell
(c) Solar cell
(d) Photoelectric cell
Ans: a
34. Which of the following should be used for
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extinguishing electrical fires ?
(a) Water
(b) Carbon tetrachloride fire extinguisher
(c) Foam type fire extinguisher
(d) CO2 fire extinguisher
Ans: b
35. Low power factor is usually not due to
(a) arc lamps
(b) induction motors
(c) fluorescent tubes
(d) incandescent lamp
Ans: d
36. Ships are generally jpowered by
(a) nuclear power plants
(b) hydraulic turbines
(e) diesel engines
(d) steam accumulators
(e) none of the above
Ans: c
37. Direct conversion of heat into electrical
energy is possible through
(a) fuel cells
(b) solar cells
(c) MHD generators
(d) none of the above
Ans: c
38. Which of the following place is not
associated with nuclear power plants in India ?
(a) Narora
(b) Tarapur
(c) Kota
(d) Benglore
Ans: d
39. During load shedding
(a) system power factor is changed
(b) some loads are switched off
(c) system voltage is reduced
(d) system frequency is reduced Efficiency is the
secondary consideration in
Ans: b
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40. which of the following plants ?
(a) Base load plants
(b) Peak load plants
(c) Both (a) and (b)
(d) none of the above
Ans: b
41. Air will not be the working substance in
which of the following ?
(a) Closed cycle gas turbine
(b) Open cycle gas turbine
(c) Diesel engine
(d) Petrol engine
Ans: a
42. A nuclear power plant is invariably used as a
(a) peak load plant
(b) base load plant
(c) stand-by plant
(d) spinning reserve plant
(e) any of the above
Ans: b
43. power plant is expected to have the longest
life.
(a) Steam
(b) Diesel
(c) Hydroelectric
(d) Any of the above
Ans: c
44. power plant cannot have single unit of
100 MW.
(a) Hydroelectric
(b) Nuclear
(c) Steam
(d) Diesel
(e) Any of the above
Ans: d
45. Which of the following, in a thermal power
plant, is not a fixed cost ?
(a) Fuel cost
(b) Interest on capital
(c) Depreciation
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(d) Insurance charges
Ans: a
46. _______ will offer the least load.
(a) Vacuum cleaner
(b) Television
(c) Hair dryer
(d) Electric shaver
Ans: d
47. In ______ fuel transportation cost is least.
(a) nuclear power plants
(b) diesel generating plants
(c) steam power stations
Ans: a
48. Which of the following equipment
provides fluctuating load ?
(a) Exhaust fan
(b) Lathe machine
(c) Welding transformer
(d) All of the above
Ans: c
49. The increased load during summer months
is due to
(a) increased business activity
(b) increased water supply
(c) increased use of fans and air conditioners
(d) none of the above
Ans: c
50 is the reserved generating capacity
available for service under emergency
conditions which is not kept in operation but in
working order,
(a) Hot reserve
(b) Cold reserve
(c) Spinning reserve
(d) Firm power
Ans: b
51. Generating capacity connected to the bus
bars and ready to take load when switched on is
known as
(a) firm power
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(b) cold reserve
(c) hot reserve
(d) spinning reserve
Ans: d
52. offers the highest electric load.
(a) Television set
(b) Toaster
(c) Vacuum cleaner
(d) Washing machine
Ans: b
53. _______ industry has the least power
consumption per tonne of product.
(a) Soap
(b) Sugar
(c) Vegetable oil
(d) Caustic soda
Ans: c
54. With reference to a power station which of
the following is not a fixed cost ?
(a) Fuel cost
(b) Interest on capital
(c) Insurance charges
(d) Depreciation
Ans: a
55. _______ is invariably used as base load
plant.
(a) Diesel engine plant
(b) Nuclear power plant
(c) Gas turbine plant
(d) Pumped storage plant
Ans: b
56. In a power plant if the maximum demand
on the plant is equal to the plant capacity, then
(a) plant reserve capacity will be zero
(b) diversity factor will be unity
(c) load factor will be unity
(d) load factor will be nearly 60%
Ans: a
57. Incase of ______ fuel transportation is the
major problem.
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(a) diesel power plants
(b) nuclear power plants
(c) hydro-electric power plants
(d) thermal power plants
Ans: d
58. Which of the following power plants need
the least period for installation ?
(a) Thermal power plant
(b) Diesel power plant
(c) Nuclear power plant
(d) Hydro-electric power plant
Ans: b
59. For which of the following power plants
highly skilled engineers are required for running
the plants ?
(a) Nuclear power plants
(b) Gas turbine power plants
(c) Solar power plants
(d) Hydro-electric power plants
Ans: a
60. In which of the following power plants the
maintenance cost is usually high ?
(a) Nuclear power plant
(b) Hydro-electric power plants
(c) Thermal power plants
(d) Diesel engine power plants
Ans: c
61. ________ is invariably used for peak load
(a) Nuclear power plant
(b) Steam turbine plant
(c) Pumped storage plant
(d) None of the above
Ans: c
62. Which of the following is not an operating
cost ?
(a) Maintenance cost
(b) Fuel cost
(c) Salaries of high officials
(d) Salaries of operating staff
Ans:
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63. Which of the following is the essential
requirement of peak load plant ?
(a) It should run at high speed
(b) It should produce high voltage
(c) It should be small in size
(d) It should be capable of starting quickly
Ans: d
64. Large capacity generators are invariably
(a) water cooled
(b) natural air cooled
(c) forced air cooled
(d) hydrogen cooled
Ans: d
65. By the use of which of the following power
factor can be improved ?
(a) Phase advancers
(b) Synchronous compensators
(c) Static capacitors
(d) Any of the above
Ans: d
66. An induction motor has relatively high
power factor at
(a) rated r.p.m.
(b) no load
(c) 20 percent load
(d) near full load
(e) none of the above
Ans: d
67. Which of the following is the disadvantage
due to low power factor ?
(a) Poor voltage regulation
(b) Increased transmission losses
(c) High cost of equipment for a given load
(d) All of the above
Ans: d
68. In a distribution system, in order to
improve power factor, the synchronous
capacitors are installed
(a) at the receiving end
(b) at the sending end
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(c) either (a) or (b)
(d) none of the above
Ans: a
69. Satic capacitors are rated in terms of
(a) kW
(b) kWh
(e) kVAR
(d) none of the above
Ans: c
70. Which of the following is the disadvantage
of a synchronous condenser ?
(a) High maintenance cost
(b) Continuous losses in motor
(c) Noise
(d) All of the above
Ans: d
71. For a consumer the most economical
power factor is generally
(a) 0.5 lagging
(b) 0.5 leading
(c) 0.95 lagging
(d) 0.95 leading
Ans: c
72. A synchronous condenser is virtually which
of the following ?
(a) Induction motor
(b) Under excited synchronous motor
(c) Over excited synchronous motor
(d) D.C. generator
(e) None of the above
Ans: c
73. For a power plant which of the following
constitutes running cost ?
(a) Cost of wages
(b) Cost of fuel
(c) Cost of lubricants
(d) All of the above
Ans: d
74. In an interconnected system, the diversity
factor of the whole system
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(a) remains unchanged
(b) decreases
(c) increases
(d) none of the above
Ans: c
75. Generators for peak load plants are
usually designed for maximum efficiency at
(a) 25 to 50 percent full load
(b) 50 to 75 percent full load
(c) full load
(d) 25 percent overload
Ans: b
76. ________ will be least affected due to
charge in supply voltage frequency.
(a) Electric clock
(b) Mixer grinder
(c) Ceiling fan
(d) Room heater
Ans: d
77. The connected load of a IVMIM uir
consumer is around
(a) 5 kW
(b) 40 k\V
(c) 80 kW
(d) 120 kW
Ans: a
78. Which of the following is not necessarily
an advantage of interconnecting various power
stations ?
(a) Improved frequency of power supplied
(b) Reduction in total installed capacity
(c) Increased reliability
(d) Economy in operation of plants
Ans: a
79. A power transformer is usually rated in
(a) kW
(b) kVAR
(c) kWh
(d) kVA
Ans: d
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80. public sector undertaking is associated
with erection and sometimes running of
thermal power plants
(a) NTPC
(b) SAIL
(c) BEL
(d) BHEL
Ans: a
81. Most efficient plants are normally used as
(a) peak load plants
(b) base load plants
(c) either (a) or (b)
(d) none of the above
Ans:
82. For a diesel generating station the useful
life is expected to be around
(a) 15 to 20 years
(b) 20 to 50 years
(c) 50 to 75 years
(d) 75 to 100 years
Ans: a
83. Which of the following is not a method for
estimating depreciation charges ?
(a) Sinking fund method
(b) Straight line method
(c) Diminishing value method
(d) Halsey's 50—50 formula
Ans: d
84. The expected useful life of an
hydroelectric power station is around
(a) 15 years
(b) 30 years
(c) 60 years
(d) 100 years
Ans: d
85. In a load curve the highest point
represents
(a) peak demand
(b) average demand
(c) diversified demand
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(d) none of the above
Ans: a
86. Which of the following source of power is
least reliable ?
(a) Solar energy
(b) Geothermal power
(c) Wind power
(d) iMHD
Ans:
87. In India production and distribution of
electrical energy is confined to
(a) private sector
(b) public sector
(c) government sectors
(d) joint sector
(e) none of the above
Ans: b
88. A pilot exciter is provided on generators
for which of the following reasons ?
(a) To excite the poles of main exciter
(b) To provide requisite starting torque to
main exciter
(c) To provide requisite starting torque to
generator
(d) None of the above
Ans: a
89. The primary reason for low power factor is
supply system is due to installation of
(a) induction motors
(b) synchronous motors
(c) single phase motors
(d) d.c. motors
Ans: a
90. An over excited synchronous motor on
noload is known as
(a) synchronous condenser
(b) generator
(c) induction motor
(d) alternator
Ans: a
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91. Which of the following is an advantage of
static capacitor for power factor improvement ?
(a) Little maintenance cost
(b) Ease in installation
(c) Low losses
(d) All of the above
Ans: d
92. For any type of consumer the ideal tariff is
(a) two part tariff
(b) three part tariff
(c) block rate tariff
(d) any of the above
Ans: b
93. The efficiency of a plant is of least concern
when it is selected as
(a) peak load plant
(b) casual run plant
(c) either (a) or (b)
(d) base load plant
Ans: c
94. Which of the following plants is almost
inevitably used as base load plant ?
(a) Diesel engine plant
(b) Gas turbine plant
(c) Nuclear power plant
(d) Pumped storage plant
Ans: c
95. Which of the following component, in a
steam power plant, needs maximum
maintenance attention ?
(a) Steam turbine
(b) Condenser
(c) Water treatment plant
(d) Boiler
Ans: d
96. For the same cylinder dimensions and
speed, which of the following engine will
produce least power ?
(a) Supercharged engine
(b) Diesel engine
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(c) Petrol engine
(d) All of the above engines will equal power
Ans: c
97. The least share of power is provided in
India, by which of the following power plants ?
(a) Diesel power plants
(b) Thermal power plants
(c) Hydro-electric power plants
(d) Nuclear power plants
Ans: a
98. Submarines for under water movement,
are powered by which of the following ?
(a) Steam accumulators
(b) Air motors
(c) Diesel engines
(d) Batteries
Ans: d
99. An alternator coupled to a _____ runs at
slow speed, as compared to as compared to
others.
(a) diesel engine
(6) hydraulic turbine
(c) steam turbine
(d) gas turbine
Ans: b
100. The effect of electric shock on human
body depends on which of the following
(a) current
(b) voltage
(c) duration of contact
(d) all of the above
Ans: d
101. Which lightening stroke is most dangerous
?
(a) Direct stroke on line conductor
(b) Indirect stroke on conductor
(c) Direct stroke on tower top
(d) Direct stroke on ground wire
Ans: a
102. Which of the following devices may be
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used to provide protection against lightening
over voltages ?
(a) Horn gaps
(b) Rod gaps
(c) Surge absorbers
(d) All of the above
Ans: d
103. When the demand of consumers is not
met by a power plant, it will resort to which of
the following ?
(a) Load shedding
(b) Power factor improvement at the ,
generators
(c) Penalising high load consumers by increasing
the charges for electricity
(d) Efficient plant operation
Ans: a
104. Load shedding is possible through which
of the following ?
(a) Switching of the loads
(b) Frequency reduction
(c) Voltage reduction
(d) Any of the above
Ans: d
105. In power plants insurance cover is
provided for which of the following ?
(a) Unskilled workers only
(b) Skilled workers only
(c) Equipment only
(d) All of the above
Ans: d
106 A company can raise funds through
(a) fixed deposits
(b) shares
(c) bonds
(d) any of the above
Ans: d
107. Which of the following are not repayable
after a stipulated period ?
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(a) Shares
(b) Fixed deposits
(c) Cash certificates
(d) Bonds
Ans: a
108. The knowledge of diversity factor helps in
determining
(a) plant capacity
(b) average load
(c) peak load
(d) kWh generated
(e) none of the above
Ans: a
109. Which of the following is the
disadvantage of static capacitor for power
factor improvement ?
(a) Easily damaged by high voltage
(b) Cannot be repaired
(c) Short service life
(d) All of the above
Ans: d
Switchgear Protections
1. The main function of a fuse is to
(a) protect the line
(b) open the circuit
(c) protect the appliance
(d) prevent excessive currents
(e) none of the above
Ans: d
2. On which of the following routine tests are
conducted ?
(a) Oil circuit breakers
(b) Air blast circuit breakers
(c) Minimum oil circuit breakers
(d) All of the above
Ans: d
3. SF6 gas
(a) is yellow in colour
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(b) is lighter than air
(c) is nontoxic
(d) has pungent small
(e) none of the above
Ans: c
4. The arcing contacts in a circuit breaker are
made of
(a) copper tungsten alloy
(b) porcelain
(c) electrolytic copper
(d) aluminium alloy
Ans: a
5. Which of the following medium is employed
for extinction of arc in air circuit breaker ?
(a) Water
(b) Oil
(c) Air
(d) SF6
Ans: c
6. With which of the following, a circuit breaker
must be equipped for remote operation ?
(a) Inverse time trip
(b) Time-delay trip
(c) Shunt trip
(d) None of the above
(e) All of the above
Ans: c
7. Fault diverters are basically
(a) fuses
(b) relays
(c) fast switches
(d) circuit breakers
Ans: c
8. A thermal protection switch can protect
against
(a) short-circuit
(b) temperature
(c) overload
(d) over voltage
Ans: c
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9. Arc in a circuit behaves as
(a) a capackive reactance
(b) an inductive reactance
(c) a resistance increasing with voltage rise
across the arc
(d) a resistance decreasing with voltage rise
across the arc
Ans: d
10. Thermal circuit breaker has
(a) delayed trip action
(b) instantaneous trip action
(c) both of the above
(d) none of the above
Ans: a
11. Relays can be designed to respond to
changes in
(a) resistance, reactance or impedance
(b) voltage and current
(c) light intensity
(d) temperature
(e) all above
Ans: e
12. Overload relays are of...... type.
(a) induction
(b) solid state
(c) thermal
(d) electromagnetic
(e) all above
Ans: e
13. Thermal overload relays are used to
protect the motor against over current due to
(a) short-circuits
(b) heavy loads
(c) grounds
(d) all of the above
Ans: b
14. Magnetic circuit breaker has ______ trip
action.
(a) delayed
(b) instantaneous
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(c) both of the above
(d) none of the above
Ans: b
15. D.C. shunt relays are made of
(a) few turns of thin wire
(b) few turns of thick wire
(c) many turns of thin wire
(d) many turns of thick wire
Ans: c
16. The relay operating speed depends upon
(a) the spring tension
(b) the rate of flux built up
(c) armature core air gap
(d) all of the above
Ans: d
17. In order that current should flow without
causing excessive heating or voltage drop, the
relay contacts should
(a) have low contact resistance
(b) be clean and smooth
(c) be of sufficient size and proper shape
(d) have all above properties
Ans: d
18. Circuit breakers usually operate under
(a) transient state of short-circuit current
(b) sub-transient state of short-circuit current
(c) steady state of short-circuit current
(d) after D.C. component has ceased
Ans: a
19. Circuit breakers are essentially
(a) current carrying contacts called electrodes
(b) arc extinguishers
(c) circuits to break the system
(d) transformers to isolate the two systems
(e) any of the above
Ans: a
20. The current zero interruption, in oil and air
blast circuit breakers, is achieved by
(a) lengthening of the gap
(b) cooling and blast effect
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(c) both (a) and (b)
(d) deionizing the oil with forced air
(e) none of the above
Ans: c
21. Air blast circuit breaker is used for
(a) over currents
(b) short duty
(c) intermittant duty
(d) repeated duty
Ans: d
22. An efficient and a well designed protective
relaying should have
(a) good selectivity and reliability
(b) economy and simplicity
(c) high speed and selectivity
(d) all of the above
Ans: d
23. Burden of a protective relay is the power
(a) required to operate the circuit breaker
(b) absorbed by the circuit of relay
(c) developed by the relay circuit
(d) none of the above
Ans: b
24. Directional relays are based on flow of
(a) power
(b) current
(c) voltage wave
(d) all of the above
Ans: a
25. A differential relay measures the vector
difference between
(a) two currents
(b) two voltages
(c) two or more similar electrical quan¬tities
(d) none of the above
Ans: c
26. A transmission line is protected by
(a) inrush protection
(b) distance protection
(c) time graded and current graded over
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current protection
(d) both (b) and (c)
(e) none of the above
Ans: d
27. Large internal faults are protected by
(a) merz price percentage differential
protection
(b) mho and ohm relays
(c) horn gaps and temperature relays
(d) earth fault and positive sequence relays
Ans: a
28. When a transmission line is energized, the
wave that propagates on it is
(a) current wave only
(b) voltage wave only
(c) both (a) and (b)
(d) power factor wave only
Ans: c
29. Protective relays are devices that detect
abnormal conditions in electrical circuits by
measuring
(a) current during abnormal condition
(b) voltage during abnormal condition
(c) constantly the electrical quantities which
differ during normal and abnormal conditions
(d) none of the above
Ans: c
30. The voltage appearing across the contacts
after opening of the circuit breaker is
called______voltage.
