1. B. DC MOTOR
1. No-load speed of which of the following motor will be highest ?
Correct : B. Series motor
2. The direction of rotation of a D.C. series motor can be changed by
Correct : B. interchanging field terminals
3. Which of the following application requires high starting torque ?
Correct : C. Locomotive
4. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ?
Correct : A. Series motor
5. Which D.C. motor will be preferred for machine tools ?
Correct : B. Shunt motor
6. Differentially compound D.C. motors can find applications requiring
Correct : B. low starting torque
7. Which D.C. motor is preferred for elevators ?
Correct : D. Cumulative compound motor
8. According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of
Correct : A. current in the conductor aovtaat of conductor
9. If the field of a D.C. shunt motor gets opened while motor is running
Correct : C. the motor will attain dangerously high speed 1
10. Starters are used with D.C. motors because
Correct : D. to restrict armature current as there is no back e.m.f. while starting
11. In D.C. shunt motors as load is reduced
Correct : C. the speed will remain almost/constant
12. A D.C. series motor is that which
Correct : A. has its field winding consisting of thick wire and less turns
13. For starting a D.C. motor a starter is required because
Correct : B. it limits the starting current to a safe value
14. The type of D.C. motor used for shears and punches is
Correct : D. cumulative compound D.C. motor
15. If a D.C. motor is connected across the A.C. supply it will
Correct : D. burn due to heat produced in the field winding by .eddy currents
16. To get the speed of D.C, motor below the normal without wastage of electrical energy
is used.
Correct : A. Ward Leonard control
17. When two D.C. series motors are connected in parallel, the resultant speed is
Correct : C. normal speed
18. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
Correct : A. decreasing the field current
19. In a D.C. shunt motor, speed is
Correct : A. independent of armature current
20. A direct on line starter is used: for starting motors
Correct : A. iip to 5 H.P.
21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
Correct : C. The armature may burn
22. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
Correct : D. flux is practically constant in D:C. shunt motors
23. In a D.C. shunt motor, under the conditions of maximum power, the current in the
armature will be
Correct : D. more than full-load current
24. These days D.C. motors are widely used in
Correct : C. electric traction
25. By looking at which part of the motor, it can be easily confirmed that a particular
motor is D.C. motor?
Correct : C. Commutator
26. In which of the following applications D.C. series motor is invariably tried?
Correct : A. Starter for a car
27. In D.C. machines fractional pitch winding is used
Correct : D. to reduce the sparking
28. A three point starter is considered suitable for
Correct : B. shunt as well as compound motors
29. In case-the conditions for maximum power for a D.C. motor are established, the
efficiency of the motor will be
Correct : D. less than 50%
30. The ratio of starting torque to full-load torque is least in case of
Correct : B. shunt motors
31. In D.C. motor which of the following can sustain the maximum temperature rise?
Correct : C. Field winding
32. Which of the following law/rule can he used to determine the direction of rotation of
D.C. motor ?
Correct : D. Fleming's left-hand rule
33. Which of the following load normally needs starting torque more than the rated
torque?
Correct : B. Conveyors
34. The starting resistance of a D.C. motor is generally
Correct : A. low
35. The speed of a D.C. series motor is
Correct : D. inversely proportional to the armature current
36. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
Correct : C. 25% of the previous value
37. The current drawn by the armature of D.C. motor is directly proportional to
Correct : A. the torque required
38. The power mentioned on the name plate of an electric motor indicates
Correct : D. the output power available at the shaft
39. Which D.C. motor has got maximum self loading property?
Correct : D. Differentially compounded motor
40. Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy
loads?
Correct : C. Cumulatively compounded motor
41. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
Correct : C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
42. D.C. series motors are used
Correct : D. in none of the above situations.
43. For the same H.P. rating and full load speed, following motor has poor starting torque
Correct : C. differentially compounded
44. In case of conductively compensated D.C. series motors, the compensating winding is
provided
Correct : C. in series with armature winding
45. Sparking at the commutator of a D.C. motor may result in
Correct : D. all of the above
46. Which of the following motor is preferred for operation in highly explosive
atmosphere ?
