1. If I2 be the armature current, then speed of a D.C. shunt motor is
Correct : A. independent of Ia
2. 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
3. At the instant of starting when a D.C. motor is put on supply, it behaveslike
Correct : B. a low resistance circuit
4. The speed of a D.C. motor can be varied by varying
Correct : D. any of the above
5. Which one of the following is not necessarily the advantage of D.C. motors over A.C.
motors ?
Correct : A. Low cost
6. For a D.C. shunt motor if the excitation is changed
Correct : B. torque will change but power will remain constant
7. Which motor has the poorest speed control?
Correct : D. Series motor
8. The plugging gives the
Correct : C. highest torque braking
9. The armature voltage control of D.C. motor provides
Correct : C. constant torque drive
10. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor
Correct : D. is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor
11. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
Correct : B. plugging
12. Which of the following motors one will choose to drive the rotary compressor ?
Correct : D. Synchronous motor
13. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will
Correct : A. increase
14. 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
15. 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)
16. Which of the following motors is most suitable for signalling devices and many kinds of
timers ?
Correct : D. Reluctance motor
17. Which motor should not be started on no-load ?
Correct : A. Series motor
18. Ward-Leonard control is basically a
Correct : A. voltage control method
19. For constant torque drive which speed control method is preferred ?
Correct : B. Armature voltage control
20. In Ward-Leonard control the lower limit of speed is imposed by
Correct : A. residual magnetism of the generator
21. The main disadvantage of the Ward-Leonard control method is
Correct : D. all of the above
22. Regenerative method of braking is based on that
Correct : B. back e.m.f. is equal to the applied voltage
23. The hysteresis loss in a D.C. machine least depends on
Correct : D. Rate of flow of ventilating air
24. In a D.C. generator all of the following could be the effects of iron losses except
Correct : C. Increase in terminal voltage
25. 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
26. Which of the following loss in a D.C. generator varies significantly with the load
current ?
Correct : C. Armature copper loss
27. Torque developed by a D.C. motor depends upon
Correct : D. all above factors
28. D.C. shunt motors are used for driving
Correct : D. machine tools
29. In a manual shunt motor starter
Correct : A. over load relay is connected in series and no volt relay in parallel with the load
30. 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 corematerial
31. Which of the following loss in a D.C. generator is dissipated in the form of heat?
Correct : D. All of the above
32. Which of the following losses are significantly reduced by laminating the core of a
D.C. generator ?
Correct : B. Eddy current losses
33. The total losses in a well designed D.C. generator of 10 kW will be nearly
Correct : B. 500 W
34. The condition for maximum efficiency for a D.C. generator is
Correct : D. variable losses = constant losses
35. D.C. generators are normally designed for maximum efficiency around
Correct : A. full-load
36. In a D.C. generator, the iron losses mainly take place in
Correct : D. armature rotor
37. D.C. generators are installed near the load centres to reduce
Correct : B. line losses
38. The purpose of retardation test on D.C. shunt machines is to find out
Correct : A. stray losses
39. Which of the following tests will be suitable for testing two similar D.C. series motors of
large capacity ?
Correct : C. Field test
40. Hopkinson's test on D.C. machines is conducted at
Correct : C. full-load
41. During rheostat braking of D.C. series motors
Correct : A. motor is run as a generator
42. For which types of D.C. motor, dynamic braking is generally used ?
Correct : D. All of the above
43. Which method of braking is generally used in elevators ?
Correct : A. Plugging
44. In variable speed motor
Correct : B. a weaker commutating field is needed at low speed than at high speed
45. When the armature of a D.C. motor rotates, e.m.f. induced is
Correct : C. back e.m.f.
46. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping,reversing
and speed control
Correct : A. drum type controller is used
47. If a D.C. shunt motor is working at full load and if shunt field circuit suddenlyopens
Correct : A. this will make armature to take heavy current, possibly burning it
48. D.C. motor is to drive a load which has certain minimum value for most of thetime and some peak value for short duration. We will select the
Correct : A. series motor
49. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle
and peak value for short duration. We will select this
Correct : C. compound motor
50. Which D.C. motor has got maximum self relieving property ?
Correct : A. Series motor
51. In the D.C. motor the iron losses occur in
Correct : B. the armature
52. Laminations of core are generally made of
Correct : C. silicon steel
53. Which of the following could be lamina-proximately the thickness of laminations of a
D.C. machine ?
