D.C. Motors

111. Which of the following method of speed control of D.C. machine will offer minimum efficiency?

  1. Voltage control method
  2. Field control method
  3. Armature control method
  4. All above methods

Correct answer: (C)
Armature control method

112. Which of the following motor has the poorest speed regulation?

  1. Shunt motor
  2. Series motor
  3. Differential compound motor
  4. Cumulative compound motor

Correct answer: (B)
Series motor

113. Which of the following motor is preferred for operation in highly explosive atmosphere?

  1. Series motor
  2. Shunt motor
  3. Air motor
  4. Battery operated motor

Correct answer: (C)
Air motor

114. 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

Correct answer: (D)
Reluctance motor

115. Which of the following motors is usually used in house-hold refrigerators?

  1. D.C. shunt motor
  2. D.C. series motor
  3. Single phase induction motor (split phase start or induction run motor)
  4. Reluctance motor

Correct answer: (C)
Single phase induction motor (split phase start or induction run motor)

116. Which of the following motors one will choose to drive the rotary compressor?

  1. D.C. shunt motor
  2. D.C. series motor
  3. Universal motor
  4. Synchronous motor

Correct answer: (D)
Synchronous motor

117. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity?

  1. Swinburne's test
  2. Hopkinson's test
  3. Field test
  4. Brake test

Correct answer: (C)
Field test

118. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors?

  1. Low cost
  2. Wide speed range
  3. Stability
  4. High starting torque.

Correct answer: (A)
Low cost

119. Which one of the following is not the function of pole shoes in a D.C. machine?

  1. To reduce eddy current loss
  2. To support the field coils
  3. To spread out flux for better uniformity
  4. To reduce the reluctance of the magnetic path

Correct answer: (A)
To reduce eddy current loss

120. Why are the D.C. motors preferred for traction applications?

  1. Torque and speed are inversely proportional to armature current
  2. Torque is proportional to armature current
  3. Torque is proportional to square root of armature current
  4. The speed is inversely proportional to the torque and the torque is proportional to square of armature current

Correct answer: (D)
The speed is inversely proportional to the torque and the torque is proportional to square of armature current

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