| 1. |
With regards to measuring current and voltage in an AC circuit, modern AC instruments are calibrated to read:
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| 2. |
The current waveform for a purely resistive circuit:
| A. |
leads the voltage by 90 ° |
| B. |
is in phase with the voltage |
| C. |
lags the voltage by 90° |
| D. |
alternately leads and lags the voltage |
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| 3. |
Look at the following figure: 
Figure shows the voltage, current and power waveshapes for a purely resistive circuit supplied with a sinusoidal AC voltage. The waveshapes show that for a purely resistive circuit, the power curve:
| A. |
has an average value equal to the area under the voltage wave |
| B. |
has a negative value when both the voltage and current are negative |
| C. |
completes two cycles for each complete cycle of current or voltage |
| D. |
will only have a negative value if the voltage and current are positive |
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| 4. |
The power consumed by a purely resistive AC circuit can be determined using the following formula:
P = Vrms x Irms
In the formula, the symbol ‘P’ stands for the:
| A. |
peak value of the power |
| B. |
RMS value of the power |
| C. |
maximum value of the power |
| D. |
average value of the power |
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| 5. |
Figure shows a non-inductive resistor: 
The non-inductive effect is produced by winding:
| A. |
half in a clockwise direction, and then the other half anticlockwise |
| B. |
coils for magnetic fields inside the inner core from a DC voltage |
| C. |
all the coils in the same direction to produce a self-induced voltage |
| D. |
the resistor with many turns of very fine a high resistance wire |
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| 6. |
A pure resistance of 15 ohms has been connected across an AC power supply that generates a pure sinewave of 84.84 volts peak voltage. The average power consumed by this resistor will be approximately:
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| 7. |
In an inductive AC circuit, the current is continually changing in value and direction, generating an induced EMF that will continually:
| A. |
assist the change of current flow |
| B. |
assist a change in supply frequency |
| C. |
oppose the change of current flow |
| D. |
oppose the resistance of the circuit conductors |
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| 8. |
Figure 3 shows the waveforms of the voltage and current in a purely inductive AC circuit: 
Using the voltage phasor as the reference, the current phasor:
| B. |
is in phase with the voltage |
| C. |
leads and then lags by 90°E |
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| 9. |
On AC, the change in current flow gives rise to an induced EMF that opposes the current flow. The effect of this current opposition is called:
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| 10. |
The inductive reactance in an AC circuit can be calculated from the formula:
XL = 2 π f L
In the formula, the symbol ‘L’ stands for the:
| A. |
length of the circuit in metres |
| B. |
inductance of the circuit in Henrys |
| C. |
low voltage value of the conductors |
| D. |
frequency of the supply in Hertz |
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| 11. |
A coil has an inductance of 0.04 H. The inductive reactance of the coil at a frequency of 50 Hz will be:
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| 12. |
A 230 V 50 Hz supply has been applied to a coil with an inductance of 0.15 H. The current in the circuit will be approximately:
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| 14. |
Two inductors, one with an inductive reactance of 15 Ω, and the second with an inductive reactance of 10 Ω have been connected in series across a 230 V 50 Hz supply. The total inductive reactance will be:
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| 15. |
Two inductors, one with an inductive reactance of 12 Ω, and the second with an inductive reactance of 8 Ω have been connected in parallel across a 230 V 50 Hz supply. The total inductive reactance will be:
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| 16. |
Figure shows the voltage, current and power waveshapes for purely inductive circuit: 
The power waveshape shows that power is:
| A. |
fed into the inductor continuously |
| B. |
continuously fed into the AC supply |
| C. |
only consumed by the inductor when both V & I are positive |
| D. |
alternately fed into and returned from the inductor |
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| 17. |
A pure inductor with an inductive reactance of 150 W has been connected to a 230 V AC circuit. The average power consumed by this inductor is:
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| 18. |
In a purely capacitive circuit the current:
| C. |
is in phase with the voltage |
| D. |
leads and then lags the voltage |
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| 19. |
Figure shows the waveshapes of voltage, current and power for a purely capacitive circuit: 
In this circuit, the current:
| A. |
lags the applied voltage by 90°E |
| B. |
leads the applied voltage by 180°E |
| C. |
leads the applied voltage by 90°E |
| D. |
lags the applied voltage by 180°E |
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| 20. |
The capacitive reactance of a capacitor can be determined using the formula: 
In the formula the symbol ‘f’ stands for the:
| B. |
speed of the capacitor in m/s |
| C. |
current in the circuit in amperes |
| D. |
frequency of the supply in Hertz |
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| 21. |
