NEW SOUTH WALES
DE PA RT MEN T
OF
EDUCATION
AND
TRAINING
NSW
Name:
Date:
Class:
APPLIED
ELECTRICITY
D.C
2007 Work Book
DC Work Book
Page 1
SECTION A
pg 3 - 38
SECTION B
pg 39 - 59
SECTION C
pg 60 - 109
DC Work Book
Page 2
SECTION A
QUESTION 1.
The resistance of a metallic conductor is governed by its length, cross-sectional
area, temperature and the:
(a) type of material used.
(b) number of free electrons.
(c) voltage applied to it.
(d) heat dissipation.
QUESTION 2.
A material with a large number of free electrons is a good:
(a) conductor
(b) insulator
(c) semi-conductor
(d) resistor
QUESTION 3.
Conductor resistance causes temperature rise and power loss in a conductor,
this shows up as:
(a) temperature gradient along the conductor.
(b) power surge along the conductor.
(c) voltage drop along the conductor.
(d) increase in voltage along the conductor.
QUESTION 4.
Current in a circuit is directly proportional to:
(a) resistance.
(b) temperature.
(c) voltage.
(d) capacitance.
QUESTION 5.
Electric shock effects are governed by the value of the voltage, the current that
flows, the current path through the body and the:
(a) type of footwear worn.
(b) length of time of application.
(c) health of the victim.
(d) moisture in the air.
DC Work Book
Page 3
QUESTION 6.
If the length of a conductor is doubled, the conductor resistance is:
(a) doubled.
(b) halved.
(c) stays the same.
(d) increases by a factor of four.
QUESTION 7.
If the cross sectional area of a conductor is doubled, the conductor resistance is:
(a) doubled.
(b) halved.
(c) stays the same.
(d) increases by a factor of four.
QUESTION 8.
As the temperature of a copper conductor increases its resistance:
(a) increases.
(b) decreases.
(c) remains unchanged.
(d) reaches a maximum.
QUESTION 9.
The resistance of a conductor is:
(a) inversely proportional to both its length and cross sectional area (csa).
(b) directly proportional to both its length and cross sectional area.
(c) inversely proportional to its length and directly proportional to it’s csa.
(d) directly proportional to its length and inversely proportional to it’s csa.
QUESTION 10.
As a general rule, the size of a resistor determines its:
(a) power rating.
(b) age.
(c) type.
(d) voltage rating.
QUESTION 11.
A thermister with a negative temperature coefficient (NTC) will:
(a) increase its resistance with an increase in temperature.
(b) decrease its resistance with an increase in temperature.
(c) increase its resistance regardless of what the temperature does.
(d) have no change in resistance regardless of temperature change.
DC Work Book
Page 4
QUESTION 12.
Current in a series circuit is:
(a) different through each component.
(b) is proportional to the resistance.
(c) is inversely proportional to the voltage.
(d) the same through each component.
QUESTION 13.
Kirchhoff’s current law states that:
(a) the algebraic sum of all currents in a circuit is equal to zero.
(b) the algebraic sum of all currents in any one direction equals the
currents in the other direction.
(c) the current leaving a battery is dependent on the size of the battery.
(d) the algebraic sum of currents entering or leaving a node at any instant
is zero.
QUESTION 14.
If a resistor in a series circuit developed a short circuit across itself, the circuit
current would:
(a) increase.
(b) decrease.
(c) remain the same.
(d) drop to zero.
QUESTION 15.
In a parallel circuit the supply current equals the:
(a) total power divided by the total resistance.
(b) sum of the resistances divided by the voltage.
(c) current in each branch.
(d) sum of the individual branch currents.
QUESTION 16.
Kirchhoff’s voltage law states that in any closed loop the:
(a) algebraic sum of all the voltages drops is equal to zero.
(b) algebraic sum of all the voltages drops is equal to the applied voltage.
(c) algebraic sum of all the voltages drops is equal to the applied voltage
minus the biggest drop.
(d) algebraic sum of all the voltages drops is equal to the applied voltage
minus the smallest drop.
DC Work Book
Page 5
QUESTION 17.
If there is an open circuit in a component in a parallel circuit the total current
taken by the circuit will:
(a) increase.
(b) decrease.
(c) remain the same.
(d) double.
QUESTION 18.
Three resistors R1,R2 and R3 are connected in a series-parallel combination,
and R2 is equal to R3. If the total circuit flows through R1 and the currents
through R2 and R3 are equal then:
(a) R1 must be in series with the parallel combination of R2 and R3.
(b) R2 and R3 are in series with R1.
(c) R1 must be in parallel with the series combination of R2 and R3.
(d) R1 and R2 are in series with the parallel combination of R2 and R3.
QUESTION 19.
If the series resistor became open circuit in a simple series-parallel circuit, the
circuit current would:
(a) drop to zero because of the break in the circuit current path.
(b) be limited by the equivalent resistance of the parallel combination.
(c) decrease to the current taken by the parallel combination.
(d) increase to the current taken by the parallel combination.
QUESTION 20.
To ensure an accurate reading when using an ohm-meter it is important to:
(a) select the highest range.
(b) select the lowest range.
(c) check the zero reading.
(d) estimate the value being measured.
QUESTION 21.
If a short circuit occurs in a parallel branch of a group of series-parallel
connected resistors the:
(a) total circuit resistance will decrease to zero.
(b) total circuit current will increase.
(c) total circuit resistance will increase
(d) voltage drop across the series resistor will decrease..
QUESTION 22.
A varistor (VDR) is a component whose resistance changes with:
(a) heat.
(b) moisture.
(c) voltage.
(d) light.
DC Work Book
Page 6
QUESTION 23.
Capacitors consist of two conducting electrodes separated by an insulating
medium called a:
(a) dielectric.
(b) diacroic.
(c) resistivity.
(d) electrolytic.
QUESTION 24.
Capacitors can store an electric charge whose magnitude depends on:
(a) plate thickness and plate size.
(b) cross sectional area of plates and their separation.
(c) cross sectional area of plates and plate material.
(d) plate thickness and plate material.
QUESTION 25.
The energy of a capacitor is stored in:
(a) the magnetic field within the dielectric.
(b) the magnetic field around the capacitor leads.
(c) the electric field across the circuit.
(d) the electric field across the dielectric.
QUESTION 26.
A capacitor consists of:
(a) two insulated plates separated by a conductor.
(b) two conductive plates separated by a conductor.
(c) two conductive plates separated by an insulator.
(d) two conductive plates separated by a conductive spacer.
QUESTION 27.
The quantity of charge held in a capacitor is dependent on the capacitance of the
capacitor and the:
(a) voltage.
(b) current.
(c) time.
(d) plate area.
QUESTION 28.
If the length of a cable is doubled, and its diameter is doubled, the resistance of
the cable is:
(a) halved
(b) unchanged
(c) doubled
(d) quadrupled
DC Work Book
Page 7
QUESTION 29.
Any conductive material which increases its resistance when it is heated, is said
to be a:
(a) NTC
(b) PTC
(c) thermocouple
(d) non-pure element
QUESTION 30.
The unit of resistivity is the:
(a) ohm metre
(b) ohm per metre
(c) ohm metre squared
(d) ohm per metre squared
QUESTION 31.
Which of the following components of an atom has no resultant charge:
(a) electron
(b) neutron
(c) proton
(d) nucleus
QUESTION 32.
The transmission of electrical power is opposed by the resistance of the
conductors, and results in a loss of power. Which of the following is the equation
normally used to calculate this power loss:
(a) P = I²/R
(b) P = 1²R
(c) P = V²/R
(d) P = V²R
QUESTION 33. (1 Mark)
Figure 1 refers to which type of resistor:
Potentiometer
(a) Potentiometer
(b) VDR
(c) Thermistor Figure 1
(d) LDR
DC Work Book
Page 8
QUESTION 34.
A simple voltage surge diverter can be made by using:
(a) Potentiometer
(b) VDR
(c) Thermistor
(d) LDR
QUESTION 35.
If five lamps are connected in series, and the fourth lamp develops a short circuit
across itself, all lamps will:
(a) be off
(b) glow brighter
(c) glow as normal, except lamp 4 which will be off
(d) glow brighter, except lamp 4 which will be off
QUESTION 36.
A series circuit contains a number of different valued resistors. The resistor with
the largest current flowing through it will be:
(a) the smallest resistor
(b) the largest resistor
(c) the resistor with the smallest voltage drop
(d) none. Each will have the same current
QUESTION 37.
A parallel circuit, which contains three resistors each of 10 ohms, develops an
open circuit in one resistor. The total resistors of the circuit will:
(a) remain uncharged
(b) decrease
(c) increase
(d) become infinite
QUESTION 38.
Connecting more resistors in parallel produces the same general effect as:
(a) increasing the temperature of a metallic conductor
(b) increasing the cross-sectional area of a conductor
(c) increasing the length of a conductor
(d) decreasing the conductance of a conductor
DC Work Book
Page 9
Question 39 to 41 refers to figure 2 below
QUESTION 39.
If an open circuit developed in R3, the resulting circuit current would be:
(a) zero amperes, because of the open circuited resistor
(b) zero amperes, because the fuse blows
(c) 3 amperes
(d) unchanged at 5 amperes
QUESTION 40.
