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OBJECTIVE TYPE QUESTIONS

(A) Choose the Correct Answer:

1.   In a split-phase motor, the running winding should have

(a) high resistance and low inductance
(b) low resistance and high Inductance
(c) high resistance as well as high inductance
(d) low resistance as well as low inductance.
2.   If the capacitor of a single-phase motor is short-circuited
(a) the motor will not start
(b) the motor will burn
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at reduced r.p.m.
3.   In capacitor-start single-phase motors
(a)                  current in the starting winding leads the voltage
(b)                 current in the starting winding lags the voltage
(c)                  current in the starting winding is in phase with voltage in running winding.
(d)                 none of the above.
4.   In a capacitor-start and run motors the function of the running capacitor in series with the auxiliary winding is to
(a)                  improve power factor
(b)                 increase overload capacity
(c)                  reduce fluctuations in torque
(d)                 to improve torque.
5.   In a capacitor-start motor, the phase displacement between starting and running winding can be nearly
(a)                  100
(b)                 300
(c)                  600
(d)                 900
6.   In a split-phase motor
(a)                  the starting winding is connected through a centrifugal switch
(b)                 the running winding is connected through a centrifugal switch
(c)                  both starting and running windings are connected through a centrifugal switch
(d)                 centrifugal switch is used to control supply voltage.
7.   The torque developed by a single-phase motor at starting is
(a)                  more than the rated torque
(b)                 rated torque
(c)                  less than the rated torque  
(d)                 zero.
8.   Which of the following motors will give relatively high starting torque?
(a)                  Capacitor-start motor
(b)                 Capacitor run motor
(c)                  Split-phase motor
(d)                 Shaded-pole motor.
9.   Which type of capacitor is preferred for capacitor-start and run motor?
(a)                  Electrolyte capacitor
(b)                 Paper capacitor (oil filled)
(c)                  Ceramic capacitor
(d)                 Air capacitor.
10.                Which of the following motors will have relatively higher power factor?
(a)                  Capacitor-run motor
(b)                 Shaded-pole motor
(c)                  Capacitor-start motor
(d)                 Split-phase motor.
11.                In a shaded-pole motor, the shading coil usually consist of
(a)                  a single turn of heavy wire which is in parallel with running winding
(b)                 a single turn of heavy copper wire which is short-circuited and carries only induced current
(c)                  a multilayer fine gauge copper wire in parallel with running winding
(d)                 none of the above.
12.                In a shaded-pole single-phase motor, the revolving field is produced by the use of
(a)                  inductor
(b)                 capacitor
(c)                  resistor
(d)                 shading coils.
13.                A centrifugal switch is used to disconnect starting winding when motor has
(a)                  run for-about 1 minute
(b)                 run for about 5 minutes
(c)                  picked up about 50 to 70 per cent of rated speed
(d)                 picked up about 10 to 25 per cent of rated speed.
14.                If a particular application needs high speed and high starting torque, then which of the following motors will be preferred?
(a)                  Universal motor
(b)                 Shaded-pole type motor
(c)                  Capacitor-start motor
(d)                 Capacitor-start and run motor.
15.                Which motor has the highest power to weight ratio?
(a)                  Capacitor-run motor
(b)                 Capacitor-start motor
(c)                  Universal motor
(d)                 None of the above.
16.                In a universal motor the width of the brush is nearly
(a)                  half the width of commutator segment
(b)                 equal to width of the commutator segment
(c)                  equal to width of two commutator segment
(d)                 equal to width of four commutator segment.
17.                The range of efficiency for shaded-pole motors is
(a)                  95% to 99%
(b)                 80% or 90%
(c)                  50% to 75%
(d)                 5% to 35%.
18.                In a capacitor-start single-phase motor, when capacitor is replaced by a resistance
(a)                  torque will increase
(b)                 the motor will consume less power
(c)                  motor will run in reverse direction
(d)                 motor will continue to run in same direction.
19.                The power factor of a single-phase induction motor is usualIy
(a)                  lagging
(b)                 always leading
(c)                  unity
(d)                 unity to 0.8 leading.
20.                A shaded-pole motor can be used for
(a)                  toys
(b)                 hair dryers
(c)                  circulators
(d)                 any of the above.
21.                A hysteresis motor works on the principle of
(a)                  hysteresis loss
(b)                 magnetisation ofrotor
(c)                  eddy current loss
(d)                 electromagnetic induction.
22.                Which of the following motors will give the highest starting torque?
(a)                  D.C. shunt motor
(b)                 Schrage motor
(c)                  Repulsion-start and induction-run motor
(d)                 Universal motor.
23.                In repulsion motors by shifting the position of brushes
(a)                  only speed can be controlled
(b)                 speed and direction of rotation can be controlled
(c)                  speed, direction of rotation and torque can be controlled
(d)                 none of the above.
24.                Which of the following single-phase motors is reversible?
(a)                  Capacitor-start split-phase motor
(b)                 Resistance-start split-phase motor
(c)                  Reluctance motor
(d)                 None of the above.
25.                For which of the applications a reluctance motor is preferred?
