NCERT Class 12 Chapter 7 Physics Alternating Current MCQ

NCERT Class 12 Chapter 7 Physics Alternating Current MCQ | Questions & Answers: Do check this article if you wish to take up an online quiz about NCERT Class 12 Chapter 7 Physics Alternating Current. In the below section we have gathered MCQ questions related to the Alternating Current, which will help you in learning about this concept.

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1. 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

2. The phase difference between the alternating current and emf is TE/2. Which ofthe following cannot be the constituent of the circuit?

A. C alone

B. L alone

C. L and C

D. R and L

3. Energy dissipates in LCR circuit in :

A. L only

B. C only

C. R only

D. All of the above

4. Virtual value or effective value of a.c. is

A. -0.637I₀

B. -0.707I₀

C. 0.637I₀

D. 0.707I₀

5. 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

6. In an LCR-series ac circuit, the voltage across each of the component L, C and R is 50 V. The voltage across the LC-combination will be

A. 50 V

B. 50√2 V

C. 100 V

D. zero

7. In an LCR circuit, capacitance is charged from C to 2C. For resonant frequency to remain unchanged, the inductance should be changed from L to

A. 4 L

B. 2 L

C. L/2

D. L/4

8. Given the instantaneous value of current from a.c. source is I = 8 sin 623t. Find the r.m.s value of current

A. 5.656 A

B. 8 A

C. 2.848 A

D. 1.414 A

9. If the frequency of an A.C. is made 4 times of its initial value, the inductive reactance will

A. be 4 times

B. be 2 times

C. be half

D. remain the same

10. An ac circuit has a resistance of 12 ohm and an impedance of 15 ohm. The power factor of the circuit will be

A. 0.8

B. 0.4

C. 0.125

D. 1.25

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11. As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?

A. Inductor and capacitor.

B. Resistor and inductor.

C. Resistor and capacitor.

D. None

12. What is time constant

A. characteristic time with which current grows and decays

B. the time current takes to reach the minimum value only

C. time for the complete cycle

D. the time current takes to reach the peak value only

13. When an ac voltage of 220 V is applied to the capacitor C, then

A. the maximum voltage between plates is 220 V.

B. the current is in phase with the applied voltage.

C. the charge on the plate is not in phase with the applied votage.

D. power delivered to the capacitor per cycle is zero

14. In an ac circuit the voltage applied is s = s0 sin (tit. The resulting current in the circuit is I = 70 sin (cot – nil). The power consumption in the circuit is given by

CBSE Class12 Physics Alternating current (14Q)

CBSE Class12 Physics Alternating current (14Q)

A. (a)

B. (b)

C. (c)

D. (d)

15. Alternating currents can be produced by a

A. dynamo

B. choke coil

C. transformer

D. electric motor

16. Find the instantaneous voltage for an a.c. supply of 200V and 75 hertz

A. E = 282.8 sin 50πt

B. E = 282.8 sin 150πt

C. E = 282.8 sin 75πt

D. E = 282.8 sin 100πt

17. 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. ny of the above may be true depending upon the value of resistance.

18. In an LCR circuit, capacitance is charged from C to 2C. For resonant frequency to remain unchanged, the inductance should be changed from L to

A. 4 L

B. 2 L

C. L/2

D. L/4

19. In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be

A. remains same

B. doubled

C. halved

D. zero

20. Which phasor represents the relationship between alternating current and alternating e.m.f. for a resistance? CBSE Class12 Physics Alternating current (20Q)

CBSE Class12 Physics Alternating current (20Q)

A. (B)

B. (A)

C. Both A and B

D. Neither A nor B

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21. 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

22. The core of any transformer is laminated so as to

A. reduce the energy loss due to eddy currents.

B. make it light weight

C. make it robust and strong.

D. increase the secondary voltage.

23. In an alternating current circuit consisting of elements in series, the current increases on increasing the frequency of supply. Which of the following elements are likely to constitute the circuit?

A. Only resistor

B. Resistor and inductor

C. Resistor and capacitor

D. Only inductor

24. Alternating current is represented by

CBSE Class12 Physics Alternating current (24Q)

A. (A)

B. (B)

C. (C)

d. (D)

25. 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