If a short circuit developed in R2, the resulting circuit current would be:
(a) zero amperes, because the fuse blows
(b) 3 amperes
(c) unchanged at 5 amperes
(d) 15 amperes
QUESTION 41.
If the fuse was blown and the switch was open, what voltage would be measured
across the open switch terminals?
(a) Zero volts
(b) 5 volts
(c) 7.5 volts
(d) 15 volts
QUESTION 42.
Conduction of electric current through a gas is achieved by:
(a) breaking of covalent bonds
(b) the kinetic energy theory of gas
(c) dislodging protons from the nucleus of gas atoms
(d) ionisation of the gas
QUESTION 43.
The basic moving coil meter movement can be used to measure larger current, if
used in conjunction with a:
(a) series resistor
(b) multipler resistor
(c) shunt resistor
(d) loading resistor
DC Work Book
Page 10
QUESTION 44.
A major advantage that digital multimeters have over most analogue multimeters,
is:
(a) that it requires an easily obtainable 9 volt battery to operate
(b) the settling time of the indication to change in the measured value
(c) that they cannot be damaged by using a wrong function setting
(d) the very high input impedance which reduces circuit loading effects
QUESTION 45.
Decreasing the capacitance in an RC circuit, will cause the time constant to:
(a) remain the same
(b) decrease
(c) increase
(d) reach a maximum value
QUESTION 46.
When capacitors are connected in series, the total capacitance is:
(a) always greater than the largest capacitors
(b) always smaller than the smallest capacitors
(c) equal to the sum of the reciprocal of the capacitors
(d) equal to the reciprocal of the sum of the capacitors
QUESTION 47.
Polarized capacitors:
(a) can explode if connected incorrectly
(b) can be used in a wider range of applications
(c) include electrolytic and ceramic capacitors
(d) include tantalum and ceramic capacitors
QUESTION 48
If the voltage applied to a circuit is halved, the circuit current will:
(a) remain constant
(b) decrease to zero
(c) halve
(d) double
QUESTION 49
If the voltage applied to a circuit is doubled, and the resistance of the circuit is
halved, the circuit current will:
(a) remain constant
(b) halve
(c) double
(d) quadruple
DC Work Book
Page 11
QUESTION 50
The circuit draws 3A when connected to a 120V supply. What is the resistance
when the same resistance is connected to 150V supply:
(a) 60Ω
(b) 500Ω
(c) 400Ω
(d) 300Ω
QUESTION 51
The resistance of a conductor is:
(a) directly proportional to both its length and CSA
(b) inversely proportional to both its length and CSA
(c) directly proportional to its length and inversely proportional to CSA
(d) inversely proportional to its length and directly proportional to CSA.
QUESTION 52
A copper conductor’s resistance differs from the resistance of an aluminium
conductor of similar length and CSA due to what factor?
(a) Permittivity
(b) Resistivity
(c) Conductivity
(d) Inductance.
QUESTION 53
When a pure metal such as copper is heated, what is the effect on its resistance?
(a) It remains unchanged
(b) It decreases
(c) It increases
(d) It could increase or decrease depending on current flow.
QUESTION 54
When a 4mm² cable is compared to a 1mm² cable of similar length:
(a) the 4mm² cable has greater resistance
(b) the 4mm² cable will have less voltage drop for the same current
(c) the 4mm² cable will draw less current for the same voltage
(d) the 4mm² cable will get hotter for the same current.
QUESTION 55
When selecting a resistor for a particular application, what are the two most
important ratings?
(a) Resistance and power
(b) Power and voltage
(c) Power and current
(d) Voltage and resistance.
DC Work Book
Page 12
QUESTION 56
Which of the following describes the application of a VDR? It is used:
(a) as a device to measure the quantity of light
(b) in temperature measuring devices
(c) to protect equipment from voltage surges
(d) to protect motor windings from overheating.
QUESTION 57
What term is used to describe a variable resistor used to control current?
(a) Transistor
(b) Varistor
(c) LDR
(d) Rheostat.
QUESTION 58
What is the definition of a series circuit?
(a) A circuit that has only one voltage source
(b) A circuit that has only one current path
(c) A circuit that has more than one resistor
(d) A circuit that has only resistors of the same value.
QUESTION 59
When an open circuit occurs in a series circuit:
(a) the total resistance decreases
(b) the total current increases
(c) the total voltage appears across the open circuit
(d) current will flow up to the open circuit and then stop.
QUESTION 60
For the circuit of Figure 1, the voltage drops across R1, R2 and R3:
(a) are caused by different currents
(b) add up to the supply voltage
(c) are inversely proportional to current
(d) are the same as the supply voltage.
DC Work Book
Page 13
QUESTION 61
If resistor R1 in the circuit of Figure 1 becomes short circuited, the total
resistance will ___________ the total current will
and the total
power dissipated will
(a) increase, decrease, decrease
(b) decrease, increase, decrease
(c) increase, decrease, increase
(d) decrease, increase, increase.
QUESTION 62
When an open circuit occurs in one branch of a parallel circuit:
(a) equivalent circuit resistance increases
(b) current flowing in the other branches increase
(c) voltage across the open circuit decreases
(d) power developed across the open circuit increases.
QUESTION 63
For the circuit of Figure 2, the voltages across each resistor will:
(a) be the reciprocal of the total voltage
(b) add up to the total voltage
(c) all be the same
(d) be different if resistors are different values.
QUESTION 64
For the circuit of Figure 2, the total current from the supply will be:
(a) the sum of the branch currents
(b) the same as the current in each branch
(c) the addition of the reciprocals of each branch current
(d) less than the current in the branch with the lowest resistance.
QUESTION 65
For the circuit of Figure 2, the value of resistor R1:
(a) can be found by dividing the total voltage by the total current
(b) will be greater than the total equivalent resistance
(c) can be found by subtracting the value of R2 and R3 from the total
equivalent resistance
(d) can be found by dividing one third of the total voltage by total current.
DC Work Book
Page 14
QUESTION 66
A decrease in the thickness of the dielectric of a capacitor would:
(a) increase its capacitance
(b) cause it to draw less current
(c) increase its power rating
(d) increase its voltage rating.
QUESTION 67
What would the ammeter in Figure 3 read?
(a) 25 Amps
(b) 19 Amps
(c) 11 Amps
(d) 8 Amps.
QUESTION 68
The long shunt method of resistance measurement is used when the resistor
under test has a:
(a) low power rating
(b) high power rating
(c) low resistance value
(d) high resistance value.
QUESTION 69
The basic moving coil meter movement can be used to measure higher currents
if used in conjunction with a:
(a) shunt resistor
(b) multiplier resistor
(c) voltage divider
(d) digital meter.
QUESTION 70
The equivalent resistance of a parallel circuit is determined by:
(a) the sum of the individual resistors
(b) the product of the individual resistors
(c) the reciprocal of the sum of the reciprocals of the resistors
(d) the use of ohm’s law only.
DC Work Book
Page 15
QUESTION 71
If the voltage applied to a circuit is doubled the power consumption of that circuit
will be:
(a) halved
(b) doubled
(c) quartered
(d) quadrupled.
QUESTION 72
Before using an analogue ohmmeter to measure resistance it should be:
(a) set to the highest range
(b) set to the lowest range
(c) adjusted to read infinite resistance
(d) adjusted to read zero resistance.
QUESTION 73
Connecting capacitors in parallel:
(a) has the effect of increasing the total capacitance
(b) has the effect of decreasing the total capacitance
(c) has no effect on the value of the total capacitance
(d) is dangerous and will damage the capacitors.
QUESTION 74
It is most likely that the voltage across a blown fuse is:
(a) equal to the voltage across the load
(b) half of the voltage across the load
(c) zero
(d) equal to the supply voltage.
QUESTION 75
The resistance of a conductor is directly proportional to the:
(a) cross sectional area of the conductor
(b) voltage applied to the conductor
(c) length of the conductor
(d) current flowing through the conductor
QUESTION 76
If a conductor has a negative temperature coefficient, its resistance will:
(a) increase with an increase in temperature
(b) decrease with an increase in temperature
(c) be unaffected by a change in temperature
(d) remain constant throughout the negative temperature range
DC Work Book
Page 16
QUESTION 77
As the temperature of a copper conductor increases, its resistance will:
(a) increase
(b) decrease
(c) remain the same
(d) increase or decrease depending on the direction of the current flow
QUESTION 78
When selecting a resistor for a circuit, the two factors which must be considered
are:
(a) the resistance and the current rating
(b) the resistance and the voltage rating
(c) the current and the voltage rating
(d) the resistance and the power rating
QUESTION 79
A series circuit is one in which there is:
(a) only one current path
(b) more than one current path
(c) equal voltage applied to each component connected in series
(d) only one component
QUESTION 80
Six identical lamps are connected in series and draw 2 amperes from a 12 volt
d.c. supply. If one lamp became open circuited, the current in the other five
lamps would be:
(a) 2 amperes
(b) 2.4 amperes
(c) 4.8 amperes
(d) zero amperes
QUESTION 81
The equivalent resistance of a series circuit is equal to the:
(a) resistance of the highest individual resistor
(b) supply voltage multiplied by the supply current
(c) supply voltage divided by the supply current
(d) resistance of the lowest individual resistor
QUESTION 82
In a parallel circuit, the current flowing through each resistor is:
(a) the same
(b) determined by the number of resistors in parallel
(c) determined by the value of each resistor and the voltage applied
(d) limited by the size of the power supply
DC Work Book
Page 17
QUESTION 83
Three identical 8 ohm resistors are connected in parallel to a 24 volt d.c. supply.
