# MCQ on AC Circuits (Part-1)

## 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

Q.3. The standard supply frequency in India is

• 25 Hz
• 50 Hz
• 60 Hz
• 100 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

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

• 2.8 A
• 1.4 A
• Undefined

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

• form
• peak
• average
• Q-factor

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

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

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

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

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.

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

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

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

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

• 90°
• 45° lag

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 = Vmax sin ωt and i = Imax sin (ωt + ϕ). The pf of the circuit is

• sin ϕ
• cos ϕ (lagging)
• none of these

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

• selectivity
• retentivity
• resistivity
• self inductance

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

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

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

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

Q.25. If a series RLC circuit is excited by a voltage e = E sin ωt where LC < 1/ω2

• 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