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MCQs

Dc Motors

Total Questions : 240 | Page 23 of 24 pages
Question 221. When the armature of a D.C. motor rotates, e.m.f. induced is
  1.    Mutually induced e.m.f.
  2.    None of these
  3.    Back e.m.f.
  4.    Self-induced e.m.f.
 Discuss Question
Answer: Option C. -> Back e.m.f.
Question 222. Usually wide and sensitive speed control is desired in case of
  1.    Colliery winders
  2.    Centrifugal pumps
  3.    Elevators
  4.    Steel rolling mills
 Discuss Question
Answer: Option A. -> Colliery winders
Question 223. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity?
  1.    Brake test
  2.    Hopkinson's test
  3.    Field test
  4.    Swinburne's test
 Discuss Question
Answer: Option C. -> Field test
Question 224. 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 reduce the reluctance of the magnetic path
  3.    To support the field coils
  4.    To spread out flux for better uniformity
 Discuss Question
Answer: Option A. -> To reduce eddy current loss
Question 225. A three point starter is considered suitable for
  1.    Shunt, compound and series motors
  2.    Shunt as well as compound motors
  3.    Shunt motors
  4.    All D.C. motors
 Discuss Question
Answer: Option B. -> Shunt as well as compound motors
Question 226. Which of the following loss in a D.C. generator varies significantly with the load current?
  1.    Windage loss
  2.    Armature copper loss
  3.    None of these
  4.    Field copper loss
 Discuss Question
Answer: Option B. -> Armature copper loss
Question 227. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
  1.    25% of the previous value
  2.    50% of the previous value
  3.    100% of the previous value
  4.    10% of the previous value
 Discuss Question
Answer: Option A. -> 25% of the previous value
Question 228. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit
  1.    A resistance is connected parallel to the armature
  2.    Armature is temporarily open circuited
  3.    A resistance is connected in series with armature
  4.    A high value resistor is connected across the field winding
 Discuss Question
Answer: Option C. -> A resistance is connected in series with armature
Question 229. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
  1.    4.76%
  2.    2.22%
  3.    8.85%
  4.    6.77%
 Discuss Question
Answer: Option A. -> 4.76%
Question 230. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
  1.    Almost negligible
  2.    Rated full-load current
  3.    Less than full-load current
  4.    More than full-load current
 Discuss Question
Answer: Option D. -> More than full-load current

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