MCQ Electrical power (induction motors)

- 3. A. THREE PHASE INDUCTION MOTORS

1.Which of the following component is usually fabricated out of silicon steel ?
(a) Bearings
(b) Shaft
(c) Statorcore
(d) None of the above
Ans: c
2. The frame of an induction motor is usually made of
(a) silicon steel
(b) cast iron
(c) aluminium
(d) bronze
Ans: b
3. The shaft of an induction motor is made of
(a) stiff
(b) flexible
(c) hollow
(d) any of the above
Ans: a
4. The shaft of an induction motor is made of
(a) high speed steel
(b) stainless steel
(c) carbon steel
(d) cast iron
Ans: c
5.In an induction motor, no-load the slip is generally
(a) less than 1% (b) 1.5%
(c) 2%
(d) 4%
Ans: a

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 MCQ Electrical power (induction motors)

6.In medium sized induction motors, the slip is generally around (a) 0.04%
(b) 0.4%
(c) 4%
(d) 14%
Ans: c
7.In squirrel cage induction motors, the rotor slots are usually given slight skew
in order to
(a) reduce windage losses
(b) reduce eddy currents
(c) reduce accumulation of dirt and dust
(d) reduce magnetic hum
Ans: d
8.In case the air gap in an induction motor is increased
(a) the magnetising current of the rotor will decrease
(b) the power factor will decrease
(c) speed of motor will increase
(d) the windage losses will increase
Ans: b
9.Slip rings are usually made of
(a) copper
(b) carbon
(c) phospor bronze
(d) aluminium
Ans: c
10.A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor
e.m.f. will be
(a) 200 Hz
(b) 50 Hz
(c) 2 Hz
(d) 0.2 Hz
Ans: c

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 MCQ Electrical power (induction motors)

11. In Ns is the synchronous speed and s the slip, then actual running speed of
an induction motor will be
(a) Ns
(b) s.N,
(c) (l-s)Ns
(d) (Ns-l)s
Ans: c
The efficiency of an induction motor can be expected to be nearly
(a) 60 to 90%
(b) 80 to 90%
(c) 95 to 98%
(d) 99%
Ans: b
13.The number of slip rings on a squirrel cage induction motor is usually
(a) two
(b) three
(c) four
(d) none
Ans: d
14.The starting torque of a squirrel-cage induction motor is
(a) low
(b) negligible
(c) same as full-load torque
(d) slightly more than full-load torque
Ans: a
15.A double squirrel-cage induction motor has
(a) two rotors moving in oppsite direction
(b) two parallel windings in stator
(c) two parallel windings in rotor
(d) two series windings in stator
Ans: c

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 MCQ Electrical power (induction motors)

16.Star-delta starting of motors is not possible in case of

(a) single phase motors
(b) variable speed motors
(c) low horse power motors
(d) high speed motors
Ans: a
17.The term 'cogging' is associated with
(a) three phase transformers
(b) compound generators
(c) D.C. series motors
(d) induction motors
Ans: d
18.In case of the induction motors the torque is
(a) inversely proportional to (Vslip)
(b) directly proportional to (slip)2
(c) inversely proportional to slip
(d) directly proportional to slip
Ans: d
19.An induction motor with 1000 r.p.m. speed will have
(a) 8 poles
(b) 6 poles
(c) 4 poles
(d) 2 poles
Ans: b
20.The good power factor of an induction motor can be achieved if the average
flux density in the air gap is
(a) absent
(b) small
(c) large
(d) infinity
Ans: b

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 MCQ Electrical power (induction motors)

