DC Circuits
Prepared by: Alexander T. Montero, REE, RME
1. The presence of electric current is only made
known by the effect it produces. Three important
effects are _____
A. Heating, electric shock & generation
B. Heating, magnetic and electric shock
C. Generation, chemical & electric shock
D. Heating, magnetic and chemical
2. Which is the best conductor of electricity?
A. Aluminum
B. Silver
C. Copper
D. Carbon
3. Which of the following conductors has the
highest resistance?
A. Manganin
B. Nichrome
C. Constantan
D. Steel
4. In American wire gauge as the number gage
increase the wire diameter?
A. increase
B. decrease
C. does not change
D. does change
5. A copper bar is 1/2 inch by 4 inches by 20
feet. If the resistivity of the copper bar is
10.37 ohms-cmf, what is the resistance of the
copper bar?
A. 17.3x10^-6 ohm
B. 125 ohms
C. 0.0052 ohm
D. 8.15x10^-5 ohm
6. A transmission line cable consists of 19
strands of identical copper conductors, each 1.5mm
in diameter. The resistance of the cable was
measured and it is known to be 1.076 ohm with
conductivity of 1.724x10^-8 ohm-meter. What is the
physical length of the cable? Allowing 5%
increased in actual length due to twisting of each
strands.
A. 1995m
B. 2095m
C. 2000m
D. 2100m
7. 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
C. 9 times
D. unchanged
8. A one meter of annealed copper 2.5 cm in
diameter is drawn until its resistance is 100
times
the
initial
resistance,
its
diameter
afterwards is?
A. 0.79 cm
B. 0.47 cm
C. 0.25 cm
D. 0.15 cm
9. A dc motor 120V has 100A rated current. The
allowable voltage drop is 3% of input voltage.
Find the maximum distance from the supply if the
wire has a diameter of 316 mils and resistivity of
wire is 10.4 ohm-cmf.
A. 508 ft
B. 316 ft
C. 178 ft
D. 203 ft
10. A light bulb having a tungsten filament draws
a 0.5A at 110V. The cold resistance of the
filament is 20 ohms at 20 deg. Celsius with
temperature coefficient of resistance for tungsten
at this temperature of 0.005 per deg. Celsius.
Determine the operating temperature of the bulb.
A. 1220 deg C
B. 520 deg C
C. 2520 deg C
D. 2020 deg C
11. A 100V carbon-filament lamp takes 1A when
glowing with a filament temperature of 1615 deg.C.
Calculate the momentary current when the lamp is
first switched on in air temperature of 15 deg.C.
The temperature coefficient of resistance for
carbon may be taken as -0.000265 per deg.C. at 15
deg.C.
A. 1.72A
B. 0.65A
C. 0.58A
D. 1.94A
12. A 24V battery delivers 15A to a motor load in
30min per day. What is the energy delivered per
month in kWh?
A. 6.2
B. 5.4
C. 7.31
D. 0.18
13. A certain process uses warm water at rate of 2
liters per minute. The water enters at electric
heater at 25 deg.C. to 50 deg.C. Assuming no heat
losses, what is the wattage of the heater?
A. 5125
B. 6250
C. 2420
D. 3488
14. What is the watt-hour efficiency of storage
battery?
A. AH output over WH input in recharge
B. WH output based on WH input in recharge
C. WH output based on AH input in recharge
D. AH output based on AH output in recharge
15. A 12V battery has 50AH capacity. The internal
resistance is 0.1ohm. A 5ohm resistor is connected
for 5hrs. How many AH are still left?
A. 38.23
B. 3
C. 41.24
D. 11.76
16. Three resistors of 10, 15 and 20 ohms each
connected in parallel. What is the conductance?
A. 0.217mho
B. 3.41mho
C. 4.62mho
D. 0.52mho
17. Two resistance R1 and R2 are connected in
series across the voltage source where R2>R1. The
largest drop will be across _____.
A. R2
B. R1
C. Either R2 and R1
D. None of them
18. Two 24V battery supply power to a 10 ohm load.
One battery has 0.2ohm internal resistance while
the other has 0.4ohm. What is the load voltage and
power does this load draws?
A. 23.84V & 56.8W
B. 24V & 48.2W
C. 23.68V & 56.1W
D. 23.24V & 60.8W
19. Superposition theorem can be applied only to
circuits having
A. Resistive Elements
B. Linear bilateral elements
C. Non-linear elements
D. Passive elements
20. Thevenin’s resistance Rth is found ______.
A. by removing voltage sources along with their
internal resistances
B. by short-circuiting the given two terminals
C. between any two ‘open’ terminals
D. between same open terminals as for Vth
21. Efficiency of power transfer when maximum
transfer of power occurs is
A. 100%
B. 80%
C. 75%
D. 50%
22. A lead storage battery is rated at 12V. If the
internal resistance is 0.01ohm, what is the
maximum power that can be delivered to the load?
