MCQ Question for Class 12 Physics Chapter 7 Alternating Current

Refer to MCQ Class 12 Alternating Current provided below which is an important chapter in Class 12 Physics. Students should go through the MCQs questions for Class 12 Physics Chapter 7 Alternating Current with answers given below so that they are able to understand the complete topic properly. It’s important to understand the entire chapter by reading Class 12 Physics Notes also. Also, refer to MCQ Questions for Class 12 Physics for all chapters.

MCQ on Alternating Current Class 12 Physics PDF with Answers

All multiple choice questions with solutions provided below have been developed based on the latest syllabus and examination pattern issued for class 12 by CBSE and NCERT. As Alternating Current is a very important and scoring chapter in Physics Class 12, therefore, the students should carefully learn the questions and answers given below which will help them to get better scores in upcoming examinations for class 12th.

Question. A circuit when connected to an AC source of 12 V gives a current of 0.2 A. The same circuit when connected to a DC source of 12 V, gives a current of
0.4 A. The circuit is
(a) series LR
(b) series RC
(c) series LC
(d) series LCR

Question. Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication ?
(a) R = 20 W, L = 1.5 H, C = 35 mF
(b) R = 25 W, L = 2.5 H, C = 45 mF
(c) R = 15 W, L = 3.5 H, C = 30 mF
(d) R = 25 W, L = 1.5 H, C = 45 mF 

Question. Turn ratio in a step up transformer is 1 : 2 if a Lechlanche cell of 1.5 V is connected across the input, then the voltage across the output will be
(a) 0.1 V
(b) 1.5 V 
(c) 0.75 V
(d) zero

Question. In a circuit the coil of a choke : 
(a) decreases the current
(b) increases the current
(c) has high resistance to D. C. circuit
(d) no effect with the current

Question. In a circuit, the current lags behind the voltage by a phase difference of p /2, the circuit will contain which of the following : 
(a) only R
(b) only C
(c) R and C
(d) only L

Question. The coefficient of mutual inductance, when magnetic flux changes by 2 × 10–2 Wb and current changes by 0.01 A is 
(a) 8 henry
(b) 4 henry
(c) 3 henry
(d) 2 henry

Question. In an ideal parallel LC circuit, the capacitor is charged by connecting it to a D.C. source which is then disconnected. The current in the circuit
(a) becomes zero instantaneously 
(b) grows monotonically
(c) decays monotonically
(d) oscillates instantaneously

Question. A capacitor of capacitance 2μF is connected in the tank circuit of an oscillator oscillating with a frequency of 1 kHz. If the current flowing in the circuit is 2 m A, the voltage across the capacitor will be : 
(a) 0.16 V
(b) 0.32 V
(c) 79.5 V
(d) 159 V

Question. In an AC circuit the potential differences across an inductance and resistance joined in series are respectively 16 V and 20 V. The total potential difference of the source is 
(a) 20.0 V
(b) 25.6 V
(c) 31.9 V
(d) 53.5 V

Question. With the decrease of current in the primary coil from 2 amperes to zero value in 0.01s the emf generated in the secondary coil is 1000 volts. The mutual inductance of the two coils is
(a) 1.25 H
(b) 2.50 H 
(c) 5.00 H
(d) 10.00 H

Question. An AC source of angular frequency w is fed across a resistor R and a capacitor C in series.
The current registered is I. If now the frequency of source is changed to w/3 (but maintaining the same voltage), the current in the circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency w 
(a) √(3/5)
(b)√(2/5)
(c) √(1/5)
(d) √(4/5)

Question. If an AC main supply is given to be 220 V. The average emf during a positive half cycle will be
(a) 198 V
(b) 220 V 
(c) 240 V
(d) 220 √2V

Question. A 40 mF capacitor is connected to a 200 V, 50 Hz ac supply. The r.m.s value of the current in the circuit is, nearly
(a) 1.7 A
(b) 2.05 A
(c) 2.5 A
(d) 25.1 A 

Question. A small signal voltage V(t) = V0 sinwt is applied across an ideal capacitor C
(a) Current I(t) is in phase with voltage V(t).
(b) Current I(t) leads voltage V(t) by 180°.
(c) Current I(t), lags voltage V(t) by 90°.
(d) Over a full cycle the capacitor C does not consume any energy from the voltage source.

