# Objective Type Question or MCQ of Electrical Circuits and Magnetic Fields page-5

61. Which lines of forces produced by two magnetic fields, the field

a) Is stronger where the lines of force are in the same direction
b) Is stronger where the lines are in opposite direction
c) Has the same strength as for one magnet
d) Is weakest where the lines are in the same direction

Ans: (a)

62. A solenoid is a coil which

a) Acts as bar magnet only when there is no current in the conductor
b) Acts as bar magnet only when the current flows in the coil
c) Is similar to ring magnet because there is no air gap
d) Acts as bar magnet only when it has iron core

Ans: (b)

63. The force tending to make a loop of wire rotate is called

a) Energy
b) Power
c) Voltage
d) Torque

Ans: (d)

64. Motor action in a wire conducting current can be produced

a) Without any additional magnetic field
b) Move the conductor from weaker field toward stronger field
c) Move the conductor from stronger field toward a weaker field
d) Produce the motion of the conductor but not rotation

Ans: (c)

65. The r.m.s. value of an a.c. signal is 10 volts. The peak to peak value will be

a) 6.37 volts
b) 10 volts
c) 14 volts
d) 28 volts

Ans: (c)

66. When two waves are 90° out of phase

a) Each has its peak value at the same time
b) Each has its minimum value at the same time
c) One has its peak value when the other has zero value
d) One has its positive peak when the other has its negative peak

Ans: (c)

67. Which of the following can produce maximum induced voltage?

a) 1-amp. D.c. current
b) 50-amp. D.c. current
c) 1-amp. 60 cycles a.c. current
d) 1-amp. 490 cycles a.c. current

Ans: (d)

68. When the alternating voltage reverses in polarity, the current its produces

a) Reverses its direction
b) Has the same direction
c) Has phase angle of 180 degree
d) Alternates at 1.4 time the frequency of the applied voltage

Ans: (a)

69. An alternating current can induce voltage because it has

a) High r.m.s. value
b) Varying magnetic field
c) Stronger field than direct current
d) Constant magnetic field

Ans: (b)

70. If the length, number of turns, and area of a coil are doubled, the inductance of the coil is

a) The same
b) Double
d) One-quarter

Ans: (c)

71. The d.c. resistance of a coil made with 100ft of gauge No. 30 copper wire is approximately

a) Less than one ohm
b) 10.5 ohms
c) 104 ohms
d) More than 1 M Ω

Ans: (b)

72. An open coil has

a) Zero resistance and high inductance
b) Infinite resistance and zero inductance
c) Infinity resistance and normal inductance
d) Zero resistance and inductance

Ans: (b)

73. Inductive resistance is measured in ohms because it

a) Reduces the amplitude of alternating current
b) Increases the amplitude of alternating current
c) Increases the amplitude of direct current
d) Has a back e.m.f. opposing the voltage output of a battery

Ans: (a)

74.Inductive reactance applied to sine wave only because it

a) Increases with lower frequency
b) Increases with lower inductance
c) Depends on the factor 2π
d) Decreases with the higher frequencies

Ans: (c)

75. In a sine wave a.c. circuit with 90 ohms R in series with 90 ohms XL, phase angle θ equals

a) 0°
b) 60°
c) 45°
d) 90°

Ans: (c)

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