DC Motors MCQs

Question 1

There are two 2-pole d.c. machines. Main field axis of machine A is horizontal and that of B is vertical. It is preferable to purchase

Accepted Answer

any of the two machines

Answer

machine A

Answer

machnie B

Answer

none of these

Question 2

A differentially compounded d.c. generator is delivering full-load current a terminal voltage of 220 V. If its series field winding is short circuited, then its terminal voltage

Accepted Answer

becomes more than 220 V

Answer

becomes less than 220 V

Answer

remains the same

Answer

would reduce to zero.

Question 3

The mechanical power developed by a d.c. motor is maximum when the back e.m.f. is

Accepted Answer

equal to zero

Answer

equal to the applied voltage

Answer

equal to half the applied voltage

Answer

approaching the value of the applied voltage

Question 4

What happens when the supply terminals of a d.c. shunt motor are interchanged?

Accepted Answer

the motor will run at its normal speed in the same direction as before

Answer

the motor will stop

Answer

the direction of rotation will reverse

Answer

the motor will run much faster in the 96. same direction

Question 5

The volt-ampere equation for a long shunt motor is given by

Accepted Answer

VT = Eb + la (Ra + Rs)

Answer

VT= Eb + Ra la

Answer

VT = Eb ? laRa

Answer

VT = Eb ? la (Ra + Rs)

Question 6

For a d.c. series motor with saturated condition of the field circuit, the torque developed is proportional to

Accepted Answer

Answer

(c) motor will run in the opposite direction

Answer

(d) speed of the motor will change

Question 7

A 10HP series dc motor uses a diverter to controlthe speed. For a constant load torque, the speed will be minimum when the diverter resistance is

Accepted Answer

infinite

Answer

0

Answer

0.1S2

Answer

2S2

Question 8

Difference between the no load and full load speeds of a de shunt motor is of the order of

Accepted Answer

1%

Answer

5%

Answer

10%

Answer

20%

Question 9

In a dc motor, the effect of flux due to armature reaction on the main flux is to make

Accepted Answer

both (a) and (b) above

Answer

unequal flux density distribution across both sections

Answer

flux direction deviate from radial in the air gap

Answer

none of these