(a) recovery
(b) surge
(c) operating
(d) arc
(e) none of the above
Ans: a
31. Ionization in circuit breaker is facilitated
by
(a) high temperature
(b) increase of mean free path
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(c) increasing field strength
(d) all of the above
Ans: d
32. In a circuit breaker the basic problem is to
(a) maintain the arc
(b) extinguish the arc
(c) transmit large power
(d) emit the ionizing electrons
Ans: c
33. Overheating of relay contacts or contact
born out is due to
(a) slow making and breaking of load circuit
contacts
(b) foreign matter on the contact surface
(c) too low contact pressure
(d) all of the above
Ans: d
34. Interruption of large currents by relay
requires
(a) arc suppressing blow out coils
(b) wide separation of the opened contacts
(c) high speed opening of contacts
(d) all of the above
Ans: d
35. Shunt capacitance is neglected while
considering
(a) short transmission line
(b) medium transmission line
(c) long transmission line
(d) medium and long transmission lines
Ans: a
36. The arc voltage produced in A.C. circuit
breaker is always
(a) in phase with the arc current
(b) lagging the arc current by 90"
(c) leading the arc current by 90°
(d) none of the above
Ans: a
37. The time of closing the cycle, in modern
circuit breakers is
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(a) 0.003 sec
(b) 0.001 sec
(c) 0.01 sec
(d) 0.10 sec
(e) none of the above
Ans: a
38. Insulation resistance of high voltage circuit
breakers is more than
(a) 1 mega ohms
(b) 10 mega ohms
(c) 100 mega ohms
(d) 500 mega ohms
Ans: c
39. H.R.C. fuses provide best protection
against
(a) overload
(b) reverse current
(c) open-circuits
(d) short-circuits
Ans: d
40. The ground wire should not be smaller
than No ______ copper.
(a) 2
(b) 4
(c) 6
(d) 10
Ans: d
41. The delay fuses are used for the protection
of ________ .
(a) motors
(b) power outlet circuits
(c) fluorescent lamps
(d) light circuits
Ans: a
42. Which of the following is the least
expensive protection for overcurrent is low
voltage system ?
(a) Rewireable fuse
(b) Isolator
(c) Oil circuit breaker
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(d) Air break circuit breaker
(e) None of the above
Ans: a
43. Resistance grounding is used for voltage
between
(a) 33kVto66kV
(b) HkVto33kV
(c) 3.3kVandllkV
(d) none of the above
Ans: c
44. The contacts of high voltage switches used
in power system are submerged in oil. The main
purpose of the oil is to
(a) lubricate the contacts
(b) insulate the contacts from switch body
(c) extinguish the arc
(d) all of the above
(e) none of the above
Ans: c
45. In Railway applications ______ circuit
breaker is used.
(a) SFe
(b) bulk oil
(c) minimum oil
(d) air break
Ans:
46. To protect most of the electrical
equipment handling low power, the types of
relays used are
(a) thermocouple
(b) electronic and bimetallic
(c) both (a) and (b)
(d) none of the above
Ans: c
47. Wave trap is used to trap waves of
(a) power frequencies
(b) higher frequencies entering genera¬tor or
transformer units
(c) either of the above
(d) none of the above
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Ans: b
48. Ungrounded neutral transmission system
is not recommended because of system
(a) insulation being overstressed due to pver
voltages
(b) insulation overstress may lead to failure
and subsequent phase to phase faults
(c) being inadequately protected against
ground fault
(d) all of the above
Ans: d
49. The reflection co-efficient at the open
circuited end of a transmission line.
(a) zero
(b) infinity
(c) unity
(d) none of the above
Ans: c
50. For the protection of power station
buildings against direct strokes the
requirements are
(a) interception
(b) interception and conduction
(c) interception, conduction and dis-sipation
(d) interception, conduction, dissipation and
reflection
(e) none of the above
Ans: c
51. The line insulation is the insulation level of
the station equipment.
(a) less than
(b) same as
(c) more than
(d) proportional to
(e) not directly related with
Ans: e
52. The interaction between a transmission
line and communication line js minimized by
(a) transposing transmission as well as
communication lines
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(b) increasing the height of the trans-mission
line tower
(c) increasing the distance between the two
lines
(d) all of the above
Ans: d
53. When a wave propagates on a
transmission line, it suffers reflection several
times at
(a) tapping
(b) load end
(c) sending end
(d) sending and other end
(e) all of the above
Ans: d
54. Which of the following statements is
incorrect?
(a) Station batteries are used to operate relay
only
(b) The lightning arresters are basically surge
diverters
(c) An impedance relay has maximum fault
current when fault occurs near the relay
(d) A high speed relay has an operation of 1 to
2 cycles
Ans: a
55. Discrimination between main and back up
protection is provided by the use of relays
which are
(a) fact
(b) sensitive
(c) slow
(d) none of the above
Ans: c
56. Induction cup relay is operated due to
changes in
(a) current
(b) voltage
(c) impedance
(d) all of the above
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Ans: d
57. A.C. network analyser is used to solve
problems of
(a) load flow
(b) load flow and short-circuit
(c) load flow and stability
(d) load flow, short-circuit and stability
(e) none of the above
Ans: d
58. Which of the following statements is
incorrect ?
(a) Lightning arrestors are used before the
switchgear
(b) Shunt reactors are used as compensation
reactors
(c) The peak short current is (1.8 xV2) times
the A.C. component
(d) The MVA at fault is equal to base MVA
divided by per unit equivalent fault reactance
Ans: a
59. Short-circuit currents are due to
(a) single phase to ground faults
(b) phase to phase faults
(c) two phase to ground faults
(d) three phase faults
(e) any of these
Ans: e
60. To reduce short circuit fault currents are
used.
(a) reactors
(b) resistors
(c) capacitors
(d) none of the above
Ans: a
61. Bus coupler is very essential in
arrangement
(a) single bus
(b) double bus, double breaker
(c) main and transfer bus
(d) all of the above
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Ans: c
62. For cost and safety, the outdoor substa
tions are installed for voltages above
(a) 11 kV
(b) 33 kV
(c) 60kV
(d) 110kV
Ans: b
63. The short circuit in any winding of the
transformer is the result of
(a) mechanical vibration
(b) insulation failure
(c) loose connection
(d) impulse voltage
Ans: d
64 relays are used for phase faults on long
line.
(a) Impedance
(b) Reactance
(c) Either of the above
(d) None of the above
Ans: a
65. For which of the following protection from
negative sequence currents is provided ?
(a) Generators
(b) Motors
(c) Transmission line
(d) Transformers
Ans: a
66 relay is preferred for phase fault on short
transmission line.
(a) Induction type
(b) Reactance
(c) Impedance
(d) None of the above
Ans: b
67. Distance relays are generally
(a) split-phase relays
(b) reactance relays
(c) impedance relays
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(d) none of the above
Ans: d
68. For which of the following ratings of the
transformer differential protection is
recommended ?
(a) above 30 kVA.
(b) equal to and above 5 MVA
(c) equal to and above 25 MVA
(d) none of the above
Ans: b
69. A _______ is used to measure the stator %
winding temperature of the generator.
(a) thermocouple
(b) pyrometer
(c) resistance thermometer
(d) thermometer
Ans: c
70. The under voltage relay can be used for
(a) generators
(b) busbars
(c) transformers
(d) motors
(e) all of the above
Ans: e
71. The relay with inverse time characteristic
will operate within
(a) 1.5 sec
(b) 5 to 10 sec
(c) 5 to 20 sec
(d) 20 to 30 sec
(e) none of the above
Ans: b
72. The single phasing relays are used for the
protection of
(a) single phase motors only
(b) two phase motors only
(c) two single phase motors running in parallel
(d) three phase motors
Ans: d
73. Which of the following devices will receive
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voltage surge first travelling on the transmission
line ?
(a) Lightning arresters
(b) Relays
(c) Step-down transformer
(d) Switchgear
Ans: a
74. Which of the following parameter can be
neglected for a short line ?
(a) Inductance
(b) Capacitance
(c) Resistance
(d) Reactance
Ans: b
75. Series reactors should have
(a) low resistance
(b) high resistance
(c) low impedance
(d) high impedance
Ans: a
76. Which of the following circuit breakers has
high reliability and minimum maintenance ?
(a) Air blast circuit breakers
(b) Circuit breaker with SF6 gas
(c) Vacuum circuit breakers
(d) Oil circuit breakers
Ans: b
77. Arc in a circuit breaker is interrupted at
(a) zero current
(b) maximum current
(c) minimum voltage
(d) maximum voltage
Ans: a
78 transmission line has reflection coefficient
as one.
(a) Open circuit
(b) Short-circuit
(e) Long
(d) None of the above
Ans: a
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79. What will be the reflection co-efficient of
the wave of load connected to transmission line
if surge impedance of the line is equal to load ?
(a) Zero
(b) Unity
(c) Infinity
(d) None of the above
Ans: a
80. The inverse definite mean time relays are
used for over current and earth fault protection
of transformer against
(a) heavy loads
(b) internal short-circuits
(c) external short-circuits
(d) all of the above
Ans: b
81. Over voltage protection is recommended
for
(a) hydro-electric generators
(b) steam turbine generators
(c) gas turbine generators
(d) all of the above
(e) none of the above
Ans: d
82. Air blast circuit breakers for 400 kV power
system are designed to operate in
(a) 100 micro-second
(b) 50 milli-second
(c) 0.5 sec
(d) 0.1 sec
Ans: b
83. Overfluxing protection is recommended
for
(a) distribution transformer
(b) generator transformer of the power plant
(c) auto-transformer of the power plant
(d) station transformer of the power plant
Ans: b
84. Series capacitors are used to
(a) compensate for line inductive reactance
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(b) compensate for line capacitive reactance
(c) improve line voltage
(d) none of the above
Ans: a
85. Admittance relay is _______ relay.
(a) impedance
(b) directional
(c) non-directional
(d) none of the above
Ans: b
86. The material used for fuse must have
(a) low melting point and high specific
resistance
(b) low melting point and -low specific
resistance
(c) high melting point and low specific
resistance
(d) low melting point and any specific
resistance
Ans: a
87. If the fault occurs near the impedance
relay, the VII ratio will be
(a) constant for all distances
(b) lower than that of if fault occurs away from
the relay
(c) higher than that of if fault occurs away from
the relay
(d) none of the above
Ans: b
88. The torque produced in induction type
relay (shaded pole structure) is
(a) inversely proportional to the current
(b) inversely proportional to the square of the
current
(c) proportional to the current
(d) proportional to square of the current
Ans: b
89. The steady state stability of the power
system can be increased by
(a) connecting lines in parallel
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(b) connecting lines in series
(e) using machines of high impedance
(d) reducing the excitation of machines
(e) none of the above
Ans: a
90. The inductive interference between power
and communication line can be minimized by
(a) transposition of the power line
(b) transposition of the communication line
(c) both (a) and (b)
(d) increasing the distance between the
conductors
Ans: c
91. The power loss is an important factor for
the design of
(a) transmission line
(b) motor
(c) generator
(d) feeder
Ans: a
92. A fuse is connected
(a) in series with circuit
(b) in parallel with circuit
(c) either in series or in parallel with circuit
(d) none of the above
Ans: a
93. H.R.C. fuse, as compared to a rewirable
fuse, has
(a) no ageing effect
(b) high speed of operation
(c) high rupturing capacity
(d) all of the above
Ans: d
94. The fuse rating is expressed in terms of
(a) current
(b) voltage
(c) VAR
(d) kVA
Ans: a
95. The fuse blows off by
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(a) burning
(b) arcing
(c) melting
(d) none of the above
Ans: c
96. On which of the following effects of
electric current a fuse operates ?
(a) Photoelectric effect
(b) Electrostatic effect
(c) Heating effect
(d) Magnetic effect
Ans: c
97. An isolator is installed
(a) to operate the relay of circuit breaker
(b) as a substitute for circuit breaker
(c) always independent of the position of
circuit breaker
(d) generally on both sides of a circuit breaker
Ans: d
98. A fuse in a motor circuit provides
protection against
(a) overload
(b) short-circuit and overload
(c) open circuit, short-circuit and overload
(d) none of the above
Ans: b
99. Protection by fuses is generally not used
beyond
(a) 20 A
(b) 50 A
(c) 100 A
(d) 200 A
Ans: c
100. A fuse is never inserted in
(a) neutral wire
(b) negative of D.C. circuit
(c) positive of D.C. circuit
(d) phase dine
Ans: a
101. Oil switches are employed for
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(a) low currents circuits
(b) low voltages circuits
(c) high voltages and large currents circuits
(d) all circuits
Ans: c
102. A switchgear is device used for
(a) interrupting an electrical circuit
(b) switching an electrical circuit 111.
(c) switching and controlling an electri¬cal
circuit
(d) switching, controlling and protect¬ing the
electrical circuit and equipment
Ans: d
103. The fuse wire, in D.C. circuits, is inserted
in
(a) negative circuit only
(b) positive circuit only
(c) both (a) and (b)
(d) either (a) or (b)
Ans: c
104. By which of the following methods major
portion of the heat generated in a H.R.C. fuse is
dissipated ?
(a) Radiation
(b) Convection
(c) Conduction
(d) All of the above
Ans: c
105. A short-circuit is identified by
(a) no current flow
(b) heavy current flow
(c) voltage drop
(d) voltage rise
Ans: b
106. The information to the circuit breaker
under fault conditions is provided by
(a) relay
(b) rewirable fuse
(c) H.R.C. only
(d) all of the above
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Ans: a
107. To limit short-circuit current in a power
system are used.
(a) earth wires
(b) isolators
(c) H.R.C. fuses
(d) reactors
Ans: d
108. A balanced 3-phase system consists of
(a) zero sequence currents only
(b) positive sequence currents only
(c) negative and zero sequence currents
(d) zero, negative and positive sequence
currents
Ans: b
109. In a single bus-bar system there will be
complete shut down when
(a) fault occurs on the bus itself
(b) fault occurs on neutral line
(c) two or more faults occur simultaneously
(d) fault occurs with respect to earthing
Ans: a
Cables
1. The insulating material for a cable should
have
(a) low cost
(b) high dielectric strength
(c) high mechanical strength
(d) all of the above
Ans: d
2. Which of the following protects a cable
against mechanical injury ?
(a) Bedding
(b) Sheath
(c) Armouring
(d) None of the above
Ans: c
3. Which of the following insulation is used in
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cables ?
(a) Varnished cambric
(b) Rubber
(c) Paper
(d) Any of the above
Ans: d
4. Empire tape is
(a) varnished cambric
(b) vulcanised rubber
(c) impregnated paper
(d) none of the above
Ans: a
5. The thickness of the layer of insulation on the
conductor, in cables, depends upon
(a) reactive power
(b) power factor
(c) voltage
(d) current carrying capacity
Ans: c
6. The bedding on a cable consists of
(a) hessian cloth
(b) jute
(c) any of the above
(d) none of the above
Ans: c
7. The insulating material for cables should
(a) be acid proof
(b) be non-inflammable
(c) be non-hygroscopic
(d) have all above properties
Ans: d
8. In a cable immediately above metallic
sheath _____ is provided.
(a) earthing connection
(b) bedding
(c) armouring
(d) none of the above
Ans: b
9. The current carrying capacity of cables in
D.C. is more thanthat in A.C. mainly due to
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(a) absence of harmonics
(b) non-existence of any stability limit
(c) smaller dielectric loss
(d) absence of ripples
(e) none of the above
Ans: c
10. In case of three core flexible cable the
colour of the neutral is
(a) blue
(b) black
(c) brown
(d) none of the above
Ans: a
11 cables are used for 132 kV lines.