21. An induction motor is identical to

(a) D.C. compound motor
(b) D.C. series motor
(c) synchronous motor
(d) asynchronous motor
Ans: d
22. The injected e.m.f. in the rotor of induction motor must have
(a) zero frequency
(b) the same frequency as the slip fre-quency
(c) the same phase as the rotor e.m.f.
(d) high value for the satisfactory speed control
Ans: b
23. Which of the following methods is easily applicable to control the speed
of the squirrel-cage induction motor ?
(a) By changing the number of stator poles
(b) Rotor rheostat control
(c) By operating two motors in cascade
(d) By injecting e.m.f. in the rotor circuit
Ans: a
24. The crawling in the induction motor is caused by
(a) low voltage supply (b) high loads
(c) harmonics develped in the motor
(d) improper design of the machine
(e) none of the above
Ans: c
25. The auto-starters (using three auto transformers) can be used to start
cage induction motor of the following type
(a) star connected only (b) delta connected only
(c) (a) and (b) both
(d) none of the above
Ans: c

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 MCQ Electrical power (induction motors)

26. The torque developed in the cage induction motor with autostarter is
(a) k/torque with direct switching
(6) K x torque with direct switching
(c) K2 x torque with direct switching
(d) k2/torque with direct switching
Ans: c
27. When the equivalent circuit diagram of double squirrel-cage induction
motor is constructed the two cages can be considered
(a) in series (b) in parallel
(c) in series-parallel
(d) in parallel with stator
Ans: b
28.It is advisable to avoid line-starting of induction motor and use starter
because
(a) motor takes five to seven times its full load current
(b) it will pick-up very high speed and may go out of step
(c) it will run in reverse direction
(d) starting torque is very high
Ans: a
29.Stepless speed control of induction motor is possible by which of the
following methods ?
(a) e.m.f. injection in rotor eueuit
(b) Changing the number of poles
(c) Cascade operation
(d) None of the above
Ans: b
30. Rotor rheostat control method of speed control is used for
(a) squirrel-cage induction motors only
(b) slip ring induction motors only
(c) both (a) and (b) (d) none of the above
Ans: b

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 MCQ Electrical power (induction motors)

31. In the circle diagram for induction motor, the diameter of the circle
represents
(a) slip
(b) rotor current
(c) running torque
(d) line voltage
Ans: b
32. For which motor the speed can be controlled from rotor side ?
(a) Squirrel-cage induction motor
(b) Slip-ring induction motor
(c) Both (a) and (b)
(d) None of the above
Ans: b
33. If any two phases for an induction motor are interchanged
(a) the motor will run in reverse direction
(b) the motor will run at reduced speed
(c) the motor will not run
(d) the motor will burn
Ans: a
34. An induction motor is
(a) self-starting with zero torque
(b) self-starting with high torque
(c) self-starting with low torque
(d) non-self starting
Ans: c
35. The maximum torque in an induction motor depends on
(a) frequency
(b) rotor inductive reactance
(c) square of supply voltage
(d) all of the above
Ans: d

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 MCQ Electrical power (induction motors)

36. In three-phase squirrel-cage induction motors

(a) rotor conductor ends are short-circuited through slip rings
(b) rotor conductors are short-circuited through end rings
(c) rotor conductors are kept open
(d) rotor conductors are connected to insulation
Ans: b
37. In a three-phase induction motor, the number of poles in the rotor
winding is always
(a) zero
(b) more than the number of poles in stator
(c) less than number of poles in stator
(d) equal to number of poles in stator
Ans: d
38. DOL starting of induction motors is usually restricted to
(a) low horsepower motors
(b) variable speed motors
(c) high horsepower motors
(d) high speed motors
Ans: a
39. The speed of a squirrel-cage induction motor can be controlled by all of
the following except
(a) changing supply frequency
(b) changing number of poles
(c) changing winding resistance
(d) reducing supply voltage
Ans: c
40. The 'crawling" in an induction motor is caused by
(a) high loads (b) low voltage supply
(c) improper design of machine
(d) harmonics developed in the motor
Ans: d

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 MCQ Electrical power (induction motors)

