Explore topic-wise MCQs in Electrical Engineering Questions.

This section includes 122 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.

1.

Slip rings are usually made of__________?
A. carbon or graphite
B. brass or steel
C. silver or gold
D. copper or aluminium
Answer» C. silver or gold
Discussion
2.

In a synchronous motor, the maximum power developed depends on all of the following except:
A. rotor excitation
B. maximum value of coupling angle
C. direction of rotation
D. supply voltage
Answer» D. supply voltage
Discussion
3.

A synchronous motor has better power factor as compared to that of an equivalent induction motor. This is mainly because?
A. synchronous motor has no slip
B. stator supply is not required to produce magnetic field
C. mechanical load on the rotor remains constant
D. synchronous motor has large airgap
Answer» C. mechanical load on the rotor remains constant
Discussion
4.

A synchronous motor can develop synchronous torque:
A. when under loaded
B. while over-excited
C. only at synchronous speed
D. below or above synchronous speed
Answer» D. below or above synchronous speed
Discussion
5.

In a synchronous motor, damper windings are provided on____________?
A. stator frame
B. rotor shaft
C. pole faces
D. none of the above
Answer» D. none of the above
Discussion
6.

For power factor correction, synchronous motors operate at____________?
A. no-load and greatly over-excited fields
B. no-load and under-excited fields
C. normal load with minimum excitation
D. normal load with zero excitation
Answer» B. no-load and under-excited fields
Discussion
7.

Which of the following losses is not dissipated by the stator core surface in a synchronous motor?
A. Eddy current losses in the conductors
B. Iron losses in the stator
C. Copper losses in the slot portion of the conductors
D. Windage losses
E. None of the above
Answer» E. None of the above
Discussion
8.

In a synchronous motor, the breakdown torque is__________?
A. directly proportional to the square of the applied voltage
B. directly proportional to applied voltage
C. inversely proportional to applied voltage
D. none of the above
Answer» C. inversely proportional to applied voltage
Discussion
9.

The maximum power developed in a synchronous motor will depend on__________?
A. the rotor excitation only
B. the supply voltage only
C. the rotor excitation and supply volt-age both
D. the rotor excitation, supply voltage and maximum value of coupling angle (90°)
E. none of the above
Answer» E. none of the above
Discussion
10.

The construction of a synchronous motor resembles____________?
A. a series motor
B. an induction motor
C. an alternator
D. a rotary converter
Answer» D. a rotary converter
Discussion
11.

The back e.m.f. in the stator of a synchronous motor depends on____________?
A. number of poles
B. flux density
C. rotor speed
D. rotor excitation
E. none of the above
Answer» E. none of the above
Discussion
12.

The size of a synchronous motor decreases with the increase in___________?
A. flux density
B. horse power rating
C. speed
D. all of the above
Answer» B. horse power rating
Discussion
13.

Which of the following losses, in a synchronous motor, does not vary with load?
A. Windage loss
B. Copper losses
C. Any of the above
D. None of the above
Answer» B. Copper losses
Discussion
14.

In a synchronous motor, the armature current has large values for____________?
A. high excitation only
B. low excitation only
C. both high and low excitation
D. none of the above
Answer» D. none of the above
Discussion
15.

In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and load torque all are halved. The motor speed will be____________?
A. 3000 r.p.m.
B. 1500 r.p.m.
C. 750 r.p.m.
D. none of the above
Answer» C. 750 r.p.m.
Discussion
16.

If the field of a synchronous motor is underexcited, the power factor will be_____________?
A. zero
B. unity
C. lagging
D. leading
Answer» D. leading
Discussion
17.

A synchronous machine with low value of short-circuit ratio has___________?
A. lower stability limit
B. high stability limit
C. good speed regulation
D. good voltage regulation
E. none of the above
Answer» B. high stability limit
Discussion
18.

By which of the following methods the constant speed of a synchronous motor can be changed to new fixed value ?
A. By changing the supply frequency
B. By interchanging any two phases
C. By changing the applied voltage
D. By changing the load
Answer» B. By interchanging any two phases
Discussion
19.

In a synchronous motor, V-curves represent relation between____________?
A. armature current and field current
B. power factor and speed
C. field current and speed
D. field current and power factor
Answer» B. power factor and speed
Discussion
20.

The torque angle, in a synchronous motor, is the angle between_______________?
A. the supply voltage and the back e.m.f.
B. magnetising current and back e.m.f.
C. the rotating stator flux and rotor poles
D. none of the above
Answer» D. none of the above
Discussion
21.

In a 3-phase synchronous motor, the negative phase sequence exists when the motor is_______________?
A. supplied with unbalanced voltage
B. under-loaded
C. over-loaded
D. none of the above
Answer» B. under-loaded
Discussion
22.

A 3-phase synchronous motor is running clockwise. If the direction of its field current is reversed
A. the motor will stop
B. the motor continue to run in the same direction
C. the winding of the motor will burn
D. the motor will run in the reverse direction
E. none of the above
Answer» C. the winding of the motor will burn
Discussion
23.

The coupling angle or load angle of synchronous motor is defined as the angle between the__________?
A. rotor and stator teeth
B. rotor and the stator poles of opposite polarity
C. rotor and the stator poles of the same polarity
D. none of the above
Answer» C. rotor and the stator poles of the same polarity
Discussion
24.

In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
A. the motor is said to be fully loaded
B. the torque generated is maximum
C. the excitation is said to be zero per cent
D. the excitation is said to be hundred per cent
Answer» E.
Discussion
25.