(a) High tension
(b) Super tension
(c) Extra high tension
(d) Extra super voltage
Ans: d
12. Conduit pipes are normally used to protect
_____ cables.
(a) unsheathed cables
(b) armoured
(c) PVC sheathed cables
(d) all of the above
Ans: a
13. The minimum dielectric stress in a cable is
at
(a) armour
(b) bedding
(c) conductor surface
(d) lead sheath
Ans: d
14. In single core cables armouring is not done
to
(a) avoid excessive sheath losses
(b) make it flexible
(c) either of the above
(d) none of the above
Ans: a
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15. Dielectric strength of rubber is around
(a) 5 kV/mm
(b) 15 kV/mm
(c) 30 kV/mm
(d) 200 kV/mm
Ans: c
16. Low tension cables are generally used
upto
(a) 200 V
(b) 500 V
(c) 700 V
(d) 1000 V
Ans: d
17. In a cable, the maximum stress under
operating conditions is at
(a) insulation layer
(b) sheath
(c) armour
(d) conductor surface
Ans: d
18. High tension cables are generally used
upto
(a) 11kV
(b) 33kV
(c) 66 kV
(d) 132 kV
Ans: a
19. The surge resistance of cable is
(a) 5 ohms
(b) 20 ohms
(c) 50 ohms
(d) 100 ohms
Ans: c
20. PVC stands for
(a) polyvinyl chloride
(b) post varnish conductor
(c) pressed and varnished cloth
(d) positive voltage conductor
(e) none of the above
Ans: a
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21. In the cables, the location of fault is
usually found out by comparing
(a) the resistance of the conductor
(b) the inductance of conductors
(c) the capacitances of insulated conductors
(d) all above parameters
Ans: c
22. In capacitance grading of cables we use a
______ dielectric.
(a) composite
(b) porous
(c) homogeneous
(d) hygroscopic
Ans: a
23. Pressure cables are generally not used
beyond
(a) 11 kV
(b) 33 kV
(c) 66 kV
(d) 132 kV
Ans: c
24. The material for armouring on cable is
usually
(a) steel tape
(b) galvanised steel wire
(c) any of the above
(d) none of the above
Ans: c
25. Cables, generally used beyond 66 kV are
(a) oil filled
(b) S.L. type
(c) belted
(d) armoured
Ans: a
26. The relative permittivity of rubber is
(a) between 2 and 3
(b) between 5 and 6
(c) between 8 and 10
(d) between 12 and 14
Ans: a
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27. Solid type cables are considered unreliable
beyond 66 kV because
(a) insulation may melt due to higher
temperature
(b) skin effect dominates on the conduc¬tor
(c) of corona loss between conductor and
sheath material
(d) there is a danger of breakdown of
insulation due to the presence of voids
Ans: d
28. If the length of a cable is doubled, its
capacitance
(a) becomes one-fourth
(b) becomes one-half
(c) becomes double
(d) remains unchanged
Ans: c
29. In cables the charging current
(a) lags the voltage by 90°
(b) leads the voltage by 90°
(c) lags the voltage by 180°
(d) leads the voltage by 180°
Ans: b
30. A certain cable has an insulation of relative
permittivity 4. If the insulation is replaced by
one of relative permittivity 2, the capacitance of
the cable will become
(a) one half
(6) double
(c) four times
(d) none of the above
Ans: a
31. If a cable of homogeneous insulation has a
maximum stress of 10 kV/mm, then the
dielectric strength of insulation should be
(a) 5 kV/mm
(b) 10 kV/mm
(a) 15 kV/mm
(d) 30 kV/mm
Ans: b
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32. In the cables, sheaths are used to
(a) prevent the moisture from entering the
cable
(b) provide enough strength
(e) provide proper insulation
(d) none of the above
Ans: a
33. The intersheaths in the cables are used to
(a) minimize the stress
(b) avoid the requirement of good insulation
(c) provide proper stress distribution
(d) none of the above
Ans: c
34. The electrostatic stress in underground
cables is
(a) same at the conductor and the sheath
(b) minimum at the conductor and maximum
at the sheath
(c) maximum at the conductor and minimum
at the sheath
(d) zero at the conductor as well as on the
sheath
(e) none of the above
Ans: c
35. The breakdown of insulation of the cable
can be avoided economically by the use of
(a) inter-sheaths
(b) insulating materials with different
dielectric constants
(c) both (a) and (b)
(d) none of the above
Ans: c
36. The insulation of the cable decreases with
(a) the increase in length of the insulation
(b) the decrease in the length of the insulation
(c) either (a) or (b)
(d) none of the above
Ans: a
37. A cable carrying alternating current has
(a) hysteresis losses only
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(b) hysteresis and leakage losses only
(c) hysteresis, leakage and copper losses only
(d) hysteresis, leakage, copper and friction
losses
Ans: b
38. In a cable the voltage stress is maximum at
(a) sheath
(6) insulator
(e) surface of the conductor
(d) core of the conductor
Ans: d
39. Capacitance grading of cable implies
(a) use of dielectrics of different
permeabilities
(b) grading according to capacitance of cables
per km length
(c) cables using single dielectric in different
concentrations
(d) capacitance required to be introduced at
different lengths to counter the effect of
inductance
(e) none of the above
Ans: a
40. Underground cables are laid at sufficient
depth
(a) to minimise temperature stresses
(b) to avoid being unearthed easily due to
removal of soil
(c) to minimise the effect of shocks and
vibrations due to gassing vehicles, etc.
(d) for all of the above reasons
Ans: c
41. The advantage of cables over overhead
transmission lines is
(a) easy maintenance
(b) low cost
(c) can be used in congested areas
(d) can be used in high voltage circuits
Ans: c
42. The thickness of metallic shielding on
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cables is usually
(a) 0.04 mm
(b) 0.2 to 0.4 mm
(e) 3 to 5 mm
(d) 40 to 60 mm
Ans: a
43. Cables for 220 kV lines are invariably
(a) mica insulated
(b) paper insulated
(c) compressed oil or compressed gas
insulated
(d) rubber insulated
(e) none of the above
Ans: c
44. Is a cable is to be designed for use on 1000
kV, which insulation would you prefer ?
(a) Polyvinyle chloride
(b) Vulcanised rubber
(c) Impregnated paper
(d) Compressed SFe gas
(e) none of the above
Ans: d
45. If a power cable and a communication
cable are to run parallel the minimum distance
between the two, to avoid interference, should
be
(a) 2 cm
(b) 10 cm
(c) 50 cm
(d) 400 cm
Ans: c
46. Copper as conductor for cables is used as
(a) annealed
(b) hardened and tempered
(c) hard drawn
(d) alloy with chromium
Ans: a
47. The insulating material should have
(a) low permittivity
(b) high resistivity
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(c) high dielectric strength
(d) all of the above
Ans: d
48. The advantage of oil filled cables is
(a) more perfect impregnation
(b) smaller overall size
(c) no ionisation, oxidation and formation of
voids
(d) all of the above
Ans: d
49. The disadvantage with paper as insulating
material is
(a) it is hygroscopic
(6) it has high capacitance
(c) it is an organic material
(d) none of the above
Ans: a
50. The breakdown voltage of a cable depends
on
(a) presence of moisture
(b) working temperature
(c) time of application of the voltage
(d) all of the above
Ans: d
51. It is difficult to maintain oil filled cables.
(a) Yes
(b) No
Ans: a
51. In capacitance grading a homogeneous
dielectric is used.
(a) Yes
(b) No
Ans: b
52. In congested areas where excavation is
expensive and inconvenient 'draw in system' of
laying of underground cables
is often adopted.
(a) Yes
(b) No
Ans: a
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53. Natural rubber is obtained from milky sap
of tropical trees.
(a) Yes
(b) No
Ans: a
54. Rubber is most commonly used insulation
in cables.
(a) Yes
(b) No
Ans: a
55. Polyethylene has very poor dielectric and
ageing properties.
(a) Yes
(b) No
Ans: b
56. The metallic sheath may be made of lead or
lead alloy or of aluminium.
(a) Yes
(b) No
Ans: b
Electrical Machine Design
1. Which of the following is the major
consideration to evolve a good design ?
(a) Cost
(b) Durability
(c) Compliance with performance criteria as
laid down in specifications
(d) All of the above
Ans: d
2 impose limitation on design.
(a) Saturation
(b) Temperature rise
(c) Efficiency
(d) Power factor
(e) All above
Ans: e
3. The efficiency of a machine should be as
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______ as possible to reduce the operating
cost.
(a) high
(b) low
(c) either of the above
(d) none of the above
Ans: a
4. If an insulating material is operated beyond
the maximum allowable temperature, its life is
(a) drastically increased
(b) drastically reduced
(c) unaffected
(d) none of the above
Ans: b
5. The design of mechanical parts is
particularly important in case of _____ speed
machines.
(a) low
(b) medium
(c) high
(d) any of the above
Ans: c
6. In induction motors, the length of air gap in
kept as small as mechanically possible is order
to have
(a) low power factor
(b) high power factor
(c) high over load capacity
(d) any of the above
Ans: b
7. In ______ machines, the size of the shaft is
decided by the critical speed which depends on
the deflection of the shaft.
(a) small
(b) medium
(c) large
(d) any of the above.
Ans: c
8. The length cf air gap to be provided in
______ is primarily determined by power factor
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consideration.
(a) d.c. series motor .
(b) d.c. shunt motor
(c) induction motor
(d) synchronous motor
Ans: c
9. Electrical machines having a power output
upto about 750 W may be
called_______machines.
(a) small size
(b) medium size
(c) large size
(d) any of the above
Ans: a
10. Electrical machines having power outputs
ranging from a few kW upto approximately 250
kW may be classified as
(a) small size machines
(b) medium size machines
(c) large size machines
(d) any ofthe above
Ans: b
11. Commercial available medium size
machines have a speed range of ______ .
(a) 200 to 400 r.p.m.
(b) 600 to 1000 r.p.m.
(c) 1000 to 1500 r.p.m.
(d) 2000 to 2500 r.p.m.
Ans: d
12. The action of electromagnetic machines
can be related to which ofthe following basic
principles ?
(a) Induction
(b) Interaction
(c) Alignment
(d) All of the above
Ans: d
13. The change in flux linkages can be caused
in which ofthe following ways ?
(a) The flux is constant with respect to time
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and is stationary and the coil moves through it
(b) The coil is stationary with respect to flux
and the flux varies in magnitude with respect to
time
(c) Both the changes mentioned above occure
together, i.e., the coil moves through a time
varying field
(d) All ofthe above
Ans: d
14 is universally used for windings of electrical
machines because it is easily workable without
any possibility of fracture.
(a) Silver
(b) Steel
(c) Aluminium
(d) Copper
Ans: d
15. Aluminium when adopted as a conductor
material in ______ transformers, decreases the
overall cost of the transformer
(a) small size
(b) medium size
(c) large size
(d) any of the above size
Ans: a
16. Which ofthe following materials is used in
the manufacture of resistance grids to be used
in the starters of large motors ?
(a) Copper
(b) Aluminium
(c) Steel
(d) Cast-iron
Ans: d
17. Materials exhibiting zero value of
resistivity are known as ______ .
(a) conductors
(b) semiconductors
(c) insulators
(d) superconductors
Ans: d
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18. ________ has a lowrelative permeability
and is used principally in field frames when cost
is of primary importance and extra weight is not
objectionable.
(a) Cast steel
(b) Aluminium
(c) Soft steel
(d) Cast iron
Ans: d
19 ______is extensively used for those
portions of magnetic circuit which carry steady
flux and need superior mechanical properties ?
(a) Grey cast-iron
(b) Cast steel
(c) High carbon steel
(d) Stainless steel
Ans: b
20. Hot rolled sheets have ______ value of
permeability
(a) zero
(b) low
(c) high
(d) none ofthe above
Ans: b
21. The heated parts of an electrical machine
dissipate heat into their surroundings by which
of the following modes of heat dissipation ?
(a) Conduction
(b) Convection
(c) Radiation
(d) All ofthe above
Ans: d
22. The heat dissipated by from a surface
depends upon its temperature and its
characteristics like colour, roughness etc.
(a) conduction
(b) convection
(c) radiation
(d) any ofthe above
Ans: c
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23. The mcrease in heat dissipation by air
blasts is due to increase in
(a) conduction
(b) convection
(e) radiation
(d) any ofthe above
Ans: b
24. On which of the following variables heat
convected depends ?
(a) Power density
(b) Temperature difference between heated
surface and coolant
(c) Thermal resistivity, density, specific heat
(d) Gravitational constant
(e) All ofthe above
Ans: e
25. Which ofthe following methods is used for
air cooling of turbo-alternators ?
(a) One sided axial ventilation
(b) Two sided axial ventilation
(c) Multiple inlet system
(d) All ofthe above
Ans: d
26. Multiple inlet system of air cooling of
turbo-alternators can be used for machines of
rating upto
(a) 10 MW
(b) 30 MW
(c) 60 MW
(d) 150 MW
Ans: c
27. Which ofthe following is an advantage of
hydrogen cooling ?
(a) Increase in efficiency
(b) Increase in ratings
(c) Increase in life
(d) Smaller size of coolers
(e) All ofthe above
Ans: e
28. The density of hydrogen is _____ times
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the density of air.
(a) 0.07
(b) 1.5
(c) 2.5
(d) 3.5
Ans: a
29. Hydrogen has a heat transfer co-efficient
_____ times that of air
(a) 1.5
(b) 2.5
(c) 3.5
(d) 4.5
Ans: a
30. The thermal conductivity of hydrogen is
______ times that of air
(a) 2
(b) 3
(c) 5
(d) 7
Ans: d
31. With conventional hydrogen cooling it is
possible to increase the rating of a single unit to
(a) 50 MW
(b) 100 MW
(c) 200 MW
(d) none ofthe above
Ans: c
32. The noise produced by a ______ cooled
machine is less as the rotor moves in a medium
of smaller density.
(a) air
(b) hydrogen
(c) either (a) or (b)
(d) none of the above
Ans: b
33 cooling is the process of dissipating the
armature and field winding losses to a cooling
medium circulating within the winding
insulation wall
(a) Direct
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(b) Indirect
(c) Conventional
(d) Any ofthe above
Ans: a
34. Machines cooled by direct cooling method
may be called
(a) "supercharged"
(b) "inner cooled"
(c) "conductor cooled"
(d) any of the above
Ans: d
35. In direct cooled system using hydrogen
both stator and rotor conductors are made
(a) solid
(b) hollow
(c) perforated
(d) any ofthe above
Ans: b
36. With direct water cooling it is possible to
have ratings of about
(a) 200 MW
(b) 300 MW
(c) 400 MW
(d) 600 MW
Ans: d
37. The resistivity of water should not be less
than
(a) 10 Q m
(b) 100 Q m
(c) 1000 Q m
(d) 2000 Q m
Ans: d
38. Direct water cooling of rotor winding
presents
(a) no mechanical difficulties
(b) lesser mechanical difficulties
(c) greater mechanical difficulties
(d) none of the above
Ans: c
39. The time taken by the machine to attain
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0.632 of its final steady temperature rise is
called
(a) heating time constant
(b) cooling time constant
(c) either (a) or (b)
(d) none of the above
Ans: a
40. In self cooled motors the cooling time
constant is about ______ than the heating
time constant because cooling conditions are
worse at standstill.
(a) 2 to 3 times greater
(b) 3 to 4 times greater
(c) 4 to 5 times greater
(d) none of the above
Ans: a
41. By which of the following methods motor
rating for variable load drives can be
determined ?
(a) Method of average losses
(b) Equivalent current method
(c) Equivalent torque method
(d) Equivalent power method
(e) All of the above.
Ans: e
42. Which of the following methods does not
take into account the maximum temperature
rise under variable load conditions ?
(a) Equivalent power method
(b) Equivalent current method
(c) Method of average losses
(d) Equivalent torque method
Ans: c
43. Which of the following methods is most
accurate ?
(a) Equivalent current method
(b) Equivalent power method
(c) Equivalent torque method
(d) Method of average losses
Ans: a
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44. By which of the following methods the
temperature rise of windings and other parts
may be determined ?
(a) Thermometer method
(6) Resistance method
(c) Embedded temperature detector method
(d) Any of the above
Ans: d
45. The slot leakage can be calculated by
making which of the following assumptions ?
(a) The current in the slot conductors is
uniformly distributed over their cross-section
(b) The leakage path is straight across the slot
and around the iron at the bottom
(c) The permanence of air paths is only
considered. The reluctance of iron paths is
assumed as zero
(d) All of the above
Ans: d
46. The value of exciting or magnetizing
current depends upon which of the following
factors ?
(a) Total m.m.f. required
(b) The number of turns in the exciting
winding
(c) The way in which the winding is distributed
(d) All of the above
Ans: d
47. Tractive magnets are operated from
(a) a.c. supply
(b) d.c. supply
(c) either a.c. or d.c. supply
(d) none of the above
Ans: c
48 electromagnets generally function as
holding magnets.
