DC Machines MCQs | DC Machines Multiple Choice Questions with Answers

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Questions
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

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

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

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

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

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

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

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

Answer: Slightly less than double
69 All d.c. machines are characterized by
A Electric brushes
B Armature
C Commutator
D Magnetic poles

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

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

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

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

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

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)

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

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

Answer: D.C. series motor
78 Left hand rule is applicable to
A Motor
B Generator
C Transformer
D Mercury are rectifier

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

Answer: Decreases/increase
80 A dc series motor is running at rated speed. If a resistance is placed in series, the speed of the motor
A Increases
B Decreases
C Remains unchanged
D Increases very much

Answer: Decreases
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