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DC Motor MCQ Questions And Answers

D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

81. A three-point starter is considered suitable for

(a) shunt motors

(b) shunt as well as compound motors

(c) shunt, compound and series motors

(d) all D.C. motors

Ans: b

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

(a) 100%

(b) around 90%

(c) anywhere between 75% and 90%

(d) less than 50%

Ans: d

83. The ratio of starting torque to full-load torque is least in case of

(a) series motors

(b) shunt motors

(c) compound motors

(d) none of the above

Ans: b

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84. Which D.C. motor has got maximum self-loading property?

(a) Series motor

(b) Shunt motor

(c) Cumulatively compounded ‘motor

(d) Differentially compounded motor

Ans: d

85. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?

(a) Series motor

(b) Shunt motor

(c) Cumulatively compounded motor

(d) Differentially compounded motor

Ans: c

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

(a) nothing will happen to the motor

(b) this will make armature to take heavy current, possibly burning it

(c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

(d) motor will run at very slow speed

Ans: c

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87. D.C. series motors are used

(a) where load is constant

(b) where load changes frequently

(c) where constant operating speed is needed

(d) in none of the above situations.

Ans: d

88. For the same H.P. rating and full load speed, following motor has poor starting torque

(a) shunt

(b) series

(c) differential compound

(d) cumulative compound

Ans: c

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

(a) as separately wound unit

(6) in parallel with armature winding

(c) in series with armature winding

(d) in parallel with field winding

Ans: c

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

(a) damage to commutator segments

(b) damage to commutator insulation

(c) increased power consumption

(d) all of the above

Ans: d

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DC Motor MCQ Questions And Answers

D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

71. Which motor has the poorest speed control?

(a)Differentially compounded motor

(b) Cumulatively compounded motor

(c) Shunt motor

(d) Series motor

Ans: d

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72. The plugging gives the

(a) zero torque braking

(b) smallest torque braking

(c) highest torque braking

(d) none of the above

Ans: c

73. The armature voltage control of D.C. motor provides

(a) constant voltage drive

(b) constant current drive

(c) constant torque drive

(d) none of the above

Ans: c

74. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?

(a) The motor will stop

(b) The motor will continue to run

(c) The armature may burn

(d) The motor will run noisy

Ans: c

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

(a) back e.m.f  is equal to armature drop

(b) armature drop is negligible

(c) flux is proportional to armature current

(d) flux is practically constant in DC shunt motors

Ans: d

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

(a) almost negligible

(b) rated full-load current

(c) less than full-load current

(d) more than full-load current

Ans: d

77. These days D.C. motors are widely used in

(a) pumping sets

(b) air compressors

(c) electric traction

(d) machine shops

Ans: c

78. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?

(a) Frame

(b) Shaft

(c) Commutator

(d) Stator

Ans: c

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

(a) Starter for a car

(b) Drive for a water pump

(c) Fan motor

(d) Motor operation in A.C. or D.C.

Ans: a

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

(a) to improve cooling

(b) to reduce copper losses

(c) to increase the generated e.m.f.

(d) to reduce the sparking

Ans: d

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DC Motor MCQ Questions And Answers

D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

61. The armature voltage control of D.C. motor provides

(a) constant torque drive

(b) constant voltage drive

(c) constant current drive

(d) none of the above

Ans: a

62. 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 circuits

(a) a resistance is connected in series with armature

(b) a resistance is connected parallel to the armature

(c) armature is temporarily open circuited

(d) a high value resistor is connected across the field winding

Ans: a

63. The speed of a D.C. shunt motor can be increased by

(a) increasing the resistance in armature circuit

(b) increasing the resistance in field circuit

(c) reducing the resistance in the field circuit

(d) reducing the resistance in the armature circuit

Ans: b

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64. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator?

(a) Providing laminations in armature core

(b) Providing laminations in stator

(c) Using non-magnetic material for frame

(d) Using material of low hysteresis co-efficient for armature core material

Ans: d

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

(a) remain unchanged

(b) reduce to one-fourth value

(c) increase four folds

(d) be doubled

Ans: a

66. At the instant of starting when a D.C. motor is put on supply, it behaves like

(a) a highly resistive circuit

(6) a low resistance circuits

(c) a capacitive circuit

(d) none of the above

Ans: b

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68. The speed of a D.C. motor can be varied by varying

(a) field current

(b) applied voltage

(c) resistance in series with armature

(d) any of the above

Ans: d

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

(a) Low cost

(b) Wide speed range

(c) Stability

(d) High starting torque.

Ans: a

70. For a D.C. shunt motor if the excitation is changed

(a) torque will remain constant

(b) torque will change but power will remain constant

(c) torque and power both will change

(d) torque, power and speed, all will change

Ans: b

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DC Motor MCQ Questions And Answers

D.C Motor: [ ISRO,DRDO,DMRC,SAIL, ODNANCE, HAL, WBSEDCL, RAILWAY & Others competitive] DC Motor MCQ Questions And Answers

51. Three-point starter can be used for

(a) series motor only

(b) shunt motor only

(c) compound motor only

(d) both shunt and compound motor

Ans: d

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52. The total losses in a well-designed D.C. generator of 10 kW will be nearly

(a) 100 W

(b) 500 W

(c) 1000 W

(d) 1500 W

Ans:b
53. Speed control by Ward Leonard method gives uniform speed variation

(a) in one direction

(b) in both directions

(c) below normal speed only

(d) above normal speed only.

Ans: b

54. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be

(a) level compounded

(b) under compounded

(c) cumulatively compounded

(d) differentially compounded

Ans: c

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55. Following motor is used where high starting torque and wide speed range control is required.

(a) Single phase capacitor start

(b) Induction motor

(c) Synchronous motor

(d) D.C. motor

Ans: d

56. As -the load is increased the speed of D.C. shunt motor will

(a) reduce slightly

(b) increase slightly

(c) increase proportionately

(d) remains unchanged

Ans: a

57. The armature torque of the D.C. shunt motor is proportional to

(a) field flux only

(b) armature current only

(c) both (a) and (b)

(d) none of the above

Ans: b

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

(a) Voltage control method

(b) Field control method

(c) Armature control method

(d) All above methods

Ans: c

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59. Usually wide and sensitive speed control is desired in case of

(a) centrifugal pumps

(b) elevators

(c) steel rolling mills

(d) colliery winders

Ans: d

60. 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

(a) 2.36%

(b) 4.76%

(c) 6.77%

(d) 8.84%

Ans: b

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