Class 12th Physics Most VVI Objective Alternating Current Chapter

Alternating Current

1. In an LCR series ac circuit, the voltage across each of the components L, C and R is 50 Volt. The voltage across LC combination is :

(A) 50 Volt

(B) 25 Volt

(C) 100 Volt

(D) 0 Volt

 Answer:- D

2. The phase difference between current and voltage in an AC circuit is θ. Then power factor will be:

(A) cosθ

(B) sinθ

(C) tanθ

(D) 1 θ

 Answer:- A

3. The working principle of choke coil is based on

(A) Conservation of angular momentum

(B) Self induction

(C) Mutual induction

(D) Conservation of momentum

 Answer:- B

4. In a step up transformer the number of coils in primary coils is N1 and N2 in secondary. Then :-

(A) NI = N2

(B) NI < N2

(C) NI > N2

(D) None of these

 Answer:- B

5. The device that increases AC voltage is called –

(A) resistor

(B) step-down transformer

(C) step-up transformer

(D) transformer

 Answer:- C

6. The oscillation frequency of an LC circuit is f. If both the capacitance and inductance be doubled, the frequency will become –

(A) f / 4

(B) 2f

(C) 4f

(D) f / 2

 Answer:- D

7. In LCR-circuit, L = 8.0 H, C = 0.5 μF, and R = 100 Ω are connected in series. The resonant frequency will be

(A) 600 radian/second

(B) 500 radian/second

(C) 600 hertz

(D) 500 hertz

 Answer:- B

8. A choke coil is used to control current in a circuit of

(A) ac only

(B) dc only

(C) both ac and dc

(D) None of these

 Answer:- A

9. Step-down transformer increases

(A) current

(B) voltage

(C) wattage

(D) None of these

 Answer:- A

10. The thermal effect of alternating current is practically

(A) Joule heating

(B) Peltier heating

(C) Thomson effect

(D) None of these

 Answer:- A

11. The power factor of a choke coil is about

(A) 90°

(B) 0

(C) 1

(D) 180°

 Answer:- B

12. The power factor of a condenser is

(A) 90°

(B) 1

(C) 180°

(D) 0

 Answer:- D

13. For which of the following, capacitor works as infinite resistance ?

(A) DC

(B) AC

(C) both DC and AC

(D) None of these

 Answer:- A

14. L-C circuit without AC-source is called

(A) oscillatory circuit

(B) drift circuit

(C) hysteresis circuit

(D) None of these

 Answer:- A

15. S.I. unit of Impedance is

(A) henry

(B) ohm

(C) tesla

(D) None of these

 Answer:- B

16. The equation of an AC is I = 60sin100πt. The root mean square value will be

(A) 60√2

(B) 60 / √2

(C) 100

(D) zero

 Answer:- B

17. The value of phase difference between current and emf in an AC circuit with resistance only, is

(A) zero

(B) π / 2

(C) π

(D) 2π

 Answer:- A

18. The unit of reactance is

(A) ohm

(B) farad

(C) ampere

(D) mho

 Answer:- A

19. The unit of capacitive reactance is

(A) farad

(B) ohm

(C) maxwell

(D) ampere

 Answer:- B

20. The impedance of L-R series circuit is

(A) R = ωL

(B) R2 + ω2L2

(C) √R22L2

(D) R

 Answer:- C

21. In LCR circuit energy loss in circuit is

(A) in inductance

(B) in resistance

(C) in condenser

(D) All of above

 Answer:- B

22. The frequency of domestic electricity supply is 50 Hz. The frequency at which current becomes zero is

(A) 25

(B) 50

(C) 100

(D) 200

 Answer:- C

23. The frequency of alternating current supply in India is

(A) 50 hertz

(B) 60 hertz

(C) 100 hertz

(D) 220 hertz

 Answer:- C

24. The conversion of electrical energy into thermal energy in a transformer is called

(A) copper loss

(B) iron loss

(C) hysterisis loss

(D) None of these

 Answer:- A

25. In A.C. circuit, the current and voltage are given by i = 5 cos wt and V = 200sin wt respectively. Power loss in the circuit

(A) 20W

(B) 40W

(C) 1000W

(D) zero

 Answer:- D

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