1. What is the power factor of an AC circuit having zero power factor?
A.
0
B.
0.5
C.
1
D.
2
Correct Answer:
0
Explanation:
A zero power factor means that the power factor, cos φ, is equal to zero.
2. In a zero-power-factor AC circuit, the phase difference between voltage and current is:
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
90°
Explanation:
Since power factor is cos φ and cos 90° = 0, voltage and current differ in phase by 90°.
3. The average power consumed in a circuit with zero power factor is:
A.
Maximum
B.
Zero
C.
Half of the maximum power
D.
Equal to the apparent power
Correct Answer:
Zero
Explanation:
Average AC power is P = VI cos φ. For zero power factor, cos φ = 0, so the average power is zero.
4. A current that flows in an AC circuit but consumes no average power is called:
A.
Direct current
B.
Wattless current
C.
Short-circuit current
D.
Leakage current
Correct Answer:
Wattless current
Explanation:
At zero power factor, current flows while the average power consumed is zero; therefore, it is called wattless current.
5. Which type of ideal AC circuit has zero power factor?
A.
Purely resistive circuit
B.
Purely inductive circuit
C.
Resistive circuit with unity power factor
D.
DC circuit with constant voltage
Correct Answer:
Purely inductive circuit
Explanation:
In a pure inductive circuit, current lags voltage by 90°, giving a power factor of cos 90° = 0.
6. Which other ideal circuit can have zero power factor?
A.
Purely capacitive circuit
B.
Purely resistive circuit
C.
Resistive-inductive circuit with zero phase difference
D.
Circuit containing only a battery
Correct Answer:
Purely capacitive circuit
Explanation:
In a pure capacitive circuit, current leads voltage by 90°, so the power factor is cos 90° = 0.
7. If the rms voltage is 100 V, the rms current is 2 A, and the power factor is zero, what is the average power?
A.
0 W
B.
50 W
C.
100 W
D.
200 W
Correct Answer:
0 W
Explanation:
Using P = Vᵣₘₛ Iᵣₘₛ cos φ, the power is 100 × 2 × 0 = 0 W.
8. In a zero-power-factor circuit, the current and voltage are:
A.
In phase
B.
Exactly opposite in phase
C.
Perpendicular in phase relationship
D.
Always of equal magnitude
Correct Answer:
Perpendicular in phase relationship
Explanation:
A phase difference of 90° represents a perpendicular phase relationship and produces zero power factor.
9. For a zero-power-factor AC circuit, the real power is what fraction of the apparent power?
A.
Zero
B.
One-fourth
C.
One-half
D.
Equal to the apparent power
Correct Answer:
Zero
Explanation:
Real power P equals apparent power VI multiplied by the power factor. With zero power factor, real power is zero.
10. What happens to energy in an ideal zero-power-factor circuit during one complete AC cycle?
A.
It is continuously consumed as heat
B.
It is supplied and returned, giving zero net energy consumption
C.
It is permanently stored in the source
D.
It is converted entirely into light
Correct Answer:
It is supplied and returned, giving zero net energy consumption
Explanation:
In an ideal inductive or capacitive circuit, energy is temporarily stored and returned to the source, so the net average power is zero.
Short questions are currently unavailable for this page.