1.
In an electric motor , the electromagnetic torque developed is

A

In opposite direction to both load torque and frictional torque

B

In the same direction as the load torque but in opposite direction to frictional torque

C

In the same direction is the load torque and frictional torque

D

In the same directional as the frictional torque but in the opposite direction to the load torque

Answer/ Hint

2.
The torque speed characteristic of a dc shunt motor is

A

A rectangular hyperbola

B

A drooping straight line

C

A parabola

D

None of the above

Answer/ Hint

3.
The horse power obtained from the motor shaft is called the

A

1 HP

B

BHP

C

Useful output

D

None of these

Answer/ Hint

4.
In a dc motor , the shaft torque is less than armature torque . This is due to

A

Eddy current loss

B

Hysteresis loss

C

Stray loss

D

All of the above

Answer/ Hint

5.
The mechanical output available at the dc motor shaft is equal to

A

Electrical power input to motor

B

Electrical power input less iron and friction losses

C

Electrical power input less copper losses

D

Electrical power input less total losses (copper loss, iron loss, friction and windage losses)

Answer/ Hint

6.
7.
For small values of armature current Ia, the torque developed by a dc series motor is proportional to

A

B

C

D

Answer/ Hint

8.
For higher values of armature current Ia, the torque developed by a dc series motor is proportional to

A

B

C

D

Answer/ Hint

9.
For higher value of armature current, the speed of a dc series motor is

A

Proportional to armature current

B

Proportional to the square of armature current

C

Inversely proportional to armature current

D

Constant

Answer/ Hint

10.

11.
In comparison to shunt and compound motors a dc series motor develops high torque at start. It is due to its comparatively

A

Few series turns

B

Stronger series field

C

Larger armature current

D

Smaller armature resistance

Answer/ Hint

12.
A fly wheel is normally fitted to

A

Dc series motor driving a constant torque load

B

Separately excited dc motor driving pulsed torque load

C

Cumulatively compound motor driving torque load

D

Differentially compound motor driving pulsed torque load

Answer/ Hint

13.
An electric motor with “constant output power ” will have a torque speed characteristic in the form of a

A

Straight line through the origin

B

Straight line parallel to speed axis

C

Circle about the origin

D

Rectangular hyperbola

Answer/ Hint

14.
15.
An electric train employing a dc series motor is running at a fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in

A

Drop in speed and rise in current

B

Rise in speed and drop in current

C

Rise in speed and rise in current

D

Drop in speed with current unaltered

Answer/ Hint

16.
In a dc series motor, if armature current is reduced to 70 % of its original value , the torque of the motor will be reduced by

A

49%

B

51%

C

50%

D

70%

Answer/ Hint

17.
When the torque of a dc series motor is tripled the power approximately increases by

A

33%

B

50%

C

75%

D

150%

Answer/ Hint

18.
When an electric train is moving down a hill, the dc motor will operate is a dc

A

Series motor

B

Series generator

C

Shunt motor

D

Shunt generator

Answer/ Hint

19.
A dc series motor must not be started on no load because it would

A

Not develop starting torque

B

Fail to start without load

C

Run at dangerously high speed

D

Draw more current without producing sufficient torque

Answer/ Hint

20.
In case of a dc series motor it is possible to have finite no load speed if a resistance is connected across its

A

Field terminals

B

Armature terminal

C

Field and armature together

D

It is always very high at no load

Answer/ Hint

21.
If an additional resistance is connected in series with a dc series motor operating at rated speed of the motor will

A

Reduce

B

Increase

C

Remain unaltered

D

Oscillate around the normal speed

Answer/ Hint

22.
If a resistance is connected across the armature of a dc series motor , it speed for a constant load torque will

A

Increase

B

Decrease

C

Remain unaltered

D

Become zero

Answer/ Hint

23.
Field diverter method of speed control of a dc series motor gives speeds above rated one due to reduction of

A

Field current

B

Armature current

C

Line current

D

None of these

Answer/ Hint

24.
The field diverter resistance for a dc series motor is of the order of

A

0.1 Ω

B

10 Ω

C

50 Ω

D

100Ω

Answer/ Hint

25.
The current drawn by a dc motor at starting is

A

Zero

B

Very low

C

Normal

D

Very high

Answer/ Hint

26.
High inrush of current during a starting of a dc motor can efficiently be restricted to a safer value by increasing the ……..resistance

A

Shunt field

B

Armature circuit

C

Both a and b

D

None of these

Answer/ Hint

27.
The dc motor draws high current at the starting instant due to absence of back emf . In order to prevent this high inrush of current at start, a resistance is connected

A

Across the field

B

Across the armature

C

In series with the armature

D

In series with the filed

Answer/ Hint

28.
For efficient operation of a dc motor, the additional resistance inserted in he armature circuit should be

A

Increased in steps

B

Cut out in steps

C

Left in the armature circuit

D

Removed immediately after start

Answer/ Hint

29.
Three point starters are not suitable for application where speed variation by flux control is required because the motor may

A

Not start

B

Run away

C

Stop at very high speed

D

Stop at very slow speed

Answer/ Hint

30.
If the no –voltage release in a dc motor starter fails to operate on failure of supply, on resumption of supply the motor will

A

Not start automatically

B

Start automatically without trouble

C

Develop very low starting torque

D

Get damaged due to flow of excessive current in the armature

Answer/ Hint