Question. A coil has an inductance of 0.7 henry and is joined in series with a resistance of 220 W. When the alternating emf of 220 V at 50 Hz is applied to it then the phase through which current lags behind the applied emf and the wattless component of current in the circuit will be respectively 
(a) 30°, 1 A
(b) 45°, 0.5 A
(c) 60°, 1.5 A
(d) none of these

Question. In a AC circuit the voltage and current are described by V 200sin (319-Π/6) volts and i 50sin (314t+Π/6) respectively. The average power dissipated in the circuit is : 
(a) 2.5 watts
(b) 5.0 watts
(c) 10.0 watts
(d) 50.0 watts

Question. If we decrease the frequency of the applied A.C. with a purely capacitive load, do (1) the amplitude of Vc and (2) amplitude of Ic increase, decrease of remain the same. 
(a) (1) increase (2) same
(b) (1) same (2) increase
(c) (1) same (2) decrease
(d) (1) decrease (2) same

Question. An inductor coil of inductance L is cut into two equal parts and both the parts are connected in parallel. The net inductance is : 
(a) L
(b) L/2
(c) L/4
(d) 2 L.

Question. An inductance L having a resistance R is connected to an alternating source of angular frequency w. The Quality factor Q of inductance is 
(a) R/ wL
(b) (wL/R)2
(c) (R /wL)1/2
(d) wL/R

Question. In an A.C. circuit, the current flowing in inductance is I = 5 sin (100 t – p/2) amperes and the potential difference is V = 200 sin (100 t) volts. The power consumption is equal to 
(a) 1000 watt
(b) 40 watt
(c) 20 watt
(d) zero

Question. L, C, R represent physical quantities inductance, capacitance and resistance respectively. The combinations which have the dimensions of frequency are 
(a) 1/RC
(b) R/L
(c) 1/ LC
(d) C/L

Question. An inductance L having a resistance R is connected to an alternating source of angular frequency w. The Quality factor Q of inductance is 
(a) R/ wL
(b) (wL/R)2
(c) (R /wL)½
(d) wL/R

Question. A step down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in the primary coil will be 
(a) 1600 amp
(b) 20 amp
(c) 4 amp
(d) 1.5 amp

Question. The mutual inductance of a pair of coils, each of N turns, is M henry. If a current of I ampere in one of the coils is brought to zero in t second, the emf induced per turn in the other coil, in volt, will be
(a) MI /t
(b) NMI /t
(c) MN /It
(d) MI /Nt

Question. An A.C. circuit containing only capacitance, the current : 
(a) lags the voltage by 90°
(b) leads the voltage by 90°
(c) remains in phase with voltage
(d) leads the voltage in 180°

Question. A choke coil has: 
(a) Low inductance and low resistance
(b) High inductance and high resistance
(c) Low inductance and high resistance
(d) High inductance and low resistance

Question. The tuning circuit of a radio receiver has a resistance of 50W, an inductor of 10 mH and a variable capacitor. A 1 MHz radio wave produces a potential difference of 0.1 mV. The values of the capacitor to produce resonance is (Take Π² = 10) 
(a) 2.5 pF
(b) 5.0 pF
(c) 25 pF
(d) 50 pF

Question. A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be 
(a) 4.0 A
(b) 8.0 A
(c) 20√13 A
(d) 2.0 A

Question. The primary winding of a transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an A.C. supply of 20 V, 50 Hz. The secondary will have an output of
(a) 2 V, 50 Hz
(b) 2 V, 5 Hz
(c) 200 V, 50 Hz
(d) 200 V, 500 Hz.

Question. A coil of 40 henry inductance is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
(a) 5 seconds
(b) 1/5 seconds
(c) 40 seconds
(d) 20 seconds

Question. An ideal coil of 10H is connected in series with a resistance of 5W and a battery of 5V. After 2 sec the connection is made, the current flowing in ampere in the circuit is 
(a) (1 – e–1)
(b) (1 – e)
(c) e
(d) e–1

Question. An inductor, a resistor and a capacitor are joined in series with an AC source. As the frequency of the source is slightly increased from a very low value, the reactance of the
(a) inductor increases
(b) resistor increases
(c) capacitor increases
(d) circuit increases

Question. In an A.C. circuit, Irms and I0 are related as
(a) Irms = ΠI0
(b) Irms = √2 I0
(c) Irms = I0/Π
(d) Irms = I0 /√ 2

Question. Two cables of copper are of equal lengths. One of them has a single wire of area of cross-section A, while other has 10 wires of cross-sectional area A/10 each. Give their suitability for transporting A.C. and D.C.
(a) only multiple strands for A.C., either for D.C.
(b) only multiple strands for A.C., only single strand for D.C.
(c) only single strand for D.C., either for A.C.
(d) only single strand for A.C., either for D.C.

