Multiple choice questions on dc motor # 10

                           Hi friends, this is post about objectives of electrical engineering with emphasis on dc motor check out and comment...

1) A dc shunt motor is running on no-load at 600 rpm. If the motor is run, on no-load, continuously for 2 hrs , the speed of the motor after 12 hr run will
A) be 600 rpm
B) exceed 600 rpm
C) fall below 600 rpm
D) be 450 rpm

Ans:B

2) A belt-driven cumulative compounded 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

3) Which of the following dc motors will have least percentage increase of input current, for the same percentage increase in torque?
A) cumulative compound
B) Differential compound
C) shunt
D) series

Ans:D

4) A dc shunt motor is driving a mechanical load at rated voltage with normal excitation. If the load torque is increased to double of the normal one, the speed of the motor will
A) become half
B) become double
C) increase slightly
D) fall slightly

Ans:D

5) 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 is halved
B) armature current of motor is halved and that of the generator is unaltered
C) armature current of generator is halved and that of the motor is unaltered
D) armature current of both motor and generator are unaltered

Ans:A

6) In case of a dc series motor it is possible to have finite no-load speed if a resistance is connected across its
A) field terminals
B) armature terminals
C) field and armature together
D) it is always very high at no-load

Ans:B

7) An electric train employing a dc series motor is running at a fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in
A) drop in speed and rise in current
B) rise in speed and drop in current
C) rise in speed and rise in current
D) drop in speed with current unaltered

Ans:A

8) A dc shunt motor is driving a constant torque load with normal excitation. If the field current is halved then the motor will run at
A) rated speed
B) half of rated speed
C) double of rated speed
D) slightly less than double the rated speed

Ans:D

9) A dc series motor is running at rated speed with out any additional resistance in series. If an additional resistance is placed in series, the speed of motor
A) increases
B) decreases
C) remains unaltered
D) oscillates around the rated speed

Ans:B

10) T is the load torque of a dc series motor having linear magnetization and negligible armature resistance. speed of the motor is
A) inversely proportional to √T
B) directly proportional to √T
C) inversely proportional to T^2
D) directly proportional to T^2

Ans:A

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