(a)                  Electric shavers
(b)                 Refrigerators
(c)                  Signalling and timing devices
(d)                 Lifts and hoists.
26.                In repulsion motors
(a)                  speed remains constant
(b)                 speed variation is within 5%
(c)                  speed varies with load
(d)                 speed varies only with change in applied voltage.
27.                In single-phase repulsion motors power factor is
(a)                  always leading
(b)                 high at low speeds
(c)                  always unity
(d)                 high at high speeds.
28.                The motor used on small lathes is usually
(a)                  universal motor
(b)                 d.c. shunt motor
(c)                  single-phase capacitor run motor
(d)                 3-phase synchronous motor.
29.                Which of the following motors is preferred for tape recorders?
(a)                  Shaded-pole motor
(b)                 Hysteresis motor
(c)                  Two value capacitor motor
(d)                 Universal motor.
30.                A single-phase induction motor is
(a)                  inherently self-starting with high torque
(b)                 inherently self-starting with low torque
(c)                  inherently non-self-starting with low torque
(d)                 inherently non-self-starting with high torque.
31.                A schrage motor can run on
(a)                  zero slip
(b)                 negative slip
(c)                  positive slip
(d)                 all of the above.
32.                A universal motor can run on
(a)                  A.C. only
(b)                 D.C. only
(c)                  either A.C. or D.C.
(d)                 none of the above.
33.                Which of the following single-phase motors is suitable for timing and control purposes?
(a)                  Reluctance motor
(b)                 Series motor
(c)                  Repulsion motor
(d)                 Universal motor.
34.                In case of a shaded-pole motor the direction of rotation of the motor is
(a)                  from main-pole to shaded-pole
(b)                 from shaded-pole to main pole
(c)                  either of the above depending on voltage
(d)                 either of the above depending on power factor.
35.                In case of high speed universal motor which of the following needs more attention?
(a)                  End play
(b)                 Air gap
(c)                  Insulation in rotor
(d)                 Balancing of rotor.
36.                The wattage rating for a ceiling fan motor will be in the range
(a)                  50 to 250 W
(b)                 250 to 500 W
(c)                  50 to 150 W
(d)                 10 to 20 W
37.                The wattage of motor for driving’ domestic sewing machine will be around
(a)                  100 to 150 W
(b)                 40 to 75 W
(c)                  10 to 30 W
(d)                 5 to 10 W.
38.                Which of the following single-phase motors has relatively poor starting torque?
(a)                  Universal motor
(b)                 Repulsion motor
(c)                  Capacitor motor
(d)                 All single phase motors have zero starting torque.
39.                Which type of load is offered by cranes and hoists ?
(a)                  gradually varying load
(b)                 non-reversing, no-load start
(c)                  reversing, light start
(d)                 reversing, heavy start.
40.                The speed of a universal motor is generally reduced by using
(a)                  gear trains
(b)                 V-belts
(c)                  brakes
(d)                 chains.
41.                Which of the following motors can be used for unity power factor?
(a)                  Capacitor run motor
(b)                 Shaded-pole motor
(c)                  Hysteresis motor
(d)                 Schrage motor.
42.                When a D.C. series motor is connected to A.C. supply, the power factor will be low because of
(a)                  high inductance of field and armature circuits
(b)                 induced current in rotor due to variations afflux
(c)                  fine copper wire winding
(d)                 none of the above.
43.                The direction of rotation of universal motor can be reversed by reversing the flow of current through
(a)                  armature winding
(b)                 field winding
(c)                  either armature winding or field winding
(d)                 none of the above.
44.                In which single-phase motor, the rotor has no teeth or winding?
(a)                  Split-phase motor
(b)                 Reluctance motor
(c)                  Hysteresis motor
(d)                 Universal motor.
45.                Which motor is normally free from mechanical and magnetic vibrations?
(a)                  Split-phase motor
(b)                 Universal motor
(c)                  Hysteresis motor
(d)                 Shaded-pole motor,
46.                As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for
(a)                  fans
(b)                 blowers
(c)                  sound equipment
(d)                 mixer grinders.
47.                A reluctance motor
(a)                  is self-starting
(b)                 is constant speed motor
(c)                  needs no D.C. excitation
(d)                 all of the above.
48.                In a hysteresis motor, the rotor must have
(a)                  retentivity
(b)                 resistivity
(c)                  susceptibility
(d)                 none of the above.
49.                The rotor of a hysteresis motor is made of
(a)                  aluminium
(b)                 cast iron
(c)                  chrome steel
(d)                 copper.
50.                The electric motor used in portable drills is
(a)                  capacitor-run motor
(b)                 hysteresis motor
(c)                  universal motor
(d)                 repulsion motor.
51.                Which of the following applications always has some load whenever switched on?
(a)                  Vacuum cleaners
(b)                 Fan motors
(c)                  Pistol drills
(d)                 All of the above.
52.                The speed control of universal motor used for sewing machines is by
(a)                  friction
(b)                 varying the resistance
(c)                  tapping the field
(d)                 centrifugal mechanism.

