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MCQs

Dc Motors

Total Questions : 240 | Page 8 of 24 pages
Question 71. In D.C. machines the residual magnetism is of the order of
  1.    2 to 3 percent
  2.    10 to 15 percent
  3.    20 to 25 percent
  4.    50 to 75 percent
 Discuss Question
Answer: Option A. -> 2 to 3 percent
Question 72. In a D.C. generator, the iron losses mainly take place in
  1.    Yoke
  2.    Commutator
  3.    Armature conductors
  4.    Armature rotor
 Discuss Question
Answer: Option D. -> Armature rotor
Question 73. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
  1.    Frame
  2.    Shaft
  3.    Commutator
  4.    Stator
 Discuss Question
Answer: Option C. -> Commutator
Question 74. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
  1.    Runs as a generator
  2.    Does not run as a generator
  3.    Also runs as a motor comes to stop after sometime
  4.    None of these
 Discuss Question
Answer: Option A. -> Runs as a generator
Question 75. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
  1.    Drum type controller is used
  2.    Three point starter is used
  3.    Four point starter is used
  4.    All above can be used
 Discuss Question
Answer: Option A. -> Drum type controller is used
Question 76. Ward-Leonard control is basically a
  1.    Voltage control method
  2.    Field diverter method
  3.    Field control method
  4.    Armature resistance control method
 Discuss Question
Answer: Option A. -> Voltage control method
Question 77. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
  1.    D.C. shunt motor
  2.    D.C. series motor
  3.    Induction motor
  4.    Reluctance motor
 Discuss Question
Answer: Option D. -> Reluctance motor
Question 78. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
  1.    4.0
  2.    2.0
  3.    1.0
  4.    0.5
 Discuss Question
Answer: Option D. -> 0.5
Question 79. Which of the following losses are significantly reduced by laminating the core of a D.C. generator?
  1.    Hysteresis losses
  2.    Eddy current losses
  3.    Copper losses
  4.    Windage losses
 Discuss Question
Answer: Option B. -> Eddy current losses
Question 80. In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
  1.    100%
  2.    Around 90%
  3.    Anywhere between 75% and 90%
  4.    Less than 50%
 Discuss Question
Answer: Option D. -> Less than 50%

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