## Thursday, 18 November 2021

### UNIT 4 PHYSICS : MCQ ON ELECTROMAGNETIC INDUCTION

Multiple Choice Questions Choose the correct alternative. Each question is

carrying one mark.

1. The power factor for a purely capacitive circuit is :

• (a) 1
• (b) √2
• (c) 1/√2
• (d) Zero

2. Phase difference between voltage and current when an a.c. source is connected to an inductor :

• (a) 0°
• (b) 90°
• (c) 45°
• (d) 180°

3. Phase difference between voltage and current when an a.c. source is connected to a capacitor :

• (a) 90°
• (b) 45°
• (C) 180°
• (d) 0°

4. Which quantity is increased in step-down transformer ?

• (a) Resistance
•  (b) Power
• (c) Current
• (d) Charge

5. The power in series RLC-circuit with AC source  is given by :

• (a) zero
• (b) VI sinɸ
• (c) VI
• (d) VI cosɸ

6. The r.m.s. value of an a.c. is 5 A. Its maximum value will be :

• (a) 10 A
• (b) 5√2A
• (c) 5/√2A
• (d) 5√3A

7. In LCR-circuit, the capacitance is changed from C to 4C. For the same resonance frequency, the inductance should be changed from L to :

• (a) 2L
• (b) 4L
• (c) L/2
• (d) L/4

8. The ratio of primary to secondary turns in an ideal transformer are 2 : 1. If the power input is P, then power output is :

• (a) 2P
• (b) P
• (C) P/2
• (d) none of these.

9. Power dissipated in a series LCR-circuit at resonance is :

• (a)  I^{2}R
• (b) zero
• (c) I^{2}⍵L
• (d) \frac{I^{2}}{⍵C}

10. Phase difference between the voltage drop across R and C in a series LCR-circuit connected to an a.c. source is :

• (a) zero
• (b) 90°
• (c) 180°
• (d) 45°

11. Power factor is one for :

• (a) pure inductor
• (b) pure capacitor
• (c) pure resistor
• (d) either an inductor or a capacitor.

12. The square root of the product of inductance and capacitance has dimensions of:

• (a) length
• (b) mass
• (c) time
• (d) no dimensions.

13. In an a.c, circuit the current lags behind the voltage by the circuit contains :

• (a) only R
• (b) only L
• (c) only C
• (d) R and L both.

14. The power factor of LCR circuit at resonance is :

• (a) zero
• (b) 1/2
• (c) 1/√2
• (d) 1

15. If ɸ is the phase difference between the instantaneous values of voltage V and current I in an a.c. circuit, then the average power loss over a complete cycle is:

• (a) VI sinɸ
• (b) VI cosɸ
• (c) VI
• (d) VI/2

16. The values of L, C and R for a circuit are 1H, 9F and 3Ω. What is the quality factor for the circuit at resonance ?

• (a) 1
• (b) 9
• (c) 1/9
• (d) 1/3

17. In a transformer, loss due to eddy currents is minimised by :

• (a) laminating the core
• (b) laminating the core of steel
• (c) increasing the number of turns of primary coil
• (d) lubricating the core.

18. The core of a transformer is laminated to reduce:

• (a) flux leakage
• (b) hysteresis loss
• (c) output power
• (d) eddy current

19. An A.C. source of voltage E = 20 sin100t in connected cross a resistance 20Ω. The rms value of the current in circuit is:

• (a) 1A
• (b) 1/2A
• (c) √2A
• (d) 1/ √2A

20. The rate of change of current of 10 A/s in a coil produces an e.m.f. of 5 V. Then the self

inductance of the coil in henry is :

• (a) 0.5
• (b) 0.25
• (c) 1
• (d) 1.25.

21. The instantaneous voltage through a device of impedance 20Ω is e = 80 sin1001t. The effective value of the current is:

• (a) 3A
• (b) 2.828 A
• (c) 1.732 A
• (d)  √2A

22. A pure inductance coil of 30 mH is connected to an a.c. source of 220 V. The r.m.s current in

the coil is :

• (a) 50.35 A
• (b) 23.4 A
• (C) 30.5 A
• (d) 12.3 A.

23. An LCR series circuit is at resonance. Then :

• (a) the phase difference between current and voltage is 90°
• (b) the phase difference between current and voltage is 45°
• (c) its impedance is purely resistive
• (d) its impedance is zero.

24. An LCR series a.c. circuit is at resonance with 10 V each across L, C and R. If the resistance is halved, the respective voltages across L, C and R are :

• (a) 10 V, 10 V and 5 V
• (b) 10 V, 10 V and 10 V
• (c) 20V, 20 V and 5 V
• (d) 20 V, 20 V and 10 V

25. 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

26. A capacitor :

• (a) blocks AC but provides an easy path for DC
• (b) blocks DC but provides an easy path for AC
• (c) blocks both AC and DC
• (d) offers easy path for AC and DC

27. When AC source is connected across series LCR  combination, maximum power loss will occur when :

• (a) current and voltage are in phase
• (b) current from source is minimum
• (c) inductance is minimum
• (d) capacitance is maximum

28. A transformer works on the principle of:

• (a) self induction
• (b) electrical inertia
• (c) mutual induction
• (d) magnetic effect of the electrical current