Due to which of the following reasons a synchronous motor fails to pull into synchronism after applying D.C. field current?
A. High field current
B. Low short circuit ratio
C. High core losses
D. Low field current
Answer» E.
Discussion
26.

The net armature voltage of a synchronous motor is equal to the_______________?
A. vector sum of Eb and V
B. arithmetic sum of Eb and V
C. arithmetic difference of Eb and V
D. vector difference of Eh and V
Answer» E.
Discussion
27.

A rotory converter can also be run as a___________?
A. d.c. shunt motor
B. d.c. series motor
C. d.c. compound motor
D. induction motor
E. synchronous motor
Answer» F.
Discussion
28.

In a synchronous motor, the damping winding is generally used to______________?
A. reduce noise level
B. reduce the eddy currents
C. provide starting torque only
D. prevent hunting and provide the starting torque
E. none of the above
Answer» E. none of the above
Discussion
29.

The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as__________?
A. locked-rotor torque
B. synchronous torque
C. pull up torque
D. reluctance torque
Answer» B. synchronous torque
Discussion
30.

If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then_____________?
A. the stator current will be zero
B. the stator current will be very small
C. the stator current will be very high
D. the back e.m.f. will be more than the supply voltage
E. none of the above
Answer» B. the stator current will be very small
Discussion
31.

A synchronous motor which works on a leading power factor and does not drive a mechanical load is called as_________?
A. static condenser
B. condenser
C. synchronous condenser
D. none of the above
Answer» D. none of the above
Discussion
32.

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will__________?
A. stop
B. run as induction motor
C. function as static condenser
D. burn with dense smoke
Answer» B. run as induction motor
Discussion
33.

The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as___________?
A. pull-up torque
B. pull-in torque
C. pull-out torque
D. none of the above
Answer» C. pull-out torque
Discussion
34.

A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have_____________?
A. no change of power factor
B. lagging power factor with over-excitation
C. leading power factor with under-excitation
D. leading power factor with over-excitation
Answer» E.
Discussion
35.

The maximum value of torque that a synchronous motor can develop without losing its synchronism, is known as_____________?
A. slip torque
B. pull-out torque
C. breaking torque
D. synchronising torque
Answer» E.
Discussion
36.

The duration of sudden snort-circuit test on a synchronous motor is usually about_____________?
A. one hour
B. one minute
C. one second
D. none of the above
Answer» D. none of the above
Discussion
37.

A synchronous motor develops maximum power when load angle is____________?
A. 45°
B. 60°
C. 90°
D. 120°
Answer» D. 120°
Discussion
38.

The armature current of the synchronous motor
A. has large values for low excitation i niy
B. has large values for high excitation only
C. has large values for low and high excitation
D. any of the above
Answer» D. any of the above
Discussion
39.

Exciters of synchronous machines are______________?
A. d.c. series machines
B. d.c. shunt machines
C. d.c. compound machines
D. any of the above
Answer» C. d.c. compound machines
Discussion
40.

The ratio of starting torque to running torque in a synchronous motor is____________?
A. zero
B. one
C. two
D. infinity
Answer» B. one
Discussion
41.

While starting a synchronous motor by induction motor action, field winding is usually_____________?
A. connected to D.C. supply
B. short-circuited by low resistance
C. kept open-circuited
D. none of the above
Answer» C. kept open-circuited
Discussion
42.

The magnitude of field flux in a 3-phase synchronous motor?
A. varies with power factor
B. varies with speed
C. varies with the load
D. remains constant at all loads
Answer» E.
Discussion
43.

Which of the following motors is non-self starting ?
A. D.C. series motor
B. synchronous motor
C. Squirrel cage induction motor
D. Wound round induction motor
Answer» C. Squirrel cage induction motor
Discussion
44.

The power factor of a synchronous motor is better than that of induction motor because
A. stator supply is relieved of responsibility of producing magnetic field
B. mechanical load on the motor can be adjusted
C. synchronous motor runs at synchronous speed
D. synchronous motor has large air gap
Answer» B. mechanical load on the motor can be adjusted
Discussion
45.

When the voltage applied to a synchronous motor is increased, which of the following will reduce?
A. Stator flux
B. Pull in torque
C. Both A. and (b)
D. None of the above
Answer» E.
Discussion
46.

A synchronous motor will always stop when:______________?
A. supply voltage fluctuates
B. load in motor varies
C. excitation winding gets disconnected
D. supply voltage frequency changes
Answer» D. supply voltage frequency changes
Discussion
47.

When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop_________________?
A. inductor motor torque
B. induction generator torque
C. synchronous motor torque
D. d.c. motor toque
E. none of the above
Answer» C. synchronous motor torque
Discussion
48.

Armature of a synchronous machine is____________?
A. of reducing number of slip rings on the rotor
B. armature is associated with large power as compared to the field circuits
C. of difficulty of providing high voltage insulation on rotor
D. all of the above reasons
Answer» E.
Discussion
49.

If one-phase of a 3-phase synchronous motor is short-circuited, motor will ______________?
A. will refuse to start
B. will overheat in spots
C. will not come upto speed
D. will fail to pull into step
Answer» B. will overheat in spots
Discussion
50.

The maximum speed variation in a 3-phase synchronous motor is____________?
A. 10 per cent
B. 6 per cent
C. 4 per cent
D. per cent
E. zero
Answer» F.
Discussion