DC Motors MCQs

Question 1

Which of the following methods gives the greatest braking torque?

Accepted Answer

Plugging

Answer

Regenerative braking

Answer

Rheostatic braking

Answer

None of the above

Question 2

A brake test on D.C. motors restricted to

Accepted Answer

small horse power motors

Answer

variable speed motors

Answer

high speed motors

Answer

open frame type motors.

Question 3

In D.C. generator, on no load

Accepted Answer

magnetic neutral axis coincides with geometrical neutral axis

Answer

magnetic neutral axis moves from geometrical neutral axis in the opposite direction of rotation

Answer

magnetic neutral axis moves from geometrical neutral axis in the direction of rotation

Answer

none of the above

Question 4

If B is the flux density, / the length of conductor and v the velocity of conductor, then induced e.m.f. is given by

Accepted Answer

B/v

Answer

B/v2

Answer

B/2v

Answer

Bpv2

Question 5

For generating large currents on D.C. generators which winding is generally preferred?

Accepted Answer

Lap winding

Answer

Progressive wave winding

Answer

Retrogressive wave winding

Answer

Current depends on design

Question 6

The purpose of providing dummy coils in a generator is

Accepted Answer

to provide mechanical balance for the rotor

Answer

to enhance flux density

Answer

to amplify voltage

Answer

to reduce eddy currents

Question 7

In a D.C. generator, the armature reaction results in

Accepted Answer

demagnetisation of the leading pole tip and magnetisation of the trailing pole tip

Answer

demagnetisation of the centres of poles

Answer

magnetisation of interpoles

Answer

magnetisation of the leading tip and demagnetisation of the trailing pole tip

Question 8

In a D.C. generator is case the brushes are moved so as to bring them in magnetic neutral axis, thcn, there will be

Accepted Answer

cross-magnetisation as well as demagnetization

Answer

demagnetization

Answer

cross-magnetisation

Answer

none of the above

Question 9

The polarity of a D.C. generator can be reversed by

Accepted Answer

reversing the field current

Answer

increasing field current

Answer

reversing field current as well as direction of rotation

Answer

any of the above