31. If the self-inductance of a solenoid is 2 Henry and the current flowing through it is 2A, the energy in the electromagnetic field will be

- 8 J
- 2 J
- 16 J
- 4 J

32. When the current in a coil is increased from 2 A to 4 A in 0.05 seconds, the e.m.f. induced in the coil is 8V. The self-inductance of the coil is

- 0.8 H
- 0.4 H
- 0.2 H
- 0.1 H

33. Mutual inductance between two magnetically coupled coils depends on

- number of turns only
- permeability of the core only
- cross-sectional area of their common core only
- all of the above

34. The energy stored in the magnetic field of a solenoid 10 cm long and 2 cm diameter, with 1000 turns of carrying current of 10 A is

- 1.15 J
- 0.015 J
- 0.19 J
- 0.5 J

35. The rate of change of current in a 4 H inductor is 2 Amps/sec. Find the voltage across the inductor.

- 8 V
- 0.8 V
- 2 V
- 16 V

36. Mutual inductance between two coils is 4 H. If current in one coil changes at the rate of 2A/sec, then emf induced in the other coil is?

- 5 V
- 0.5 V
- 2 V
- 8 V

37. The mutual inductance between two unity coupled coils of 9H and 4H will be

- 6 H
- 13 H
- 36 H
- 2.2 H

38. If the co-efficient of coupling between two coils is increased, mutual inductance between the coils

- is increased
- changes depend on current
- is decreased
- remains unchanged

39. If the number of turns of a coil is increased, its inductance

- is increased
- remains the same
- is decreased
- none of the options

40. Two coupled coils with L_{1} = L_{2} = 0.6 have a coupling coefficient of K = 0.8. The turn ratio N_{1}/N_{2} is

- 4
- 2
- 1
- 0.5

41. The magnetic field energy in an inductor changes from maximum value to minimum value in 5 msec when connected to an a.c. source. The frequency of the source is

- 50 Hz
- 200 Hz
- 500 Hz
- 20 Hz

42. The energy stored in the magnetic field of a solenoid 30 cm long and 3 cm diameter with 1000 turns of wire carrying current of 10A is

- 0.15 J
- 0.5 J
- 1.15 J
- 0.015 J

43. A circuit has inductance of 2 H. If the circuit current changes at the rate of 10 A/sec, then self-induced emf is

- 5 V
- 0.2 V
- 20 V
- 10 V

44. The principle of mutual induction is applied in the case of

- alternator
- synchronous motor
- wattmeter
- transformer

45. Which of the following expressions depicts the coefficient of self inductance?

(where l = length of magnetic circuit and a = area of cross-section of magnetic circuit through which flux is passing and μ = permeability)

- N
^{2}μa/l - N
^{3}μa/l - N
^{2}a/μl - N
^{2}μal

46. Energy stored in the magnetic field of inductor L carrying current is

- LI
^{2} - (1/2)LI
^{2} - 2LI
- (1/2)LI

47. A 100 mH coil carries a current of 1 A. Energy stored in the magnetic field

- 1 J
- 0.05 J
- 1.5 J
- 2.5 J

48. The induced e.m.f. in a coil of 0.08 mH carrying 2A current is reversed in 0.4 seconds

- 0.16 mV
- 0.4 mV
- 0.8 mV
- 0.064 mV

49. On a power grid the load is generally

- capacitive
- resistive
- inductive
- all of these

50. The current in an inductor changes 200 mA in 4ms and induces a voltage of 100 mV. The value of inductor is

- 2 mH
- 0.5 mH
- 8 mH
- 4 mH

51. A coil has an inductance of 1 henry if a current changing at the rate of 1 amp/sec.

- induces 1 volt in another coil
- causes a back emf of 1 volt
- causes an adding emf of 1 volt
- causes transformer action

52. Two uncoupled 3 H inductors are connected in parallel. Their total inductance is

- 1.5 H
- 6 H
- 2 H
- 3 H

53. A coil having an inductance of 150 mH is carrying a current of 5 Amp. If the current is reduced to zero in 1 milliseconds, the self-induced emf will be

- 125 V
- 375 V
- 500 V
- 750 V

54. The induction coil works on the principle of

- self-induction
- mutual induction
- ampere’s rule
- fleming right hand rule

55. At a particular instant an inductance of 1 H carries a current of 2 A while the voltage across it is 1V. The energy stored in the inductance in Joules is

- 1/2
- 1
- 3/2
- 2

56. The e.m.f. induced is 2 V when current is changing at the rate of 0.5 A/s. The self-inductance of coil is

- 4
- 2
- 1
- none of these

57. Inductance affects the direct current flows

- only at the time of turning off
- only at the time of turning on
- at the time of turning on and off
- at all the time of operations

58. Higher the self-inductance of a coil

- lesser its weber-turns
- lower the emf induced
- greater the flux produced by it
- longer the delay in establishing steady current through it

59. The differential coupling of two coils in series connection has self-inductance of 2 mH and 4 mH and a mutual inductance of 0.15 mH. The equivalent inductance of the combination is

- 5.7 mH
- 5.85 mH
- 6 mH
- 6.15 mH

60. A coil having 90 turns is connected to a 120 V, 60 Hz source. If the effective value of the magnetizing current is 4 A, then calculate the value of inductance of the coil.

- 79.6 mH
- 121.2 mH
- 32.2 mH
- 83.16 mH