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) √R2+ω2L2
(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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