d c generators MCQs – Page 3

Practise focused d c generators questions with marked answers for exam preparation and subject revision.

d c generators Mcqs

41. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be________________?
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A. cross magnetisation only

B. cross magnetisation as well as magnetisation

C. crossmagnetisation as well as demagnetising

D. demagnetisation only

42. Which of the following generators will be preferred if they are required to be run in parallel?
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A. Compound generators

B. Series generators

C. Shunt generators

D. None of the above

43. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ?
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A. The field of that generator is weakened

B. That generator takes large share of loads

C. The speed of that generator is increased

D. The direction of that generator is reversed

44. For both lap and wave windings, there are as many commutator bars as the number of_____________?
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A. armature conductors

B. poles

C. winding elements

D. slots

45. The purpose of providing dummy coils in a generator is____________?
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A. to enhance flux density

B. to amplify voltage

C. to reduce eddy current losses

D. to provide mechanical balance for the rotor

46. 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___________ ?
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A. Lap winding

B. Depends on other features of design

C. Wave winding

D. Either of A. and B. above

47. In D.C. generators, current to the external circuit from armature is given through_____________?
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A. slip rings

B. commutator

C. none of above

D. solid connection

48. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when_______________?
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A. the generator runs on full load

B. the generator runs on designed speed

C. the generator runs on overload

D. there is no load on|he generator

49. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be_____________?
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A. about 2 V

B. zero

C. about 50 V

D. 220 V

50. 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_______________?
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A. E/2

B. E

C. slightly less than E

D. 2E

51. Copper brushes in D.C. machine are used_____________?
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A. where low voltage and high currents are involved

B. where high voltage and small cur-rents are involved

C. in both of the above cases

D. in none of the above cases

52. The demagnetising component of armature reaction in a D.C. generator___________?
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A. reduces interpoles flux density

B. reduces generator e.m.f.

C. increases armature speed

D. results in sparking trouble

53. A D.C. generator can be considered as____________?
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A. rotating amplifier

B. rectifier

C. primemover

D. power pump

54. In D.C. generators, lap winding is used for______________?
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A. high voltage, low current

B. high voltage, high current

C. low voltage, low current

D. low voltage, high current

55. In a separately excited generator supplying rated load the armature reaction.
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A. is always present

B. is always absent

C. may be sometimes present

D. none of the above

56. Armature reaction in a generator results in_____________?
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A. damagnetising the center of all poles

B. magnetising the center of all poles

C. demagnetisation of leading pole tip and magnetisation of trailing pole tip

D. demagnetisation of trailing pole tip and magnetisation of leading pole tip

57. Flemings right-hand rule regarding direction of induced e.m.f., correlates__________?
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A. magnetic flux, direction of force and direction of motion of conductor

B. magnetic field strength, induced voltage and current

C. magnetic flux, direction of motion and the direction of e.m.f. induced

D. magnetic flux, direction of current flow and resultant force

58. For a D.C. machines laboratory following type of D.C. supply will be suitable___________?
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A. synchronous motor D.C. generator set

B. rotary converter

C. induction motor D.C. generator set

D. mercury are rectifier

59. The main factor which leads to unstable parallel operation of flat and over compounded generators is_____________?
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A. unequal series field resistances

B. their rising voltage characteristics

C. unequal speed regulation of their primemovers

D. unequal number of turns in their series field windings

60. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be____________?
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A. none of the above

B. greater than 150 V

C. less than 150 V

D. 150 V

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