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Multiple Choice Question (MCQ) of D.C. Machines page-8

71. Two dc series motors connected in series are driving the same mechanical load. If now the motors are connected in parallel, the speed becomes

a) Slightly more than double
b) Slightly less than double
c) Slightly more than half
d) Slightly less than half

Ans: (a)

72. The direction of rotation of a dc series motor can be reversed by interchanging

a) The supply terminals only
b) The field terminals only
c) The supply and the field terminals
d) None of these

Ans: (b)

73. By putting a variable resistance (diverter) across the series field in a dc series motor, speed above normal can be obtained because

a) Armature current decreases
b) Flux gets reduced
c) Line current gets decreased
d) None of these

Ans: (b)

74. The speed of a dc series motor decreases if the flux in the field winding

a) Remains constant
b) Decreases
c) Increases
d) None of these

Ans: (c)

75. The speed of a series dc motor at no load is

a) Zero
b) Medium
c) High
d) Tending to infinity

Ans: (d)

76. Which of the following dc motors has the least reduction in speed from no load to rated load?

a) Shunt motor with commutating poles
b) Series motor with commutating poles
c) Series motor without commutating poles
d) Compound motor without commutating poles

Ans: (a)

77. Which of the following statements about a series motor is correct

a) It can run easily without load.
b) It has poor torque.
c) It has an almost constant speed.
d) Its field winding consists of small number of thick wires.

Ans: (d)

78. The output power of any electrical motor is taken from

a) The armature
b) The conductors
c) The coupling mounted on the shaft
d) The poles

Ans: (c)

79. Torque of a motor is

a) Force on N-m acting on the rotor
b) Product of tangential force on the rotor and its radius
c) The electrical power in kW
d) Power given to the load

Ans: (b)

80. In a dc machine dull yellow spark indicates

a) Winding fault
b) Excessive brush wear
c) Excessive noise
d) None of these

Ans: (d)

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