41. The power factor of an induction motor under no-load conditions will be
closer to
(a) 0.2 lagging (b) 0.2 leading
(c) 0.5 leading (d) unity
Ans: a
42. The 'cogging' of an induction motor can be avoided by
(a) proper ventilation
(b) using DOL starter
(c) auto-transformer starter
(d) having number of rotor slots more or less than the number of stator slots
(not equal)
Ans: d
43. If an induction motor with certain ratio of rotor to stator slots, runs at 1/7
of the normal speed, the phenomenon will be termed as
(a) humming (b) hunting
(c) crawling (d) cogging
Ans: c
44. Slip of an induction motor is negative when
(a) magnetic field and rotor rotate in opposite direction
(b) rotor speed is less than the syn-chronous speed of the field and are in the
same direction
(c) rotor speed is more than the syn-chronous speed of the field and are in
the same direction
(d) none of the above
Ans: c
45. Size of a high speed motor as compared to low speed motorfor the same
H.P. will be
(a) bigger (b) smaller
(c) same
(d) any of the above
Ans: b

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 MCQ Electrical power (induction motors)

46. A 3-phase induction motor stator delta connected, is carrying full load and
one of its fuses blows out. Then the motor
(a) will continue running burning its one phase
(b) will continue running burning its two phases
(c) will stop and carry heavy current causing permanent damage to its
winding
(d) will continue running without any harm to the winding
Ans: a
47. A 3-phase induction motor delta connected is carrying too heavy load and
one of its fuses blows out. Then the motor
(a) will continue running burning its one phase
(b) will continue running burning its two phase
(c) will stop and carry heavy current causing permanent damage to its
winding
(d) will continue running without any harm to the winding
Ans: c
48. Low voltage at motor terminals is due to
(a) inadequate motor wiring
(b) poorely regulated power supply
(c) any one of the above
(d) none of the above
Ans: c
49. In an induction motor the relationship between stator slots and rotor
slots is that
(a) stator slots are equal to rotor slots
(b) stator slots are exact multiple of rotor slots
(c) stator slots are not exact multiple of rotor slots
(d) none of the above
Ans: c

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 MCQ Electrical power (induction motors)

50. Slip ring motor is recommended where

(a) speed control is required
(6) frequent starting, stopping and reversing is required
(c) high starting torque is needed
(d) all above features are required
Ans: d
51. As load on an induction motor goes on increasing
(a) its power factor goes on decreasing
(b) its power factor remains constant
(c) its power factor goes on increasing even after full load
(d) its power factor goes on increasing upto full load and then it falls again
Ans: d
52. If a 3-phase supply is given to the stator and rotor is short circuited rotor
will move
(a) in the opposite direction as the direction of the rotating field
(b) in the same direction as the direction of the field
(c) in any direction depending upon phase squence of supply
Ans: b
53. It is advisable to avoid line starting of induction motor and use starter
because
(a) it will run in reverse direction
(b) it will pick up very high speed and may go out of step
(c) motor takes five to seven times its fullload current
(d) starting torque is very high
Ans: c
54. The speed characteristics of an induction motor closely resemble the
speedload characteristics of which of the following machines
(a) D.C. series motor (b) D.C. shunt motor
(c) universal motor
(d) none of the above
Ans: b

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 MCQ Electrical power (induction motors)

55. Which type of bearing is provided in small induction motors to support

the rotor shaft ?
(a) Ball bearings (b) Cast iron bearings
(c) Bush bearings (d) None of the above
Ans: a
56. A pump induction motor is switched on to a supply 30% lower than its
rated voltage. The pump runs. What will eventually happen ? It will
(a) stall after sometime (b) stall immediately
(c) continue to run at lower speed without damage
(d) get heated and subsequently get damaged
Ans: d
57. 5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the
following r.p.m. Which motor will be the costliest ?
(a) 730 r.p.m. (b) 960 r.p.m.
(c) 1440 r.p.m. (d) 2880 r.p.m.
Ans: a
58. A 3-phase slip ring motor has
(a) double cage rotor (b) wound rotor
(c) short-circuited rotor (d) any of the above
Ans: b
59. The starting torque of a 3-phase squirrel cage induction motor is
(a) twice the full load torque
(b) 1.5 times the full load torque
(c) equal to full load torque
Ans: b
60. Short-circuit test on an induction motor cannot be used to determine
(a) windage losses
(b) copper losses
(c) transformation ratio
(d) power scale of circle diagram
Ans: a

