# 120+ DC Motor Solved MCQs

41
63.3k
101.

## The condition for maximum efficiency for a D.C. generator is

A. eddy current losses = stray losses
B. hysteresis losses = eddy current losses
C. copper losses = 0
D. variable losses = constant losses
Answer» D. variable losses = constant losses
102.

## D.C. generators are normally designed for maximum efficiency around

B. rated r.p.m.
C. rated voltage
D. all of the above
103.

## In a D.C. generator, the iron losses mainly take place in

A. yoke
B. commutator
C. armature conductors
D. armature rotor
104.

A. iron losses
B. line losses
C. sparking
D. corona losses
105.

## The purpose of retardation test on D.C. shunt machines is to find out

A. stray losses
B. eddy current losses
C. field copper losses
D. windage losses
106.

## Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?

A. Swinburne's test
B. Hopkinson's test
C. Field test
D. Brake test
107.

108.

## During rheostat braking of D.C. series motors

A. motor is run as a generator
B. motor is reversed in direction
C. motor is run at reduced speed
D. none
Answer» A. motor is run as a generator
109.

## For which types of D.C. motor, dynamic braking is generally used ?

A. Shunt motors
B. Series motors
C. Compound motors
D. All of the above
Answer» D. All of the above
110.

## Which method of braking is generally used in elevators ?

A. Plugging
B. Regenerative braking
C. Rheostatic braking
D. None of the above
111.

## In variable speed motor

A. a stronger commutating field is needed at low speed than at high speed
B. a weaker commutating field is needed at low speed than at high speed
C. same commutating field is needed at low speed than at high speed
D. none of the above is correct
Answer» B. a weaker commutating field is needed at low speed than at high speed
112.

## When the armature of a D.C. motor rotates, e.m.f. induced is

A. self-induced e.m.f.
B. mutually induced e.m.f.
C. back e.m.f.
D. none of the above
113.

## Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control

A. drum type controller is used
B. three point starter is used
C. four point starter is used
D. all above can be used
Answer» A. drum type controller is used
114.

## If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

A. this will make armature to take heavy current, possibly burning it
B. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
C. nothing will happen to motor
D. motor will come to stop
Answer» A. this will make armature to take heavy current, possibly burning it
115.

## D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the

A. series motor
B. shunt motor
C. compound motor
D. any of the above
116.

## D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this

A. series motor
B. shunt motor
C. compound motor
D. any of the above
117.

## Which D.C. motor has got maximum self relieving property ?

A. Series motor
B. Shunt motor
C. Cumulatively compounded motor
D. Differentially compounded motor
118.

## In the D.C. motor the iron losses occur in

A. the field
B. the armature
C. the brushes
D. the commutator
119.

## The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by

A. reducing the field current
B. decreasing the armature current
C. increasing the armature current
D. increasing the excitation current
Answer» A. reducing the field current
120.

## One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven

A. runs as a generator
B. does not run as a generator
C. also runs as a motor comes to stop after sometime
D. none
Answer» A. runs as a generator