Correct : C. Air motor
47. If the supply voltage for a D.C. motor is increased, which of the following will decrease?
Correct : C. Full-load current
48. Which one of the following is not the function of pole shoes in a D.C. machine ?
Correct : A. To reduce eddy current loss
49. The mechanical power developed by a shunt motor will be maximum when the ratio
of back e.m.f. to applied voltage is
Correct : D. 0.5
50. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
Correct : C. Variable speed operation
51. In D.C. machines the residual magnetism is of the order of
Correct : A. 2 to 3 per cent
52. Which D.C. motor is generally preferred for cranes and hoists ?
Correct : A. Series motor
53. Three point starter can be used for
Correct : D. both shunt and compound motor
54. Sparking, is discouraged in a D.C. motor because
Correct : B. commutator gets damaged
55. Speed control by Ward Leonard method gives uniform speed variation
Correct : B. in both directions
56. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor,
compound motor will have to be
Correct : C. cumulatively compounded
57. Following motor is used where high starting torque and wide speed range control is
required.
Correct : D. D.C. motor
58. In a differentially compounded D.C. motor, if shunt field suddenly opens
Correct : A. the motor will first stop and then run in opposite direction as series motor
59. Which of the following motor has the poorest speed regulation ?
Correct : B. Series motor
60. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make
use of
Correct : A. D.C. series motor
61. As -the load is increased the speed of D.C. shunt motor will
Correct : A. reduce slightly
62. The armature torque of the D.C. shunt motor is proportional to
Correct : B. armature current only
63. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
Correct : C. Armature control method
64. Usually wide and sensitive speed control is desired in case of
Correct : D. colliery winders
65. 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
Correct : B. 4.76%
66. The armature voltage control of D.C. motor provides
Correct : A. constant torque drive
67. 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
Correct : A. a resistance is connected in series with armature
68. The speed of a D.C. shunt motor can be increased by
Correct : B. increasing the resistance in field circuit
69. If I2 be the armature current, then speed of a D.C. shunt motor is
Correct : A. independent of Ia
70. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed
by the motor will
Correct : A. remain unchanged
71. At the instant of starting when a D.C. motor is put on supply, it behaves like
Correct : B. a low resistance circuit
72. The speed of a D.C. motor can be varied by varying
Correct : D. any of the above
73. Which one of the following is not necessarily the advantage of D.C. motors over A.C.
motors ?
Correct : A. Low cost
74. For a D.C. shunt motor if the excitation is changed
Correct : B. torque will change but power will remain constant
75. Which motor has the poorest speed control?
Correct : D. Series motor
76. The plugging gives the
Correct : C. highest torque braking
77. The armature voltage control of D.C. motor provides
Correct : C. constant torque drive
78. If the terminals of armature of D.C. motor are interchanged, this action will offer
following kind of braking
Correct : B. plugging
79. Which of the following motors one will choose to drive the rotary compressor ?
Correct : D. Synchronous motor
80. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
Correct : A. increase
81. Why are the D.C. motors preferred for traction applications ?
Correct : D. The speed is inversely proportional to the torque and the torque is proportional to square of armature current
82. Which of the following motors is usually used in house-hold refrigerators ?
Correct : C. Single phase induction motor (split phase start or induction run motor)
83. Which of the following motors is most suitable for signalling devices and many kinds
of timers ?
Correct : D. Reluctance motor
84. Which motor should not be started on no-load ?
Correct : A. Series motor
85. Ward-Leonard control is basically a
Correct : A. voltage control method
86. For constant torque drive which speed control method is preferred ?
Correct : B. Armature voltage control
87. In Ward-Leonard control the lower limit of speed is imposed by
Correct : A. residual magnetism of the generator
88. The main disadvantage of the Ward-Leonard control method is
Correct : D. all of the above
89. Regenerative method of braking is based on that
Correct : B. back e.m.f. is equal to the applied voltage
90. The hysteresis loss in a D.C. machine least depends on
Correct : D. Rate of flow of ventilating air
91. In a D.C. generator all of the following could be the effects of iron losses except
Correct : C. Increase in terminal voltage
92. The losses occurring in a D.C. generator are given below. Which loss is likely to have
highest proportion at rated load of the generator ?
Correct : C. armature copper loss
93. Which of the following loss in a D.C. generator varies significantly with the load
current ?
Correct : C. Armature copper loss
94. Torque developed by a D.C. motor depends upon
Correct : D. all above factors
95. D.C. shunt motors are used for driving
Correct : D. machine tools
96. In a manual shunt motor starter
Correct : A. over load relay is connected in series and no volt relay in parallel with the load
97. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C.
generator ?
Correct : D. Using material of low hysteresis co-efficient for armature core material
98. Which of the following loss in a D.C. generator is dissipated in the form of heat?
Correct : D. All of the above
99. Which of the following losses are significantly reduced by laminating the core of a
D.C. generator ?
Correct : B. Eddy current losses
100. The total losses in a well designed D.C. generator of 10 kW will be nearly