multiple choice questions on dc generator # 11

This are some of the multiple choice questions that are asked in Indian engineering services check out and comment if you have any doubts........

1) A 4-pole dc generator is running at 1500 rpm. The frequency of current in armature winding is
A) 50 HZ
B) 150 HZ
C) 25 HZ
D) 100 HZ

Ans:A

2) The air-gap between the yoke and armature in a dc motor is kept small
A) To achieve a stronger magnetic field
B) To avoid overheating of the machine
C) To avoid locking of the armature
D) To avoid transverse motion

Ans:A

3) In the block diagram of a separately excited dc motor how does the armature induced emf appear as
A) Positive feedback
B) Negative feedback
C) Disturbance input
D) Output

Ans:B

4) A 400 V D.C shunt motor takes 5A at no-load Ra = 0.5 ohms, Rf = 200 ohms. What is the ratio of speed from full load to no-load, when the D.C shunt motor takes 50 A on full load?
A) 0.94
B) 0.8
C) 0.6
D) 0.4

Ans:A

5) The dummy coils in d.c machine are useful to
A) Increase the efficiency
B) Improve the commutation
C) Reduce the cost of the machine
D) Maintain mechanical balance of armature

Ans:D

6) The armature resistance of a 6-pole lap wound is 0.05 ohms. If the armature is rewound using a wave winding the armature resistance will be
A) 0.45 ohm
B) 0.30 ohm
C) 0.15 ohm
D) 0.10 ohm

Ans:A

7) A belt-driven cumulative compound dc-generator is delivering power to the dc mains. If the belt snaps, then the machine will run as a
A) Cumulative compounded motor in the same direction
B) Differentially compounded motor in the same direction
C) Cumulative compounded motor in the opposite direction
D) Differentially compounded motor in the opposite direction

Ans:B

8) In arc welding in order to obtain steady arc, one should use
A) DC series generator
B) DC differentially compounded generator
C) DC shunt generator
D) DC cumulatively compounded generator

Ans:B

9) The type of dc generator used for welding purposes is a
A) Series generator
B) Shunt generator
C) Cumulatively compounded generator
D) Differentially compounded generator

Ans:D

10) A separately excited dc generator is feeding a dc shunt motor. If the load torque on the motor is halved approximately
A) Armature current of both motor and generator are halved
B) Armature current of motor is halved and that of generator is unaltered
C) Armature currents of generator is halved and that of motor is unaltered
D) Armature currents of both motor and generator are unaltered

Ans:A

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