# Physics Class 12th Chapter 7 Alternating Current Most VVI Objective Questions

Q.1. The unit of reactance is

(A) Ohm

(C) Ampere

(D) Mho

Ans :- (A)

Q.2. Impedance of L-R circuit is

(A) R+ωL

(B) R²+ω²L²

(C) √R+ωL

(D) √R²+ω²L²

Ans:- (D)

Q.3. If φ is the phase difference between a.c. current and e.m.f then the value of power factor is

(A) tan φ

(B) cos²φ

(c) sinφ

(D) cosφ

Ans:- (D)

Q.4. The power factor of L-R circuit is

(A) R+ ωL

(B) R / √R²+L²ω

(C) R+ √R²+ω² L²

(D) ωL/R

Ans:- (B)

Q.5. The equation of an ac is represented by 1=0.6 sin 100πt the frequency of ac is

(A) 50π

(B) 50

(C) 100π

(D) 100

Ans:- (B)

Q.6. What is SI unit of alternating current

(A) Coulomb

(B) Coulomb-second

(C) Ampere

(D) Henry

Ans:- (C)

Q.7. Unit of inductive reactance (Xl) is

(A) Ohm

(B) Ohm- Meter

(C) Ampere

(D) Volt

Ans:- (A)

Q.8. Unit of impedance (Z) is

(A) Volt

(B) Henry

(C)Watt

(D) Ohm

Aans:- (D)

Q.9. Thevalue of V in the =circuit shown is

(A) 20V

(B) Zero

(C) Can not be soid

(D) none of these

Ans:- (A)

Q.10. A Choke coil is

(A) An inductor

(B) A resistor

(C) A capacitor

(D) None of these

Ans:- (A)

Q.11. If the phase difference between the current and voltage is negative it means that the current

(B) Lags the voltage

(C) Both ‘A’ and  ‘B’

(D) None of these

Ans:- (A)

Q.12. If a coil is open then  inducatnce L and R(Resistance) becomes

(A) Infinity and Zero

(B) Zero and infinity

(C) Infinity and infinity

(D) Zero and Zero

Ans:- (B)

Q.13. For high frequency capacitor offers

(A) More reactance

(B) Zero reactance

(C) Less reactance

(D) Noneof these

Ans:- (C)

Q.14. Current in a circuit is wattless if

(A) inductance in the circuit is zero

(B) Resistance in the circuit is zero

(C) Current is alternating

(D) Resistance and inductance both and zero

Ans:-(B)

Q.15. How can we improve the φ-factor of a series  resonant circuit

(A) By decreasing ‘R’

(B) By decreasing capacitance

(C) By increasing indvctance

(D) All  of above

Ans:-(D)

Q.16. Alternating current can be produced by

(A) A transformer

(B) An electric motor

(C) Dynamo

(D) None od these

Ans:- (C)

Q.17. The frequency of alternating current mains in india is

(A) 25Hℤ

(B) 50HZ

(C) 30HZ

(D) 60HZ

Ans:-(B)

Q.18. Alternating current shows

(A) Chemical effect

(B) Magnetic effect

(C) Heating effect

(D) None of these

Ans:-(C)

Q.19. Hot wire ammeters are used for measueing

(A) D.C only

(B) A.C only

(C) Both a.c and d.c

(D) None of these

Ans:-(C)

Q.20. Alernating current ismeasured by

(A) An ammeter

(B) Heating effect of current

(C) Thermopile

(D) None of these

Ans:- (B)

Q.21. How wire instruments measure

(A) Peak value of a.c

(B) Average value of a.c

(C) Rms value of a.c

(D) None of these

Ans:-(C)

Q.22. The power factor of purely resistive a.c circuit is

(A) Zero

(B) One

(C) infinite

(D) O.S

Ans:-(B)

Q.23.The power factor is one for

(A) pure resistor only

(B) Pure inductor only

(C) Pure Capacitor Only

(D) None of these

Ans:- (A)

Q.24. A choke coil has

(A) High inductance and high resistance

(B) High inductance and low resistance

(C) Low inductance and low resistance

(D) None of these

Ans:-(B)

Q.25. Alternating current of 3A is the same as

(A) 3 coulomb/Second

(B) 3ohm/meter

(C) 3 joule/coulomb

(D) None of these

Ans:- (A)

Q.26. The choke coil is used to control

(A) A.c

(B) D.c

(C) both a.c and D.c

(D) None of these

Ans:- (A)

Q.27. The ratio of peak value and r.m.s value of ac is

(A) 2

(B) √2

(C) 1/√2

(D) 1/2

Ans:-(B)

Q.28. An a.c circuit contains capacitor the resistance offered by the capacitor is increased

(A) By decreasing the angular frequency

(B) By decreasing the capacitance of capacitor

(C)  both ‘A’ and ‘B’ are correct

(D) Non of these

Ans:-(C)

Q.29. An Lc circuit cannot produce oscillations when

(A) Capacitance is large

(B)Inductance is large

(C) resistance is large

(D) none of these

Ans:- (C)

Q.30. In a LR circuit the correct rises to final value slowly when

(A) Lis small

(B) Lis large

(C) Lis zero

(D) none of these

Ans:- (B)

Q.31. The rms voltage of an a.c. is 220v. the peak value is

(A) 220√2v

(B) √2/220v

(C) 220v

(D) 220√2v

Ans:- (D)

Q.32. The maximum value of the power factor is

(A) 1

(B) 2

(C) Infinity

(D) 100

Ans:- (A)

Q.33. The power factor of an a.c. circuit is o.s. what will be the phase difference between voltage and current in this circuit

(A) 9⁰

(B) 180⁰

(C) 60⁰

(D) 0⁰

Ans:- (c)

Q.34. The reading of a hot wire voltmeter is 220 volt the peak value of A.c. voltage

(A) 311 volt

(B) 320 volt

(C) 211 volt

(D) 0 volt

Ans:- (A)

Q.35. A choke coil is perferred to a rheosantin an a.c. circuit as it

(A) increases current

(B) increases power

(C) Consumes almost zero power

(D) none of these

Ans:- (C)

Q.36. For high frequency indutet offers

(A) more reactance

(B) Zero reactance

(C) Less reactance

(D) none of these

Ans:- (A)

Q.37. Transformer are used in

(A) direct current

(B) Alternating current

(C) both d.c.and a.c

(D) none of these

Ans:- (B)

Q.38. Transformer is used to convert

(A) a.c. into d.c.

(B) d.c. into a.c.

(C) low voltage to highand vice versa

(D) none of these

Ans:- (C)

Q.39. An a.c. circuit contains inductor ,the inductive reactance is increased

(A) By increasing the angular frequency

(B) By incrreasing inductance

(C) Both ‘A’and ‘B’ are correct

(D) none of these

Ans:-(C)