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MCQ of D.C motor page-12


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71. Which of the following test can be conducted on all types of dc machines?

A) Field’s test
B) Brake test
C) Running down test
D) Swinburne’s test.

Ans : (B)

72. A cumulatively compound dc motor runs at a full load speed of 480 rpm. Now if the series field of the motor is short-circuited, then the full load speed will be

A) more than 480 rpm
B) 480 rpm
C) less than 480 rpm
D) zero.

Ans : (A)

73. A Dc motor is driving a load that requires constant output power. The pu value of torque with its field current reduced to half would be (consider rated quantities as 1.0 pu).

A) 1.5 pu
B) 2.0 pu
C) 1.0 pu
D) 0.5 pu.

Ans : (D)

74. In case of a shunt motor if the supply voltage is increased by 20% which of the following will decrease?

A) Starting torque
B) Full load speed
C) Full load current
D) None of the above.

Ans : (C)

75. The motor enclosure used in woodworking industry is :

A) Flame-proof type
B) Protected type
C) Splash proof type
D) Totally enclosed fan cooled type.

Ans : (C)

76. The starter for a dc motor also provides protection to the motor against damage

A) due to short circuits in the equipment
B) from long-term over loads
C) from excessive starting currents
D) all of the above.

Ans : (D)

77. Which one among the following has the highest numerical value in a stepper motor ?

A) Ripple torque
B) Dynamic torque
C) Holding torque
D) Detent torque.

Ans : (C)

78. In series-parallel control of dc series motors, the torque in series arrangement is

A) four times the torque in parallel arrangement
B) one fourth of torque in parallel arrangement
C) half of torque in parallel arrangement
D) same as torque in parallel arrangement.

Ans : (A)

79. When the direction of power flow reverses, a differentially compounded motor becomes

A) a series motor
B) a shunt motor
C) a cumulatively compounded generator
D) a differentially compounded generator.

Ans : (C)

80. The speed of a dc shunt motor can be controlled by

A) changing the field resistance
B) changing the terminal voltage applied to the armature
C) inserting a resistor in series with the armature circuit
D) any of the above.

Ans : (D)


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