Alternating Current MCQs

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 1. What is the frequency of the AC Mains in India?

  1. 60 Hz
  2. 50 Hz
  3. 40 Hz
  4. 30 Hz

Answer: (b) 50 Hz

Explanation: The frequency of the AC Mains in India is 50 Hz.

2. An alternating current can be produced by

  1. Choke Coil
  2. Dynamo
  3. Electric Motor
  4. Transformer

Answer: (b) Dynamo

Explanation: An alternating current can be produced by a dynamo.

3. Which of the following can measure an alternating current?

  1. Voltmeter
  2. Ammeter
  3. Suspended coil galvanometer
  4. Moving coil galvanometer

Answer: (b) Ammeter

Explanation: Ammeter can measure an alternating current.

4. Which of the following circuits exhibits maximum power dissipation?

  1. Pure Inductive Circuit
  2. Pure Capacitive Circuit
  3. Pure Resistive Circuit
  4. None of the above

Answer: (c) Pure Resistive Circuit

Explanation: A pure resistive circuit exhibits maximum power dissipation.

5. What happens to the inductive reactance when the frequency of the AC supply is increased?

  1. Increases
  2. Decreases
  3. Remains the same
  4. Decreases inversely

Answer: (a) increases

Explanation: The inductive reactance of the AC supply increases with the frequency of the AC supply.

6. What happens to the quality factor of an LCR circuit if the resistance is increased?

  1. Increases
  2. Decreases
  3. Remains the same
  4. None of the above

Answer: (b) Decreases

Explanation: The quality factor of an LCR circuit decreases if the resistance of the circuit is increased.

7. Which of the following statements is true about the LCR circuit connected to an AC source at resonance?

  1. Voltage across R equals the applied voltage.
  2. Voltage across R is zero.
  3. Voltage across C is zero.
  4. Voltage across L equals the applied voltage.

Answer: (a) R equals the applied voltage.

Explanation: At resonance, R equals the applied voltage.

8. The impedance in the series LCR circuit is minimum at the resonance frequency.

  1. True
  2. False

Answer: (a) True

Explanation: The impedance in the series LCR circuit is minimum at the resonance frequency.

9. When is the current in a circuit wattless?

  1. When the inductance of the circuit is zero.
  2. When the resistance of the circuit is zero.
  3. When the current is alternating.
  4. When both resistance and inductance are zero.

Answer: (b) When the resistance of the circuit is zero.

Explanation: The current in a circuit is wattless when the resistance of the circuit is zero.

10. The power factor is one for which of the following?

  1. Pure capacitor
  2. Pure inductor
  3. Pure resistor
  4. All of the above

Answer: (c) Pure resistor

Explanation: The power factor is unity for the pure resistor.

11. In an AC circuit containing only capacitor, the current ?

        a. leads the voltage by 180 degree
        b. lags the voltage by 90 degree
         c. leads the voltage by 90 degree
         d.none of this

Answer : (c)  leads the voltage by 90 degree

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