If one of the resistors became open circuited, the current through each of the
remaining resistors would be:
(a) 1.5 amperes
(b) 3 amperes
(c) 6 amperes
(d) zero amperes
QUESTION 84
A circuit consists of two resistors (each 10Ω) connected in parallel to a 20 volt
d.c. supply. If a third 10Ω resistor is connected in parallel, the current drawn from
the supply would:
(a) decrease
(b) remain the same
(c) increase
(d) overload the power supply
QUESTION 85
To increase the range of a moving coil voltmeter, an appropriate resistor could be
connected in:
(a) parallel with the moving coil
(b) series with the moving coil
(c) parallel with the component being measured
(d) series with the component being measured
QUESTION 86
When measuring the insulation resistance of a final subcircuit, you should use:
(a) an ohmmeter
(b) a Wheatstone Bridge
(c) any moving coil meter
(d) a megger
QUESTION 87
Before using an analogue ohmmeter to measure resistance, it is important to:
(a) estimate the value of the resistance to be measured
(b) select the highest range
(c) select the lowest range
(d) zero the meter
QUESTION 88
A capacitor is an electrical device that could be used to:
(a) store an electric charge
(b) induce a voltage
(c) convert alternating current to direct current
(d) convert direct current to alternating current
DC Work Book
Page 18
QUESTION 89
If the distance between the plates of a capacitor is halved, its capacitance will:
(a) be halved
(b) be doubled
(c) be increased by four times
(d) remain the same
QUESTION 90
A 20k ohm resistor is connected in series with a 100 microfarad capacitor to a 20
volt supply. After 10 seconds, the voltage across the capacitor will have risen to
approximately:
(a) 6.3 volts
(b) 12.6 volts
(c) 18.9 volts
(d) 20 volts
QUESTION 91
In the atomic structure of an atom, a negative charge is exhibited by the:
(a) atom
(b) neutron
(c) electron
(d) proton
QUESTION 92
An atom which has lost or gained an electron is termed:
(a) an ion
(b) an isotope
(c) an atom
(d) a neutron
QUESTION 93
A material that requires a relatively large amount of energy to remove electrons
from the outer shell or energy level is termed:
(a) a conductor
(b) an insulator
(c) a semi-conductor
(d) a neutral material
QUESTION 94
A solution capable of conducting an electric current is called:
(a) an electrolyte
(b) an electrolysis
(c) a dielectric solution
(d) an hydroelectric solution
DC Work Book
Page 19
QUESTION 95
If the resistance of a circuit is doubled, (voltage constant) the power consumed
by the circuit will:
(a) be doubled
(b) be halved
(c) increase by four times
(d) decrease by four times
QUESTION 96
If the voltage applied to a circuit is doubled, (resistance constant) the power
consumed by the circuit will:
(a) be doubled
(b) be halved
(c) increase by four times
(d) decrease by four times
QUESTION 97
The two effects of an electric current which are always present whenever current
flows are:
(a) chemical and magnetic
(b) heat and physiological
(c) chemical and physiological
(d) heat and magnetic
QUESTION 98
Heat flows from a body of higher temperature to a body of a:
(a) lower temperature
(b) smaller mass
(c) larger mass
(d) constant temperature
QUESTION 99
The best method of accurately measuring a resistance of 0.04 ohms would be:
(a) an ohmmeter
(b) a megger
(c) a Wheatstone Bridge
(d) the voltmeter-ammeter method using the long shunt connection
QUESTION 100
The resistance of an ideal voltmeter would be:
(a) less than 10Ω
(b) between 10Ω and 1,000Ω
(c) between 1,000Ω and 10,000Ω
(d) infinity
DC Work Book
Page 20
QUESTION 101
Which one of the following units is an S.I derived unit:
(a) ampere
(b) newton
(c) kilogram
(d) metre
QUESTION 102
A cable with a slightly smaller cross sectional area, but carrying the same load
current, is to replace an existing cable in a circuit. The new cable will:
(a) operate at a higher temperature
(b) be able to carry more current
(c) have the same voltage drop
(d) cause a smaller voltage drop
QUESTION 103
Resistors are specified by their value of resistance and by their maximum:
(a) voltage rating
(b) power dissipation
(c) current rating
(d) heat dissipation
QUESTION 104
The largest resistor in a series circuit, will have the:
(a) smallest current
(b) smallest voltage drop
(c) largest current
(d) largest voltage drop
QUESTION 105
The resistivity of a conductor depends on its:
(a) length
(b) cross sectional area
(c) material composition
(d) diameter
QUESTION 106
A power supply is to be constructed from a number of identical battery cells.
Connecting three cells in series would, relative to one cell:
(a) triple the voltage of the supply and triple the internal resistance of the
supply.
(b) triple the internal resistance of the supply but with no change voltage.
(c) reduce the internal resistance of the supply to a third without changing
the voltage.
(d) triple the voltage of the supply but without changing the internal
resistance.
DC Work Book
Page 21
QUESTION 107
The ability of a device to store an electric charge best describes the electrical
property of:
(a) inductance
(b) resistance
(c) capacitance
(d) conductance
QUESTION 108
If the voltage applied to a parallel network of FOUR (4) equal resistors is
doubled, the power dissipated by the resistor network is:
(a) doubled
(b) quadrupled
(c) quartered
(d) halved
QUESTION 109
The standard unit of electric power is the:
(a) coulomb
(b) ampere
(c) watt
(d) volt
QUESTION 110
The light emitted by an incandescent lamp is due to:
(a) extreme temperature of the filament
(b) electromagnetic effect
(c) ionisation of the gas within the bulb
(d) electrolysis
QUESTION 111
A primary cell is one that:
(a) can be recharged
(b) cannot be recharged
(c) can have its electrolyte readily changed
(d) uses nickel and cadmium as electrodes
QUESTION 112
Electric shock initially affects the body’s:
(a) arterial system
(b) muscular system
(c) skeletal system
(d) nervous system
DC Work Book
Page 22
QUESTION 113
If an open circuit occurs in one branch of a parallel circuit the total resistance of
the circuit will:
(a) decrease
(b) remain the same
(c) increase
(d) become infinite
QUESTION 114
Resistors A and B are connected in parallel. Resistor A has half the resistance of
Resistor B. The current flowing through Resistor B is:
(a) one half of the supply current
(b) twice as much as the current flowing in resistor A
(c) two thirds of the supply current
(d) one third of the supply current
QUESTION 115
If the value of resistor R1 in the circuit of Figure 1 is increased, the equivalent
circuit resistance between A and B will:
(a) increase A
(b) decrease
(c) remain the same supply
(d) cannot tell without knowing circuit values B
QUESTION 116
If the resistor R2 of Figure 1 (previously) was short circuited, the overall power
consumed by the circuit will:
(a) increase
(b) decrease
(c) remain the same
(d) cannot tell without knowing circuit values
QUESTION 117
A Wheatstone bridge is best suited to measuring:
(a) insulation resistance
(b) very low voltage
(c) low values of resistance
(d) low values of current
DC Work Book
Page 23
QUESTION 118
If three lamps are connected in series, and the middle lamp develops an open
circuit, there is no current in:
(a) lamp one only
(b) any of the lamps
(c) lamp three only
(d) lamp two only
QUESTION 119
Increasing the resistance in a series RC circuit will:
(a) maximise the voltage drop across R at switch-on
(b) maximise the voltage drop across C at switch-on
(c) increase the total circuit current
(d) reduce the time constant of the circuit
QUESTION 120
If all other factors remain unchanged, changing the dielectric of a capacitor from
air to mica will increase the capacitance because mica has a higher value of:
(a) permittivity
(b) retentivity
(c) resistivity
(d) permeability
QUESTION 121
To measure the current in a load, the load should be connected in:
(a) series with a voltmeter
(b) parallel with a voltmeter
(c) series with an ammeter
(d) parallel with an ammeter
QUESTION 122
The two effects that are always present when an electric current flows are:
(a) magnetic and chemical
(b) chemical and physiological
(c) magnetic and heat
(d) heat and chemical
QUESTION 123
A high rupturing capacity fuse operates by:
(a) melting the silica inside the cartridge to stop current flow
(b) heating the bimetal strip to interrupt the circuit current
(c) melting the fuse element to isolate the circuit
(d) heating the thermal contacts to open the circuit
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QUESTION 124
If the voltage applied to a resistor is halved, the power dissipated will:
(a) double
(b) decrease to a quarter
(c) halve
(d) increase by four times
QUESTION 125
Power in a d.c. circuit can be determined by multiplying together the readings
from two separate instruments. These instruments are the:
(a) wheatstone bridge and ammeter
(b) ammeter and ohmmeter
(c) voltmeter and wattmeter
(d) ammeter and voltmeter
QUESTION 126
The ability to do work is termed:
(a) power
(b) velocity
(c) force
(d) energy
QUESTION 127
Power may be defined as the:
(a) force over a given distance
(b) rate at which work is done
(c) total electrical energy
(d) ability to store energy
QUESTION 128
At a given value of electrical pressure, a closed switch:
(a) prevents current flow
(b) will de-energise the load
(c) isolates the power
(d) allows current to flow
QUESTION 129
Motors and generators are rated in terms of their:
(a) full-load output power
(b) no-load output power
(c) full-load input power
(d) no-load input power
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QUESTION130
Current flow in a solid conductor is the result of the movement of:
(a) negative ions
(b) neutrons
(c) protons
(d) free electrons
QUESTION 131
A solution capable of conducting an electric current is called:
(a) a semi-conductor
(b) an isotope
(c) a dielectric
(d) an electrolyte
QUESTION 132
The piezoelectric effect is used to convert:
(a) heat energy to electrical energy
(b) light energy to electrical energy
(c) magnetism to electrical energy
(d) mechanical energy to electrical energy
QUESTION 133
A practical use for the magnetic effect of current is a:
(a) relay
(b) radiator
(c) primary cell
(d) electrolysis bath
QUESTION 134
An electric motor rotates as a result of the:
(a) piezoelectric effect of current
(b) chemical effect of current
(c) mechanical effect of current
(d) magnetic effect of current
QUESTION 135
The chemical effect of current can be used to:
(a) operate a contactor
(b) recharge a secondary cell
(c) store an electric field
(d) create a thermocouple
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QUESTION 136
A device that produces an electromotive force proportional to temperature is a:
(a) thermistor
(b) varistor
(c) thermocouple
(d) thermostat
QUESTION 137
A rheostat is a type of:
(a) voltage dependent resistor
(b) variable resistor
(c) photoresistor
(d) heating resistor
QUESTION 138
Three resistors of equal value are connected in parallel across a 24 V supply.
