| 1. | With regards to measuring current and voltage in an AC circuit, modern AC instruments are calibrated to read:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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:
|
| 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 |
|
| 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 |
|
| 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:
|
| 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 |
|
| 11. | A coil has an inductance of 0.04 H. The inductive reactance of the coil at a frequency of 50 Hz will be:
|
| 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:
|
| 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:
|
| 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:
|
| 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 |
|
| 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:
|
| 18. | In a purely capacitive circuit the current:
| C. | is in phase with the voltage |
| D. | leads and then lags the voltage |
|
| 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 |
|
| 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 |
|
| 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:
|
| 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 |
|
| 23. | When two capacitors are connected in parallel, the total capacitance:
| D. | equals the difference between the two |
|
| 24. | An 22 uF capacitor has been connected in series with a 47 uF capacitor. The total capacitance of the combination is approximately:
|
| 25. | An 16 uF capacitor has been connected in parallel with a 22 uF capacitor. The total capacitance of the combination is approximately:
|
| 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:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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:
|
| 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 |
|
| 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:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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:
|
| 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:
|
| 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 |
|
| 43. | The true power consumed by a single-phase AC circuit can be determined using the formula:
|
| 44. | In an AC the product of the measured line voltage and line current is called the:
|
| 45. | The reactive power in an AC circuit is sometimes called:
|
| 46. | Figure shows the power triangle for an AC circuit: 
In the diagram, the side marked ‘S’ represents the:
|
| 47. | In an AC circuit, the power factor is the factor by which the apparent power is multiplied to obtain the:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 51. | The power factor of an AC circuit can be found using the formula, Power factor = :
| B. | volt-amperes x current |
|
| 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:
|
| 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:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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:
|
| 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 |
|
| 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 |
|
| 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 |
|
| 61. | In an AC circuit, when the capacitive reactance and inductive reactance are exactly equal, the circuit is said to be:
|
| 62. | The major characteristics of the series resonant circuit are a power factor of unity and a:
| D. | maximum capacitive reactance |
|
| 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 |
|
| 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 |
|
| 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 |
|
| 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:
|