A 16 uF capacitor has been connected to a 230 V 50 Hz supply. The capacitive reactance of this capacitor in this circuit will be approximately:
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| 22. |
When two capacitors are connected in series, the total capacitance:
| A. |
is double the capacitance of any one |
| D. |
remains the same as the largest one |
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| 23. |
When two capacitors are connected in parallel, the total capacitance:
| D. |
equals the difference between the two |
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| 24. |
An 22 uF capacitor has been connected in series with a 47 uF capacitor. The total capacitance of the combination is approximately:
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| 25. |
An 16 uF capacitor has been connected in parallel with a 22 uF capacitor. The total capacitance of the combination is approximately:
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| 26. |
Two 10 uF capacitors have been connected in parallel across a 230 V AC supply. The current drawn from the supply will be approximately:
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| 27. |
The average power consumed by a purely capacitive circuit:
| A. |
is maximum when the current is leading |
| C. |
equals the value of the supply voltage |
| D. |
will be minimum when the current is lagging |
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| 28. |
Figure shows a resistor and an inductor connected in series across an AC supply: 
In this circuit, the current will:
| A. |
be in phase with the voltage |
| D. |
always be a large value |
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| 29. |
Figure shows the phasor diagram for an AC circuit with resistor and capacitor in series: 
The diagram shows that in this type of circuit, the current phasor:
| A. |
lags the voltage across the capacitor |
| B. |
leads the voltage across the resistor |
| C. |
lags the voltage across the resistor |
| D. |
leads the supply voltage phasor |
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| 30. |
In an AC circuit containing resistance, inductance and capacitance in series, the voltage drop across the inductor will:
| A. |
be 180°E out of phase with the voltage drop across the capacitance |
| B. |
lead the voltage drop across the capacitance by 90°E |
| C. |
lag the voltage drop across the capacitance by 90°E |
| D. |
be in phase with the voltage drop across the capacitance |
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| 31. |
The following phasor diagram is for a resistor, inductor and capacitor connected in series across an AC supply: 
The value of the phase angle F is:
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| 32. |
The following formula can be used to determine the impedance of an AC circuit with resistance, inductance and capacitance in series: Z = √(R2 + (XL – XC)2)
In the formula, the term XL stands for the value of the:
| A. |
capacitive reactance in Ohms |
| C. |
inductive reactance in Ohms |
| D. |
reactance of the capacitor in microfarads |
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| 33. |
A resistance of 50 Ω has been connected in series with an inductive reactance of 160 Ω and a capacitive reactance of 40 Ω. The impedance of the circuit will be:
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| 34. |
In a parallel AC circuit, the voltage is:
| A. |
common to all the components |
| B. |
equal to the sum of the branch voltages |
| C. |
larger than any branch voltage |
| D. |
equal the phasor sum of the branch currents |
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| 35. |
Figure shows a resistor and inductor connected in parallel across an AC supply: 
In this circuit, the current through the inductor will:
| A. |
lead the supply voltage |
| B. |
lag the supply voltage |
| C. |
be in phase with the supply voltage |
| D. |
equal the current through the resistance |
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| 36. |
Figure shows a resistor connected in parallel, with an inductor and resistor in series, across an AC supply. 
In this circuit, the current through the inductor will:
| A. |
lag the supply voltage by 90°E |
| B. |
lead the supply voltage by 90°E |
| C. |
lead the supply voltage by less than 90°E |
| D. |
lag the supply voltage by less than 90°E |
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| 37. |
Figure 10 shows the phasor diagram for a resistor and capacitor connected in parallel across an AC supply: 
In this circuit, the current through the capacitor:
| A. |
leads the supply voltage by 90°E |
| B. |
is in phase with the supply voltage |
| C. |
leads the supply voltage by approximately 30°E |
| D. |
lags the supply voltage by 90°E |
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| 38. |
When drawing the phasor diagram for R, L and C in parallel across an AC supply, the reference phasor is normally the:
| A. |
current through inductor |
| C. |
current through the capacitor |
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| 39. |
In an, AC circuit with R, L and C in parallel, the total supply current is:
| A. |
the arithmetic sum of the branch currents |
| C. |
the phasor sum of the branch currents |
| D. |
equal to the resistive current minus the inductive current |
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| 40. |
A resistance of 57.5 Ω has been connected to a 230 V 50 Hz supply, in parallel with an inductive reactance of 57.5 Ω and a capacitive reactance of 230 Ω. The total supply current will be:
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| 41. |
An AC circuit with R, L and C in parallel, has the following branch currents.