The voltage across the third resistor will be:
(a) OV
(b) 8V
(c) 18V
(d) 24V
QUESTION 139
The chemical effect of electric current flow can cause:
(a) corrosion of underground pipes
(b) electrical disturbances to data signals
(c) overheating of cables
(d) induced voltages in cables
QUESTION 140
The practical unit of electrical energy is the:
(a) kilowatt second
(b) kilojoule second
(c) kilojoule hour
(d) kilowatt hour
QUESTION 141
Two 60 ohm resistors are connected in parallel to a 120 volt supply. If one
resistor becomes open-circuited the current in the other resistor will be:
(a) 0 ampere
(b) 0.5 ampere
(c) 2 amperes
(d) 4 amperes
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QUESTION 142
If the output of a motor is 6 kilowatts and the input power is 8 kilowatts, then the
efficiency of the system is:
(a) 2%
(b) 25%
(c) 50%
(d) 75%
QUESTION 143
If a resistor in the parallel section of a series-parallel circuit becomes open circuit,
the total circuit current will:
(a) remain constant
(b) increase
(c) drop to a lower value
(d) decrease to zero
QUESTION 144
If a resistor in the series section of a series-parallel circuit is replaced with one of
much higher resistance, the total circuit power will:
(a) increase
(b) decrease
(c) remain unchanged
(d) drop to zero
QUESTION 145
When converting chemical energy to electrical energy, to increase the output
voltage:
(a) several cells can be connected in parallel
(b) a lower concentrate of acid can be used
(c) larger electrodes can be used
(d) several cells can be connected in series
QUESTION 146
An analogue multimeter has a sensitivity of 500 ohms/volt. The internal
resistance of the meter when used on the 50 volt range is:
(a) 0.1Ω
(b) 10Ω
(c) 500Ω
(d) 25 000Ω
QUESTION 147
If a voltmeter has low sensitivity, this means the voltmeter is:
(a) highly accurate
(b) not very accurate
(c) made with a high internal resistance
(d) made with a low internal resistance
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QUESTION 148
The best method of accurately measuring a very low value of resistance would
be by using:
(a) a Wheatstone bridge
(b) an insulation resistance tester
(c) the long shunt voltmeter/ammeter method
(d) an analogue ohmmeter on a high range
QUESTION 149
Before using an analogue multimeter to measure resistance it is important to:
(a) adjust the meter to read zero
(b) ensure supply is connected to the resistor
(c) estimate the resistance value
(d) check the pointer is reading infinity
QUESTION 150
A resistor has 6R8 stamped on its body. This means the resistor is:
(a) 6 watts, 8 ohms
(b) 6 ohms, 8 watts
(c) 6.8 ohms
(d) 6.8 watts
QUESTION 151
A light dependent resistor, when exposed to light:
(a) decreases its resistance at a non-linear rate
(b) increases its resistance at a non-linear rate
(c) decreases its resistance at a linear rate
(d) increases its resistance at a linear rate.
QUESTION 152
The instrument used to measure the power consumed by an electric circuit is
a/an:
(a) Ammeter
(b) Voltmeter
(c) Ohmmeter
(d) Wattmeter.
QUESTION 153
The standard unit for conductance is the:
(a) Ohm-metre
(b) Siemen
(c) Mho
(d) Coulomb.
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QUESTION 154
The efficiency of an electric circuit may be defined as the ratio of the:
(a) output power to the input power
(b) input power to the output power
(c) power losses to the output power
(d) power losses to the input power.
QUESTION 155
The piezo-electric effect causes certain crystals to produce a voltage when they:
(a) are placed under a light source
(b) have mechanical stress applied
(c) are heated above the ambient temperature
(d) are moved through a magnetic field.
QUESTION 156
Electric current through a copper conductor is a result of the movement of:
(a) free electrons
(b) negative ions
(c) positive ions
(d) copper atoms.
QUESTION 157
The resistance of a conductor is said to be:
(a) inversely proportional to its resistivity
(b) proportional to its area
(c) inversely proportional to its length
(d) proportional to its length.
QUESTION 158
A material having a positive temperature co-efficient of resistance:
(a) does not change its resistance with a change in temperature
(b) decreases its resistance with a decrease in temperature
(c) decreases its resistance with an increase in temperature
(d) increases its resistance with a decrease in temperature.
QUESTION 159
In a series circuit containing three resistances, if a short circuit occurred across
one of the resistances:
(a) the total resistance of the circuit would fall to zero
(b) the total current flowing through the circuit would fall to zero
(c) the current through the short circuited resistor would fall to zero
(d) the supply voltage would fall to zero.
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QUESTION 160
A series circuit is defined as a circuit which has:
(a) only one power supply
(b) only one load
(c) only one control switch
(d) only one current path.
QUESTION 161
To convert volts into kilo-volts:
(a) multiply the volts by 1000
(b) divide the volts 10
(c) multiply the volts by 10
(d) divide the volts by 1000.
QUESTION 162
If a resistor in the parallel section of a series-parallel circuit became open
circuited, the voltage drop across the parallel section would:
(a) increase
(b) equal the supply voltage
(c) remain constant
(d) decrease.
QUESTION 163
The severity of an electric shock is mostly dependent upon:
(a) the value of the current flowing through the body
(b) the time the current is flowing in the body
(c) the path taken by the current flowing through the body
(d) all of the above.
QUESTION 164
Increasing the plate area of a capacitor:
(a) decreases its capacitance
(b) decreases its dielectric strength
(c) increases its capacitance
(d) increases its dielectric strength.
QUESTION 165
Power may be defined as the:
(a) ability to do the required work
(b) rate at which the work is done
(c) energy required to complete the task
(d) force exerted on the object.
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QUESTION 166
Conduction of an electric current through a gas is achieved by:
(a) ionisation of the gas
(b) polarization of the gas
(c) equalization of the gas
(d) separation of the gas.
QUESTION 167
Connecting resistors in parallel produces the same general effect as:
(a) increasing the temperature of a metallic conductor
(b) increasing the cross sectional area of a conductor
(c) increasing the length of a conductor
(d) decreasing the conductance of a conductor.
QUESTION 168
The equivalent resistance of a parallel circuit is:
(a) greater than any branch resistance
(b) equal to the sum of the branch resistances
(c) smaller than any branch resistance
(d) increases with an additional branch.
QUESTION 169
For a fuse to operate as intended, it uses:
(a) the chemical effect of current
(b) the heating effect of current
(c) the magnetic effect of current
(d) the physiological effect of current.
QUESTION 170
In an R-C circuit, when first turned on and knowing the capacitor is fully
discharged, the capacitor is said to be fully charged after:
(a) 1 time constant
(b) 2 time constants
(c) 5 time constants
(d) 10 time constants.
QUESTION 171
Increasing the capacitance in an R-C circuit will cause the:
(a) maximum value of circuit current to increase
(b) time constant of the circuit to increase
(c) time constant of the circuit to decrease
(d) maximum value of circuit current to decrease.
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QUESTION 172
If the voltage applied to a series circuit is doubled and the circuit resistance is
also doubled, the circuit current would:
(a) halve its value
(b) double its value
(c) remain constant
(d) fall to zero.
