DC Motors MCQs

Question 1

In Field's test for series motors one motor drives the other machine as

Accepted Answer

separately excited generator

Answer

cumulative compound generator

Answer

differential compound generator

Answer

series generator

Question 2

A motor for punching machines is usually subjected to

Accepted Answer

intermittent load

Answer

no load

Answer

continuous part load

Answer

continuous full load

Question 3

Which of the following is not necessarily the advantage of D.C. motors over A.C. motors?

Accepted Answer

Low cost

Answer

Better speed control

Answer

High starting torque

Answer

Wide speed range

Question 4

The armature shaft of a D.C. motor must be able to withstand

Accepted Answer

all of the above

Answer

any unbalanced magnetic pull on the armature core

Answer

twisting strains due to transmission of torque

Answer

bending moment due to the weight of the armature and commutator

Question 5

Which of the following loss of D.C.motor decreases with increase in load?

Accepted Answer

none of the above

Answer

Friction and windage loss

Answer

Core loss

Answer

Brush contact loss

Question 6

In an overloaded motor main danger arises due to

Accepted Answer

winding getting overheated

Answer

busbars getting heated

Answer

starter getting damaged

Answer

bearing getting overheated

Question 7

A wide and very sensitive speed control is usually required in case of

Accepted Answer

all of the above

Answer

elevators

Answer

steel rolling mills

Answer

colliery winders

Question 8

For which application a D.C. motor is preferred over an A.C. motor?

Accepted Answer

Variable speed operation

Answer

High speed operation

Answer

Low speed operation

Answer

Fixed speed operation

Question 9

Regenerative braking on D.C. shunt motors is used when

Accepted Answer

the load has overhauling characteristics

Answer

the load is variable

Answer

the load also acts as a braking force

Answer

the load is constantly decreasing