CBSE Class 12 Physics Alternating Current MCQs Set A

CBSE Class 12 Physics Alternating Current MCQs Set A with answers available in Pdf for free download.
  • Physics
  • The MCQ Questions for Class 12 Physics with answers have been prepared as per the latest 2021 syllabus.

  • Q.1 Alternating current cannot be measured by D.C. ammeter, because

    Options:

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

    Answer=D

    Q.2  A.C. power is transmitted from a powerhouse at a high voltage as

    Options:

    (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

    Answer=B

    Q.3 If the frequency of an A.C. is made 4 times of its initial value, the inductive reactance will

    Options:

    (a) be 4 times (b) be 2 times
    (c) behalf       (d) remain the same

    Answer=A

    Q.4 When an ac voltage of 220 V is applied to the capacitor C, then

    Options:

    (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 voltage.
    (d) power delivered to the capacitor per cycle is zero

    Answer=D

    Q.5 An A.C. source is connected to a resistive circuit. Which of the following is true?

    Options:

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

    Answer=C

    Q.6 With the increase in the frequency of an A.C. supply, the inductive reactance

    Options:

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

    Answer=B

    Q.7 The capacitive reactance in an A.C. circuit is

    Options:

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

    Answer=A

    Q.8 In which of the following circuits the maximum power dissipation is observed?

    Options:

    (a) Pure capacitive circuit (b) Pure inductive circuit
    (c) Pure resistive circuit (d) None of these

    Answer=C

    Q.9 In an L.C.R. series a.c. circuit, the current

    Options:
    (a) is always in phase with the voltage
    (b) always lags the generator voltage
    (c) always leads the generator voltage
    (d) None of these

    Answer=D

    Q.10 If an LCR series circuit is connected to an ac source, then at resonance the voltage across

    Options:
    (a) R is zero
    (b) R equals the applied voltage
    (c) C is zero
    (d) L equals the applied voltage

    Answer=B

    More Questions...............

    1. In general in an alternating current circuit

    (a) the average value of current is zero

    (b) the average value of square of the current is zero
     
    (c) average power dissipation is zero
     
    (d) the phase difference between voltage and current is zero

    2. 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
     
    3. 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

    4. 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

    5. Alternating currents can be produced by a

    (a) dynamo

    (b) choke coil
     
    (c) transformer
     
    (d) electric motor
     
    6. The alternating current of equivalent value of I0√2 is

    (a) peak current
     
    (b) r.m.s. current

    (c) D.C. current
     
    (d) all of these
     
    7. The parallel combination of inductor and capacitor is called as
     
    (a) rectifier circuit 
     
    (b) tank circuit

    (c) acceptor circuit
     
    (d) filter circuit

    8. The peak value of the a.c. current flowing throw a resistor is given by

    (a) I = e/R

    (b) I = e/R
     
    (c) I = e
     
    (d) I = R/e
     
    9. The alternating current can be measured with the help of

    (a) hotwire ammeter
     
    (b) hotwire voltmeter
     
    (c) moving magnet galvanometer
     
    (d) suspended coil type galvanometer
     
    10. Alternating current can not be measured by D.C. ammeter, because

    (a) A. C. is virtual
     
    (b) A. C. changes its direction
     
    (c) A. C. can not pass through D.C. ammeter
     
    (d) the average value of A. C for the complete cycle is zero
11. The core of transformer is laminated to reduce

(a) flux leakage
 
(b) hysteresis
 
(c) copper loss 
 
(d) eddy current
 
12. A transformer is based on the principle of

(a) mutual induction

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

13. The transformation ratio in the step-up transformer is

(a) one
 
(b) greater than one

(c) less than one
 
(d) the ratio greater or less than one depends on the other factor
 

14. 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.
 
15. In which of the following circuits the maximum power dissipation is observed?

(a) Pure capacitive circuit
 
(b) Pure inductive circuit
 
(c) Pure resistive circuit
 
(d) None of these
16. 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

17. The average power dissipated in a pure inductance is

(a) 1/2LI2
 
(b) LI2
 
(c) LI2 / 4
 
(d) zero
 
19. In the case of an inductor

(a) voltage lags the current by Î /2
 
(b) voltage leads the current by Î /2
 
(c) voltage leads the current by  Π/3
 
(d) voltage leads the current by Π/4
 
18. 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
 
19. Quantity that remains unchanged in a transformer is

(a) voltage
 
(b) current
 
(c) frequency 
 
(d) None of these
 
20. 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
 
21. An inductance L having a resistance R is connected to an alternating source of angular frequency Ï‰ The Quality factor Q of inductance is

(a) R/ ωL
 
(b) (ωL/R)2
 
(c) (R /ωL)½
 
(d) Ï‰L/R
 
22. A capacitor acts as an infinite resistance for

(a) DC

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

23. 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
 
24. Of the following about capacitive reactance which is correct?

(a) The reactance of the capacitor is directly proportional to its ability to store charge
 
(b) Capacitive reactance is inversely proportional to the frequency of the current

(c) Capacitive reactance is measured in farad
 
(d) The reactance of a capacitor in an A.C. circuit is similar to the resistance of a capacitor in a D.C. circuit

25. Phase difference between voltage and current in a capacitor in an ac circuit is

(a) Ï€ 
 
(b) Ï€/2

(c) 0
 
(d) Ï€/3
 
26. 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
 
27. 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.

28. In LCR circuit if resistance increases quality factor

(a) increases finitely
 
(b) decreases finitely

(c) remains constant
 
(d) None of these
 
29. 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

30. With increase in frequency of an A.C. supply, the impedance of an L-C-R series circuit

(a) remains constant
 
(b) increases
 
(c) decreases
 
(d) decreases at first, becomes minimum and then increases.

31. If an LCR series circuit is connected to an ac source, then at resonance the voltage across

(a) R is zero
 
(b) R equals the applied voltage

(c) C is zero
 
(d) L equals the applied voltage
 
32. 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
33. In an L.C.R. series a.c. circuit, the current

(a) is always in phase with the voltage
 
(b) always lags the generator voltage
 
(c) always leads the generator voltage
 
(d) None of these

34. An LCR series circuit, connected to a source E, is at resonance. Then the voltage across

(a) R is zero
 
(b) R equals applied voltage

(c) C is zero
 
(d) L equals applied voltage
 
35. A transformer is employed to

(a) convert A.C. into D.C.
 
(b) convert D.C. into A.C.
 
(c) obtain a suitable A.C. voltage

(d) obtain a suitable D.C. voltage
 
36. Transformers are used

(a) in DC circuit only
 
(b) in AC circuits only

(c) in both DC and AC circuits
 
(d) neither in DC nor in AC circuits
 
 
37. Power factor of the A. C. circuit varies between

(a) 0 to 0.5
 
(b) 0.5 to 1
 
(c) 0 to 1

(d) 1 to 2

38. The graph between inductive reactance and frequency is

(a) parabola
 
(b) straight line

(c) hyperbola
 
(d) an arc of a circle
 
39. For minimum dissipation of energy in the circuit the power factor should be

(a) large

(b) small
 
(c) moderate
 
(d) can not say
 
 
40. The transformer voltage induced in the secondary coil of a transformer is mainly due to

(a) a varying electric field

(b) a varying magnetic field
 
(c) the vibrations of the primary coil
 
(d) the iron core of the transformer