Resistive branch – 12 A
Inductive branch – 11 A
Capacitive branch – 6 A
The phase angle between the supply voltage and the supply current will be approximately:
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| 42. |
When resistance and inductance are combined in one circuit, there will be a value of power consumed that is dependent on the:
| A. |
capacitive load, in the circuit |
| B. |
resistive load, in the circuit |
| C. |
inductive load, in the circuit |
| D. |
size of the inductive reactance |
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| 43. |
The true power consumed by a single-phase AC circuit can be determined using the formula:
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| 44. |
In an AC the product of the measured line voltage and line current is called the:
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| 45. |
The reactive power in an AC circuit is sometimes called:
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| 46. |
Figure shows the power triangle for an AC circuit: 
In the diagram, the side marked ‘S’ represents the:
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| 47. |
In an AC circuit, the power factor is the factor by which the apparent power is multiplied to obtain the:
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| 48. |
For all electrical power work with sinusoidal waveforms, the power factor is equal to the:
| A. |
phase angle between the voltage and the current |
| B. |
sine of the phase angle between the voltage and the current |
| C. |
tangent of the phase angle between the voltage and the current |
| D. |
cosine of the phase angle between the voltage and the current |
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| 49. |
Generally, the lower the value of the power factor in an AC circuit, the:
| A. |
greater will be the current required to supply the same true power |
| B. |
less will be the current required to supply the same true power |
| C. |
less will be the phase angle between the voltage and current |
| D. |
greater will be time taken for the current to pass through |
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| 50. |
One of the major causes of a low power factor is:
| A. |
transformers running near full load |
| B. |
lightly loaded electric motors |
| D. |
diesel driven alternators |
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| 51. |
The power factor of an AC circuit can be found using the formula, Power factor = :
| B. |
volt-amperes x current |
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| 52. |
A single phase motor draws 2.175 A from a 230 V supply. A wattmeter in the circuit shows 400 W. The power factor of this circuit is approximately:
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| 53. |
An inductor draws 11.5 A on 230 V DC and 5.75 A when connected to 230 V AC. The angle of lag between the voltage and current when on AC will be:
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| 54. |
Look at the following diagram: 
When the switch S1 is closed in figure, the reading on the ammeter will:
| D. |
be the capacitor current only |
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| 55. |
Look at the following diagram: 
When the switch S1 is closed in figure, the power factor of the circuit will:
| D. |
move toward 0.1 lagging |
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| 56. |
Figure shows the phasor diagram of an electric motor connected to 230 V AC supply: 
If a capacitor is connected in parallel with the motor, the phasor to represent the capacitor current would be drawn:
| A. |
vertically down from position 1 |
| B. |
vertically down from position 3 |
| C. |
vertically up from position 2 |
| D. |
vertically up from position 1 |
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| 57. |
A single-phase 230 V 50 Hz induction motor draws 7.5 A at 0.6 power factor. If a 47 μF capacitor is connected across the line, then the combined line current will be approximately:
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| 58. |
The purpose of using capacitors to improve the power factor is to provide a:
| A. |
lagging current to counteract the lagging current drawn by the load |
| B. |
leading current to counteract the leading current drawn by the load |
| C. |
leading current to counteract the lagging current drawn by the load |
| D. |
lagging current to counteract the leading current drawn by the load |
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| 59. |
When using a power triangle to solve AC circuits the reactive power can be found using the formula:
Q = V I √1 – PF2)
In the formula the symbol PF stands for the:
| C. |
power factor of the circuit |
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| 60. |
When an electrical circuit has its power factor corrected to unity, the current is:
| C. |
same value as the voltage |
| D. |
brought into phase with the voltage |
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| 61. |
In an AC circuit, when the capacitive reactance and inductive reactance are exactly equal, the circuit is said to be:
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| 62. |
The major characteristics of the series resonant circuit are a power factor of unity and a:
| D. |
maximum capacitive reactance |
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| 63. |
When an inductor and capacitor are connected in parallel and their respective reactances are equal, the reactive currents are:
| A. |
equal but 90° out of phase with each other |
| B. |
not equal but 180° out of phase with each other |
| C. |
equal but 180° out of phase with each other |
| D. |
not equal but 90° out of phase with each other |
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| 64. |
When the supply frequency to a parallel resonant circuit is varied, the resistance in the circuit is unchanged but the impedance will be:
| A. |
minimum only at the resonant frequency |
| B. |
maximum at frequencies other than the resonant frequency |
| C. |
maximum only if the resonant frequency is 50 Hz |
| D. |
maximum only at the resonant frequency |
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| 65. |
In an AC circuit at resonance, energy is being transferred back and forth from the:
| A. |
electromagnetic field of the inductor to the electrostatic field of the capacitor |
| B. |
electrostatic field of the inductor to the electrostatic field of the capacitor |
| C. |
electrostatic field of the inductor to the electromagnetic field of the capacitor |
| D. |
electromagnetic field of the inductor to the electromagnetic field of the capacitor |
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| 66. |
A 10 Ω resistor, 0.25 H inductor and a 40.52 μF capacitor have been connected in series across a variable frequency AC supply. The resonant frequency of the circuit will be:
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