(a) Tractive
(b) Portative
(c) Either of the above
(d) None of the above
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Ans: b
49. Which of the following is the commonly
used type of electromagnets ?
(a) Flat-faced armature type
(b) Horse shoe type
(c) Flat-faced plunger type
(d) All of the above
Ans: d
50 are used for construction of core of
electromagnets.
(a) Soft magnetic materials
(b) Hard magnetic materials
(c) Either (a) or (b)
(d) None of the above
Ans: a
51. The design of electromagnets is based
upon which of the following fundamental
equations ?
(a) Force equation
(b) Magnetic circuit equation
(c) Heating equation
(d) Voltage equation
(e) All of the above
Ans: e
52. When the two coil sides forming a coil are
spaced exactly one pole pitch apart they are
said to be of
(a) short pitch
(b) full pitch
(c) either of the above
(d) none of the above
Ans: b
53 are always double layer type.
(a) Closed windings
(b) Open windings
(c) Either of the above
(d) None of the above
Ans: a
54. The distance between the starts of two
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consecutive coils measured in terms of coil
sides is called
(a) front pitch
(b) winding pitch
(c) commutator pitch
(d) back pitch
Ans: b
55. The winding where dummy coils are used
is sometimes called
(a) duplex winding
(b) triplex winding
(c) forced winding
(d) none of the above
Ans: c
56. Dummy coil should not be used in
(a) small machines
(b) large machines
(c) either (a) or (b)
(d) none of the above
Ans: b
57. Power transformers have rating
(a) equal to 50 kVA
(6) equal to 100 kVA
(c) above 200 kVA
(d) none of the above
Ans: c
58. Power transformers should be designed to
have maximum efficiency
(a) at one-fourth load
(b) at one-half load
(c) at or near full load
(d) any of the above
Ans: c
59. In transformers using hot rolled steel, the
cross-section of the yoke is made about _____
greater than that of the core
(a) 5 percent
(b) 10 percent
(c) 15 percent
(d) 30 percent
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(e) none of the above
Ans: c
60. Yokes with rectangular cross-section are
used for
(a) small capacity transformers
(b) medium capacity transformers
(c) large capacity transformers
(d) any of the above
Ans: a
61. The cold rolled grain oriented steel has
______ permeability in the direction of the
grain orientation.
(a) minimum
(b) maximum
(c) nil
(d) none of the above
Ans: b
62. Cylindrical windings using circular
conductors, employed in transformers, are
(a) single layered
(b) double layered
(c) multi-layered
(d) none of the above
Ans: c
63. Helical windings are used in
(a) distribution transformers
(b) power transformers
(c) shell type transformers
(d) none of the above
Ans: b
64. Multi-layer helical windings are commonly
used in the transformers as high voltage
windings
(a) upto 20 kV
(b) upto 50 kV
(c) upto 80 kV
(d) for 110 kV and above
Ans: d
65. Disc windings are primarily used in
(a) short capacity transformers
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(b) medium capacity transformers
(c) high capacity transformers
(d) any of the above
Ans: c
66. The heat dissipating capability of
transformers of ratings higher than 30 kVA in
increased by providing which of the following ?
(a) Corrugations
(b) Fins
(c) Tubes
(d) Radiator tanks
(e) All of the above
Ans: e
67. Transformers with a capacity of upto
_____ have a cooling radiator system with
natural cooling
(a) 2 MVA
(b) 5 MVA
(c) 7.5 MVA
(d) 10 MVA
Ans: d
68. The forced oil and air circulation method is
usual one for transformers of capacities
(a) upto 5 MVA
(b) upto 10 MVA
(c) upto 20 MVA
(d) 30 MVA upwards
Ans: d
69. The flash point of transformer oil should
be higher than
(a) 40°C
(b) 60°C
(c) 80°C
(d) 104°C
Ans: d
70. The voltage control in electric supply
networks in required on account of which of the
following reasons ?
(a) Adjustment of voltage at consumers
premises within statutory limits
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(b) Control of active and reactive power
(c) Adjustment of short period daily and
seasonal voltage variations in accordance with
variations of load
(d) All of the above
Ans: d
71. D.C. windings are
(a) sometimes 2-layer type
(b) never 2-layer type
(c) always 2-layer type
(d) none of the above
Ans: c
72. The usual values of maximum flux
densities for distribution transformers using hot
rolled silicon steel are
(a) 0.5 to 0.8 Wb/m2
(b) 0.8 to 1.0 Wb/m2
(c) 1.1 to 1.35 Wb/m2
(d) 1.4 to 1.8 Wb/m2
Ans: c
73. For 275 kV transformers, using cold rolled
grain oriented steel, which of the following
values of flux density may be used?
(a) 1.0 Wb/m2
(b) 1.1 Wb/m2
(c) 1.3 Wb/m2
(d) 1.6 Wb/m2
(e) None of the above
Ans: d
74. For large power transformers, self oil
cooled type or air blast type which of the
following values of current density may be used
?
(a) 1.0 to 1.2 A/mm2
(b) 1.5 to 2.0 A/mm2
(c) 2.2 to 3.2 A/mm2
(d) 3.2 to 4.2 A/mm2
Ans: c
75. A current density of _____ is ilsed for large
power transformers with forced circulation of
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oil or with water cooling coils
(a) 1.5 to 2.5 A/mm2
(b) 3.5 to 4.5 A/mm2
(c) 4.0 to 5.0 A/mm2
(d) 5.4 to 6.2 A/mm2
Ans: d
76. The high voltage winding is usually which
of the following type ?
(a) Cylindrical winding with circular
conductors
(b) Cross-over winding with either circular or
small rectangular conductors
(c) Continuous disc type winding with
rectangular conductors
(d) All of the above types
Ans: d
77. Which of the following is the basic
consideration in the design of insulation ?
(a) Electrical considerations
(b) Mechanical considerations
(c) Thermal considerations
(d) All of the above
Ans: d
78. A practical formula for determining the
thickness of insulation between low voltage and
high voltage windings is
(a) 1 + 0.2 kVmm
(6) 2 + 0.5 kVmm
(c) 4 + 0.7 kV mm
(d) 5 + 0.9 kV mm
Ans: d
79. The insulation between windings and
grounded core and the insulation between the
windings of the same phase is called
(a) minor insulation
(b) major insulation
(c) either of the above
(d) none of the above
Ans: b
80. The cylindrical windings using circular
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conductors are used for current rating of
(a) upto 20 A
(b) upto 40 A
(c) upto 60 A
(d) upto 80 A
Ans: d
81. The surge phenomenon is particularly
important in case of
(a) low voltage transformers
(b) medium voltage transformers
(c) high voltage transformers
(d) any of the above
Ans: c
82. Which of the following in an application of
D.C. motors?
(a) Traction
(b) Drives for process industry
(c) Battery driven vehicles
(d) Automatic control
(e) All of the above
Ans: e
83. D.C. servomotors are used in
(a) purely D.C. control systems
(6) purely AC. control systems
(c) both D.C. and AC. control systems
(d) none of the above
Ans: a
84. The stator of a D.C. machine comprises of
(a) main poles
(6) interpoles
(c) frame
(d) all of the above
Ans: d
85. The laminations of the armature of a D.C.
machine are usually _____ thick.
(a) 0.1 to 0.2 mm
(b) 0.2 to 0.3 mm
(c) 0.3 to 0.4 mm
(d) 0.4 to 0.5 mm
Ans: d
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86. is usually used for brush rockers
(a) Mild steel
(b) Copper
(c) Aluminium
(d) Cast-iron
Ans: d
87. ______ brushes are fragile and cause
excessive wear of commutator,
(a) Natural graphite
(b) Hard carbon
(c) Electro graphitic
(d) Metal graphite
Ans: a
88. Which of the following brushes can be
used for high values of current density ?
(a) Metal graphite brushes
(b) Hard carbon brushes
(c) Electro-graphitic brushes
(d) Natural graphite brushes
Ans: a
89 ________ is the common method of
applying brushes to the commntator.
(a) Radial
(b) Trailing
(c) Reaction
(d) All of the above
Ans: d
90. Which of the following problem arises in
D.C. motors which are fed from thyristor bridge
circuits ?
(a) Increased I R losses
(b) Increased core losses
(c) Poor commutation
(d) Change in motor parameters
(e) All of the above
Ans: e
91. The weight of copper of both armature
and field windings decreases with _____ in
number of poles.
(a) increase
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(b) decrease
(c) either of the above
(d) none of the above
Ans: a
92. In a D.C. machine the number of brush
arms is _____ the number of poles.
(a) less than
(b) equal to
(c) greater than
(d) none of the above
Ans: b
93. In a D.C. machine the current per brush
arm should not be more than
(a) 100 A
(6) 200 A
(e) 300 A
(d) 400 A
Ans: d
94. In a D.C. machine, the value of peripheral
speed should not, normally, exceed
(a) 10 m/s
(b) 20 m/s
(c) 30 m/s
(d) 40 m/s
Ans: c
95. In D.C. machines the width of the duct is
usually
(a) 4 mm
(b) 6 mm
(c) 8 mm
(d) 10 mm
Ans: d
96. D.C. machines designed with a large value
of air gap length have
(a) worst, ventilation
(b) poor ventilation
(c) better ventilation
(d) none of the above
Ans: c
97. In D.C. machines, ir order to prevent
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excessive distortion of field form by the
armature reaction, the field mmf must be made
(a) equal to that of armature mmf
(b) less in comparison with the arma¬ture
mmf
(c) large in comparison with the arma-ture
mmf
(d) none of the above
Ans: c
98. In D.C. machines, the ____ in field mmf
results in increase in size and cost of machines.
(a) increase
(b) decrease
(c) either of the above
(d) none of the above
Ans: a
99. The operation of a D.C. machine with large
air gap lengths is comparatively
(a) quiet
(b) noisy
(c) either of the above
(d) none of the above
Ans: a
100. Which of the following methods may be
adopted to reduce the effects of armature
reaction ?
(a) Increase in length of air gap at pole tips
(b) Increasing reluctance of pole tips
(c) Compensating windings
(d) Interpoles
(e) All of the above
Ans: e
101. In D.C. machines the usual limit of slot
pitch is
(a) between 5 to 10 mm
(b) between 10 to 15 mm
(c) between 15 to 20 mm
(d) between 25 to 35 mm
Ans: d
102. In D.C. machines the number of slots per
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pole usually lies
(a) between 2 to 4
(b) between 6 to 8
(c) between 9 to 16
(d) between 20 to 30
Ans: c
Measurement and Instrumentation
1. The use of _____ instruments is merely
confined within laboratories as stand¬ardizing
instruments.
(a) absolute
(b) indicating
(c) recording
(d) integrating
(e) none of the above
Ans: a
2. Which of the following instruments indicate
the instantaneous value of the electrical
quantity being measured at the time at which it
is being measured ?
(a) Absolute instruments
(b) Indicating instruments
(c) Recording instruments
(d) Integrating instruments
Ans: b
3. _____ instruments are those which measure
the total quantity of electricity delivered in a
particular time.
(a) Absolute
(b) Indicating
(c) Recording
(d) Integrating
Ans: d
4. Which of the following are integrating
instruments ?
(a) Ammeters
(b) Voltmeters
(c) Wattmeters
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(d) Ampere-hour and watt-hour meters
Ans: d
5. Resistances can be measured with the help
of
(a) wattmeters
(b) voltmeters
(c) ammeters
(d) ohmmeters and resistance bridges
(e) all of the above
Ans: d
6 According to application, instruments are
classified as
(a) switch board
(b) portable
(c) both (a) and (b)
(d) moving coil
(e) moving iron
(f) both (d) and (e)
Ans: c
7. Which of the following essential features is
possessed by an indicating instrument ?
(a) Deflecting device
(b) Controlling device
(c) Damping device
(d) All of the above
Ans: d
8. A _____ device prevents the oscillation of
the moving system and enables the latter to
reach its final position quickly
(a) deflecting
(b) controlling
(c) damping
(d) any of the above
Ans: c
9. The spring material used in a spring control
device should have the following property.
(a) Should be non-magnetic
(b) Most be of low temperature co-efficient
(c) Should have low specific resistance
(d) Should not be subjected to fatigue
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(e) All of the above
Ans: e
10. Which of the following properties a
damping oil must possess ?
(a) Must be a good insulator
(b) Should be non-evaporating
(c) Should not have corrosive action upon the
metal of the vane
(d) The viscosity of the oil should not change
with the temperature
(e) All of the above
Ans: e
11. A moving-coil permanent-magnet
instrument can be used as _____ by using a low
resistance shunt.
(a) ammeter
(b) voltmeter
(c) flux-meter
(d) ballistic galvanometer
Ans: a
12. A moving-coil permanent-magnet
instrument can be used as flux-meter
(a) by using a low resistance shunt
(b) by using a high series resistance
(c) by eliminating the control springs
(d) by making control springs of large moment
of inertia
Ans: c
13. Which of the following devices may be
used for extending the range of instruments ?
(a) Shunts
(b) Multipliers
(c) Current transformers
(d) Potential transformers
(e) All of the above
Ans: e
14. An induction meter can handle current
upto
(a) 10 A
(b) 30 A
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(c) 60 A
(d) 100 A
Ans: d
15. For handling greater currents induction
wattmeters are used in conjunction with
(a) potential transformers
(b) current transformers
(c) power transformers
(d) either of the above
(e) none of the above
Ans: b
16. Induction type single phase energy meters
measure electric energy in
(a) kW
(b) Wh
(c) kWh
(d) VAR
(e) None of the above
Ans: c
17. Most common form of A.C. meters met with
in every day domestic and industrial
installations are
(a) mercury motor meters
(b) commutator motor meters
(c) induction type single phase energy meters
(d) all of the above
Ans: c
18. Which of the following meters are not
used on D.C. circuits
(a) Mercury motor meters
(b) Commutator motor meters
(c) Induction meters
(d) None of the above
Ans: c
19. Which of the following is an essential part
of a motor meter ?
(a) An operating torque system
(b) A braking device
(c) Revolution registering device
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(d) All of the above
Ans: d
20. A potentiometer may be used for
(a) measurement of resistance
(b) measurement of current
(c) calibration of ammeter
(d) calibration of voltmeter
(e) all of the above
Ans: e
21 is an instrument which measures the
insulation resistance of an electric circuit
relative to earth and one another,
(a) Tangent galvanometer
(b) Meggar
(c) Current transformer
(d) None of the above
Ans: b
22. The household energy meter is
(a) an indicating instrument
(b) a recording instrument
(c) an integrating instrument
(d) none of the above
Ans: c
23. The pointer of an indicating instrument
should be
(a) very light
(b) very heavy
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
24. The chemical effect of current is used in
(a) D.C. ammeter hour meter
(b) D.C. ammeter
(c) D.C. energy meter
(d) none of the above
Ans: a
25. In majority of instruments damping is
provided by
(a) fluid friction
(b) spring
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(c) eddy currents
(d) all of the above
Ans: c
26. An ammeter is a
(a) secondary instrument
(b) absolute instrument
(c) recording instrument
(d) integrating instrument
Ans: a
27. In a portable instrument, the controlling
torque is provided by
(a) spring
(b) gravity
(c) eddy currents
(d) all of the above
Ans: a
28. The disc of an instrument using eddy
current damping should be of
(a) conducting and magnetic material
(b) non-conducting and magnetic material
(c) conducting and non-magnetic material
(d) none of the above
Ans: c
29. The switch board instruments
(a) should be mounted in vertical position
(6) should be mounted in horizontal position
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
30. The function of shunt in an ammeter is to
(a) by pass the current
(b) increase the sensitivity of the ammeter
(c) increase the resistance of ammeter
(d) none of the above
Ans: a
31. The multiplier and the meter coil in a
voltmeter are in
(a) series
(b) parallel
(c) series-parallel
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(d) none of the above
Ans: a
32. A moving iron instrument can be used for
(a) D.C. only
(b) A.C. only
(c) both D.C. and A.C.
Ans: c
33. The scale of a rectifier instrument is
(a) linear
(b) non-linear
(c) either (a) or (b)
(d) neither (a) nor (b)
Ans: a
34. For measuring current at high frequency
we should use
(a) moving iron instrument
(b) electrostatic instrument
(c) thermocouple instrument
(d) none of the above
Ans: c
35. The resistance in the circuit of the moving
coil of a dynamometer wattmeter should be
(a) almost zero
(b) low
(c) high
(d) none of the above
Ans: c
36. A dynamometer wattmeter can be used
for
(a) both D.C. and A.C.
(b) D.C. only
(c) A.C. only
(d) any of the above
Ans: a
37. An induction wattmeter can be used for
(a) both D.C. and A.C.
