M.C.Q : Alternating Current ( 1 to 10)


1. The frequency for which a 5.0μF capacitor has a reactance of 1000 Ω is given by

(A) 1000/π cycle /sec

(B) 100/π cycle /sec

(C) 200 cycle /s

(D) 5000 cycles /sec

2. In an a.c. circuit V and I are given by V = 50 sin50t volt and I = 100 sin(50t + π/3) mA. The power dissipated in the circuit

(A) 2.5 kW

(B) 1.25 kW

(C) 5.0 kW

(D) 500 watt

3. The average power dissipation in pure inductance in ac circuit, is

(A) 1/2Li2

(B) 2Li2

(C) Li2/4

(D) zero.

4. Circuit as shown in figure below, choose the correct statement.

(A) current in resistance R and current in inductor L will be in 90° phase difference.

(B) potential drop across R and potential drop across L will be in same phase.

(C) current through C and current through L will be in 90° phase difference.

(D) current in R and current in L will be in same phase.

5. In a series L, R, C, circuit which is connected to a.c. source. When resonance is obtained then net impedance Z will be

(A) Z = R

(B) Z = ωL -1/ωC

(C) Z = ωL

(D) Z = 1/ωC

6. An L,C, R series circuit is connected to a.c. source. At resonance, the applied voltage and the current flowing through the circuit will have a phase difference of

(A) π/4

(B) zero.

(C) π

(D) π/2

7. The reciprocal of impedance is called

(A) reactance.

(B) admittance.

(C) inductance.

(D) conductance.

8. The root-mean-square value of an alternating current of 50Hz frequency is 10 ampere. The time taken by the alternating current in reaching from zero to maximum value and the peak value of current will be

(A) 2×10-2 sec and 14.14 amp.

(B) 1 ×10-2 sec and 7.07 amp.

(C) 5 ×10-3 sec and 7.07 amp.

(D) 5×10-3 sec and 14.14 amp.

9. A coil of resistance 2000Ω and self-inductance 1.0 Henry has been connected to an a.c. source of frequency 2000/2π Hz. The phase difference between voltage and current is

(A) 30°

(B) 60°

(C) 45°

(D) 75°

10. In a series resonant circuit, the a.c. voltage across resistance R, inductance L and capacitance C are 5V, 10V and 10V, respectively. The a.c. voltage applied to the circuit will be

(A) 20V

(B) 10V

(C) 5V

(D) 25V


1. (B)    2. (B)   3. (D)    4. (A)    5. (A)    6. (B)    7. (D)    8. (D)    9. (C)    10. (C)   

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