# MCQ Questions for Class 12 Physics Chapter 7 Alternating Current with Answers

Question 1.

The average value of a cover a complete cycle is:

(a) l_{0}

(b) \(\frac{l_0}{2}\)

(c) \(\frac{l_0}{√2}\)

(d) zero

## Answer

Answer: (d) zero

Question 2.

Power factor of an ac circuit is a measure of:

(a) virtual power

(b) power lost in the circuit

(c) mean power

(d) all the above

## Answer

Answer: (b) power lost in the circuit

Question 3.

The dimensional formula of L/R is similar to that of:

(a) frequency

(b) time

(c) length

(d) none of these

## Answer

Answer: (b) time

Question 4.

Which of the following has dimensions different from the rest?

(a) L/R

(b) \(\frac{1}{RC}\)

(c) \(\sqrt{LC}\)

(d) RC

## Answer

Answer: (b) \(\frac{1}{RC}\)

Question 5.

The dimensional formula of impedance is;

(a) [ML^{2}T^{-2}A^{-2}]

(b) [ML^{2}T^{-3}A^{-2}]

(c) [ML^{2}T^{-2}A^{-1}]

(d) [ML^{2}T^{-2}A^{-3}]

## Answer

Answer: (b) [ML^{2}T^{-3}A^{-2}]

Question 6.

Energy dissipates in LCR circuit in :

(a) L only

(b) C only

(c) R only

(d) All of the above

## Answer

Answer: (c) R only

Question 7.

An iron core transformer with a turns ratio of 8 : 1 has 120 V applied across the primary. The voltage across the

(a) 15 V

(b) 120 V

(c) 180 V

(d) 960 V

## Answer

Answer: (a) 15 V

Question 8.

What is the ratio of inductive and capacitance reactances in an ac circuit?

(a) 1

(b) ω²L

(c) ω²LC

(d) l

## Answer

Answer: (c) ω²LC

Question 9.

An acceptor circuit is :

(a) series resonant circuit

(b) parallel resonant circuit

(c) LCR circuit

(d) None of these

## Answer

Answer: (a) series resonant circuit

Question 10.

A broadcast circute broadcasts at 300 m band. A condenser of capacitance 2.4 lµF is available. The value of the inductance required for resonant circuit is:

(a) 10^{-4} H

(b) 10^{-8} H

(c) 10^{-6} H

(d) 10^{-2} H

## Answer

Answer: (b) 10^{-8} H

Question 11.

In series resonant circuit:

(a) reactance is zero

(b) current is zero

(c) voltage is zero

(d) None of these

## Answer

Answer: (d) None of these

Question 12.

In parallel resonant circuit:

(a) impedance is very high

(b) current is very high

(c) voltage is very high

(d) None of these

## Answer

Answer: (a) impedance is very high

Question 13.

The no. of turns in the primary coil of a transformer is 200 and the no. of turns in the secondary is 10. If 240 V a.c. is applied to primary, the output from the secondary

(a) 6 V

(b) 12 V

(c) 24 V

(d) 48 V

## Answer

Answer: (b) 12 V

Question 14.

Transformer works on the principle of:

(a) convertor

(b) invertor

(c) mutual induction

(d) self-induction

## Answer

Answer: (c) mutual induction

Question 15.

Which of the following effects is not shown in alternating current ?

(a) Chemical effect

(b) Magnetic effect

(c) Heating current

(d) All of these

## Answer

Answer: (a) Chemical effect

Question 16.

An ac ammeter connected in series in an ac circuit reads 5A. The peak value of current:

(a) 5 A

(b) 5√2A

(c) \(\frac{5}{√5}\) A

(d) zero

## Answer

Answer: (b) 5√2A

Question 17.

The phase difference b/w the A.C. and e.m.f. \(\frac{π}{2}\) Which of the following can not be the instituent of the circuit?

(a) LC

(b) L alone

(c) C alone

(d) RL

## Answer

Answer: (d) RL

Question 18.