(6) D.C. only
(c) A.C. only
(d) any of the above
Ans: b
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38. The pressure coil of a wattmeter should be
connected on the supply side of the current coil
when
(a) load impedance is high
(b) load impedance is low
(c) supply voltage is low
(d) none of the above
Ans: a
39. In a low power factor wattmeter the
pressure coil is connected
(a) to the supply side of the current coil
(b) to the load side of the current coil
(c) in any of the two meters at connection
(d) none of the above
Ans: b
40. In a low power factor wattmeter the
compensating coil is connected
(a) in series with current coil
(b) in parallel with current coil
(c) in series with pressure coil
(d) in parallel with pressure coil
Ans: c
41. In a 3-phase power measurement by two
wattmeter method, both the watt meters had
identical readings. The power factor of the load
was
(a) unity
(6) 0.8 lagging
(c) 0.8 leading
(d) zero
Ans: a
42. In a 3-phase power measurement by two
wattmeter method the reading of one of the
wattmeter was zero. The power factor of the
load must be
(a) unity
(b) 0.5
(c) 0.3
(d) zero
Ans: b
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43. The adjustment of position of shading
bands, in an energy meter is done to provide
(a) friction compensation
(b) creep compensation
(c) braking torque
(d) none of the above
Ans: a
44. An ohmmeter is a
(a) moving iron instrument
(b) moving coil instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
45. When a capacitor was connected to the
terminal of ohmmeter, the pointer indicated a
low resistance initially and then slowly came to
infinity position. This shows that capacitor is
(a) short-circuited
(b) all right
(c) faulty
Ans: b
46. For measuring a very high resistance we
should use
(a) Kelvin's double bridge
(b) Wheat stone bridge
(c) Meggar
(d) None of the above
Ans: c
47. The electrical power to a meggar is
provided by
(a) battery
(b) permanent magnet D.C. generator
(c) AC. generator
(d) any of the above
Ans: b
48. In a meggar controlling torque is provided
by
(a) spring
(b) gravity
(c) coil
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(d) eddy current
Ans: c
49. The operating voltage of a meggar is about
(a) 6 V
(b) 12 V
(c) 40 V
(d) 100 V
Ans: d
50. Murray loop test can be used for location
of
(a) ground fault on a cable
(b) short circuit fault on a cable
(c) both the ground fault and the short-circuit
fault
(d) none of the above
Ans: c
51. Which of the following devices should be
used for accurate measurement of low D.C.
voltage ?
(a) Small range moving coil voltmeter
(b) D.C. potentiometer
(c) Small range thermocouple voltmeter
(d) None of the above
Ans: b
52. It is required to measure the true open
circuit e.m.f. of a battery. The best device is
(a) D.C. voltmeter
(b) Ammeter and a known resistance
(c) D.C. potentiometer
(d) None of the above
Ans: c
53. A voltage of about 200 V can be measured
(a) directly by a D.C. potentiometer
(b) a D.C. potentiometer in conjunction with a
volt ratio box
(c) a D.C. potentiometer in conjunction with a
known resistance
(d) none of the above
Ans: b
54. A direct current can be measured by
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(a) a D.C. potentiometer directly
(b) a D.C. potentiometer in conjunction with a
standard resistance
(c) a D.C. potentiometer in conjunction with a
volt ratio box
(d) none of the above
Ans: b
55. To measure a resistance with the help of a
potentiometer it is
(a) necessary to standardise the
potentiometer
(b) not necessary to standardise the
potentiometer
(c) necessary to use a volt ratio box in
conjunction with the potentiometer
(d) none of the above
Ans: b
56. A phase shifting transformer is used in
conjunction with
(a) D.C. potentiometer
(b) Drysdale potentiometer
(c) A.C. co-ordinate potentiometer
(d) Crompton potentiometer
Ans: b
57. Basically a potentiometer is a device for
(a) comparing two voltages
(b) measuring a current
(c) comparing two currents
(d) measuring a voltage
(e) none of the above
Ans: a
58. In order to achieve high accuracy, the slide
wire of a potentiometer should be
(a) as long as possible
(b) as short as possible
(c) neither too small not too large
(d) very thick
Ans: a
59. To measure an A. C. voltage by using an
A.C. potentiometer, it is desirable that the
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supply for the potentiometer in taken
(a) from a source which is not the same as the
unknown voltage
(b) from a battery
(c) from the same source as the unknown
voltage
(d) any of the above
Ans: c
60. The stator of phase shifting transformer
for use in conjunction with an A.C.
potentiometer usually has a
(a) single-phase winding
(b) two-phase winding
(c) three-phase winding
(d) any of the above
Ans: b
61. In an AC. co-ordinate potentiometer, the
currents in the phase and quadrature
potentiometer are adjusted to be
(a) out of phase by 90°
(6) out of phase by 60°
(c) out of phase by 30°
(d) out of phase by 0°
(e) out of phase by 180°
Ans: a
62. A universal RLC bridge uses
(a) Maxwell bridge configuration for
measurement of inductance and De Santas
bridge for measurement of capacitance
(b) Maxwell Wein bridge for measurement of
inductance and modified De Santy's bridge for
measurement of capacitance
(c) Maxwell Wein bridge for measurement of
inductance and Wein bridge for measurement
of capacitance
(d) Any of the above.
Ans: b
63. For measurements on high voltage
capacitors, the suitable bridge is
(a) Wein bridge
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(b) Modified De Santy's bridge
(c) Schering bridge
(d) Any of the above
(e) None of the above
Ans: c
64. In an Anderson bridge, the unknown
inductance is measured in terms of
(a) known inductance and resistance
(b) known capacitance and resistance
(c) known resistance
(d) known inductance
Ans: b
65. Wagner earthing device is used to
eliminate errors due to
(a) electrostatic coupling
(b) electromagnetic coupling
(c) both (a) and (b)
(d) none of the above
Ans: a
66. For measurement of mutual inductance
we can use
(a) Anderson bridge
(b) Maxwell's bridge
(c) Heaviside bridge
(d) Any of the above
Ans: c
67. For measurement of inductance having
high value, we should use
(a) Maxwell's bridge
(b) Maxwell Wein bridge
(c) Hay's bridge
(d) Any of the above
Ans: c
68. If the current in a capacitor leads the
voltage by 80°, the loss angle of the capacitor is
(a) 10°
(b) 80°
(c) 120°
(d) 170°
Ans: a
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69. In a Schering bridge the potential of the
detector above earth potential is
(a) a few volts only
(6) 1 kV
(c) 5 kV
(d) 10 kV
Ans: a
70. To avoid the effect of stray magnetic field
in A.C. bridges we can use
(a) magnetic screening
(b) Wagner earthing device
(c) wave filters
(d) any of the above
Ans: a
71. If an inductance is connected in one arm
of bridge and resistances in the remaining three
arms
(a) the bridge can always be balanced
(b) the bridge cannot be balanced
(c) the bridge can be balanced if the
resistances have some specific values
Ans: b
72. A power factor meter has
(a) one current circuit and two pres¬sure
circuits
(b) one current circuit and one pressure
circuit
(c) two current circuits and one pres¬sure
circuit
(d) none of the above
Ans: a
73. The two pressure coils of a single phase
power factor meter have
(a) the same dimensions and the same
number of turns
(b) the same dimension but different number
of turns
(c) the same number of turns but different
dimensions
(d) none of the above
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Ans: a
74. In a single phase power factor meter the
phase difference between the currents in the
two pressure coils is
(a) exactly 0°
(b) approximately 0°
(c) exactly 90°
(d) approximately 90°
Ans: c
75. In a dynamometer 3-phase power factor
meter, the planes of the two moving coils are at
(a) 0°
(b) 60°
(c) 90°
(d) 120°
Ans: d
76. In a vibrating reed frequency meter the
natural frequencies of two adjacent reeds have
a difference of
(a) 0.1 Hz
(b) 0.25 Hz
(c) 0.5 Hz
(d) 1.5 Hz
Ans: c
77. In a Weston frequency meter, the
magnetic axes of the two fixed coils are
(a) parallel
(b) perpendicular
(c) inclined at 60°
(d) inclined at 120°
Ans: b
78. A Weston frequency meter is
(a) moving coil instrument
(b) moving iron instrument
(c) dynamometer instrument
(d) none of the above
Ans: b
79. A Weston synchronoscope is a
(a) moving coil instrument
(b) moving iron instrument
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(c) dynamometer instrument
(d) none of the above
Ans: c
80. In a Weston synchronoscope, the fixed
coils are connected across
(a) bus-bars
(b) incoming alternator
(c) a lamp
(d) none of the above
Ans: b
81. In Weston synchronoscope the moving coil
is connected across
(a) bus-bars
(b) incoming alternator
(c) fixed coils
(d) any of the above
Ans: a
82. The power factor of a single phase load
can be calculated if the instruments available
are
(a) one voltmeter and one ammeter
(b) one voltmeter, one ammetqr and one
wattmeter
(c) one voltmeter, one ammeter and one
energy meter
(d) any of the above
Ans: b
83. The desirable static characteristics of a
measuring system are
(a) accuracy and reproducibility
(b) accuracy, sensitivity and reproducibility
(c) drift and dead zone
(d) static error
Ans: b
84. The ratio of maximum displacement
deviation to full scale deviation of the
instrument is called
(a) static sensitivity
(b) dynamic deviation
(c) linearity
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(d) precision or accuracy
Ans: c
85. Systematic errors are
(a) instrumental errors
(b) environmental errors
(c) observational errors
(d) all of the above
Ans: d
86. Standard resistor is made from
(a) platinum
(b) maganin
(c) silver
(d) nichrome
Ans: b
87. Commonly used standard capacitor is
(a) spherical type
(b) concentric cylindrical type
(c) electrostatic type
(d) multilayer parallel plate type
Ans: b
88. Operating torques in analogue
instruments are
(a) deflecting and control
(b) deflecting and damping
(c) deflecting, control and damping
(d) vibration and balancing
Ans: c
89. Commonly used instruments in power
system measurement are
(a) induction
(b) moving coil or iron
(c) rectifier
(d) electrostatic
Ans: a
90. Damping of the Ballistic galvanometer is
made small to
(a) get first deflection large
(b) make the system oscillatory
(c) make the system critically damped
(d) get minimum overshoot
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Ans: a
91. If an instrument has cramped scale for
larger values, then it follows
(a) square law
(b) logarithmic law
(c) uniform law
(d) none of the above
Ans: b
92. Volt box is a component to
(a) extend voltage range
(6) measure voltage
(c) compare voltage in a box
(d) none of the above
Ans: a
93. E.m.f. of a Weston cell is accurately
measured by
(a) electrostatic voltmeter
(b) hot wire voltmeter
(c) isothermal voltmeter
(d) electrodynamic voltmeter
Ans: a
94. The gravity controlled instrument has
crowded scale because current is proportional
to
(a) balancing weight
(b) deflection angle
(c) sine of deflection angle
Ans: c
95. A sensitive galvanometer produces large
deflection for a
(a) small value of current
(b) large value of current
(c) large value of power
(d) large value of voitage
(e) none of the above
Ans: a
96. A multirangq instrument has
(a) multiple shunt or series resistances inside
the meter
(b) multicoii arrangement
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(c) variable turns of coil
(d) multi range meters inside the
measurement system
(e) any of the above
Ans: a
97. The rectifier instrument is not free from
(a) temperature error
(b) wave shape error
(c) frequency error
(d) all of the above
Ans: c
98. Alternating current is measured by
(a) induction ammeter
(b) permanent magnet type ammeter
(c) electrostatic ammeter
(d) moving iron repulsion type voltmeter
Ans: a
99. Most sensitive galvanometer is
(a) elastic galvanometer
(b) vibration galvanometer
(c) Duddlb galvanometer
(d) spot ballistic galvanometer
Ans: d
100. Instrument transformers are
(a) potential transformers
(b) current transformers
(c) both (a) and (b)
(d) power transformers
Ans: c
101. An instrument transformer is used to
extend the range of
(a) induction instrument
(b) electrostatic instrument
(c) moving coil instrument
(d) any of the above
Ans: a
102. Wattmeter cannot be designed on the
principle of
(a) electrostatic instrument
(b) thermocouple instrument
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(c) moving iron instrument
(d) electrodynamic instrument
Ans: c
103. In an energymeter braking torque is
produced to
(a) safe guard it against creep
(b) brake the instrument
(c) bring energy meter to stand still
(d) maintain steady speed and equal to
driving torque
Ans: d
104. Various adjustments in an energy meter
include
(a) light load or friction
(b) lag and creep
(c) overload and voltage compensation
(d) temperature compensation
(e) all of the above
Ans: e
105. The power of a n-phase circuit can be
measured by using a minimum of
(a) (n - 1) wattmeter elements
(b) n wattmeter elements
(c) (n + 1) wattmeter elements
(d) 2n wattmeter elements
Ans: a
106. Two holes in the disc of energymeter are
drilled at the opposite sides of the spindle to
(a) improve its ventilation
(b) eliminate creeping at no load
(c) increase its deflecting torque
(d) increase its braking tcrque
Ans: b
107. Which of the following is measured by
using a vector voltmeter ?
(a) Amplifier gain and phase shift
(b) Filler transfer functions
(c) Complex insersion loss
(d) All of the above
Ans: d
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108. The principle on which vector voltmeter
is based is
(a) that it works on the principle of complex
variation
(b) that it measures the response of linear
ramp voltage
(c) same as digital meter
(d) that it measures the amplitude of a single
at two points and at the same time measures
their phase difference
Ans: d
109. To measure radio frequency, the suitable
frequency meter is
(a) Weston frequency meter
(b) reed vibrator frequency meter
(c) hetrodyne frequency meter
(d) electrical resonance frequency meter
Ans: c
Control Systems
1. In an open loop control system
(a) Output is independent of control input
(b) Output is dependent on control input
(c) Only system parameters have effect on the
control output
(d) None of the above
Ans: a
2. For open control system which of the
following statements is incorrect ?
(a) Less expensive
(b) Recalibration is not required for
maintaining the required quality of the output
(c) Construction is simple and maintenance
easy
(d) Errors are caused by disturbances
Ans: b
3. A control system in which the control action
is somehow dependent on the output is known
as
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(a) Closed loop system
(b) Semiclosed loop system
(c) Open system
(d) None of the above
Ans: a
4. In closed loop control system, with positive
value of feedback gain the overall gain of the
system will
(a) decrease
(b) increase
(c) be unaffected
(d) any of the above
Ans: a
5. Which of the following is an open loop
control system ?
(a) Field controlled D.C. motor
(b) Ward leonard control
(c) Metadyne
(d) Stroboscope
Ans: a
6. Which of the following statements is not
necessarily correct for open control system ?
(a) Input command is the sole factor
responsible for providing the control action
(b) Presence of non-linearities causes
malfunctioning
(c) Less expensive
(d) Generally free from problems of nonlinearities
Ans: b
7. In open loop system
(a) the control action depends on the size of
the system
(b) the control action depends on system
variables
(c) the control action depends on the input
signal
(d) the control action is independent of the
output
Ans: d
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8 has tendency to oscillate.
(a) Open loop system
(b) Closed loop system
(c) Both (a) and (b)
(d) Neither (a) nor (b)
Ans: b
9. A good control system has all the following
features except
(a) good stability
(b) slow response
(c) good accuracy
(d) sufficient power handling capacity
Ans: b
10. A car is rtyining at a constant speed of 50
km/h, which of the following is the feedback
element for the driver ?
(a) Clutch
(b) Eyes
(c) Needle of the speedometer
(d) Steering wheel
(e) None of the above
Ans: c
11. The initial response when tne output is not
equal to input is called
(a) Transient response
(b) Error response
(c) Dynamic response
(d) Either of the above
Ans: a
12. A control system working under unknown
random actions is called
(a) computer control system
(b) digital data system
(c) stochastic control system
(d) adaptive control system
Ans: c
13. An automatic toaster is a ______ loop
control system.
(a) open
(b) closed
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(c) partially closed
(d) any of the above
Ans: a
14. Any externally introduced signal affecting
the controlled output is called a
(a) feedback
(b) stimulus
(c) signal
(d) gain control
Ans: b
15. A closed loop system is distinguished from
open loop system by which of the following ?
(a) Servomechanism
(b) Feedback
(c) Output pattern
(d) Input pattern
Ans: b
16 is a part of the human temperature control
system.
(a) Digestive system
(b) Perspiration system
(c) Ear
(d) Leg movement
Ans: b
17. By which of the following the control
action is determined when a man walks along a
path ?
(a) Brain
(b) Hands
(c) Legs
(d) Eyes
Ans: d
18 is a closed loop system.
(a) Auto-pilot for an aircraft
(6) Direct current generator
(c) Car starter
(d) Electric switch
Ans: a
19. Which of the following devices are
commonly used as error detectors in
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instruments ?
(a) Vernistats
(b) Microsyns
(c) Resolvers
(d) Any of the above
Ans: d
20. Which of the following should be done to
make an unstable system stable ?
