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MCQ of Electrical Machines page-1

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1.The fleming left-hand rule is applicable to

(a) generator
(c) transformer
(d) (a) and (b) both
(e) (a) or (b)

2. The eddy current losses in the transformer will be reduced if

(a) the laminations are think
(b) number of turns in the primary winding is reduced
(c) the number of turns in the secondary winding is reduced
the laminations are thin

3. The speed of d.c. series motor at no load is

(a) zero
(b) 1500 r.p.m.
(d) 3000 r.p.m.
(e) none of the above

4. A sinusoidal voltage of frequency 1 Hz is applied to the field of d.c. generator. The armature voltage will be

(a) 1 Hz square wave
1 Hz sinusoidal voltage
(c) d.c. voltage
(d) none of the above

5. The function of the commutator in a d.c. machine is

(a) to change alternating current to a direct current
(b) to improve commutation
(c) for easy control
to change alternating voltage to direct voltage

6. The phase sequence of voltage generated in the alternator can be reversing its field current.

(a) true

7. The rotation of three phase induction motor can be reversed by interchanging any two of the supply phases.

(b) false

8. The starting torque of the three phase induction motor can be increased by

(a) increasing the rotor reactance
increasing the rotor resistance
(c) increasing the stator resistance
(d) none of the above

9. In the induction motor the torque is

proportional to slip
(b) inversely proportional to slip
(c) proportional to the square of the slip
(d) none of the above

10. The single phase induction motor (capacitor start capacitor run ) basically is

(a) single phase motor
two phase motor
(c) a.c series motor
(d) none of the above

11.For the equal output the total current is more in

(a) wave winding
lap winding
(c) simplex lap winding
(d) none of the above

12. The maximum starting torque in the induction motor is developed when

(a) the reactance of the rotor is half of the resistance
(b) the reactance of the rotor is twice of the rotor resistance
the reactance of the rotor is equal to the rotor resistance
(d) none of the above

13. The direction of rotation of a d.c. series motor can be changed

(a) by interchanging supply terminals
by interchanging field terminals
(c) either (a) or (b)
(b)none of above

14. A d.c. shunt generator driven at a normal speed in the normal direction fails to build up armature voltage because

(a)the resistance of armature is high.
(b) field current is not sufficiently high.
there is no residual magnetism.
(d) field winding has small number of turns.

15. The skin effect can be reduced

By increasing the radius of the conductor
(b) By decreasing the radius of the conductor
(c) By increasing the frequency of the supply
(d) If the hollow conductor is used
(e) (b) and (d) both

16. If a d.c. motor is connected across a.c. supply, the d.c. motor will

Burn as the eddy currents in the field produce heat
(b) Run at its normal speed
(c) Run at a lower speed
(d) Run continuously but the sparking takes place at the burshes

17. What would happen if the field of d.c. shunt motor is opened?

(a) The speed of the motor will be reduced
(b) It will continue to run at its normal speed
The speed of the motor will be enormously high and might destroy itself
(d) The current in the armature will increase

18. A single phase induction motor can be on two or three phase lines.

(a) true

19. What is the standard direction of a motor ?

(a) Clockwise when looking at the front end of the motor
Counter-clockwise when looking at the front end of the motor

20. If the field of a synchronous motor is under excited the power factor will be

(b) leading
(c) unity
(d) more than unity

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