## MCQ on AC Circuits

MCQ on AC Circuits, Alternating Current MCQ, MCQ on Alternating Current, Multiple Choice Questions on MCQ on AC Circuits, Engineering MCQ, Basic Electrical Engineering MCQ

### Multiple Choice Questions

Q.1. A current is said to be direct current when its

- magnitude remains constant with time
- magnitude changes with time
- direction changes with time
- magnitude and direction changes with time

**Answer: **magnitude remains constant with time

Q.2. A current is said to be alternating when it changes in

- magnitude only
- direction only
- both magnitude and direction
- none of the above

**Answer: **both magnitude and direction

Q.3. The standard supply frequency in India is

- 25 Hz
- 50 Hz
- 60 Hz
- 100 Hz

**Answer:** 50 Hz

Q.4. The angular frequency of an alternating quantity is a mathematical quantity obtained by multiplying the frequency ** f** of the alternating quantity by a factor

- π/2
- π
- 2 π
- 4 π

**Answer:** 2 π

Q.5. A constant current of 2.8 A exists in a resistor. The RMS value of current is

- 2.8 A
- about 2 A
- 1.4 A
- Undefined

**Answer:** 2.8 A

Q.6. The ratio of effective value to average value is called the …. factor.

- form
- peak
- average
- Q-factor

**Answer: **form

Q.7. The RMS value of a sine wave is 100 A. Its peak value is

- 70.7 A
- 141 A
- 150 A
- 282.8 A

**Answer:** 141 A

Q.8. When the two quantities are in quadrature the phase angle between them will be

- 45° or π/4 radians
- 90° or π/2 radians
- 135° or 3π/4 radians
- 60° or π/3 radians

**Answer:** 90° or π/2 radians

Q.9. In ac circuits the power curve is a sine wave having

- same frequency as that of voltage
- double the frequency of the voltage
- half the frequency of the voltage
- none of the above

**Answer:** double the frequency of the voltage

Q.10. Electrical power converted into heat due to the flow of an alternating current through an ohmic resistance is called the …….. power.

- heating
- true
- reactive
- apparent

**Answer:** true

Q.11. Average power in a purely resistive circuit is equal to

- zero
- product of average values of current and voltage
- product of peak values of current and voltage
- product of rms or effective values of current and voltage

**Answer:** product of RMS or effective values of current and voltage

Q.12. If an alternating triangular voltage is applied to a resistor, the shape of the current waveform will be ……. waveform.

- triangular
- sawtooth
- sinusoidal
- square

**Answer:** triangular

Q.13. The purely inductive circuit takes power from the ac mains when

- both applied voltage and current increase
- both applied voltage and current decrease
- applied voltage decreases but current increases
- applied voltage increases but current decreases

**Answer:** applied voltage decreases but current increases

Q.14. Which of the following statements associated with a purely capacitive circuit is not true?

- Power consumed is zero.
- Heat produced is zero.
- Power factor is unity.
- Work done is zero.
- Power factor is zero.

**Answer:** Power factor is unity.

Q.15. A two-terminal black box contains a series combination of a resistor and an unknown two-terminal linear device. As soon as the battery is connected to the black box the current is found to be zero. The device is

- an inductor
- a capacitor
- a resistor
- an unknown

**Answer:** an inductor

Q.16. The reactance offered by a capacitor to alternating current of frequency 50 Hz is 10 Ω. If the frequency is increased to 100 Hz, reactance becomes:

- 20 ohms
- 5 ohms
- 2.5 ohms
- 40 ohms

**Answer:** 5 ohms

Q.17. The apparent power and active power is drawn are equal for an ac circuit of:

- inductive type
- capacitive type
- resistive type
- none of these

**Answer:** resistive type

Q.18. When a sinusoidal voltage is applied across R-L series circuit having R = X_{L}, the phase angle will be:

- 90°
- 45° lag
- 45° leading
- 90° leading

**Answer:** 45° leading

Q.19. In a series R-L circuit

- voltage drops across R and L are in phase
- voltage drop across L leads the voltage drop across R by 90°
- voltage drop across L lags behind the voltage drop across R by 90°
- voltage drops across R and L are in phase opposition

**Answer:** voltage drop across L leads the voltage drop across R by 90°

Q.20. In an ac circuit, the applied voltage and current drawn are represented as v = V_{max} sin ωt and i = I_{max} sin (ωt + ϕ). The pf of the circuit is

- sin ϕ
- cos ϕ (lagging)
- cos ϕ (leading)
- none of these

**Answer:** cos ϕ (leading)

Q.21. Q-factor of a coil is the measure of its

- selectivity
- retentivity
- resistivity
- self inductance

**Answer:** selectivity

Q.22. In a series R-C circuit current …….. with the increase in frequency.

- increases
- decreases
- remains unaltered
- None of the above

**Answer: **increases

Q.23. A 100 W, 100 V bulb is to be supplied from 220 V, 50 Hz supply. Which of the following arrangements is preferable?

- Additional pure inductance in series with lamp.
- Additional resistance in series with the lamp.
- Additional inductance and capacitance in series with the lamp.
- None of the above

**Answer: **Additional pure inductance in series with the lamp.

Q.24. The source in the circuit shown is a sinusoidal source. The supply voltage across various elements is marked in the figure. The input voltage is

- 10 V
- 5 V
- 27 V
- 24 V

**Answer:** 5 V

Q.25. If a series RLC circuit is excited by a voltage e = E sin ωt where LC < 1/ω^{2}

- current lags behind the applied voltage
- current leads the applied voltage
- current is in phase with the applied voltage
- voltage across L and C are equal

**Answer:** current leads the applied voltage