Class 12 Physics MCQ Questions of Alternating Current with Answers with Answers are prepared as per the Latest Exam Pattern and syllabus. Students can solve these Alternating Current Class 12 MCQ Questions with Answers and assess their preparation level. These MCQ Questions for Class 12 with answers for a quick revision of the Chapter thereby helping you to enhance subject knowledge.

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Practice MCQ Question for Class 12 Physics chapter-wise 

1. An acceptor circuit is :

(a) series resonant circuit
(b) parallel resonant circuit
(c) LCR circuit
(d) None of these

2. In series resonant circuit:

(a) reactance is zero
(b) current is zero
(c) voltage is zero
(d) None of these

3. Transformer works on the principle of:

(a) convertor
(b) invertor
(c) mutual induction
(d) self-induction

4. The phase difference b/w the A.C. and e.m.f. π/2 Which of the following can not be the constituent of the circuit?

(a) LC
(b) L alone
(c) C alone
(d) RL

 5.  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

6. A rejector circuit is:

(a) series resonant circuit
(b) parallel resonant circuit
(c) LCR circuit
(d) None of these

7. Alternating current cannot be measured by D.C. ammeter, because

(a) A. C. is virtual
(b) A. C. changes its direction
(c) A. C. cannot pass through D.C. ammeter
(d) average value of A. C for complete cycle is zero

8. A.C. power is transmitted from a power house at a high voltage as

(a) the rate of transmission is faster at high voltages
(b) it is more economical due to less power loss
(c) power cannot be transmitted at low voltages
(d) a precaution against theft of transmission lines

9. An A.C. source is connected to a resistive circuit. Which of the following is true?

(a) Current leads ahead of voltage in phase
(b) Current lags behind voltage in phase
(c) Current and voltage are in same phase
(d) Any of the above may be true depending upon the value of resistance.

10. With increase in frequency of an A.C. supply, the inductive reactance

(a) decreases
(b) increases directly with frequency
(c) increases as square of frequency
(d) decreases inversely with frequency

11. The capacitive reactance in an A.C. circuit is

(a) effective resistance due to capacity
(b) effective wattage
(c) effective voltage
(d) None of these

12. The frequency of A.C. mains in India is

(a) 30 Hz
(b) 50 Hz
(c) 60 Hz
(d) 120 Hz

13. The electric mains supply in our homes and offices is a voltage that varies like a sine function with time such a voltage is called ... A... and the current driven by it in a circuit is called the ... B... Here, A and B refer to

(a) DC voltage, AC current
(b) AC voltage, DC current
(c) AC voltage, DC voltage
(d) AC voltage, AC current

14. Alternating currents can be produced by a

(a) dynamo
(b) choke coil
(c) transformer
(d) electric motor

15. The parallel combination of inductor and capacitor is called as

(a) rectifier circuit
(b) tank circuit
(c) acceptor circuit
(d) filter circuit

16. The alternating current can be measured with the help of

(a) hot wire ammeter
(b) hot wire voltmeter
(c) moving magnet galvanometer
(d) suspended coil type galvanometer

17. The core of transformer is laminated to reduce

(a) flux leakage
(b) hysteresis
(c) copper loss
(d) eddy current

18. A transformer is based on the principle of

(a) mutual induction
(b) self induction
(c) Ampere’s law
(d) X-ray crystallography

19. Eddy currents in the core of transformer can't be developed by

(a) increasing the number of turns in secondary coil
(b) taking laminated transformer
(c) making step down transformer
(d) using a weak a.c. at high potential

20. A capacitor acts as an infinite resistance for

(a) DC
(b) AC
(c) DC as well as AC
(d) neither AC nor DC

21. A capacitor has capacitance C and reactance X, if capacitance and frequency become double, then reactance will be

(a) 4X
(b) X/2
(c) X/4
(d) 2X

22. In LCR circuit if resistance increases quality factor

(a) increases finitely
(b) decreases finitely
(c) remains constant
(d) None of these

23. The loss of energy in the form of heat in the iron core of a transformer is

(a) iron loss
(b) copper loss
(c) mechanical loss
(d) None of these

24. Which quantity is increased in a step-down transformer?

(a) Current
(b) Voltage
(c) Power
(d) Frequency

25. 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) frequency of the ac source is decreased
(b) number of turns in the coil is reduced
(c) a capacitance of reactance X_c = X_L in included
(d) an iron rod is inserted in the coil

Answer :

1. Answer : (a) series resonant circuit

Explanation: Acceptor circuit provides the maximum response to currents at its resonant frequency. Series resonance circuit is known as acceptor circuit because the impedance at the resonance is at its minimum so as to accept the current easily such that the frequency of the accepted current is equal to the resonant frequency.