Correct : C. 0.5 m
54. The armature of D.C. generator is laminated to
Correct : D. reduce eddy current loss
55. The resistance of armature winding depends on
Correct : D. all of the above
56. The field coils of D.C. generator are usually made of
Correct : B. copper
57. The commutator segments are connected to the armature conductors by means of
Correct : A. copper lugs
58. In a commutator
Correct : C. mica is harder than copper
59. In D.C. generators the pole shoes are fastened to the pole core by
Correct : B. counter sunk screws
60. Satisfactory commutation of D.C. machines requires
Correct : D. all of the above
61. Fleming's right-hand rule regarding direction of induced e.m.f., correlates
Correct : B. magnetic flux, direction of motion and the direction of e.m.f. induced
62. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
Correct : D. direction of motion of conductor, if forefinger points along the lines of flux
63. The bearings used to support the rotor shafts are generally
Correct : A. ball bearings
64. In D.C. generators, the cause of rapid brush wear may be
Correct : D. any of the above
65. In lap winding, the number of brushes is always
Correct : B. same as the number of poles
66. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?
Correct : B. Wave winding
67. In a four-pole D.C. machine
Correct : B. alternate poles are north and south
68. Copper brushes in D.C. machine are used
Correct : A. where low voltage and high currents are involved
69. A separately excited generator as compared to a self-excited generator
Correct : D. has all above features
70. In case of D.C. machines, mechanical losses are primary function of
Correct : C. speed
71. Iron losses in a D.C. machine are independent of variations in
Correct : B. load
72. In D.C. generators, current to the external circuit from armature is given through
Correct : A. commutator
73. Brushes of D.C. machines are made of
Correct : A. carbon
74. If B is the flux density, I the length of conductor and v the velocity of conductor,
then induced e.m.f. is given by
Correct : A. Blv
75. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
Correct : B. 8
76. The material for commutator brushes is generally
Correct : D. carbon
77. The insulating material used between the commutator segments is normally
Correct : C. mica
78. In D.C. generators, the brushes on commutator remain in contact with conductors which
Correct : C. lie under interpolar region
79. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
Correct : C. crossmagnetisation as well as demagnetising
80. Armature reaction of an unsaturated D.C. machine is
Correct : A. crossmagnetising
81. D.C. generators are connected to the busbars or disconnected from them only under
the floating condition
Correct : D. all above
82. Eddy currents are induced in the pole shoes of a D.C. machine due to
Correct : C. relative rotation between field and armature
83. Equilizer rings are required in case armature is
Correct : B. lap wound
84. Welding generator will have
Correct : A. lap winding
85. In case of D.C. machine winding, number of commutator segments is equal to
Correct : A. number of armature coils
86. For a D.C. machines laboratory following type of D.C. supply will be suitable
Correct : C. induction motor D.C. generator set
87. The function of pole shoes in the case of D.C. machine is
Correct : D. to discharge all the above functions
88. In the case of lap winding resultant pitch is
Correct : D. difference of front and back pitches
89. A D.C. welding generator has
Correct : A. lap winding
90. Which of the following statement about D.C. generators is false ?
Correct : D. Equilizing bus bars are used with parallel running of D.C. shunt generators
91. The demagnetising component of armature reaction in a D.C. generator
Correct : A. reduces generator e.m.f.
92. Magnetic field in a D.C. generator is produced by
Correct : A. electromagnets
93. The number of brushes in a commutator depends on
Correct : D. amount of current to be collected
94. Compensating windings are used in D.C. generators
Correct : C. to neutralise the cross-magnetising effect of the armature reaction
95. Which of the following components of a D.C, generator plays vital role for
providing direct current of a D.C. generator ?
Correct : B. Commutator
96. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
Correct : C. using carbon brushes of superior quality
97. In D.C. generators, lap winding is used for
Correct : B. low voltage, high current
98. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generatorA and B will be
Correct : B. 3 : 1
99. The voltage drop for which of the following types of brush can be expected to be
least?
Correct : C. Metal graphite brushes
100. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be