1. In a purely inductive AC circuit, the current differs in phase from the voltage by
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
90°
Explanation:
In a purely inductive circuit, the current lags behind the voltage by 90°, so the phase difference is 90°.
2. In a purely capacitive AC circuit, the current
A.
lags behind the voltage by 90°
B.
leads the voltage by 90°
C.
is in phase with the voltage
D.
has a phase difference of 180° with the voltage
Correct Answer:
leads the voltage by 90°
Explanation:
For a pure capacitor, the current leads the applied voltage by 90°.
3. When voltage and current are in phase in an AC circuit, the phase difference between them is
A.
0°
B.
30°
C.
60°
D.
90°
Correct Answer:
0°
Explanation:
Voltage and current are in phase when their phase difference is zero.
4. Wattless current is associated with a voltage-current phase difference of
A.
0°
B.
30°
C.
60°
D.
90°
Correct Answer:
90°
Explanation:
A wattless current occurs when voltage and current differ in phase by 90°, making the average power zero.
5. If the current lags behind the voltage by 90°, the circuit is ideally
A.
Resistive
B.
Inductive
C.
Capacitive
D.
Non-reactive
Correct Answer:
Inductive
Explanation:
In an ideal inductive circuit, current lags the voltage by 90°.
6. If the current leads the voltage by 90°, the circuit is ideally
A.
Resistive
B.
Inductive
C.
Capacitive
D.
Purely conducting
Correct Answer:
Capacitive
Explanation:
In an ideal capacitive circuit, current leads the voltage by 90°.
7. For an AC circuit with voltage-current phase difference of 90°, the average power consumed is
A.
Maximum
B.
Half of the maximum power
C.
Zero
D.
Equal to the apparent power
Correct Answer:
Zero
Explanation:
The average power is proportional to cos φ. For φ = 90°, cos 90° = 0, so the average power is zero.
8. The phase difference between voltage and current in a purely resistive AC circuit is
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
0°
Explanation:
In a purely resistive circuit, voltage and current rise and fall together, so they are in phase.
9. If the phase difference between voltage and current is 60°, the power factor of the circuit is
A.
0
B.
0.5
C.
1
D.
2
Correct Answer:
0.5
Explanation:
Power factor is cos φ. For a phase difference of 60°, the power factor is cos 60° = 0.5.
10. A circuit has a power factor of 1. The phase difference between its voltage and current is
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
0°
Explanation:
Power factor equals cos φ. A power factor of 1 occurs when φ = 0°, meaning voltage and current are in phase.
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