ANSWERS

 

1.   b

2.   a

3.   a

4.   a

5.   d

6.   a

7.   d

8.   a

9.   b

10.                a

11.                b

12.                d

13.                c

14.                a

15.                c

16.                c

17.                d

18.                d

19.                a

20.                d

21.                a

22.                b

23.                b

24.                a

25.                c

26.                c

27.                d

28.                c

29.                b

30.                c

31.   d

32.   c

33.   a

34.   a

35.   d

36.   c

37.   a

38.   c

39.   d

40.                a

41.                d

42.                a

43.                c

44.                c

45.                c

46.                c

47.                d

48.                a

49.                c

50.                c

51.                c

52.                b

 

(B) Say ‘Yes’ or ‘No’:

1.   In a capacitor-start motor, the phase displacement between starting and running winding can be nearly 900.
2.   In a split-phase motor the staring winding is connected through a centrifugal switch.
3.   In a shaded-pole single-phase motor, the revolving field is produced by the use of capacitor.
4.   A universal motor has the highest power to weight ratio.
5.   The range of efficiency for shaded-pole motors is 80 to 90%.
6.   The power factor of a single-phase induction motor is usually lagging.
7.   A hysteresis motor works on the principle of eddy current loss.
8.   Capacitor-start split-phase motor is reversible.
9.   A reluctance motor is preferred for signalling and timing devices.
10.                The wattage rating for a ceiling fan motor varies from 50 to 150 W.
11.                A …… motor is an incremental motion machine.
12.                A stepper motor rotates continuously.
13.                The stepper motor is used in digitally controlled position control system in open loop mode.
14.                In stepper motors no sensors are needed for position and speed sensing.
15.                A stepper motor cannot be readily interfaced with microprocessor.
16.                In ……. stepper motor the rotor is made of ferite or rare earth material which is permanently magnetised.
17.                In a …….. stepped motor the stator has only one set of winding-excited poles which interact with the two rotor stacks.
18.                ….. servo-motors are preferred for very high power systems.
19.                A.C. servo-motors are best suited for low power applications.
20.                ….. construction is used for very low inertia applications.

ANSWERS

 

1.   Yes
2.   Yes
3.   No
4.   Yes
5.   No
6.   Yes
7.   No
8.   Yes
9.   Yes
10.                Yes
11.                Stepper
12.                No
13.                Yes
14.                Yes
15.                No
16.                Permanent-magnet
17.                hybrid
18.                D.C.
19.                Yes
20.                Drag-cup.