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Multiple Choice Question (MCQ) of D.C. Machines page-6


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51. All d.c. machines are characterized by

a) Electric brushes
b) Armature
c) Commutator
d) Magnetic poles

Ans: (c)

52. Armature voltage control is suitable if d.c. machine is driven at constant

a) Torque
b) Magnetic field
c) Speed
d) Current

Ans: (a)

53. Current normally used to excite synchronous and d.c. generators is

a) D.C
b) A.C. single phase
c) A.C. two phase
d) A.C. three phase

Ans: (a)

54. In all electric machines, basic action taking place is

a) Motor action
b) Generator action
c) Both (a) and (b)
d) All of these

Ans: (c)

55. In case of a motor

a) Only motor action takes place
b) Motor action precedes generator action
c) Generator action precedes motor action
d) Both take place precedes simultaneously

Ans: (b)

56. All rotating machines are basically

a) D.C. machines
b) A.C. machines
c) Electro-mechanical convertors
d) Heat converters

Ans: (c)

57. All machines have the structure such that

a) Armature is rotating and field is fixed
b) Field is rotating and armature is fixed
c) Either (a) or (b)
d) None of these

Ans: (a)

58. All electrical machines have poles with

a) A hetro-polar structure
b) A horse shoe structure
c) (a) above (b)
d) None of these

Ans: (a)

59. Maximum number of brushes which can be used in a machine is

a) 2
b) 4
c) 6
d) Number of poles in the machine or 2

Ans: (d)

60. Voltage applied across the shunt motor has to

a) Overcome the back emf
b) Supply armature ohmic drop
c) Supply fied ohmic drop
d) Both (a) and (b)

Ans: (d)


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