Question. A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when
(a) a capacitance of reactance XC = XL is included in the same circuit.
(b) an iron rod is inserted in the coil.
(c) frequency of the AC source is decreased.
(d) number of turns in the coil is reduced.

Question. In an ac circuit an alternating voltage 200 2 sin100 t volts is connected to a capacitor of capacity 1 mF. The r.m.s. value of the current in the circuit is
(a) 10 mA
(b) 100 mA
(c) 200 mA
(d) 20 mA 

Question. A transformer having efficiency of 90% is working on 200 V and 3 kW power supply. If the current in the secondary coil is 6 A, the voltage across the
secondary coil and the current in the primary coil respectively are
(a) 300 V, 15 A
(b) 450 V, 15 A
(c) 450 V, 13.5 A
(d) 600 V, 15 A

Question. The primary of a transformer when connected to a dc battery of 10 volt draws a current of 1 mA. The number of turns of the primary and secondary windings are 50 and 100 respectively. The voltage in the secondary and the current drawn by the circuit in the secondary are respectively
(a) 20 V and 2.0 mA
(b) 10 V and 0.5 mA
(c) Zero volt and therefore no current
(d) 20 V and 0.5 mA 

Question. A capacitor of capacity C has reactance X. If capacitance and frequency become double then reactance will be
(a) 4X
(b) X/2
(c) X/4
(d) 2X

Question. An alternating voltage V = V₀ sin ϖt is applied across a circuit. As a result, a current I = I₀ sin (ϖt – π/2) flows in it. The power consumed per cycle is
(a) zero
(b) 0.5 V₀I₀
(c) 0.707 V₀I₀
(d) 1.414 V₀I₀

Question. A transformer is used to light a 140 W, 24 V bulb from a 240 V a.c. mains. The current in the main cable is 0.7 A. The efficiency of the transformer is
(a) 63.8 %
(b) 83.3 %
(c) 16.7 %
(d) 36.2 %

Question. The impedance in a circuit containing a resistance of 1 Ω and an inductance of 0.1 H in series, for AC of 50 Hz, is
(a) 100 √10Ω
(b) 10 √10Ω
(c) 100Ω
(d) 10Ω

Question. The frequency of A.C. mains in India is
(a) 30 c/s
(b) 50 c/s
(c) 60 c/s
(d) 120 c/s

Question. The primary winding of a transformer has 100 turns and its secondary winding has 200 turns. The primary is connected to an A.C. supply of 120 V and the current flowing in it is 10 A. The voltage and the current in the secondary are
(a) 240 V, 5 A
(b) 240 V, 10 A
(c) 60 V, 20 A
(d) 120 V, 20 A

Question. A step down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in the primary coil will be
(a) 1600 amp
(b) 20 amp
(c) 4 amp
(d) 1.5 amp

Question. A 12 W resistor and a 0.21 henry inductor are connected in series to an a.c. source operating at 20 volt, 50 cycle. The phase angle between the current and source voltage is
(a) 30º
(b) 40º
(c) 80º
(d) 90º

Question. The primary winding of transformer has 500 turns whereas its secondary has 5000 turns. The primary is connected to an A.C. supply of 20 V, 50 Hz. The secondary will have an output of
(a) 2 V, 5 Hz
(b) 200 V, 500 Hz
(c) 2V, 50 Hz
(d) 200 V, 50 Hz

Question. An alternating voltage E (in volts) = 200 √2 sin 100 t is connected to one micro farad capacitor through an a.c. ammeter. The reading of the ammeter shall be
(a) 100 mA
(b) 20 mA
(c) 40 mA
(d) 80 mA

Question. In the given circuit, the current drawn from the source is
(a) 20 A
(b) 10 A
(c) 5 A
(d) 5 √2 A

Question. In an A.C. circuit, a resistance of R ohm is connected in series with an inductance L. If phase angle between voltage and current be 45°, the value of inductive reactance will be
(a) R/4
(b) R/2
(c) R
(d) cannot be found with given data

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