(a) The gain of the system should be
decreased
(b) The gain of the system should be
increased
(c) The number of poles to the loop transfer
function should be increased
(d) The number of zeros to the loop transfer
function should be increased
Ans: b
21 increases the steady state accuracy.
(a) Integrator
(b) Differentiator
(c) Phase lead compensator
(d) Phase lag compensator
Ans: a
22. A.C. servomotor resembles
(a) two phase induction motor
(b) Three phase induction motor
(c) direct current series motor
(d) universal motor
Ans: a
23. As a result of introduction of negative
feedback which of the following will not
decrease ?
(a) Band width
(b) Overall gain
(c) Distortion
(d) Instability
Ans: a
24. Regenerative feedback implies feedback
with
(a) oscillations
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(b) step input
(c) negative sign
(d) positive sign
Ans: d
25. The output of a feedback control system
must be a function of
(a) reference and output
(b) reference and input
(e) input and feedback signal
(d) output and feedback signal
Ans: a
26 is an open loop control system.
(a) Ward Leonard control
(b) Field controlled D.C. motor
(c) Stroboscope
(d) Metadyne
Ans: b
27. A control system with excessive noise, is
likely to suffer from
(a) saturation in amplifying stages
(b) loss of gain
(c) vibrations
(d) oscillations
Ans: a
28. Zero initial condition for a system means
(a) input reference signal is zero
(b) zero stored energy
(c) ne initial movement of moving parts
(d) system is at rest and no energy is stored in
any of its components
Ans: d
29. Transfer function of a system is used to
calculate which of the following ?
(a) The order of the system
(b) The time constant
(c) The output for any given input
(d) The steady state gain
Ans: c
30. The band width, in a feedback amplifier.
(a) remains unaffected
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(b) decreases by the same amount as the gain
increase
(c) increases by the sane saaaajajt as the gain
decrease
(d) decreases by the same amount as the gain
decrease
Ans: c
31. On which of the following factors does the
sensitivity of a closed loop system to gain
changes and load disturbances depend ?
(a) Frequency
(b) Loop gain
(c) Forward gain
(d) All of the above
Ans: d
32. The transient response, with feedback
system,
(a) rises slowly
(b) rises quickly
(c) decays slowly
(d) decays quickly
Ans: d
33. The second derivative input signals modify
which of the following ?
(a) The time constant of the system
(b) Damping of the system
(c) The gain of the system
(d) The time constant and suppress the
oscillations
(e) None of the above
Ans: d
34. Which of the following statements is
correct for any closed loop system ?
(a) All the co-efficients can have zero value
(6) All the co-efficients are always non-zero
(c) Only one of the static error co-efficients has
a finite non-zero value
(d) None of the above
Ans: c
35. Which of the following statements is
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correct for a system with gain margin close to
unity or a phase margin close to zero ?
(a) The system is relatively stable
(b) The system is highly stable
(c) The system is highly oscillatory
(d) None of the above
Ans: c
36. Due to which of the following reasons
excessive bond width in control systems should
be avoided ?
(a) It leads to slow speed of response
(b) It leads to low relative stability
(c) Noise is proportional to band width
(d) None of the above
Ans: c
37. In a stable control system backlash can
cause which of the following ?
(a) Underdamping
(b) Overdamping
(c) Poor stability at reduced values of open
loop gain
(d) Low-level oscillations
Ans: d
38. In an automatic control system which of
the following elements is not used ?
(a) Error detector
(b) Final control element
(c) Sensor
(d) Oscillator
Ans: d
39. In a control system the output of the
controller is given to
(a) final control element
(b) amplifier
(c) comparator
(d) sensor
(e) none of the above
Ans: a
40. A controller, essentially, is a
(a) sensor
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(b) clipper
(c) comparator
(d) amplifier
Ans: c
41. Which of the following is the input to a
controller ?
(a) Servo signal
(b) Desired variable value
(c) Error signal
(d) Sensed signal
Ans:
42. The on-off controller is a _____ system.
(a) digital
(b) linear
(c) non-linear
(d) discontinuous
Ans:
43. The capacitance, in force-current analogy,
is analogous to
(a) momentum
(b) velocity
(c) displacement
(d) mass
Ans: d
44. The temperature, under thermal and
electrical system analogy, is considered
analogous to
(a) voltage
(b) current
(c) capacitance
(d) charge
(e) none of the above
Ans: a
45. In electrical-pneumatic system analogy the
current is considered analogous to
(a) velocity
(b) pressure
(c) air flow
(d) air flow rate
Ans: d
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46. In liquid level and electrical system
analogy, voltage is considered analogous to
(a) head
(b) liquid flow
(c) liquid flow rate
(d) none of the above
Ans: a
47. The viscous friction co-efficient, in forcevoltage analogy, is analogous to
(a) charge
(b) resistance
(c) reciprocal of inductance
(d) reciprocal of conductance
(e) none of the above
Ans: b
48. In force-voltage analogy, velocity is
analogous to
(a) current
(b) charge
(c) inductance
(d) capacitance
Ans: a
49. In thermal-electrical analogy charge is
considered analogous to
(a) heat flow
(b) reciprocal of heat flow
(c) reciprocal of temperature
(d) temperature
(e) none of the above
Ans: d
50. Mass, in force-voltage analogy, is
analogous to
(a) charge
(b) current
(c) inductance
(d) resistance
Ans: c
51. The transient response of a system is
mainly due to
(a) inertia forces
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(b) internal forces
(c) stored energy
(d) friction
Ans: c
52 signal will become zero when the feedback
signal and reference signs are equal.
(a) Input
(b) Actuating
(c) Feedback
(d) Reference
Ans: b
53. A signal other than the reference input
that tends to affect the value of controlled
variable is known as
(a) disturbance
(b) command
(c) control element
(d) reference input
Ans: a
54. The transfer function is applicable to
which of the following ?
(a) Linear and time-in variant systems
(b) Linear and time-variant systems
(c) Linear systems
(d) Non-linear systems
(e) None of the above
Ans: a
55. From which of the following transfer
function can be obtained ?
(a) Signal flow graph
(b) Analogous table
(c) Output-input ratio
(d) Standard block system
(e) None of the above
Ans: a
56 is the reference input minus the primary
feedback.
(a) Manipulated variable
(b) Zero sequence
(c) Actuating signal
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(d) Primary feedback
Ans: c
57. The term backlash is associated with
(a) servomotors
(b) induction relays
(c) gear trains
(d) any of the above
Ans:
58. With feedback _____ increases.
(a) system stability
(b) sensitivity
(c) gain
(d) effects of disturbing signals
Ans: a
59. By which of the following the system
response can be tested better ?
(a) Ramp input signal
(b) Sinusoidal input signal
(c) Unit impulse input signal
(d) Exponentially decaying signal
Ans: c
60. In a system zero initial condition means
that
(a) The system is at rest and no energy is
stored in any of its components
(b) The system is working with zero stored
energy
(c) The system is working with zero reference
signal
Ans: a
61. In a system low friction co-efficient
facilitates
(a) reduced velocity lag error
(b) increased velocity lag error
(c) increased speed of response
(d) reduced time constant of the system
Ans: a
62. Hydraulic torque transmission system is
analog of
(a) amplidyne set
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(b) resistance-capacitance parallel circuit
(c) motor-generator set
(d) any of the above
Ans:
63. Spring constant in force-voltage analogy is
analogous to
(a) capacitance
(b) reciprocal of capacitance
(c) current
(d) resistance
Ans: b
64. The frequency and time domain are
related through which of the following?
(a) Laplace Transform and Fourier Integral
(b) Laplace Transform
(c) Fourier Integral
(d) Either (b) or (c)
Ans: a
65. An increase in gain, in most systems, leads
to
(a) smaller damping ratio
(b) larger damping ratio
(c) constant damping ratio
(d) none of the above
Ans: a
66. Static error co-efficients are used as a
measure of the effectiveness of closed loop
systems for specified ________ input signal.
(a) acceleration
(b) velocity
(c) position
(d) all of the above
Ans: d
67. A conditionally stable system exhibits poor
stability at
(a) low frequencies
(b) reduced values of open loop gain
(c) increased values of open loop gain
(d) none of the above
Ans: b
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68. The type 0 system has ______ at the
origin.
(a) no pole
(b) net pole
(c) simple pole
(d) two poles
(e) none of the above
Ans: a
69. The type 1 system has ______ at the
origin.
(a) no pole
(b) net pole
(c) simple pole
(d) two poles
Ans: c
70. The type 2 system has at the origin.
(a) no net pole
(b) net pole
(c) simple pole
(d) two poles
Ans: d
71. The position and velocity errors of a type-2
system are
(a) constant, constant
(b) constant, infinity
(c) zero, constant
(d) zero, zero
Ans: c
72. Velocity error constant of a system is
measured when the input to the system is unit
_______ function.
(a) parabolic
(b) ramp
(c) impulse
(d) step
Ans: b
73. In case of type-1 system steady state
acceleration is
(a) unity
(b) infinity
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(c) zero
(d) 10
Ans: b
74. If a step function is applied to the input of
a system and the output remains below a
certain level for all the time, the system is
(a) not necessarily stable
(b) stable
(c) unstable
(d) always unstable
(e) any of the above
Ans: a
75. Which of the following is the best method
for determining the stability and transient
response ?
(a) Root locus
(b) Bode plot
(c) Nyquist plot
(d) None of the above
Ans: a
76. Phase margin of a system is used to
specify which of the following ?
(a) Frequency response
(b) Absolute stability
(c) Relative stability
(d) Time response
Ans: c
77. Addition of zeros in transfer function
causes which of the following ?
(a) Lead-compensation
(b) Lag-compensation
(c) Lead-lag compensation
(d) None of the above
Ans: b
78. technique is not applicable to nonlinear
system ?
(a) Nyquist Criterion
(b) Quasi linearization
(c) Functional analysis
(d) Phase-plane representation
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Ans: a
79. In order to increase the damping of a
badly underdamped system which of following
compensators may be used ?
(a) Phase-lead
(b) Phase-lag
(c) Both (a) and (b)
(d) Either (a) and (b)
(e) None of the above
Ans: a
80. The phase lag produced by transportation
relays
(a) is independent of frequency
(b) is inverseh'proportional to frequency
(c) increases linearly with frequency
(d) decreases linearly with frequency
Ans: c
81. In a stable control system saturation can
cause which of the following ?
(a) Low-level oscillations
(b) High-level oscillations
(c) Conditional stability
(d) Overdamping
Ans: a
82. Which of the following can be measured
by the use of a tacho-generator ?
(a) Acceleration
(b) Speed
(c) Speed and acceleration
(d) Displacement
(e) None of the above
Ans: b
83 is not a final control element.
(a) Control valve
(b) Potentiometer
(c) Electro-pneumatic converter
(d) Servomotor
Ans: b
84. Which of the following is the definition of
proportional band of a controller ?
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(a) The range of air output as measured
variable varies from maximum to minimum
(b) The range of measured variables from set
value
(c) The range of measured variables through
which the air output chan¬ges from maximum
to minimum
(d) Any of the above
(e) None of the above
Ans: c
85. In pneumatic control systems the control
valve used as final control element converts
(a) pressure signal to electric signal
(b) pressure signal to position change
(c) electric signal to pressure signal
(d) position change to pressure signal
(e) none of the above
Ans: b
86. Pressure error can be measured by which
of the following ?
(a) Differential bellows and straingauge
(b) Selsyn
(c) Strain gauge
(d) Strain gauge and potentiometer
Ans: a
87. Which of the following devices is used for
conversion of co-ordinates ?
(a) Microsyn
(b) Selsyn
(c) Synchro-resolver
(d) Synchro-transformer
Ans: c
88. The effect of error damping is to
(a) provide larger settling lime
(b) delay the response
(c) reduce steady state error
(d) any of the above
(e) none of the above
Ans: c
89 technique gives quick transient and
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stability response
(a) Root locus
(b) Bode
(c) Nyquist
(d) Nichols
Ans: a
90. A phase lag lead network introduces in the
output
(a) lag at all frequencies
(b) lag at high frequencies and lead at low
frequencies
(c) lag at low frequencies and lead at high
frequencies
(d) none of the above
Ans: c
91. Which of the following is the non-linearity
caused by servomotor ?
(a) Static friction
(b) Backlash
(c) Saturation
(d) None of the above
Ans: c
92 can be extended to systems which are
time-varying ?
(a) Bode-Nyquist stability methods
(b) Transfer functions
(c) Root locus design
(d) State model representatives
Ans: d
93. When the initial conditions of a system are
specified to be zero it implies that the system is
(a) at rest without any energy stored in it
(b) working normally with reference input
(c) working normally with zero reference input
(d) at rest but stores energy
Ans: d
94. Which of the following is an
electromechanical device ?
(a) Induction relay
(b) Thermocouple
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(c) LVDT
(d) Any of the above
(e) None of the above
Ans: c
95. A differentiator is usually not a part of a
control system because it
(a) reduces damping
(b) reduces the gain margin
(c) increases input noise
(d) increases error
Ans: c
96. If the gain of the critical damped system is
increased it will behave as
(a) oscillatory
(b) critically damped
(c) overdamped
(d) underdamped
(e) none of the above
Ans: d
97. In a control system integral error
compensation _______ steady state error
(a) increases
(b) minimizes
(c) does not have any effect on
(d) any of the above
Ans: b
98. With feed back _____ reduces.
(a) system stability
(6) system gain
(c) system stability and gain
(d) none of the above
Ans: b
99. An amplidyne can give which of the
following characteristics ?
(a) Constant current
(b) Constant voltage
(c) Constant current as well as constant
voltage
(d) Constant current, constant voltage and
constant power
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(e) None of the above
Ans: d
100. Which of the following can be measured
byLVDT?
(a) Displacement
(b) Velocity
(c) Acceleration
(d) Any of the above
Ans: d
101 directly converts temperature into
voltage.
(a) Thermocouple
(b) Potentiometer
(c) Gear train
(d) LVDT
(e) None of the above
Ans: a
102. The transfer function technique is
considered as inadequate under which of the
following conditions ? (a) Systems having
complexities and non-linearities
(b) Systems having stability problems
(c) Systems having multiple input
dis¬turbances
(d) All of the above
Ans: d
103. Which of the following is the output of a
thermocouple ?
(a) Alternating current
(b) Direct current
(c) A.C. voltage
(d) D.C. voltage
(e) None of the above
Ans: d
104. A.C. servomotor is basically a
(a) universal motor
(b) single phase induction motor
(c) two phase induction motor
(d) three phase induction motor
Ans: c
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105. The first order control system, which is
well designed, has a
(a) small bandwidth
(b) negative time constant
(c) large negative transfer function pole
(d) none of the above
Ans: c
106. Which of the following is exhibited by
Root locus diagrams ?
(a) The poles of the transfer function for a set
of parameter values
(b) The bandwidth of the system
(c) The response of a system to a step input
(d) The frequency response of a system
(e) None of the above
Ans: a
Industrial Drives
1. The selection of an electric motor for any
application depends on which of the following
factors ?
(a) Electrical characteristics
(b) Mechanical characteristics
(c) Size and rating of motors
(d) Cost
(e) All of the above
Ans: e
2. For a particular application the type of
electric-and control gear are determined by
which of the following considerations ?
(a) Starting torque
(b) Conditions of environment
(c) Limitation on starting current
(d) Speed control range and its nature
(e) All of the above
Ans: e
3. Which ofthefollowingmotors is preferred
for traction work ?
(a) Universal motor
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(b) D.C. series motor
(c) Synchronous motor
(d) Three-phase induction motor
Ans:
4 Which of the following motors always starts
on load ?
(a) Conveyor motor
(b) Floor mill motor
(c) Fan motor
(d) All of the above
Ans: d
5 is preferred for automatic drives.
(a) Squirrel cage induction motor
(b) Synchronous motors
(c) Ward-Leonard controlled D.C. motors
(d) Any of the above
Ans: c
6. When the load is above _____ a synchronous
motor is found to be more economical.
(a) 2 kW
(b) 20 kW
(c) 50 kW
(d) 100 kW
Ans: d
7. The load cycle for a motor driving a power
press will be
(a) variable load
(b) continuous
(c) continuous but periodical
(d) intermittent and variable load
Ans: d
8. Light duty cranes are used in which of the
following ?
(a) Power houses
(b) Pumping stations
(c) Automobile workshops
(d) All of the above
Ans: d
9. While selecting an electric motor for a floor
mill, which electrical characteristics will be of
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least significance ?
(a) Running characteristics
(b) Starting characteristics
(c) Efficiency
(d) Braking
Ans: d
10. Which of the following motors are preferred for overhead travelling cranes ?
(a) Slow speed motors
(b) Continuous duty motors
(c) Short time rated motors
(d) None of the above
Ans: c
11 is preferred for synthetic fibre mills.
(a) Synchronous motor
(b) Reluctance motor
(c) Series motor
(d) Shunt motor
Ans: b
12. Ward-Leonard controlled D.C. drives are
generally used for ______ excavators.