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 MCQ Electrical power (induction motors)

61. In a three-phase induction motor

(a) iron losses in stator will be negligible as compared to that in rotor
(6) iron losses in motor will be neg¬ligible as compared to that in rotor
(c) iron losses in stator will be less than that in rotor
(d) iron losses in stator will be more than that in rotor
Ans: d
62. In case of 3-phase induction motors, plugging means
(a) pulling the motor directly on line without a starter
(b) locking of rotor due to harmonics
(c) starting the motor on load which is more than the rated load
(d) interchanging two supply phases for quick stopping
Ans: d
63. Which is of the following data is required to draw the circle diagram for
an induction motor ?
(a) Block rotor test only
(b) No load test only
(c) Block rotor test and no-load test
(d) Block rotor test, no-load test and stator resistance test
Ans: d
64. In three-phase induction motors sometimes copper bars are placed deep
in the rotor to
(a) improve starting torque
(b) reduce copper losses
(c) improve efficiency
(d) improve power factor
Ans: a
65. In a three-phase induction motor
(a) power factor at starting is high as compared to that while running
(b) power factor at starting is low as compared to that while running
(c) power factor at starting in the same as that while running
Ans: b

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 MCQ Electrical power (induction motors)

66. The vafcie of transformation ratio of an induction motor can be found by

(a) open-circuit test only
(b) short-circuit test only
(c) stator resistance test
(d) none of the above
Ans: b
67. The power scale of circle diagram of an induction motor can be found
from
(a) stator resistance test
(6) no-load test only
(c) short-circuit test only
(d) noue of the above
Ans: c
68. The shape of the torque/slip curve of induction motor is
(a) parabola (b) hyperbola
(c) rectangular parabola (d) straigth line
Ans: c
69. A change of 4% of supply voltage to an induction motor will produce a
change of appromimately
(a) 4% in the rotor torque
(b) 8% in the rotor torque
(c) 12% in the rotor torque
(d) 16% in the rotor torque
Ans: d
70. The stating torque of the slip ring induction motor can be increased by
adding
(a) external inductance to the rotor
(b) external resistance to the rotor
(c) external capacitance to the rotor
(d) both resistance and inductance to rotor
Ans: b

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 MCQ Electrical power (induction motors)

71. A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of
960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be
(a) 0.01
(b) 0.02
(c) 0.03
(d) 0.04
Ans: d
72. The complete circle diagram of induetion motor can be drawn with the
help of data found from
(a) noload test
(6) blocked rotor test
(c) stator resistance test
(d) all of the above
Ans: d
73.In the squirrel-cage induction motor the rotor slots are usually given slight
skew
(a) to reduce the magnetic hum and locking tendency of the rotor
(b) to increase the tensile strength of the rotor bars
(c) to ensure easy fabrication
(d) none of the above
Ans: a
74. The torque of a rotor in an induction motor under running condition is
maximum
(a) at the unit value of slip
(b) at the zero value of slip
(c) at the value of the slip which makes rotor reactance per phase equal to
the resistance per phase
(d) at the value of the slip which makes the rotor reactance half of the rotor
Ans: c

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 MCQ Electrical power (induction motors)

75. What will happen if the relative speed between the rotating flux of stator
and rotor of the induction motor is zero ?
(a) The slip of the motor will be 5%
(b) The rotor will not run
(c) The rotor will run at very high speed
(d) The torque produced will be very large
Ans: b
76. The circle diagram for an induction motor cannot be used to determine
(a) efficiency (b)power factor
(c) frequency (d)output
Ans: a
77. Blocked rotor test on induction motors is used to find out
(a) leakage reactance
(b) power factor on short circuit
(c) short-circuit current under rated voltage
(d) all of the above
Ans: d
78. Lubricant used for ball bearing is usually
(a) graphite (b) grease
(c) mineral oil (d) molasses
Ans: b
79. An induction motor can run at synchronous speed when
(a) it is run on load
(b) it is run in reverse direction
(c) it is run on voltage higher than the rated voltage
(d) e.m.f. is injected in the rotor circuit
Ans: d