QUESTION 173
Resistors are rated by their value of resistance and the:
(a) voltage they can safely withstand
(b) current they can safely conduct
(c) power they can safely dissipate
(d) material they are made from.
QUESTION 174
A Capacitor may be defined as a device used to:
(a) store an electric charge
(b) create an electric charge
(c) control an electric charge
(d) utilize an electric charge.
QUESTION 175
If all other factors remain constant while the diameter of a conductor is doubled,
the resistance of the conductor will:
(a) double
(b) quadruple
(c) halve
(d) quarter.
QUESTION 176
100 mA in amperes would be:
(a) 0.01 amperes
(b) 0.1 amperes
(c) 10 amperes
(d) .001 amperes
QUESTION 177
The practical unit for electrical energy is the:
(a) kilowatt hour
(b) kilojoule hour
(c) kilowatt second
(d) kilojoule second
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QUESTION 178
A 56k ohm resistor has a resistance of:
(a) 560 ohms
(b) 5.6 ohms
(c) 5600 ohms
(d) 0.0056 ohms
QUESTION 179
Voltage applied to a circuit with the switch closed will:
(a) prevent current flow
(b) isolate the supply
(c) allow current to flow
(d) disconnect the load
QUESTION 180
Commercial billing of electrical accounts is charged per:
(a) watt
(b) watt second
(c) kilowatt hour
(d) kilojoule hour
QUESTION 181
Two conductive materials separated by insulating material would be:
(a) an inductor
(b) a capacitor
(c) a rheostat
(d) a resistor
QUESTION 182
Current flow in an electrical circuit may occur when:
(a) electrons can move freely
(b) electrons are held tightly in their orbit
(c) protons and neutrons are balanced
(d) protons can move freely
QUESTION 183
A meter connected in parallel with the load would be:
(a) a wheatstone bridge
(b) a voltmeter
(c) a wattmeter
(d) an ammeter
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QUESTION 184
Current flowing in a series circuit will:
(a) be greater in lower value components
(b) be the same value in all components
(c) increase as it passes through each component
(d) decrease as it passes through each component
QUESTION 185
As the temperature of motor windings increases the current in the windings will:
(a) reduce
(b) increase
(c) remain the same
(d) continually change
QUESTION 186
Resistance of a conductor is dependent on it’s:
(a) applied voltage, current, and cross sectional area
(b) applied voltage, length and the type of material
(c) length, cross sectional area, and applied voltage
(d) length, cross sectional area and the type of material
QUESTION 187
Two effects that always occur when an electric current flows are:
(a) physiological and heat
(b) heat and magnetic
(c) chemical and physiological
(d) magnetic and chemical
QUESTION 188
Piezo-electric devices may be used:
(a) in microphones
(b) in motors
(c) in thermo-couples
(d) in semi-conductors
QUESTION 189
Doubling the length of a cable where all other characteristics stay the same will
cause the resistance of the cable to:
(a) halve
(b) double
(c) stay the same
(d) increase four times
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QUESTION 190
Two 10 ohm resistors are connected in parallel to the supply. If another 10 ohm
resistor is placed in parallel with the first two resistors the circuit current would:
(a) decrease
(b) increase
(c) stay the same
(d) fall to zero
QUESTION 191
If a resistor in the parallel section of a series-parallel circuit becomes open circuit,
the total current will:
(a) remain constant
(b) increase
(c) decrease to a lower level
(d) decrease to zero
QUESTION 192
Heat will be produced when current flows in:
(a) a pure capacitor
(b) a pure inductor
(c) a pure resistor
(d) all of the above
QUESTION 193
The material to be selected when a semiconductor type material is required is:
(a) copper
(b) plastic
(c) iron
(d) silicon
QUESTION 194
Electrical pressure is measured in:
(a) volts
(b) current
(c) resistance
(d) capacitance
QUESTION 195
Current in a circuit is directly proportional to:
(a) resistance
(b) voltage
(c) conductance
(d) resistivity
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QUESTION 196
An electric shock is an example of:
(a) the heating effect of an electric current
(b) the magnetic effect of an electric current
(c) the physiological effect of an electric current
(d) the chemical effect of an electric current
QUESTION 197
The resistance of a typical ammeter will be:
(a) under 1 ohm
(b) under 10 ohms
(c) above 50,000 ohms
(d) above 1 mega ohm
QUESTION 198
A common device used to produce a small voltage by having two different metals
joined to form a junction is called:
(a) a diode
(b) a thermocouple
(c) a piezo-electric cell
(d) a photovoltaic cell
QUESTION 199
Specifications for purchasing a resistor would be:
(a) resistance value, current rating and tolerance
(b) power rating and current rating
(c) voltage rating and power rating
(d) resistance value, tolerance and power rating
QUESTION 200
Doubling the resistance in a series connected circuit will cause the current to:
(a) double
(b) halve
(c) stay the same as it was
(d) increase four times
QUESTION 201
An open circuit in one branch of a parallel circuit will cause the total circuit
resistance to:
(a) increase
(b) decrease
(c) not change
(d) consume more power
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QUESTION 202
A circuit consists of three resistors. Resistors Ri and R2 are connected in
parallel. R3 is connected in series with the parallel combination. If R2 was short
circuited the total circuit current would:
(a) remain unaltered
(b) fall to zero
(c) increase
(d) decrease
QUESTION 203
An instrument having a voltage coil and a current coil would be:
(a) a wheatstone bridge
(b) an ammeter
(c) a voltmeter
(d) a wattmeter
QUESTION 204
The voltage generated by an insulation tester is usually in the range of
(a) 1.5 to 3volts
(b) 10 to 100 volts
(c) 500 to 1000 volts
(d) 5000 to 50,000 volts
QUESTION 205
Increasing the capacitance of an RC circuit will cause the time constant to:
(a) remain the same
(b) increase
(c) decrease
(d) reach a maximum value on charging
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SECTION B
QUESTION 1.
When a one kilogram body is moved a distance of one metre the force involved
is
QUESTION 2.
Electric energy is charged by the supply company at a rate called a tariff. This
tariff is a rate in cents per _____________________ used.
QUESTION 3.
The ohm is the unit for electrical ______________________
QUESTION 4.
The unit of electric current is the ________________________
QUESTION 5.
If the voltage applied to a resistor is doubled the power dissipated by the resistor
will be _____________________________
QUESTION 6.
For the SI unit for energy, it means that energy is measured in ______________
QUESTION 7.
Power is defined as the
at which _____________ is done.
QUESTION 8.
One limited form of protection from electric shock is the use of a core-balance
transformer. This device is usually referred to as an _______________________
QUESTION 9.
The four effects of an electric current are the _____________ effect, the
_____________ effect, the ______________________ effect and the
_________________ effect.
QUESTION 10.
List the four commonly used methods to produce an emf.
____________________, __________________, _______________________
, _________________
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Page 39
QUESTION 11.
The total resistance of a series circuit is the _____________________ of the
individual resistances.
QUESTION 12.
The total resistance of a parallel circuit is
the smallest resistor.
than the value of
QUESTION 13.
If the total resistance of a circuit is doubled, the circuit current will
QUESTION 14.
A voltage of 0.0012 volts, expressed in millivolts, equals ____________mV.
QUESTION 15.
Capacitors are rated according to their ________________ value, their
__________________ and their type of____________________
QUESTION 16.
When purchasing a specific resistor, the two main characteristics that must be
stated, are:
1)
2)
QUESTION 17
If all other factors remain unchanged, what would happen to the resistance of a
conductor, if the conductor’s diameter is halved:
QUESTION 18
When purchasing a specific capacitor, the two main characteristics that must be
stated, are:
1)
2)
QUESTION 19
To lower the total resistance of a circuit, further resistance maybe connected in
________________________________ with the original circuit.
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Page 40
QUESTION 20
When resistors are connected in series, maximum power dissipation will always
be from the resistor with the _______________________________ resistance.
Question 6 to 8 refers to Table 1 below
QUESTION 21
Determine the value for a resistor with coloured bands in the following order:
i) Grey, Red, Yellow, Gold =
ii) Yellow, Violet, Black, Silver, Red =
QUESTION 22
Determine the coloured bands for a resistor with the following values:
i)
3.92 MΩ ±1% =
ii)
0.65Ω ± 10% =
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Page 41
QUESTION 23
Determine the resistance range for the following two resistors:
i)6.7k ohm ±1% = __________________ to ________________
ii)18R ohm ±10% =__________________ to _________________
QUESTION 24
Give an example of either a device or equipment that uses a photo-resistor:
QUESTION 25
Give an example of either a device or equipment, that uses a thermistor:
QUESTION 26
The main function of the instrument called “a megger” is to measure
_____________ resistance.
QUESTION 27
A voltage divider circuit is generally regarded as what type of circuit.
QUESTION 28
An electric current produces four effects, two of which are always present. They
are
&
.
QUESTION 29
The
effect of electric current is used in the electroplating process
QUESTION 30
The ______________________ effect is used to produce an e.m.f. in a
microphone.
QUESTION 31
The ________________________effect is used to ignite the gas in an electronic
(cigarette) lighter.