(a) Light duty
(b) Medium duty
(c) Heavy duty
(d) All of the above
Ans: c
13. Which of the following motors is used for
elevators ?
(a) Induction motor
(b) Synchronous motor
(c) Capacitor start single phase motor
(d) Any of the above
Ans: a
14. Which part of a motor needs maximum
attention for maintenance ?
(a) Frame
(b) Rearing
(c) Stator winding
(d) Rotor winding
Ans: b
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15 need frequent starting and stopping of
electric motors,
(a) Paper mills
(b) Grinding mills
(c) Air-conditioners
(d) Lifts and hoists
Ans: d
16. Which feature, while selecting a.motor for
centrifugal pump, will be of least significance ?
(a) Starting characteristics
(b) Operating speed
(c) Horse power
(d) Speed control
Ans: d
17. _______ motor is a constant speed motor.
(a) Synchronous motor
(b) Schrage motor
(c) Induction motor
(d) Universal motor
Ans: a
18. The starting torque in case of centrifugal
pumps is generally
(a) less than running torque
(b) same as running torque
(c) slightly more than running torque
(d) double the running torque
Ans: a
19. Which of the following motors are best for
the rolling mills ?
(a) Single phase motors
(b) Squirrel cage induction motors
(c) Slip ring induction motors
(d) D.C. motors
Ans: d
20 is not a part of ball bearing ?
(a) Inner race
(b) Outer race
(c) Cage
(d) Bush
Ans: d
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21. The starting torque of a D.C. motor is
independent of which of the following?
(a) Flux
(b) Armature current
(c) Flux and armature current
(d) Speed
Ans: d
22. Rotor of a motor is usually supported on
_______ bearings.
(a) ball or roller
(b) needle
(c) bush
(d) thrust
Ans: a
23. For which of the following applications
D.C. motors are still preferred ?
(a) High efficiency operation
(b) Reversibility
(c) Variable speed drive
(d) High starting torque
Ans: c
24. In a paper mill where constant speed is
required
(a) synchronous motors are preferred
(b) A.C. motors are preferred
(c) individual drive is preferred
(d) group drive is preferred
Ans: c
25. A reluctance motor
(a) is provided with slip rings
(b) requires starting gear
(c) has high cost
(d) is compact
Ans: d
26. The size of an excavator is usually
expressed in terms of
(a) 'crowd' motion
(b) angle of swing
(c) cubic metres
(d) travel in metres
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Ans: c
27. For blowers which of the following motor
is preferred ?
(a) D.C. series motor
(b) D.C. shunt motor
(c) Squirrel cage induction motor
(d) Wound rotor induction motor
Ans: b
28. Belted slip ring induction motor is almost
invariably used for
(a) water pumps
(b) jaw crushers
(c) centrifugal blowers
(d) none of the above
Ans: b
29. Which of the following is essentially
needed while selecting a motor ?
(a) Pulley
(b) Starter
(c) Foundation pedal
(d) Bearings
Ans: b
30. Reluctance motor is a
(a) variable torque motor
(b) low torque variable speed motor
(c) self starting type synchronous motor
(d) low noise, slow speed motor
Ans: c
31 method of starting a three phase induction
motor needs six terminals.
(a) Star-delta
(b) Resistance starting
(c) Auto-transformer
(d) None of the above
Ans: a
32. In ______ method of staging three phase
induction motors the starting voltage is not
reduced.
(a) auto-transformer
(b) star-delta
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(c) slip ring
(d) any of the above
Ans: c
33. In jaw crushers a motor has to often start
against ______ load.
(a) heavy
(b) medium
(c) normal
(d) low
Ans: a
34. For a motor-generator set which of the
following motors will be preferred ?
(a) Synchronous motor
(b) Slip ring induction motor
(c) Pole changing induction motor
(d) Squirrel cage induction motor
Ans: a
35. Which of the following motors is usually
preferred for kiln drives ?
(a) Cascade controlled A.C. motor
(b) Slip ring induction motor
(c) Three phase shunt wound com-mutator
motor
(d) Any of the above
Ans: d
36. Heat control switches are used in
(a) transformers
(b) cooling ranges
(c) three phase induction motors
(d) single phase
Ans: b
37 has relatively wider range of speed control.
(a) Synchronous motor
(6) Ship ring induction motor
(c) Squirrel cage induction motor
(d) D.C. shunt motor
Ans: d
38. In squirrel cage induction motors which of
the following methods of starting cannot be
used ?
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(a) Resistance in rotor circuit
(b) Resistance in stator circuit
(c) Auto-transformer starting
(d) Star-delta starting
Ans: a
39. In which of the following applications the
load on motor changes in cyclic order ?
(a) Electric shovels
(b) Cranes
(c) Rolling mills
(d) All of the above
Ans: d
40. Flame proof motors are used in
(a) paper mills
(b) steel mills
(c) moist atmospheres
(d) explosive atmospheres
Ans: d
41. Which of the following machines has
heavy fluctuation of load ?
(a) Printing machine
(b) Punching machine
(c) Planer
(d) Lathe
Ans: b
42. For derries and winches which of the
following drives can be used ?
(a) Pole changing squirrel cage motors
(b) D.C. motors with Ward-leonard con-trol
(c) A.C. slip ring motors with variable
resistance
(d) Any of the above
Ans: d
43. Battery operated scooter for braking uses
(a) plugging
(b) mechanical braking
(c) regenerative braking
(d) rheostatic braking
Ans: b
44 has least range of speed control.
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(a) Slip ring induction motor
(b) Synchronous motor
(c) D.C. shunt motor
(d) Schrage motor
Ans: b
45 has the least value of starting torque to full
load torque ratio.
(a) D.C. shunt motor
(b) D.C. series motor
(c) Squirrel cage induction motor
(d) Slip ring induction motor
Ans: c
46. In case of _______ speed control by
injecting e.m.f. in the rotor circuit is possible,
(a) d.c. shunt motor
(b) schrage motor
(c) synchronous motor
(d) slip ring induction motor
Ans: d
47. A pony motor is used for the starting
which of the following motors ?
(a) Squirel cage induction motor
(b) Schrage motor
(c) Synchronous motor
(d) None of the above
Ans: c
48. In ________ the speed can be varied by
changing the position of brushes.
(a) slip ring motor
(b) schrage motor
(c) induction motor
(d) repulsion motor
Ans: b
49. In which of the following applications
variable speed operation is preferred ?
(a) Exhaust fan
(b) Ceiling fan
(c) Refrigerator
(d) Water pump
Ans: b
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50. Heavy duty cranes are used in
(a) ore handling plants
(b) steel plants
(c) heavy engineering workshops
(d) all of the above
Ans: d
51. The travelling speed of cranes varies from
(a) 20 to 30 m/s
(b) 10 to 15 m/s
(c) 5 to 10 m/s
(d) 1 to 2.5 m/s
Ans: d
52. Besides a constant speed a synchronous
rotor possesses which of the following
advantages ?
(a) Lower cost
(b) Better efficiency
(c) High power factor
(d) All of the above
Ans: c
53. By the use of which of the followingm
D.C. can be obtained from AC. ?
(a) Silicon diodes
(b) Mercury arc rectifier
(c) Motor generator set
(d) Any of the above
Ans: d
54. Which of the following motors is preferred
when quick speed reversal is the main
consideration ?
(a) Squirrel cage induction motor
(b) Wound rotor induction motor
(e) Synchronous motor
(d) D.C. motor
Ans: d
55. Which ofthefollowing motors is preferred
when smooth and precise speed control over a
wide range is desired ?
(a) D.C. motor
(b) Squirrel cage induction motor
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(c) Wound rotor induction motor
(d) Synchronous motor
Ans: a
56. For crane travel which of the following
motors is normally used ?
(a) Synchronous motor
(b) D.C. differentially compound motor
(c) Ward-Leonard controlled D.C. shunt motor
(d) AC. slip ring motor
Ans: d
57. The capacity of a crane is expressed in
terms of
(a) type of drive
(b) span
(c) tonnes
(d) any of the above
Ans: c
58. The characteristics of drive for crane
hoisting and lowering are which of the following
?
(a) Precise control
(b) Smooth movement
(c) Fast speed control
(d) All of the above
Ans: d
59. Which of the following motors is preferred
for boom hoist of a travelling crane ?
(a) Single phase motor
(b) Synchronous motor
(c) A.C. slip ring motor
(d) Ward-Leonard controlled D.C. shunt motor
Ans: c
60. A wound rotor induction motor is
preferred, as compared to squirrel cage
induction motor, when major consideration is
(a) slop speed operation
(b) high starting torque
(c) low windage losses
(d) all of the above
Ans: b
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61. Which of the following motors has series
characteristics ?
(a) Shaded pole motor
(b) Repulsion motor
(c) Capacitor start motor
(d) None of the above
Ans: b
62. Which of the following happens when
star-delta starter is used ?
(a) Starting voltage is reduced
(b) Starting current is reduced
(c) Both (a) and (b)
(d) None of the above
Ans: c
63. For a D.C. shunt motor which of the
following is incorrect 7
(a) Unsuitable for heavy duty starting
(b) Torque varies as armature current
(c) Torque-armature current is a straight line
(d) Torque is zero for zero armature current
Ans: a
64. For which of the following applications
motor has to start with high acceleration?
(a) Oil expeller
(b) Floor mill
(c) Lifts and hoists
(d) Centrifugal pump
Ans: c
65. Which of the following types of motor
enclosure is safest ?
(a) Totally enclosed
(b) Totally enclosed fan cooled
(c) Open type
(d) Semi closed
Ans: b
66. While selecting motor for an air
conditioner which of the following
characteristics is of great importance ?
(a) Type of bearings
(b) Type of enclosure
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(c) Noise
(d) Arrangement for power transmis¬sion
(e) None of the above
Ans: c
67. The diameter of the rotor shaft for an
electric motor depends on which of the
following ?
(a) r.p.m. only
(b) Horse power only
(c) Horse power and r.p.m.
(d) Horse power, r.p.m. and power factor
Ans: c
68. Which of the following alternatives will be
cheaper ?
(a) A 100 H.P. AC. three phase motor
(b) Four motors of 25 H.P. each
(c) Five motors of 20 H.P. each
(d) Ten motors of 10 H.P. each
Ans: a
69. The cost of an induction motor will
increase as
(a) horsepower rating increases but r.p.m.
decreases
(b) horsepower rating decreases but r.p.m.
increases
(c) horsepower rating and operating speed
increases
(d) horsepower rating and operating speed
decreases
Ans: a
70. In series motor which of the following
methods can be used for changing the flux per
pole ?
(a) Tapped field control
(b) Diverter field control
(c) Series-parallel control
(d) Any of the above
Ans: d
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Electric Traction
1. Which of the following is an advantage of
electric traction over other methods of traction
?
(a) Faster acceleration
(b) No pollution problems
(c) Better braking action
(d) All of the above
Ans: a
2. Which of the following is the voltage for
single phase A.C. system ?
(a) 22 V
(b) 440 V
(c) 5 kV
(d) 15 kV
(e) None of the above
Ans: a
3. Long distance railways use which of the
following ?
(a) 200 V D.C.
(b) 25 kV single phase A.C. 10.
(c) 25 kV two phase A.C.
(d) 25 kV three phase A.C.
Ans: b
4. The speed of a locomotive is controlled by
(a) flywheel
(b) gear box
(c) applying brakes 11.
(d) regulating steam flow to engine
Ans: b
5. Main traction systems used in India are,
those using
(a) electric locomotives
(b) diesel engine locomotives
(c) steam engine locomotives
(d) diesel electric locomotives
(e) all of the above
Ans: e
6, in India diesel locomotives are
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manu¬factured at
(a) Ajmer
(b) Varanasi
(c) Bangalore
(d) Jamalpur
Ans: b
7. For diesel locomotives the range of
horsepower is
(a) 50 to 200
(b) 500 to 1000
(c) 1500 to 2500
(d) 3000 to 5000
Ans: c
8. _______ locomotive has the highest
operational availability.
(a) Electric
(b) Diesel
(c) Steam
Ans: a
9. The horsepower of steam locomotives is
(a) upto 1500
(b) 1500 to 2000
(c) 2000 to 3000
(d) 3000 to 4000
Ans: a
10. The overall efficiency of steam locomo¬tive
is around
(a) 5 to 10 percent
(b) 15 to 20 percent
(c) 25 to 35 percent
(d) 35 to 45 percent
Ans: a
11. In tramways which of the following motors
is used ?
(a) D.C. shunt motor
(b) D.C. series motor
(c) A.C. three phase motor
(d) AC. single phase capacitor start motor
Ans: b
12. In a steam locomotive electric power is
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provided through
(a) overhead wire
(b) battery system
(c) small turbo-generator
(d) diesel engine generator
Ans: c
13. Which of the following drives is suitable
for mines where explosive gas exists ?
(a) Steam engine
(b) Diesel engine
(c) Battery locomotive
(d) Any of the above
Ans: c
14. In case of locomotives the tractive power
is provided by
(a) single cylinder double acting steam engine
(b) double cylinder, single acting steam
engine
(c) double cylinder, double acting steam
engine
(d) single stage steam turbine
Ans: c
15. Overload capacity of diesel engines is
usually restricted to
(a) 2 percent
(b) 10 percent
(c) 20 percent
(d) 40 percent
Ans: a
16. In case of steam engines the steam
pressure is
(a) 1 to 4 kgf/cm2
(b) 5 to 8 kgf/cm2
(c) 10 to 15 kgf/cm2
(d) 25 to 35 kgf/cm2
Ans: c
17.. The steam engine provided on steam
locomotives is
(a) single acting condensing type
(b) single acting non-condensing type
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(e) double acting condensing type
(d) double acting non-condensing type
Ans: b
18. Electric locomotives in India are
manufactured at
(a) Jamalpur
(b) Bangalore
(c) Chittranjan
(d) Gorakhpur
Ans: c
19. The wheels of a train, engine as well as
bogies, are slightly tapered to
(a) reduce frietion
(b) increase friction
(c) facilitate braking
(d) facilitate in taking turns
Ans: d
20. Automatic signalling is used for which of
the following trains ?
(a) Mail and express trains
(b) Superfast trains
(c) Suburban and Urban electric trains
(d) All trains
Ans: b
21. The efficiency of diesel locomotives is
nearly
(a) 20 to 25 percent
(b) 30 to 40 percent
(c) 45 to 55 percent
(d) 60 to 70 percent
Ans: a
22. The speed of a superfast train is
(a) 60 kmph
(b) 75 kmph
(c) 100 kmph
(d) more than 100 kmph
Ans: d
23. The number of passanger coaches that can
be attached to a diesel engine locomotive on
broad gauge is usually restricted to
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(a) 5
(b) 10
(c) 14
(d) 17
Ans: b
24. Which of the following state capitals is not
on broad gauge track ?
(a) Lucknow
(b) Bhopal
(c) Jaipur
(d) Chandigarh
Ans: c
25. Which of the following is the advantage of
electric braking ?
(a) It avoids wear of track
(b) Motor continues to remain loaded during
braking
(c) It is instantaneous
(d) More heat is generated during braking
Ans: a
24. Which of the following braking systems on
the locomotives is costly ?
(a) Regenerative braking on electric
locomotives
(b) Vacuum braking on diesel locomo-tives
(c) Vacuum braking on steam locomo-tives
(d) All braking systems are equally costly
Ans: a
27. Tractive effort is required to
(a) overcome the gravity component of train
mass
(b) overcome friction, windage and curve
resistance
(c) accelerate the train mass
(d) do all of the above
Ans: d
28. For given maximum axle load tractive
efforts of AC. locomotive will be
(a) less than that of D.C. locomotive
(b) more than that of D.C. locomotive
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(c) equal to that of D.C. locomotive
(d) none of the above
Ans: b
29. Co-efficient of adhesion reduces due to
the presence of which of the following ?
(a) Sand on rails
(b) Dew on rails
(c) Oil on the rails
(d) both (b) and (c)
Ans: d
30. Due to which of the following co-efficient
of adhesion improves ?
(a) Rust on the rails
(b) Dust on the rails
(c) Sand on the rails
(d) All of the above
Ans: d
31. Quadrilateral speed-time curve pertains to
which of the following services ?
(a) Main line service
(b) Urban service
(c) Sub-urban service
(d) Urban and sub-urban service
Ans: d
32. Which of the following is the disadvantage
of electric traction over other systems of
traction ?
(a) Corrosion problems in the under-ground
pipe work
(b) Short time power failure interrupts traffic
for hours
(c) High capital outlay in fixed instal-lations
beside route limitation
(d) Interference with communication lines
(c) All of the above
Ans: c
33. Co-efficient of adhesion is
(a) high in case of D.C. traction than in the
case of AC. traction
(b) low in case of D.C. traction than in the
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case of AC. traction
(c) equal in both AC. and D.C. traction
(d) any of the above
Ans: b
34. Speed-time curve of main line service
differs from those of urban and suburban
services on following account
(a) it has longer free running period
(b) it has longer coasting period
(c) accelerating and braking periods are
comparatively smaller
(d) all of the above
Ans: d
35. The rate of acceleration on suburban
orurban services is restricted by the
consideration of
(a) Engine power
(b) Track curves
(c) Passenger Discomfort
(d) Track size
Ans: c
36. The specific energy consumption of a train
depends on which of the following ?
