physics : class12 Pure Capacitive Circuit : Wattless Current : Electromagnetic Induction and Alternating Currents MCQ Questions and Answers
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Pure Capacitive Circuit
MCQ questions and answers.
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MCQ Questions
1. In a pure capacitive AC circuit, the current leads the voltage by what phase angle?
A.
0°
B.
45°
C.
90°
D.
180°
Correct Answer:
90°
Explanation:
In a pure capacitive circuit, the current leads the applied voltage by 90°.
2. What is the average power consumed by a pure capacitor connected to an AC source?
A.
Zero
B.
VI
C.
V/I
D.
I²R
Correct Answer:
Zero
Explanation:
The phase difference between voltage and current is 90° in a pure capacitive circuit, so the average power is P = VI cos 90° = 0.
3. The capacitive reactance of a capacitor in an AC circuit is given by which expression?
A.
X_C = 2πfC
B.
X_C = 1/(2πfC)
C.
X_C = 2πf/C
D.
X_C = C/(2πf)
Correct Answer:
X_C = 1/(2πfC)
Explanation:
The capacitive reactance is X_C = 1/(2πfC), where f is frequency and C is capacitance.
4. What happens to the capacitive reactance when the frequency of the AC supply is increased?
A.
It increases
B.
It decreases
C.
It remains unchanged
D.
It becomes zero at every frequency
Correct Answer:
It decreases
Explanation:
Since X_C = 1/(2πfC), capacitive reactance decreases as the frequency increases.
5. In a pure capacitive circuit, which quantity leads the other?
A.
Voltage leads current
B.
Current leads voltage
C.
Voltage and current are always in phase
D.
Voltage and current have no phase relation
Correct Answer:
Current leads voltage
Explanation:
For a pure capacitor, the current reaches its maximum value one-quarter cycle before the voltage, so current leads voltage by 90°.
6. The power factor of a pure capacitive AC circuit is
A.
1
B.
0
C.
0.5
D.
−1
Correct Answer:
0
Explanation:
The power factor is cos φ. For a pure capacitive circuit, φ = 90°, so the power factor is cos 90° = 0.
7. If the capacitance of a pure capacitive circuit is increased, its capacitive reactance at a fixed frequency
A.
Increases
B.
Decreases
C.
Remains constant
D.
First increases and then decreases
Correct Answer:
Decreases
Explanation:
Because X_C = 1/(2πfC), increasing capacitance decreases the capacitive reactance when frequency is fixed.
8. A pure capacitor connected to an AC source is called a wattless component because it
A.
Consumes maximum real power
B.
Consumes no average power
C.
Produces direct current
D.
Has zero capacitance
Correct Answer:
Consumes no average power
Explanation:
A pure capacitor stores energy during part of the cycle and returns it during another part, so its average power consumption is zero.
9. The opposition offered by a pure capacitor to the flow of alternating current is called
A.
Resistance
B.
Inductive reactance
C.
Capacitive reactance
D.
Conductance
Correct Answer:
Capacitive reactance
Explanation:
In an AC circuit, the opposition offered by a capacitor is called capacitive reactance, represented by X_C.
10. In a pure capacitive circuit, the energy supplied by the AC source is
A.
Completely converted into heat
B.
Stored in the electric field and returned to the source
C.
Permanently stored as magnetic energy
D.
Converted into mechanical energy
Correct Answer:
Stored in the electric field and returned to the source
Explanation:
A capacitor stores energy in its electric field and returns it to the source during the opposite part of the AC cycle, resulting in zero average power consumption.
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