Olete.in – MCQs, Mock Tests & Government Job Prep | PI (AC/DC) simulation MCQ on AC Circuits

A current is said to be direct current when its

1. magnitude remains constant with time
2. magnitude changes with time
3. direction changes with time
4. magnitude and direction changes with time

✅ Correct Answer: 1

A current is said to be alternating when it changes in

1. magnitude only
2. direction only
3. both magnitude and direction
4. none of the above

✅ Correct Answer: 3

The standard supply frequency in India is

1. 25 Hz
2. 50 Hz
3. 60 Hz
4. 100 Hz

✅ Correct Answer: 2

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

1. π/2
2. π
3. 2 π
4. 4 π

✅ Correct Answer: 3

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

1. 2.8 A
2. about 2 A
3. 1.4 A
4. Undefined

✅ Correct Answer: 1

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

1. form
2. peak
3. average
4. Q-factor

✅ Correct Answer: 1

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

1. 70.7 A
2. 141 A
3. 150 A
4. 282.8 A

✅ Correct Answer: 2

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

1. 45° or π/4 radians
2. 90° or π/2 radians
3. 135° or 3π/4 radians
4. 60° or π/3 radians

✅ Correct Answer: 2

In ac circuits the power curve is a sine wave having

1. same frequency as that of voltage
2. double the frequency of the voltage
3. half the frequency of the voltage
4. none of the above

✅ Correct Answer: 2

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

1. heating
2. true
3. reactive
4. apparent

✅ Correct Answer: 2

Average power in a purely resistive circuit is equal to

1. zero
2. product of average values of current and voltage
3. product of peak values of current and voltage
4. product of rms or effective values of current and voltage

✅ Correct Answer: 4

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

1. triangular
2. sawtooth
3. sinusoidal
4. square

✅ Correct Answer: 1

The purely inductive circuit takes power from the ac mains when

1. both applied voltage and current increase
2. both applied voltage and current decrease
3. applied voltage decreases but current increases
4. applied voltage increases but current decreases

✅ Correct Answer: 3

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

1. Power consumed is zero.
2. Heat produced is zero.
3. Power factor is unity.
4. Work done is zero.

✅ Correct Answer: 3

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

1. an inductor
2. a capacitor
3. a resistor
4. an unknown

✅ Correct Answer: 1

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:

1. 20 ohms
2. 5 ohms
3. 2.5 ohms
4. 40 ohms

✅ Correct Answer: 2

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

1. inductive type
2. capacitive type
3. resistive type
4. none of these

✅ Correct Answer: 3

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

1. 90°
2. 45° lag
3. 45° leading
4. 90° leading

✅ Correct Answer: 3

In a series R-L circuit

1. voltage drops across R and L are in phase
2. voltage drop across L leads the voltage drop across R by 90°
3. voltage drop across L lags behind the voltage drop across R by 90°
4. voltage drops across R and L are in phase opposition

✅ Correct Answer: 2

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

1. sin ϕ
2. cos ϕ (lagging)
3. cos ϕ (leading)
4. none of these

✅ Correct Answer: 3

Q-factor of a coil is the measure of its

1. selectivity
2. retentivity
3. resistivity
4. self inductance

✅ Correct Answer: 1

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

1. increases
2. decreases
3. remains unaltered
4. None of the above

✅ Correct Answer: 1

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

1. Additional pure inductance in series with lamp.
2. Additional resistance in series with the lamp.
3. Additional inductance and capacitance in series with the lamp.
4. None of the above

✅ Correct Answer: 1

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

1. 10 V
2. 5 V
3. 27 V
4. 24 V

✅ Correct Answer: 2

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

1. current lags behind the applied voltage
2. current leads the applied voltage
3. voltage across L and C are equal
4. current is in phase with the applied voltage

✅ Correct Answer: 2

A small capacitance is added to a highly inductive circuit,

1. the angle between voltage and current will increase
2. the pf will increase
3. the pf will decrease
4. the power drawn will decrease

✅ Correct Answer: 2

Under the condition of resonance in the RLC series circuit, the power factor of the circuit is

1. 0.5 lagging
2. 0.5 leading
3. unity
4. zero

✅ Correct Answer: 3

When a sinusoidal voltage is applied across the R-L parallel circuit so that R = XL, the phase angle will be:

1. 45° lag
2. 45° leading
3. 90° lag
4. 90 leading

✅ Correct Answer: 2

The power factor of an inductive circuit is usually improved by adding a capacitor to it in:

1. series
2. parallel
3. either in series or parallel
4. None of These

✅ Correct Answer: 3

The quantity (12 + j9) represents the resistive and reactive components of the current drawn by an ac circuit. The phase angle between the applied voltage and the current is:

1. 41.4°
2. 53.13°
3. 36.87°
4. 48.6°

✅ Correct Answer: 3

The Parallel R-C circuit behaves as a purely capacitive circuit at ………… frequencies.

1. very low
2. low
3. high
4. very high

✅ Correct Answer: 4

Consider the following statements with respect to a series R-L-C circuit under resonance condition: All the applied voltage appears across R. There is no voltage across either L or C. The voltage across L and C equal and equal to their maximum values. Of these statements

1. 1 alone is correct.
2. 2 alone is correct.
3. 1 and 3 are correct.
4. 1 and 2 are correct.

✅ Correct Answer: 1

In a series R-L-C circuit, the magnitude of resonance frequency can be changed by changing the value of

1. R only.
2. L only.
3. C only.
4. L or C.

✅ Correct Answer: 4

A series-resonant circuit implies

1. zero pf and maximum current
2. unity pf and maximum current
3. unity pf and minimum current
4. zero pf and minimum current

✅ Correct Answer: 2

In an R-L-C parallel circuit, the line current at resonance is

1. minimum at unity power factor
2. minimum at lagging pf
3. maximum at leading pf
4. maximum at lagging pf

✅ Correct Answer: 1

A parallel resonant circuit can be employed

1. as a high impedance
2. to amplify certain frequencies
3. to amplify voltage
4. both high impedance and reject a small band of frequencies

✅ Correct Answer: 4

16. In a 3-phase system, the EMFs are

1. 30° apart
2. 40° apart
3. 90° apart
4. 120° apart

✅ Correct Answer: 4

A 3-phase 6.6/0.4 kV transformer is to supply a load at 230 V. Its secondary should be connected in

1. star
2. delta
3. open-delta
4. series

✅ Correct Answer: 4

In the case of a delta connected load, if one resistor is removed, the power will become

1. zero
2. one-third
3. two-third
4. None of these

✅ Correct Answer: 3

In the balanced 3-phase voltage system generated by a star connected alternator, VYB lags ER by

1. 90 degrees
2. 120 degrees
3. 60 degrees
4. 30 degrees

✅ Correct Answer: 1

In the 2 WM method of power measurement, one of the W.M. will show negative reading when the load pf angle is strictly

1. less than 30°
2. less than 60°
3. greater than 30°
4. greater than 60°

✅ Correct Answer: 4

While measuring power in a three-phase load by 2 WM method. The reading of two wattmeters are equal and opposite, when

1. pf is unity
2. load is balanced
3. phase angle is between 60° and 30°
4. the load is purely inductive

✅ Correct Answer: 4

A lamp load is given a supply from 3-phase, 4-wire 230/400 V, A.C. supply system. If a 3- phase motor is now switched on across the same supply, then neutral current will

1. increase
2. decrease
3. remain unchanged
4. be unpredictable

✅ Correct Answer: 2