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Page 42
QUESTION 32
Discuss what effect, if any, a high resistance connection at point X, would have
on the operation of the circuit.
QUESTION 33
Which one of the four effects of current covers the effect of electrocution on the
human body.
QUESTION 34
The term _______________________ is used to describe a person or device’s
ability to do work.
QUESTION 35
A _____________________is the meter that measure the amount of power used
by a device.
QUESTION 36
An atom with a loss of________________________ is termed a positive ion.
QUESTION 37
The _____________________ is the practical unit of capacitance.
QUESTION 38
If a load is placed across part of a voltage divider circuit, it would be known as a
____________________________ connected circuit.
QUESTION 39
Give one example of either a device, or equipment, which uses the physiological
effect of current:
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QUESTION 40
Draw in the space below the correct symbol for the following:
The resistor colour code below may be used for Questions 44 and 45.
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Page 44
QUESTION 41
The pressure in an electric circuit is measured using a/an
__________________________
QUESTION 42
The resistance of a/an ____________________________is low because it is
connected in ___________________________________________ with the
load.
QUESTION 43
An application that uses the chemical effect of an electric current is
________________
QUESTION 44
An electric motor uses the _____________________________ effect of an
electric current.
QUESTION. 45
The resistance of a VDR varies with changes in _______________________.
QUESTION 46
If all other factors remain constant and the CSA of a conductor is halved, its
resistance will
QUESTION 47
The equivalent resistance of FOUR (4) resistors connected in parallel would be
less than the
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Page 45
QUESTION 48
Using the information provided in Table 1, complete the following table:
QUESTION 49
Briefly explain the difference between a resistor that has five coloured bands and
one which has only four.
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Page 46
QUESTION 50.
If the cross sectional area of a conductor is doubled, and the length is also
doubled, the resistance of the conductor would _____
_
QUESTION 51
(a) Use the colour code table provided to determine the value of a resistor which
has the following colour bands: Yellow, Violet, Red, Gold.
(b) What would be the possible resistance range for the resistor, based on its
tolerance?
QUESTION 52
List TWO (2) common household appliances, which use the power dissipation
property of resistors to operate.
(a)
(b)
QUESTION 53
The equivalent resistance of several resistors connected in series is always
__________________ than the largest individual resistor value in the circuit.
QUESTION 54
In a series circuit the algebraic sum of the voltages around a closed loop (i.e.
circuit) is equal to _______________________
QUESTION 55
The type of circuit in which the equivalent circuit resistance is less than the
smallest individual resistance of any resistor is a ______________________
circuit.
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Page 47
QUESTION 56
The quantity of charge held in a capacitor is dependent on the
_________________ of the capacitor and the __________________________
QUESTION 57
The zero end of the scale of an analogue ohmmeter is found at the
____________________ end of the multimeter.
QUESTION 58
The use of a short-shunt connected ammeter and voltmeter in a circuit is best for
measuring _________________ values of resistance.
QUESTION 59
List TWO (2) factors, beside the area of the plates, that will determine the
capacitance of a capacitor.
(a) __________________________
(b) __________________________
QUESTION 60
TWO (2) examples of non-linear resistors are:
(a) __________________________
(b) __________________________
QUESTION 61
TWO (2) practical electrical insulating materials are:
(a) __________________________
(b) __________________________
QUESTION 62
There are a number of effects of electricity, one of which is the heating effect.
Name TWO (2) other effects.
(a) __________________________
(b) __________________________
QUESTION 63
An electrical device installed to protect people from electric shock is known as:
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Page 48
QUESTION 64
A secondary cell
recharged.
is
one
that
________________________________be
QUESTION 65
The current capacity of a group of primary cells connected together can be
increased by connecting them in _________________
QUESTION 66
Ideally, the internal resistance of a voltmeter is as _________________as
possible, while the internal resistance of the ammeter is as
__________________as possible.
QUESTION 67
Give TWO (2) examples of polarised capacitors:
___________________________ and ________________________________
QUESTION 68
The variable resistor that you could use to control a 10 A current in a circuit is
known as a ______________________________
QUESTION 69
Convert the following to the units shown, using the correct prefix and unit
abbreviations:
(a) 0.4 17 micro-farads to nano-farads _______________________________
(b) 37.45 micro-amperes to milli-amperes
(c) 36876 joules to kilo-joules
(d) 774 micro-henries to henries _________________________________
(e) 63.4 x 10 kilo-grams to grams
QUESTION 70
Express the following in engineering notation using the best correct prefix
symbol.
(a) 1.25 x 10 watts ________________________________________________
(b) 0.00037 amperes
(c) 0.064 x 10 seconds ______________________________________________
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QUESTION 71
Draw the connections necessary on Figure 1 below, so that current through
resistor R1 will be 2 amperes.
QUESTION 72
Convert the flowing multiples and submultiples back to the base units:
(a) 710 MJ is equal to
Joules
(b) 8.2 kΩ is equal to
Ohms
(c) 1200 µF is equal to Farad
(d) 24.5 mA is equal to Amperes
QUESTION 73
A resistor with a resistance of 4.7 MΩ is equal to
kΩ
QUESTION 74
When heat is applied to an electrolyte, its resistance will
QUESTION 75
The current flowing in a circuit is
proportional to the applied
voltage and
proportional to the circuit resistance.
QUESTION 76
The prefix used for a unit multiplied by 10‾⁶ is
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QUESTION 77
Transpose the following equations for the subjects shown:
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QUESTION 78
Draw the standard symbols for the following electrical components:
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QUESTION 79.
The value of the unknown current in Figure 2 below is
QUESTION 80.
Electrical cells can be classified into two types. The type of cell that can be
recharged is termed a
cell.
QUESTION 81.
A series circuit consists of two resistors having values of 68Ω and 82Ω. The
smallest voltage drop will occur across the ____________ resistor.
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Page 53
QUESTION 82.
Use the resistor colour code in Table 1 below to answer the following questions.
State the resistance and tolerance percentage of the following four band resistors
with the colour bands indicated:
(a) Green, Blue, Yellow, Gold
Resistance:
Tolerance:
(b) Brown, Red, Orange, Silver
Resistance: _______________________
Tolerance: ________________________
(c) State the colour code of a four band resistor having a value of 47Ω and a
tolerance of 10%:
DC Work Book
Page 54
QUESTION 83
The
process.
effect of electric current is used in the electroplating
QUESTION 84
A wattmeter consists of a
supply and a
coil connected in parallel with the
coil connected in series with the load.
QUESTION 85
A generator produces an emf due to the relative motion between a
and a magnetic field.
QUESTION 86
The unit for electrical energy is the
QUESTION 87
The conductivity of copper is
aluminium.
than the conductivity of
QUESTION 88
The chemical reactions cannot be reversed in a
cell.
QUESTION 89
The total power consumed by a circuit is the
dissipation of each of the individual circuit components.
of the power
QUESTION 90
If a resistor in a parallel circuit became open circuit, the total circuit resistance
would
and total circuit power consumption would
QUESTION 91
Power in an electrical circuit would be measured by a/an
QUESTION 92
An electrical stove uses the
effect of an electrical current.
QUESTION 93
The resistance of a PTC resistor
temperature.
with an increase in
QUESTION 94
An atom that has gained an electron is called a/an
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Page 55
QUESTION 95
The current in a series circuit that has an open circuit would be
QUESTION 96
The resistance of a conductor is directly proportional to it’s
QUESTION 97
Any material that will allow current to flow will have the characteristics of
resistance and
QUESTION 98
The ratings required on an electrolytic capacitor are
QUESTION 99
Current is
proportional to resistance.
and
proportional to voltage and
QUESTION 100
In the space provided connect a 15 ohm resistor to a 20 volt supply.
Include a control device and protection.
The meters to be connected in the circuit are to be a voltmeter measuring the
load voltage, an ammeter for measuring load current, and a wattmeter to
measure the total power.
NOTE: Use the correct symbols.
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Page 56
QUESTION 101
Use the resistor colour code in Table 1 below to answer the following questions.
(a) State the resistance and tolerance percentage of the following four band
resistors with the colour bands indicated:
Red, Violet, Orange, Gold.
Resistance
Tolerance
Brown, Red, Orange, Silver.
Resistance
Tolerance
(b) State the colour code of a four band resistor having a value of 82 1 and a
tolerance of 10%.
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Page 57
QUESTION 102
In the space below draw the correct symbol.
DC Work Book
Page 58
QUESTION 103
Change the subject for the following formulae.
P=I²R
Find I
XL=2πfL
Find f
QUESTION 104
The graph below represents a 5Ω resistor. Calculate the voltage required to
cause a current of 3 amperes to flow.
Voltage would be
DC Work Book
Page 59
SECTION C
QUESTION 1.
If a force of 520 N is exerted on a body and moves it 4.3 metres.
a) calculate the amount of work done.
b) If the body took 5 seconds to cover the distance, what power was being used?
QUESTION 2.
A 5 kW motor has an operating efficiency of 78%. What is the input power
requirement.
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Page 60
QUESTION 3.
