DC Machines Multiple Choice Questions with Answers

61 Frog leg winding is

A Same as simplex winding

B Same as duplex winding

C Combined lap and wave windings on a single rotor

D Duplex wave winding on a single rotor

View Answer

Answer: Combined lap and wave windings on a single rotor

62 In a compound dc motor, the shunt field winding as compared to series winding will have

A More turns of smaller diameter

B Less turns of larger diameter

C More turns of larger diameter

D Less turns of smaller diameter

View Answer

Answer: More turns of smaller diameter

63 In dc motor, the amount of flux leakage depends on

A Length of air gap

B Shape of the magnet core

C Flux density used in core and teeth

D All of these

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Answer: All of these

64 The direction of rotation of a dc motor can be reversed by reversing the connection to

A Armature

B Series field

C Shunt field

D Any of the above

View Answer

Answer: Armature

65 When an electric traian is moving down a hill the dc motor acts as

A Dc series motor

B Dc shunt motor

C Dc series generator

D Dc shunt generator

View Answer

Answer: Dc series generator

66 If the armature current of a dc motor is increased keeping the field flux constant, then the developed torque

A Increases proportionately

B Decreases in reverse proportion

C Remains constant

D Increases proportional to the square root of current

View Answer

Answer: Increases proportionately

67 The armature current drawn by a dc motor is proportional to

A The speed of the motor

B Flux required in the moor

C Torque required

D Voltage applied to the motor

View Answer

Answer: Torque required

68 A dc shunt motor is driving a constant torque load with rated excitation. If the field current is reduced to half, then the speed of the motor will become

A Half

B Slightly more than half

C Double

D Slightly less than double

View Answer

Answer: Slightly less than double

69 All d.c. machines are characterized by

A Electric brushes

B Armature

C Commutator

D Magnetic poles

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Answer: Commutator

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

A Torque

B Magnetic field

C Speed

D Current

View Answer

Answer: Torque

71 In all electric machines, basic action taking place is

A Motor action

B Generator action

C Both (a) and (b)

D All of these

View Answer

Answer: Both (a) and (b)

72 All rotating machines are basically

A D.C. machines

B A.C. machines

C Electro-mechanical convertors

D Heat converters

View Answer

Answer: Electro-mechanical convertors

73 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

View Answer

Answer: Armature is rotating and field is fixed

74 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

View Answer

Answer: Number of poles in the machine or 2

75 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)

View Answer

Answer: Both (a) and (b)

76 If field of d.c. shunt motor is opened, then

A Current in the armature will increase

B It will run at its normal speed

C Speed of motor will be reduced

D Speed of motor will be high

View Answer

Answer: Speed of motor will be high

77 Which of the following motors has high starting torque?

A D.C. shunt motor

B Induction motor

C D.C. series motor

D A.C. series motor

View Answer

Answer: D.C. series motor

78 Left hand rule is applicable to

A Motor

B Generator

C Transformer

D Mercury are rectifier

View Answer

Answer: Motor

79 A dc series motor is running with a diverter connected across its field winding. If the diverter resistance is increased, then the speed of the motor

A Decreases/increase

B Increase

C Remains unchanged

D Becomes very high

View Answer