The Q factor of an LCR circuit at resonance is :

(a) \(\sqrt{R^2+ω^2L^2}\)

(b) \(\sqrt{R^2+(\frac{1}{cω}})^2\)

(c) \(\frac{ω_rL}{R}\)

(d) \(\sqrt{R^2+\frac{1}{c^2ω^2}}\)

## Answer

Answer: (c) \(\frac{ω_rL}{R}\)

Question 19.

Faraday constant:

(a) depends on the amount of the electrolyte

(b) depends on the current in the electrolyte

(c) is a universal constant

(d) depends on the amount of charge passed through the electrolyte

## Answer

Answer: (c) is a universal constant

Question 20.

The natural frequency of an L -C-Circuit is equal to :

(a) \(\frac{\sqrt{LC}}{2π}\)

(b) \(\frac{1}{3π\sqrt{LC}}\)

(c) \(\frac{1}{2π}\sqrt{\frac{L}{C}}\)

(d) \(\frac{1}{2π}\sqrt{\frac{C}{L}}\)

## Answer

Answer: (b) \(\frac{1}{3π\sqrt{LC}}\)

Question 21.

In the series L-C-R circuit, the voltmeter and ammeter readings are:

(a) V = 100 Volts, I = 2A

(b) V = 100 Volts, I = 5A

(c) V = 1000 Volts, I = 2A

(d) V = 300 Volts, I = 1A

## Answer

Answer: (a) V = 100 Volts, I = 2A

Question 22.

The band width of a series resonant circuit is :

(a) f_{0}/Q_{0}

(b) \(\frac{R}{2πL}\)

(c) \(\frac{R}{4πL}\)

(d) 4R

## Answer

Answer: (a) f_{0}/Q_{0}

Question 23.

A rejector circuit is:

(a) series resonant circuit

(b) parallel resonant circuit

(c) LCR circuit

(d) None of these

## Answer

Answer: (b) parallel resonant circuit

Question 24.

The inductive reactance of an inductor coil of \(\frac{1}{π}\) H at 50 Hz is:

(a) \(\frac{50}{π}\) Ω

(b) \(\frac{π}{50}\) Ω

(c) 100 Ω

(d) 50 Ω

## Answer

Answer: (c) 100 Ω

Question 25.

In pure inductive circuit current

(a) lags behind emf by π/2

(b) leads the emf by π/2

(c) lags behind emf by π

(d) leads the emf by π

## Answer

Answer: (a) lags behind emf by π/2

Question 26.

The current through an inductor of 1H is given by I = 3t sin t. The voltage across the inductor of 1 H is:

(a) 3 sin t + 3 cos t

(b) 3 sin t + 3t cos t

(c) 3 cos t + t sin t

(d) 3t cos t + sin t

## Answer

Answer: (b) 3 sin t + 3t cos t

Question 27.

Two coils X and Y are connected in series across a 240 V, 50 Hz supply. The resistance of X is 5Ω and inductance of Y is 0.02 H. The power consumed is 3 kW and the power factor is 0.75. The impedance of the circuit is:

(a) 0.144 Ω

(b) 1.44 Ω

(c) 14.4 Ω

(d) 144 Ω

## Answer

Answer: (c) 14.4 Ω

Question 28.

In the above problem, the value of the resistance of the coil Y is:

(a) 0.58 Ω

(b) 5.8 Ω

(c) 1.16 Ω

(d) 11.6 Ω

## Answer

Answer: (b) 5.8 Ω

Question 29.

An electric circuit containing capacitor only suffers:

(a) equal resistance for A.C. and D.C.

(b) Resistance of A.C. > Resistance of D.C.

(c) Resistance for A.C. < Resistance of D.C.

(d) offers infinite resistance for D.C.

## Answer

Answer: (d) offers infinite resistance for D.C.

Question 30.

The average power dissipation in pure inductance or capacitance is:

(a) \(\frac{1}{2}\) LI²

(b) \(\frac{3}{2}\) CV²

(c) either (a) or (b)

(d) zero

## Answer

Answer: (d) zero

## 0 Comments