Find the length of Nichrome wire required to wind a 250 ohm resistor, if the
resistivity of Nichrome wire is 112 x 10ˉ⁸ ohm/m with a csa of 0.01mm².
QUESTION 4.
The copper winding of an electric motor has a resistance of 242 ohms at 15°C.
What is its resistance at 40 °C. (a0 for copper is 0.00427 ohm / °C).
QUESTION 5.
Two capacitors, a 10 uF and a 5 uF are connected in series. Find the equivalent
capacitance.
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Page 61
QUESTION 6.
In the circuit below the voltage across the capacitor rose to 15.1 volts in one time
constant of 34 seconds. Determine the value of the resistor ‘R’.
QUESTION 7.
The current through two series connected resistors is 250 mA when connected to
a 14 volt d.c. supply. If the resistance of one resistor is 25 ohms, determine the
value of the second resistor.
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Page 62
QUESTION 8.
Two resistors are connected in parallel to a 24 volt d.c. supply. The resistance of
one of the resistors is 48 ohms. If the total current leaving the supply is 750 mA.
What is the value of the second resistor.
QUESTION 9.
Calculate total circuit current for the circuit below for the following conditions:
a)
with Switch A open and Switch B closed.
b)
with Switch B closed and Switch A closed.
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Page 63
QUESTION 10.
Shown below is the voltage charge/discharge curves for a capacitor. Using these
curves, calculate the following:
A capacitor in a RC circuit becomes fully charged to 80 volts in a time of 10
seconds.
a) What would have been the voltage across the capacitor after 5 seconds.
b) When a discharge is initiated, after the capacitor has been fully charged, what
will be the voltage across the capacitor after 7.25 seconds.
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Page 64
QUESTION 11
The diagram drawn in figure 4 below shows the components of a circuit. Draw
the connections that are required to meet the following description:
a) R1 and R2 are connected in parallel, (0.5 mark)
b) R3 and R4 are connected in parallel, (0.5 mark)
c) R5 and R6 are connected in series, (0.5 mark)
d) The series connected group of resistors are connected in between the
two parallel groups of resistors, (0.5 mark)
e) The ammeter A1 is to measure the circuit current, (1 mark)
f) The ammeter A2 is to measure the current flowing into R3, (1 mark)
g) The voltmeter V1 is to measure the voltage drop across R2, (1 mark)
h) The voltmeter V2 is to measure the voltage drop across R5, (1 mark)
i) The circuit is to be protected by the fuse, (0.5 mark)
j) The circuit is to be control by the switch S1, (0.5 mark)
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QUESTION 12
What would be the resistance of a copper 2.5mm² conductor with a length of 0.1
kilometres? (p for copper = 1.72 x 10ˉ⁸ ohm.metre)
QUESTION 13
A conductor having a cross-sectional area of 1.5 mm² and a length of 0.75km
has a resistance of 400 ohms. Calculate the resistance of a similar conductor
having a cross-sectional area of 2.5 mm², and a length of 300m.
QUESTION 14
Calculate the shunt resistance needed to allow a 10mA (10) ammeter movement
to accurately read a current of 1 A.
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Page 66
QUESTION 15
With reference to figure 6 below, calculate the:
(a) total resistance of the circuit.
(b) current in the 680 ohm resistor.
(c) power consumed by the 680 ohm resistor.
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Page 67
QUESTION 16
With reference to figure 7 below, calculate the:
(a) total resistance of the circuit.
(b) power dissipated in the 120 ohm resistor.
(c) current through the 60 ohm resistor.
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Page 68
QUESTION 17
With reference to figure 8 below, calculate the:
(a)
(i) Charging current at 1 Time Constant.
(ii) Voltage drop across the 12OΩ resistor at one time constant after the
switch closes on charge.
(b)
Discharge current, flowing through the 480Ω resistor, at one time constant
after the fully charged capacitor is switched to discharge.
(c)
Plate area of the capacitor, if the dielectric has a thickness of 0.06mm and
a permittivity of 26x10‾⁸
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QUESTION 18
With reference to figure 10 below, calculate the:
Note ALL resistors in figure 10 below have the same value, 30 ohms
(a) equivalent resistance of figure 10 as seen by the power supply.
(b) current flowing through the resistor R3.
(c) voltage drop across the resistor R4.
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QUESTION 19
If the efficiency of a 7.5 kW, 240 V d.c. motor is 90%, calculate the current drawn
from the supply when operating at its rated load.
QUESTION 20
How much would it cost per week to run a 6 kW electric room heater for six hours
per day if the cost of electricity is 20 cents per unit?
QUESTION 21
Determine the resistance of a 75 m length of 2.5 mm² copper conductor if the
resistivity of copper is 1.72 x 10‾⁸ ohm metres.
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QUESTION 22
The resistance of a heating element is 100 ohms at 20°C. Calculate the
resistance of the element at its operating temperature of 1000°C if the
temperature co-efficient of resistance of the heating element is 0.002 ohms per
degree Celsius.
QUESTION 23
A conductor with a length of 60 m and a csa of 1.5 mm² has a resistance of 0.3
ohms. Determine the resistance of a similar conductor whose length is 75m and
csa is 2.5mm².
QUESTION 24
Two resistors of 10 ohms and 25 ohms are connected in parallel. If the current
through the 10 ohm resistor is 5 amperes, how much current is flowing through
the 25 ohm resistor?
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QUESTION 25
A series circuit consists of three resistors (R1 = 47 ohms, R2 = 82 ohms and R3
68 ohms respectively) and is connected to a 100 V d.c. supply.
Using Standard symbols, draw a diagram to illustrate this circuit and include in
your diagram:
(a) a voltmeter to measure the supply voltage
(b) a voltmeter to measure the voltage across R2 and
(c) an ammeter to measure the current flowing through R3
(d) determine the reading on the voltmeter across R2
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QUESTION 26
Three resistors of 150 ohms, 180 ohms and 220 ohms are connected in parallel
to a 100 V d.c. supply. Calculate:
(a) the equivalent resistance of the circuit
(b) the current taken from the supply
(c) the power consumed by the 180 Ω resistor.
QUESTION 27
A 24 V lamp is to be dimmed using a switch and a series resistor. The circuit is
connected to a 24 V d.c. supply.
(a) Draw a circuit diagram to show how the switch would be connected in the
circuit.
(b) If the lamp, when dimmed draws 0.8 A at 16 V, calculate the resistance and
minimum power rating of a suitable series resistor.
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QUESTION 28
For the circuit shown in Figure 1, calculate:
(a) the current drawn from the supply
(b) the voltage dropped across R5
QUESTION 29
Determine the resistance of a 6mm² circular aluminium conductor 250 metres in
length (Resistivity of aluminium = 2.85 x 10‾⁸ ohm.metres).
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QUESTION 30
The resistance of the copper wire field winding of a 24 V motor was found to be
2.46 ohms at an ambient temperature of 18 °C. Under operating conditions the
temperature of the winding rose to 55 °C. Calculate the percentage change in
field current through the winding.
(Temp coefficient of Cu = 0.00393).
QUESTION 31
Three resistors are connected in series to a 120 volt d.c. supply. R1 is 120 ohms,
R2 is 150 ohms and R3 is 330 ohms:
(a) Sketch the circuit using Australian Standard symbols, and include a switch,
an ammeter for circuit current and a voltmeter to measure voltage across R3.
Show polarities for the meter connections.
(b) Determine the circuit current:
(c) Determine the voltage drop across R3:
(d) Determine the power dissipated by resistor R2:
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QUESTION 32
THREE (3) resistors of 1800 ohms, 2200 ohms and 800 ohms are connected in
parallel across a 100 V supply. Determine the:
(a) equivalent resistance of the group:
(b) current in the 1800Ω resistor.
(c) power consumed by the 220Ω resistor.
QUESTION 33
In Figure 2 (above), calculate the:
(a) equivalent circuit resistance:
(b) current inR4:
(c) voltage drop across R2:
(d) total power used by the circuit:
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QUESTION 34
If the power consumed by the circuit of Figure 4 is 10 W, determine the:
(a) total equivalent resistance of the circuit:
(b) value of resistor R1:
(c) voltage across R4:
QUESTION 35
The d.c. voltage across resistor R2 in the circuit shown in Figure 5 below is to be
measured. The following two voltmeters are available and both are set to the 50
V d.c. range:
• a digital voltmeter with an input resistance of 10 MΩ
• an analogue voltmeter with a sensitivity of 50 kΩ per volt
Show, from the readings that would be obtained on each voltmeter, which would
provide the more accurate voltage reading across resistor R2 compared to the
reading expected.
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Page 78
QUESTION 36
Calculate the equivalent capacitance of three capacitors; 4µF, 6µF and 1200 nF
connected in:
(a) series:
(b) parallel:
(c) If 10 V d.c. is applied to the series circuit of the question above, calculate the
total charge stored.
QUESTION 37
In Figure 7 the switch is closed to position A at t = 0 seconds. 300 ms later the
switch is switched to position B. Determine the current through the resistor after
500 ms have elapsed. (ie. 200 ms after being switched to B)
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Page 79
QUESTION 38
Calculate the efficiency at 70% full load of a 50 kW electric motor which has fixed
losses of 650 watts and variable losses at 70% full load of 1800 watts.