A. 1200W
B. 7200W
C. 3600W
D. 1800W
23. In Fleming’s Right Hand Rule, which finger
point the direction of current?
A. Thumb
B. Index
C. Middle
D. Ring
24. Determine the force in pounds upon each side
of a coil of 40 turns carrying a current of 15A if
the axial length of the coil is 10 inches and the
flux density is 20000 lines per sq.inch. The
conductors are at the right angle to the flux.
A. 10.6 lbs
B. 1.3 lbs
C. 21.2 lbs
D. 12.4 lbs
25. An air core solenoid 0.5m long has 2000 turns.
The magnetic induction near the center of the
solenoid is 0.08 Tesla. What is the current in the
solenoid?
A. 24A
B. 16A
C. 2.4A
D. 1.6A
26. A substance or material having relative
permeability of less than unity is classified as:
A. Ferro-magnetic
B. Dia-magnetic
C. Para-magnetic
D. none of these
27. Permeability in a magnetic circuit corresponds
to _____ in an electric circuit.
A. resistance
B. resistivity
C. conductivity
D. conductance
28. The unit of relative permeability is _____.
A. henry/meter
B. henry
C. weber/sq.m
D. it is dimensionless
29. A solenoid has a magnetic reluctance of
2.2x10^-3. It has 300 turns and a core area of
5sq.cm. What is the flux density when the current
flowing is 1A?
A. 26300 Gauss
B. 12200 Gauss
C. 34200 Gauss
D. 21200 Gauss
30. A magnetic circuit consists of silicon steel
of 3000 permeability and an air gap. The length of
steel core is 10cm and the air gap is 2cm both
have the same cross-section of 1.5sq.cm. A current
of ½ Ampere flows through the windings to produce
2352 Maxwell flux. How many turns are in the coil?
A. 4120 turns
B. 500 turns
C. 2500 turns
D. 1250 turns
31. A magnetic circuit consists of silicon steel
3000 permeability of 10cm length and cross-section
of 1.5sq.cm and an air gap of the same crosssection and of 2cm length. A ½ Ampere flows
through 500 turns. What is the field intensity at
the air gap?
A. 250
B. 2262
C. 795
D. 1567
32. Degaussing is that process of _____.
A. removal of magnetic impurities
B. demagnetizing metallic parts
C. remagnetizing metallic parts
D. removing gases from the materials
33. Two infinitely long parallel conductors in
vacuum and separated 1 meter between centers when
a current of 1 Ampere flows through each
conductor, produce on each other a force of
A. 2x10^-2 N/m
B. 2x10^-3 N/m
C. 2x10^-5 N/m
D. 2x10^-7 N/m
34. A current of 2A through a coil sets up flux
linkages of 4Wb-turns. What is the inductance of
the coil?
A. 8 H
B. 0.5 H
C. 2 H
D. 1 H
35. As per Faraday’s law of electromagnetic
induction, an emf is induced in a conductor
whenever it _____.
A. lies perpendicular to the magnetic flux
B. lies in a magnetic field
C. cuts magnetic flux
D. moves parallel to the direction of the magnetic
field
36. The direction of induced 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
36. A magnetic coil produces 100000 maxwells with
2000 turns and with a current of 2Amp. The current
is cut-off and the flux collapses in 0.01 sec.
What is the average voltage that will appear
across the coil?
A. 20kV
B. 2000kV
C. 200V
D. 2kV
37. A 50mH inductance carries a current of 10Amp
which reverses in 5 milliseconds. What is the
average voltage induced in the inductor because of
this current reversal?
A. 100V
B. 200V
C. 400V
D. 50V
38. Find the value of an inductor which carries
2Amp of steady current and in which 20 Joules of
energy is stored?
A. 0.2 H
B. 5 H
C. 10 H
D. 0.5 H
39. When two inductors are connected in series
aiding, their total inductance is 40mH, when
connected in series opposing the inductance is
17.5mH. What is the value of mutual inductance?
A. 0.5625
B. 5.625
C. 56.25
D. 562.5
40. An emf induced by the changing of current in
the neighboring coil is called:
A. speed
B. mutually induced
C. self-induced
D. series