DC Motors MCQ Questions and Answers Quiz

31. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens

  1. nothing will happen to th£ motor
  2. this will make armature to take heavy current, possibly burning it
  3. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
  4. motor will run at very slow speed

32. If I2 be the armature current, then speed of a D.C. shunt motor is

  1. independent of Ia
  2. proportional to la
  3. varies as (Ia)
  4. varies as la

33. If the field of a D.C. shunt motor gets opened while motor is running

  1. the speed of motor will be reduced %
  2. the armature current will reduce
  3. the motor will attain dangerously high speed 1
  4. the motor will continue to nuvat constant speed

34. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will

  1. increase
  2. decrease
  3. remain same
  4. become zero

35. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?

  1. Starting torque
  2. Operating speed
  3. Full-load current
  4. All of the above

36. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking

  1. regenerative
  2. plugging
  3. dynamic braking
  4. none of the above

37. In a D.C. generator all of the following could be the effects of iron losses except

  1. Loss of efficiency
  2. Excessive heating of core
  3. Increase in terminal voltage
  4. Rise in temperature of ventilating air

38. In a D.C. generator, the iron losses mainly take place in

  1. yoke
  2. commutator
  3. armature conductors
  4. armature rotor

39. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to

  1. 100% of the previous value
  2. 50% of the previous value
  3. 25% of the previous value
  4. 10% of the previous value

40. In a D.C. shunt motor, speed is

  1. independent of armature current
  2. directly proportional to the armature current
  3. proportional to the square of the current
  4. inversely proportional to the armature current
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