2. Answer : (d) None of these

Explanation: In RLC series circuit, when the circuit current is in phase with the voltage, the circuit is said to be in Series Resonance. The resonance condition in the circuit arises when the inductive reactance is equal to the capacitive reactance. At this condition, the circuit draws the maximum current.

3. Answer : (c) mutual induction

Explanation: A transformer works on the principles of "electromagnetic induction" as a mutual induction. Mutual induction is the process by which a coil of wire magnetically induces a voltage in another closely located coil.

4. Answer : (d) RL

Explanation: If the phase difference between

V and I is π/2

∴ Power = V⋅I = VI cos π/2 = 0

Since Power is 0 it should only consists of reactive elements (L & C), Resistance R cannot be present.

 5. Answer : (c) is a universal constant

Explanation: The constant is named after the British physicist Michael Faraday. It is a universal constant. It is the amount of electric charge carried by 1 mole of electrons. Represented by F & its measuring unit is Coulombs per mole (C).

6. Answer : (b) parallel resonant circuit

Explanation: A circuit comprising a capacitor and an inductor connected in parallel, having values chosen such that the combination offers a very high impedance to signals of a particular frequency.

7. Answer : (d) average value of A. C for complete cycle is zero

Explanation: Average value of A.C. for complete cycle is zero. Hence A.C. can not be measured by D.C. ammeter.

8. Answer : (b) it is more economical due to less power loss

Explanation: In long distance transmission of electricity, long wires are used which have very high resistance, R∝ l, so direct multiplication of R into a high number will increase power wasted. So current should be low, voltage can be high because resistance is denominator, so it will reduce the power wasted as heat. So less power is wasted therefore it is more economical way.

9. Answer : (c) Current and voltage are in same phase

Explanation: When resistance is connected to A.C source, then current & voltage are in same phase.

10. Answer : (b) increases directly with frequency

Explanation:\(X_L=\omega L\rightarrow X_L\propto\omega\)

11. Answer : (a) effective resistance due to capacity

Explanation: Capacitive reactance in an A.C. circuit is \(X_C=\frac{1}{\omega C}ohm\) where C is the capacitance of capacitor & \(\omega=2\pi n\) (n is the frequency of A.C source)

12. Answer : (b) 50 Hz

Explanation: The standard frequency of alternating current in India is 50 Hz.

13. Answer : (d) AC voltage, AC current

Explanation: The electric mains supply in our homes and offices is a voltage that varies like a sine function with time. Such a voltage is called alternating voltage and the current driven by it in a circuit is called the alternating current.

14. Answer : (a) dynamo

Explanation: Dynamos and alternators are the two main types of electromagnetic generators. A commutator is used in dynamos to produce pulsating direct current. Alternators are devices that produce alternating current.

15. Answer : (b) tank circuit

Explanation: The parallel combination of inductor and capacitor is called as tank circuit.

16. Answer : (a) hot wire ammeter

Explanation: Alternating current can be measured by hot wire ammeter whereas moving coil galvanometer and tangent galvanometer are used to measure dc current.

17. Answer : (d) eddy current

Explanation: Since the core forms a closed path, current gets induced (Eddy Current). So, the core has some resistance due to which losses are produced which decreases the efficiency of the transformer. Thus, the core of a transformer is laminated to reduce the Eddy Current.

18. Answer : (a) mutual induction

Explanation: A transformer works on the principles of "electromagnetic induction" as a mutual induction. Mutual induction is the process by which a coil of wire magnetically induces a voltage in another closely located coil.

19. Answer : (b) taking laminated transformer

Explanation: Eddy currents are locally generated current loops in the transformer core. This happens because transformer core is in close proximity of the varying magnetic field of the primary.Eddy current is a loss. To reduce this loss, core is made from bundle of thin laminated sheets.

20. Answer : (a) DC

Explanation: A fully charged capacitor acts as an open circuit. As a result, the capacitor now acts as an open circuit and thus, there is no more flow of charge in this circuit. In other words, we can say that a fully charged capacitor acts as an infinite resistance for DC.

21. Answer : (c) X/4

Explanation: \(X=\frac{1}{C\omega}\)

\(X'=\frac{1}{4C\omega}\)

\(\therefore X'=\frac{X}{4}\)

22. Answer : (b) decreases finitely

Explanation: Here, \(Q=\frac{\omega^2L}{R}\)

if R resistance increases, quality factor Q decreases finitely.

23. Answer : (a) iron loss

Explanation: Iron loss is the energy loss in the form of heat due to the formation of eddy currents in the iron core of the transformer.

24. Answer : (a) Current

Explanation: In step -down transformer, voltage decreases and corresponding current increases.

25. Answer :(d) an iron rod is inserted in the coil

Explanation: Brightness of the bulb decreases when inductive reactance increases, i.e. when iron rod is inserted in the coil, its inductance L increases, hence current decreases.

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