2. Which of the following could be lamina-proximately the thickness of laminations of a D.C.
machine ?
Correct : C. 0.5 m
3. The armature of D.C. generator is laminated to
Correct : D. reduce eddy current loss
4. The resistance of armature winding depends on
Correct : D. all of the above
5. The field coils of D.C. generator are usually made of
Correct : B. copper
6. The commutator segments are connected to the armature conductors by means of
Correct : A. copper lugs
7. In a commutator
Correct : C. mica is harder than copper
8. In D.C. generators the pole shoes are fastened to the pole core by
Correct : B. counter sunk screws
9. Satisfactory commutation of D.C. machines requires
Correct : D. all of the above
10. 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
11. 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
12. The bearings used to support the rotor shafts are generally
Correct : A. ball bearings
13. In D.C. generators, the cause of rapid brush wear may be
Correct : D. any of the above
14. In lap winding, the number of brushes is always
Correct : B. same as the number of poles
15. 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
16. In a four-pole D.C. machine
Correct : B. alternate poles are north and south
17. Copper brushes in D.C. machine are used
Correct : A. where low voltage and high currents are involved
18. A separately excited generator as compared to a self-excited generator
Correct : D. has all above features
19. In case of D.C. machines, mechanical losses are primary function of
Correct : C. speed
20. Iron losses in a D.C. machine are independent of variations in
Correct : B. load
21. In D.C. generators, current to the external circuit from armature is given through
Correct : A. commutator
22. Brushes of D.C. machines are made of
Correct : A. carbon
23. 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
24. 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
25. The material for commutator brushes is generally
Correct : D. carbon
26. The insulating material used between the commutator segments is normally
Correct : C. mica
27. In D.C. generators, the brushes on commutator remain in contact with conductors
which
Correct : C. lie under interpolar region
28. 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
29. Armature reaction of an unsaturated D.C. machine is
Correct : A. crossmagnetising
30. D.C. generators are connected to the busbars or disconnected from them only under the
floating condition
Correct : D. all above
31. Eddy currents are induced in the pole shoes of a D.C. machine due to
Correct : C. relative rotation between field and armature
32. Equilizer rings are required in case armature is
Correct : B. lap wound
33. Welding generator will have
Correct : A. lap winding
34. In case of D.C. machine winding, number of commutator segments is equal to
Correct : A. number of armature coils
35. For a D.C. machines laboratory following type of D.C. supply will be suitable
Correct : C. induction motor D.C. generator set
36. The function of pole shoes in the case of D.C. machine is
Correct : D. to discharge all the above functions
37. In the case of lap winding resultant pitch is
Correct : D. difference of front and back pitches
38. A D.C. welding generator has
Correct : A. lap winding
39. 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
40. The demagnetising component of armature reaction in a D.C. generator
Correct : A. reduces generator e.m.f.
41. Magnetic field in a D.C. generator is produced by
Correct : A. electromagnets
42. The number of brushes in a commutator depends on
Correct : D. amount of current to be collected
43. Compensating windings are used in D.C. generators
Correct : C. to neutralise the cross-magnetising effect of the armature reaction
44. 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
45. 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
46. In D.C. generators, lap winding is used for
Correct : B. low voltage, high current
47. 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 generator A and B will be
