DC Motors MCQ Multiple Choice Questions Answers

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

Correct Answer is: this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

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

Correct Answer is: independent of Ia

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

Correct Answer is: the motor will attain dangerously high speed 1

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

Correct Answer is: Full-load current

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

Correct Answer is: Increase in terminal voltage

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

Correct Answer is: armature rotor

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

Correct Answer is: 25% of the previous value

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

Correct Answer is: independent of armature current

Q: 41. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

Correct Answer is: more than full-load current

Q: 42. In a differentially compounded D.C. motor, if shunt field suddenly opens

Correct Answer is: the motor will first stop and then run in opposite direction as series motor

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

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

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

independent of Ia
proportional to la
varies as (Ia)
varies as la

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

the speed of motor will be reduced %
the armature current will reduce
the motor will attain dangerously high speed 1
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

increase
decrease
remain same
become zero

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

Starting torque
Operating speed
Full-load current
All of the above

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

regenerative
plugging
dynamic braking
none of the above

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

Loss of efficiency
Excessive heating of core
Increase in terminal voltage
Rise in temperature of ventilating air

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

yoke
commutator
armature conductors
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

100% of the previous value
50% of the previous value
25% of the previous value
10% of the previous value

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

independent of armature current
directly proportional to the armature current
proportional to the square of the current
inversely proportional to the armature current

41. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be

almost negligible
rated full-load current
less than full-load current
more than full-load current

42. In a differentially compounded D.C. motor, if shunt field suddenly opens

the motor will first stop and then run in opposite direction as series motor
the motor will work as series motor and run at slow speed in the same direction
the motor will work as series motor and run at high speed in the same direction
the motor will not work and come to stop

43. In a manual shunt motor starter

over load relay is connected in series and no volt relay in parallel with the load
over load relay is connected in paralÂ¬lel and no volt relay in series with the load
over load relay and no volt relay are both connected in series with the load
over load relay and no volt relay are both connected in parallel with the load

44. In case of conductively compensated D.C. series motors, the compensating winding is provided

as separately wound unit
in parallel with armature winding
in series with armature winding
in parallel with field winding

45. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because

back e.m.f. is equal to armature drop
armature drop is negligible
flux is proportional to armature current
flux is practically constant in D:C. shunt motors

46. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will

remain unchanged
reduce to one-fourth value
increase four folds
be doubled

47. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

100%
around 90%
anywhere between 75% and 90%
less than 50%

48. In D.C. machines fractional pitch winding is used

to improve cooling
to reduce copper losses
to increase the generated e.m.f.
to reduce the sparking

49. In D.C. machines the residual magnetism is of the order of

2 to 3 per cent
10 to 15 per cent
20 to 25 per cent
50 to 75 per cent

50. In D.C. motor which of the following can sustain the maximum temperature rise?

Slip rings
Commutator
Field winding
Armature winding

51. In D.C. shunt motors as load is reduced

the speed will increase abruptly
the speed will increase in proportion to reduction in load
the speed will remain almost/constant
the speed will reduce

52. In the D.C. motor the iron losses occur in

the field
the armature
the brushes
the commutator

53. In variable speed motor

a stronger commutating field is needed at low speed than at high speed
a weaker commutating field is needed at low speed than at high speed
same commutating field is needed at low speed than at high speed
none of the above is correct

54. In Ward-Leonard control the lower limit of speed is imposed by

residual magnetism of the generator
core losses of motor
mechanical losses of motor and genÂ¬erator together
all of the above

55. In which of the following applications D.C. series motor is invariably tried?

Starter for a car
Drive for a water pump
Fan motor
Motor operation in A.C. or D.C.

56. No-load speed of which of the following motor will be highest ?

Shunt motor
Series motor
Cumulative compound motor
Differentiate compound motor

57. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven

runs as a generator
does not run as a generator
also runs as a motor comes to stop after sometime

58. Regenerative method of braking is based on that

back e.m.f. is less than the applied voltage
back e.m.f. is equal to the applied voltage
back e.m.f. of rotor is more than the applied voltage
none of the above

59. Sparking at the commutator of a D.C. motor may result in

damage to commutator segments
damage to commutator insulation
increased power consumption
all of the above

60. Sparking, is discouraged in a D.C. motor because

it increases the input power con-sumption
commutator gets damaged
both a and b
none of the above

DC Motors MCQ Multiple Choice Questions Answers - Page 2 for Practice