QUESTION 39
Three resistors with the following values are connected in parallel and supplied
from a 120 V d.c. power supply.
R1 120Ω
R2= 180Ω
R3= 150Ω
Calculate:
(a) the equivalent resistance of the circuit
(b) the current drawn by resistor R3
(c) the power consumed by resistor R2
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QUESTION 40
Three resistors of 47Ω, 100Ω and 33Ω respectively are connected in series to a
generator. The current drawn from the generator is 2 Amperes.
(a) Determine the generator terminal voltage V
(b) Calculate the voltage across the 100Ω resistor.
(c) Calculate the power consumed by the 47Ω resistor.
(d) Determine the circuit current if the 100Ω resistor becomes short-circuited.
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QUESTION 41
Five resistors, each having a value of 150Ω are connected in parallel to a d.c.
power supply. Calculate the total current drawn from the power supply if the
terminal voltage is 200 V.
QUESTION 42
The resistance of a coil of copper wire is 27Ω at 20°C. Determine the coil’s
resistance at 100°C. The temperature coefficient of resistance for copper is
0.00393 at 20°C.
QUESTION 43
Calculate the resistance of a 2.5 km length of aluminium conductor with a
cross-sectional area of 6 mm². The resistivity of aluminium is 2.83 x 10‾⁸.
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QUESTION 44
An electric radiator is rated at 1200 W when connected to 240 V. Calculate the
resistance of the heating element.
QUESTION 45
A 500 metre drum of 1.5 mm² copper building wire has a resistance of 5.7Ω.
Determine the resistance of 750 metres of 1.0 mm² copper building wire.
QUESTION 46
A 12Ω resistor is to be manufactured using 0.4 cross-sectional area nichrome
wire. Determine the length of nichrome wire required. Nichrome has a resistivity
of 1.122 x 10‾⁶Ω/m.
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Page 83
QUESTION 47
A switch, a l2kΩ resistor and a 200µF capacitor are connected in series to a 24V
d.c. power supply.
(a) Calculate the time constant for this circuit.
(b) Determine the voltage across the capacitor after ONE (I) time constant.
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Page 84
QUESTION 48
This question refers to Figure 4. A 500 volt generator supplies a motor with a
current of 80 amperes. The voltage at the motor terminals is 480 volts.
(a) Determine the voltage drop in the connecting cables.
(b) Calculate the total cable resistance connecting the motor and the generator.
DC Work Book
Page 85
QUESTION 49.
Refer to the diagram labeled Figure 5, to answer the following:
(a) Calculate the total resistance of the circuit.
(b) Calculate the total circuit current.
(c) Determine the voltage drop across resistor R4.
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Page 86
QUESTION 50
Two capacitors C1 and C2 are connected in series to a 200 V d.c. power supply.
The total capacitance of the circuit is 96µF and capacitor C1 has a value of 120
µF.
(a) Determine the value of capacitor C2.
(b) Calculate the total charge on the circuit.
(c) Calculate the voltage across capacitor C1.
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Page 87
QUESTION 51
Draw the connections necessary to complete the circuit in Figure 1 using the
following instructions:
• R1 is paralleled with R2.
• R3 is paralleled with R4.
• The R1/R2 and R3/R4 combinations are in series.
• An ammeter is to measure the current in R3.
• A voltmeter is to measure the voltage across R1.
• The circuit is to be supplied from a l2volt DC source.
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Page 88
QUESTION 52
Draw the circuit symbols for the following electrical components:
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Page 89
QUESTION 53
Use the resistor colour code in the Table below to answer the following
questions.
(a) State the resistance and the tolerance percentage of the following four band
resistor with the colour bands indicated:
Yellow Violet Orange Red
Resistance:
Tolerance:
(b) If a colour coded resistor has a resistance value of 2.2 kΩ and a tolerance of
5%, what are the colours that would represent this?
(c) If a resistor has a specified value of 100,000 Ω and has a tolerance of 10%,
what would be the acceptable range of resistance for this resistor?
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Page 90
QUESTION 54
Determine the resistance value indicated on the meters shown in Figure 2 &
Figure 3.
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Page 91
QUESTION 55
Transpose the following equations for the subject indicated:
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Page 92
QUESTION 56
In the circuit of Figure 4, determine the current flowing in R4.
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QUESTION 57
Four resistors as illustrated in Figure 5 are supplied from a 24 volt d.c. source.
Calculate:
(a) The equivalent resistance of the circuit.
(b) The current flowing through resistor R3.
(c) The power dissipated by resistor R4.
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Page 94
QUESTION 58
Three resistors as illustrated in Figure 6 are supplied from a 12 volt d.c. source.
Calculate:
(a) The equivalent resistance of the circuit.
(b) The current flowing through resistor R3.
(c) The power dissipated by resistor R1.
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Page 95
QUESTION 59
Calculate the voltage across resistor R2 in the voltage divider circuit of Figure 7.
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Page 96
QUESTION 60
Using the values given in Figure 8, determine:
(a) The equivalent resistance of the circuit.
(b) The current flowing through R6.
(c) The voltage across R3.
(d) The total power consumed by the circuit.
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Page 97
QUESTION 61
An incandescent lamp has a cold resistance of 1400Ω. If 20 are connected in
parallel in a circuit, what would be the total resistance of the circuit?
QUESTION 62
A copper cable has a resistance of 2Ω at 25 °C. Given that the temperature coefficient of resistance for copper is 0.00393Ω/°C, what is the resistance of the
cable if the cable temperature increases to 75 °C.
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Page 98
QUESTION 63
What is the resistance of a coil of wire which has a length of 185 metres, if the
resistance of 75 metres of the same wire is 6.8Ω?
QUESTION 64
A conductor has a resistance of 1.54Ω and a csa (cross sectional area) of 2.5
mm². Determine the resistance of a second conductor having the same length
and made of the same material, but having a csa of 10mm²
QUESTION 65
A 16 mm² copper conductor is 125 metres long. Calculate the resistance of this
cable given that the resistivity of copper is 1.72 x 1 0‾⁸ Ωm.
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Page 99
QUESTION 66
An R-C circuit consists of a 68 kΩ resistor connected in series with a 100 µF
capacitor. Determine the time constant of the circuit.
QUESTION 67
An R-C circuit has a time constant of two seconds. Using the universal time
constant curve and knowing the capacitor was fully discharged before switch on:
(a) What percentage of the supply voltage will be across the capacitor after a
time period of two seconds after switch on?
(b) What percentage of the supply current will be flowing after a time period of
four seconds after switch on?
(c) What percentage of the supply voltage will be across the resistor after a time
period of five seconds after switch on?
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Page 100
QUESTION 68
From the circuit illustrated in Figure 9, determine:
(a) The total capacitance of the circuit.
(b) The total charge stored.
(c) The voltage across each capacitor.
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Page 101
QUESTION 69
From the circuit illustrated in Figure 10, determine:
(a) The total capacitance of the circuit.
(b) The total charge stored by the circuit.
(c) The charge stored by each capacitor.
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Page 102
QUESTION 70
Three resistors are to be connected in series to a 100 volt supply.
R1=15Ω, R2=25Ω, R3=10Ω.
(a) Draw the circuit.
(b) Calculate the circuit current.
(c) Calculate the voltage across R2.
(d) Calculate the power consumed by R3.
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QUESTION 71
The circuit in Figure 2 represents a parallel circuit.
Calculate the following circuit values.
(a) The supply voltage.
(b) The current I2.
(c) The resistance of R2.
(d) The power consumed by R1.
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Page 104
QUESTION 72
Calculate the resistance of a 4 mm² copper conductor when its length is 500
metres. (p for copper 1.72 x 10ˉ⁸ Ω.m).
QUESTION 73
A coil is to be wound using a copper conductor. The coil will have a resistance of
50Ω at a temperature of 25°C. Copper has a temperature co-efficient of
resistance of 0.004/°C.
(a) Calculate the resistance of the coil when it is operating at 75°C.
(b) If the supply voltage is 200 volts calculate the current when the coil is at:
(i) 25°C.
(ii) 75°C.
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QUESTION 74
A 2kW DC motor is to be connected to a 240 volt supply. The efficiency of the
motor is 80%. Calculate the full load current of the motor.
QUESTION 75
A room heater has a rating of 2.4 kW and runs for three hours every night. If the
cost of power is charged at nine cents per kilowatt hour, calculate the cost over a
13 week period.
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Page 106
QUESTION 76
(a) Calculate the time constant of the circuit.
(b) Calculate the voltage across the capacitor after one time constant.
(c) Calculate the circuit current after one minute.
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QUESTION 77
(a) Calculate the total circuit resistance.
(b) Calculate the voltage across the 6kΩ R1 resistor.
(c) Calculate the voltage drop across the 7kΩ R3 resistor.
(d) Calculate the power consumed by the 1kΩ R4 resistor.
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QUESTION 78
The circuit in figure 6 below represents a series/parallel circuit.
Calculate each of the following values.
(a) Calculate the total circuit resistance.
(b) Calculate the total circuit current.
(c) Calculate the current in R3.
(d) Calculate the power consumed by R1.
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