Correct : B. 3 : 1
48. The voltage drop for which of the following types of brush can be expected to be least ?
Correct : C. Metal graphite brushes
49. 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
Correct : B. 2E
50. The armature core of a D.C. generator is usually made of
Correct : A. silicon steel
51. Open circuited armature coil of a D.C. machine is
Correct : C. both (a) and (b)
52. For the parallel operation of two or more D.C. compound generators, we should ensure that
Correct : D. series fields of all generators should be either on positive side or negative side of the armature
53. D.C. series generator is used
Correct : C. voltage at the toad end of the feeder
54. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
Correct : D. self-excited generator
55. Interpole flux should be sufficient to
Correct : C. neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
56. D.C. generator generally preferred for charging automobile batteries is
Correct : C. long shunt compound generator
57. In a D.C. generator the number of mechanical degrees and electrical degrees will be the
same when
Correct : D. number of poles is 2
58. Permeance is the reciprocal of
Correct : B. reluctance
59. In D.C. generators the polarity of the interpoles
Correct : A. is the same as that of the main pole ahead
60. The e.m.f. generated in a D.C. generator is directly proportional to
Correct : B. speed of armature
61. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the
coil is neutralised by all of the following except
Correct : B. dummy coils
62. In D.C. generators on no-load, the air gap flux distribution in space is
Correct : D. flat topped
63. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed
increases to 1200 r.p.m., the generated e.m.f. will be nearly
Correct : C. 240 V
64. The purpose of providing dummy coils in a generator is
Correct : D. to provide mechanical balance for the rotor
65. If a D.C. generator fails to build up the probable cause could not be
Correct : B. field resistance less than the critical resistance
66. Flashing the field of D.C. generator means
Correct : B. creating residual magnetism by a D.C. source
67. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be
Correct : D. 580 V
68. In a D.C. generator the critical resistance refers to the resistance of
Correct : B. field
69. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as
to bring them
Correct : A. just ahead of magnetic neutral axis
70. Armature coil is short circuited by brushes when it lies
Correct : A. along neutral axis
71. A cumulatively compounded long shunt generator when operating as a motor would be
Correct : B. differentially compounded long shunt
72. To avoid formation of grooves in the commutator of a D.C. machine
Correct : A. the brushes of opposite polarity should track each other
73. The rapid wear of brushes takes place due to
Correct : D. all of the above factors
74. Number of tappings for each equilizer ring is equal to
Correct : A. number of pole pairs
75. A D.C. generator can be considered as
Correct : C. rotating amplifier
76. In any rotating machine that part which houses the conductors and in which e.m.f.
induced is to be utilised is called
Correct : D. armature
77. In a D.C. machine stray loss is the sum of
Correct : D. iron loss and mechanical loss
78. Lap winding is composed of
Correct : A. any even number of conductors
79. In a D.C. generator in case the resistance of the field winding is increased, then output
voltage will
Correct : B. decrease
80. An exciter for a turbo generator is a
Correct : B. shunt generator
81. In case of a flat compounded generator
Correct : C. voltage remains constant irrespec¬tive of the load
82. Which of the following generator will have negligible terminal voltage while running on
no-load ?
Correct : A. Series generator
83. Which of the following D.C. generators will be in a position to build up without any
residual magnetism in the poles ?
Correct : D. None of the above
84. In over compounded generator, full load terminal voltage is
Correct : C. more than noload terminal voltage
85. In a level compounded D.C. generator, full load terminal voltage is
Correct : B. equal to no-load terminal voltage
86. The terminal voltage of a D.C. shunt generator drops on load because of all of the
following reasons except
Correct : D. commutation
87. In a D.C. generator
Correct : C. external characteristic = magnetisation characteristic - ohmic drop - armature reaction
88. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature
voltage wave
Correct : B. will be of 5 Hz
89. A 220 V D.C. generator is run at full speed without any excitation. The open circuit
voltage will be
Correct : B. about 2 V
90. In a separately excited generator supplying rated load the armature reaction ,
Correct : A. is always present
91. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will
be
Correct : A. zero
92. Armature reaction in a generator results in
Correct : A. demagnetisation of leading pole tip and magnetisation of trailing pole tip
93. Following energized winding of a D.C. machine should not be opened as it would produce high inductive voltage which may be dangerous to personnel and may cause its own insulation failure.
Correct : D. Shunt field
94. Wave winding is composed of
Correct : C. that even number which is exact multiple of poles + 2
95. The critical resistance of the D.C. generator is the resistance of
Correct : A. field
96. When two D.C. series generators are running in parallel, an equilizer bar is used
Correct : C. so that two similar machines will pass approximately equal currents to the load
97. Which of the following generating machine will offer constant voltage on all loads ?
Correct : C. Level compounded generator .
98. Which of the following generators will be preferred if they are required to be run in
parallel ?
Correct : A. Shunt generators
99. Two generators are running in parallel. One of the generators may run as motor for
which of the following reasons ?
Correct : D. That generator takes large share of loads
100. A D.C. generator works on the principle of
Correct : C. Faraday's law of electromagnetic induction