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MCQ of D.C motor page-8


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31. For which application a dc motor is preferred over an ac motor ?

A) Fixed speed operation
B) Variable speed operation
C) High speed operation
D) Low speed operation.

Ans : (B)

32. In base of dc shunt motors as the load is increased the speed of the motor

A) reduces slightly
B) increases slightly
C) remains unaltered
D) increases in proportion to the increases in load.

Ans : (A)

33. Regenerative braking on shunt motors is used when

A) the load is variable
B) the load is constantly decreasing
C) the load has overhauling characteristics
D) the load also acts as a braking force.

Ans : (C)

34. In rheostatic braking for dc series motors

A) motor is run as a generator
B) motor is reversed in direction
C) motor is run at reduced speed.

Ans : (A)

35. A dc series motor develops a torque of 20 N-m at 3 A of load current. If the current is increased to 6 A, the torque developed will be

A) 10 N.m
B) 20 N.m
C) 40 N.m
D) 80 N.m.

Ans : (D)

36. The back emf of a dc motor depends on

A) brush material
B) type of slip rings
C) shape of conductors
D) field flux.

Ans : (D)

37. In Hopkinsonā€™s test for dc motors

A) Speeds of the motors are separately controlled
B) Both motors run at their respective rated speeds
C) Both machines are mechanically coupled
D) Both motors are run as generators.

Ans : (C)

38. A 230 V dc series motor is connected to 230 V ac supply; then

A) it will stop
B) it will burn out
C) it will run smoothly
D) it will run with less efficiency and high sparks.

Ans : (D)

39. A series motor is never started without some mechanical load on it because

A) at no load motor gives vicious sparking
B) load on the motors acts as a brake
C) at no load, losses in a series motor are high
D) at no load a series motor develops infinite speed.

Ans : (D)

40. A conductor 10 cm long lies across a magnetic field of 0.8n webers/sq.m. The force acting on the conductor when a current of 20 A passes through it will be

A) 160 N
B) 16 N
C) 1.6 N
D) 0.16 N.

Ans : (C)


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