(a) Acceleration and retardation
(b) Gradient
(c) Distance covered
(d) All of the above
Ans: d
37. The friction at the track is proportional to
(a) 1/speed
(b) l/(speed)2
(c) speed
(d) none of the above
Ans: c
38. The air resistance to the movement of the
train is proportional to
(a) speed
(b) (speed)
(c) (speed)
(d) 1/speed
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Ans: b
39. The normal value of adhesion friction is
(a) 0.12
(b) 0.25
(c) 0.40
(d) 0.75
Ans: b
40. The pulsating torque exerted by steam
locomotives causes which of the following?
(a) Jolting and skidding
(b) Hammer blow
(c) Pitching
(d) All of the above
Ans: a
41. Which of the following braking systems is
used on steam locomotives ?
(a) Hydraulic system
(b) Pneumatic system
(c) Vacuum system
(d) None of the above
Ans: c
42. Vacuum is created by which of the
following?
(a) Vacuum pump
(b) Ejector
(c) Any of the above
(d) None of the above
Ans: c
43. The resistance encountered by a trainin
motion is on account of
(a) resistance offered by air
(b) friction at the track
(c) friction at various parts of the rolling stock
(d) all of the above
Ans: d
44. Battery operated trucks are used in
(a) steel mills
(b) power stations
(c) narrow gauge traction
(d) factories for material transportation
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Ans: d
45 method can bring the locomotive to dead
stop.
(a) Plugging braking
(b) Rheostatic braking
(c) Regenerative braking
(d) None of the above
Ans: a
46. The value of co-efficient of adhesion will
be high when rails are
(a) greased
(b) wet
(c) sprayed with oil
(d) cleaned with sand
Ans: d
47. The voltage used for suburban trains in
D.C. system is usually
(a) 12 V
(b) 24 V
(c) 220 V
(d) 600 to 750 V
Ans: d
48. For three-phase induction motors which of
the following is the least efficient method of
speed control ?
(a) Cascade control
(b) Pole changing
(c) Rheostatic control
(d) Combination of cascade and pole changing
Ans: c
49. Specific energy consumption becomes
(a) more on steeper gradient
(b) more with high train resistance
(c) less if distance between stops is more
(d) all of the above
Ans: d
50. In main line service as compared to urban
and suburban service
(a) distance between the stops is more
(b) maximum speed reached is high
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(c) acceleration and retardation rates are low
(d) all of the above
Ans: d
51. Locomotive having monomotor bogies
(a) has better coefficient of adhesion
(b) are suited both for passanger as well as
freight service
(c) has better riding qualities due to the
reduction of lateral forces
(d) has all above qualities
Ans: d
52. Series motor is not suited for traction duty
due to which of the following account ?
(a)
Less current drain on the heavy load
torque
(b) Current surges after temporary switching
off supply
(c) Self relieving property
(d) Commutating property at heavy load
Ans: b
53. When a bogie negotiates a curve,
reduction in adhesion occurs resulting in
sliding. Thus sliding is acute when
(a) wheel base of axles is more
(b) degree of curvature is more
(c) both (a) and (b)
(d) none of the above
Ans: c
54. Energy consumption in propelling the train
is required for which of the following?
(a) Work against the resistance to motion
(b) Work against gravity while moving up the
gradient
(c) Acceleration
(d) All of the above
Ans: d
55. An ideal traction system should have
(a) easy speed control
(b) high starting tractive effort
(c) equipment capable of with standing large
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temporary loads
(d) all of the above
Ans: d
56 have maximum unbalanced forces
(a) Diesel shunters
(b) Steam locomotives
(c) Electric locomotives
(d) Diesel locomotives
Ans: b
57. Specific energy consumption is affected by
which of the following factors ?
(a) Retardation and acceleration values
(b) Gradient
(c) Distance between stops
(d) All of the above
Ans: d
58. In case of ________ free running and
coasting periods are generally long.
(a) main-line service
(b) urban service
(c) sub-urban service
(d) all of the above
Ans: a
59. Overhead lines for power supply to
tramcars are at a minimum height of
(a) 3 m
(b) 6 m
(c) 10 m
(d) tO m
Ans: c
60. The return circuit for tramcars is through
(a) neutral wire
(b) rails
(c) cables
(d) common earthing
Ans: b
61. Specific energy consumption is least in
_______ service.
(a) main line
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(b) urban
(c) suburban
Ans: a
62. Locomotives with monometer bogies have
(a) uneven distribution of tractive effect
(b) suitability for passanger as well as freight
service
(c) lot of skidding
(d) low co-efficient of adhesion
Ans: b
63 _______ was the first city in India to adopt
electric traction.
(a) Delhi
(b) Madras
(c) Calcutta
(d) Bombay
Ans: d
64 _______ frequency is not common in low
frequency traction system
(a) 40 Hz
(b) 25 Hz
(c) 16 Hz
Ans: a
65. For 25 kV single phase system power
supply frequency is
(a) 60 Hz
(b) 50 Hz
(c) 25 Hz
(d) 16 Hz
Ans: b
66. Power for lighting in passanger coach, in a
long distance electric train, is provided
(a) directly through overhead electric line
(b) through individual generator of bogie and
batteries
(c) through rails
(d) through locomotive
Ans: b
67. In India, electrification of railway track was
done for the first time in which of the following
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years ?
(a) 1820—1825
(b) 1880—1885
(c) 1925—1932
(d) 1947—1954
Ans: c
68. Suri transmission is
(a) electrical-pneumatic
(b) mechanical-electrical
(c) hydro-mechanical
(d) hydro-pneumatic
Ans: c
69. In case of a steam engine an average coal
consumption per km is nearly
(a) 150 to 175 kg
(b) 100 to 120 kg
(c) 60 to 80 kg
(d) 28 to 30 kg
Ans: d
70. Which of the following happens in Kando
system ?
(a) Three phase A.C. is converted into D.C.
(b) Single phase A.C. is converted into D.C.
(c) Single phase supply is converted into three
phase system
(d) None of the above
Ans: c
71. For which of the following locomotives the
maintenance requirements are the least?
(a) Steam locomotives
(b) Diesel locomotives
(c) Electric locomotives
(d) Equal in all of the above
Ans: b
72. Which of the following methods is used to
control speed of 25 kV, 50 Hz single phase
traction ?
(a) Reduced current method
(b) Tap changing control of transformer
(c) Series parallel operation of motors
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(d) All of the above
Ans: b
73. If the co-efficient of adhesion on dry rails
is 0.26, which of the following could be the
value for wet rails ?
(a) 0.3
(b) 0.26
(c) 0.225
(d) 0.16
Ans: d
74 watt-hours per tonne km is usually the
specific energy consumption for suburban
services.
(a) 15—20
(b) 50—75
(c) 120—150
(d) 160—200
Ans: b
75. The braking retardation is usually in the
range
(a) 0.15 to 0.30 km phps
(b) 0.30 to 0.6 km phps
(c) 0.6 to 2.4 km phps
(d) 3 to 5 km phps
(e) 10 to 15 km phps
Ans: d
76. The rate of acceleration on suburban
orurban service is in the range
(a) 0.2 to 0.5 km phps
(b) 1.6 to 4.0 km phps
(c) 5 to 10 km phps
(d) 15 to 25 km phps
Ans: b
77. The coasting retardation is around
(a) 0.16 km phps
(b) 1.6 km phps
(c) 16 km phps
(d) 40 km phps
Ans: a
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Heating and Welding
1. Which of the following is an advantage of
heating by electricity ?
(a) Quicker operation
(b) Higher efficiency
(c) Absence of flue gases
(d) All of the above
Ans: d
2. ________ has the highest value of thermal
conductivity.
(a) Copper
(b) Aluminium
(c) Brass
(d) Steel
Ans: a
3. Which of the following heating methods has
maximum power factor ?
(a) Arc heating
(b) Dielectric heating
(c) Induction heating
(d) Resistance heating
Ans: d
4 method has leading power factor
(a) Resistance heating
(b) Dielectric heating
(c) Arc heating
(d) Induction heating
Ans: b
5 is used for heating non-conducting
materials.
(a) Eddy current heating
(b) Arc heating
(c) Induction heating
(d) Dielectric heating
Ans: d
6. Which of the following methods of heating
is not dependent on the frequency of supply ?
(a) Induction heating
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(b) Dielectric heating
(c) Electric resistance heating
(d) All of the above
Ans: c
7. When a body reflects entire radiation
incident on it, then it is known as
(a) white body
(b) grey body
(c) black body
(d) transparent body
Ans: a
8. For the transmission of heat from one body
to another
(a) temperature of the two bodies must be
different
(b) both bodies must be solids
(c) both bodies must be in contact
(d) at least one of the bodies must have some
source of heating
Ans: a
9. Heat transfer by condition will not occur
when
(a) bodies are kept in vacuum
(b) bodies are immersed in water
(c) bodies are exposed to thermal radiations
(d) temperatures of the two bodies are
identical
Ans: d
10. A perfect black body is one that
(a) transmits all incident radiations
(b) absorbs all incident radiations
(c) reflects all incident radiations
(d) absorbs, reflects and transmits all incident
radiations
Ans: b
11. Heat is transferred simultaneously by
condition, convection and radiation
(a) inside boiler furnaces
(b) during melting of ice
(c) through the surface of the insulted pipe
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carrying steam
(d) from refrigerator coils to freezer of a
refrigerator
Ans: a
12. The process of heat transfer during the
reentry of satellites and missiles, at very high
speeds, into earth's atmosphere is known as
(a) ablation
(b) radiation
(c) viscous dissipation
(d) irradiation
Ans: a
13. Which of the following has the highest
value of thermal conductivity ?
(a) Water
(b) Steam
(c) Solid ice
(d) Melting ice
Ans: c
14. Induction heating process is based on
which of the following principles ?
(a) Thermal ion release principle
(b) Nucleate heating principle
(c) Resistance heating principle
(d) Electro-magnetic induction princi¬ple
Ans: d
15. Which of the following insulating materials
was suitable for low temperature applications ?
(a) Asbestos paper
(b) Diatomaceous earth
(c) 80 percent magnesia
(d) Cork
Ans: b
16. A non-dimensional number generally
associated with natural convection heat
transfer is
(a) Prandtl number
(b) Grashoff number
(c) Pecelet number
(d) Nusselt number
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Ans: b
17. The temperature inside a furnace is
usually measured by which of the following ?
(a) Optical pyrometer
(b) Mercury thermometer
(c) Alcohol thermometer
(d) Any of the above
Ans: a
18. Which of the following will happen if the
thickness of refractory wall of furnace is
increased ?
(a) Heat loss through furnace wall will
increase
(b) Temperature inside the furnace will fall
(c) Temperature on the outer surface of
furnace walls will drop
(d) Energy consumption will increase
Ans: c
19. The material of the heating element for a
furnace should have
(a) lower melting point
(b) higher temperature coefficient
(c) high specific resistance
(d) all of the above
Ans: c
20. In a resistance furnace the atmosphere is
(a) oxidising
(b) deoxidising
(c) reducing
(d) neutral
Ans: a
21. By which of the following methods the
temperature inside arc nace can be varied ?
(a) By disconnecting some of the heating
elements
(b) By varying the operating voltage
(c) By varying the current through heating
elements
(d) By any of the above method
Ans: d
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22. In induction heating ______ is abnormally
high.
(a) phase angle
(b) frequency
(c) current
(d) voltage
Ans: b
23. By the use of which of the following, high
frequency power supply for induction furnaces
can be obtained ?
(a) Coreless transformers
(b) Current transformers
(c) Motor-generator set
(d) Multi-phase transformer
Ans: c
24. Induction furnaces are employed for
which of the following ?
(a) Heat treatment of castings
(b) Heating of insulators
(c) Melting aluminium
(d) None of the above
Ans: a
25. In an electric room heat convector the
method of heating used is
(a) arc heating
(b) resistance heating
(c) induction heating
(d) dielectric heating
Ans: b
26. In a domestic cake baking oven the
temperature is controlled by
(a) voltage variation
(b) thermostat
(c) auto-transformer
(d) series-parallel operation
Ans: d
27. In an electric press mica is used
(a) as an insulator
(b) as a device for power factor improvement
(c) for dielectric heating
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(d) for induction heating
Ans: a
28. Induction heating takes place iitwhich of
the following ?
(a) Insulating materials
(b) Conducting materials which are
magnetic
(c) Conducting materials which are nonmagnetic
(d) Conducting materials which may or may
not be magnetic
Ans: d
29. For heating element high resistivity
material is chosen to
(a) reduce the length of heating element
(b) increase the life of the heating element
(c) reduce the effect of oxidation
(d) produce large amount of heat
Ans: a
30. In resistance heating highest working
temperature is obtained from heating elements
made of
(a) nickel copper
(b) nichrome
(c) silicon carbide
(d) silver
Ans: c
31. For intermittent work which of the
following furnaces is suitable ?
(a) Indirect arc furnace
(b) Core less furnace
(c) Either of the above
(d) None of the above
Ans: a
32. Due to which of the following reasons it is
desirable to have short arc length ?
(a) To achieve better heating
(b) To increase the life of roof refractory
(c) To have better stirring action
(d) To reduce problem of oxidation
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(e) All of the above
Ans: e
33. In the indirect resistance heating method,
maximum heat-transfer takes place by
(a) radiation
(b) convection
(c) conduction
(d) any of the above
Ans: a
34. Properly of low temperature co-eflficient
of heating element is desired due to which of
the following reasons ?
(a) To avoid initial rush of current
(b) To avoid change in kW rating with
temperature
(c) Both (a) and (b)
(d) Either (a) or (b)
Ans: c
35. Which of the following methods is used to
control temperature in resistance furnaces ?
(a) Variation of resistance
(b) Variation of voltage
(c) Periodical switching on and off of the
supply
(d) All of the above methods
Ans: d
36. It is desirable to operate the arc furnaces
at power factor of
(a) zero
(b) 0.707 lagging
(c) unity
(d) 0.707 leading
Ans: b
37. Radiations from a black body are
proportional to
(a) T1
(b) T2
(c) T3
(d) T*
Ans: d
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38. In arc furnace the function of choke is
(a) to stabilize the arc
(b) to imprpve, power factor
(c) to reduce severity of the surge
(d) none of the above
Ans: a
39. Ajax Wyatt furnace is started when
(a) it is filled below core level
(b) it is filled above core level
(c) it is fully empty
(d) none of the above
Ans: b
40. In electric press, mica is used because it is
_______ conductor of heat but/and ________
conductor of electricity.
(a) bad, good
(b) bad, bad
(c) good, bad
(d) good, good
Ans:
41. Resistance variation method of
temperature control is done by connecting
resistance elements in
(a) series
(b) parallel
(c) series-parallel connections
(d) star-delta connections
(e) all of the above ways
Ans: e
42. Hysteresis loss and eddy current loss are
used in
(a) induction heating of steel
(b) dielectric heating
(c) induction heating of brass
(d) resistance heating
Ans: a
43. In heating the ferromagnetic material by
induction heating, heat is produced due to
(a) induced current flow through the charge
(b) hysteresis loss taking place below curie
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temperature
(c) due to hysteresis loss as well as eddy
current loss takingplace in the charge
(d) none of the above factors
Ans: c
44. Radiant heating is used for which of the
following ?
(a) Annealing of metals
(b) Melting of ferrous metals
(c) Heating of liquids in electric kettle
(d) Drying of paints and varnishes
Ans: d
45. Which of the following devices is
necessarily required for automatic temperature
control in a furnace ?
(a) Thermostat
(b) Thermocouple
(c) Auto-transformer
(d) Heating elements of variable resis-tance
material
Ans: b
46. For radiant heating around 2250°C, the
heating elements are made of
(a) copper alloy
(b) carbon
(c) tungsten alloy
(d) stainless steel alloy
Ans: c
47. Which of the following is an advantage of
eddy current heating ?
(a) The amount of heat generated can be
controlled accurately
(b) Heat at very high rate can be gene-rated
(c) The area of the surface over which heat is
produced can be accurately controlled
(d) All of the above
Ans: d
48. The electrode of a direct arc furnace is
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made of
(a) tungsten
(b) graphite
(c) silver
(d) copper
Ans: b
49. Direct arc furnaces have which of the
following power factors ?
(a) Unity
(b) Low, lagging
(c) Low, leading
(d) Any of the above
Ans: b
50. In direct arc furnace, which of the
following has high value ?
(a) Current
(b) Voltage
(c) Power factor
(d) All of the above
Ans: a
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