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 MCQ Electrical power (induction motors)

80. Which motor is preferred for use in mines where explosive gases exist ?
(a) Air motor
(b) Induction motor
(c) D.C. shunt motor
(d) Synchronous motor
Ans: a
81. The torque developed by a 3-phase induction motor least depends on
(a) rotor current
(b) rotor power factor
(c) rotor e.m.f.
(d) shaft diameter
Ans: d
82. In an induction motor if air-gap is increased
(a) the power factor will be low
(b) windage losses will be more
(c) bearing friction will reduce
(d) copper loss will reduce In an induction motor
Ans: a
83. In induction motor, percentage slip depends on
(a) supply frequency
(b) supply voltage
(c) copper losses in motor
(d) none of the above
Ans: c
84. When /?2 is tne rotor resistance, .X2 the rotor reactance at supply
frequency and s the slip, then the condition for maximum torque under running
condi-tions will be
(a) sR2X2 = 1 (b) sR2 = X2
(c) R2 = sX2 (d) R2 = s2X2
Ans: c

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 MCQ Electrical power (induction motors)

85. In case of a double cage induction motor, the inner cage has
(a) high inductance arid low resistance
(b) low inductance and high resistance
(c) low inductance and low resistance
(d) high inductance and high resis¬tance
Ans: a
86. The low power factor of induction motor is due to
(a) rotor leakage reactance
(b) stator reactance
(c) the reactive lagging magnetizing current necessary to generate the
magnetic flux
(d) all of the above
Ans: d
87. Insertion of reactance in the rotor circuit
(a) reduces starting torque as well as maximum torque
(b) increases starting torque as well as maximum torque
(c) increases starting torque but maxi-mum torque remains unchanged
(d) increases starting torque but maxi-mum torque decreases
Ans: a
88. Insertion of resistance in the rotcir of an induction motor to develop a
given torque
(a) decreases the rotor current
(b) increases the rotor current
(c) rotor current becomes zero
(d) rotor current rernains same
Ans: d
89. For driving high inertia loods best type of induction motor suggested is
(a) slip ring type (b) squirrel cage type
(c) any of the above
(d) none of the above
Ans: a

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 MCQ Electrical power (induction motors)

90. Temperature of the stator winding of a three phase induction motor is

obtained by
(a) resistance rise method
(b) thermometer method
(c) embedded temperature method
(d) all above methods
Ans: d
91. The purpose of using short-circuit gear is
(a) to short circuit the rotor at slip rings
(b) to short circuit the starting resis¬tances in the starter
(c) to short circuit the stator phase of motor to form star
(d) none of the above
Ans: a
92. In a squirrel cage motor the induced e.m.f. is
(a) dependent on the shaft loading
(b) dependent on the number of slots
(c) slip times the stand still e.m.f. induced in the rotor
(d) none of the above
Ans: c
93. Less maintenance troubles are experienced in case of
(a) slip ring induction motor
(6) squirrel cage induction motor
(c) both (a) and (b)
(d) none of the above
Ans: b
94. A squirrel cage induction motor is not selected when
(a) initial cost is the main consideration
(b) maintenance cost is to be kept low
(c) higher starting torque is the main consideration
(d) all above considerations are involved
Ans: c

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 MCQ Electrical power (induction motors)

95. Reduced voltage starter can be used with

(a) slip ring motor only but not with squirrel cage induction motor
(b) squirrel cage induction motor only but not with slip ring motor
(c) squirrel cage as well as slip ring induction motor
(d) none of the above
Ans: c
96. Slip ring motor is preferred over squirrel cage induction motor where
(a) high starting torque is required
(b) load torque is heavy
(c) heavy pull out torque is required
(d) all of the above
Ans: a
97. In a star-delta starter of an induction motor
(a) resistance is inserted in the stator
(b) reduced voltage is applied to the stator
(c) resistance is inserted in the rotor
(d) applied voltage per1 stator phase is 57.7% of the line voltage
Ans: d
98. The torque of an induction motor is
(a) directly proportional to slip
(b) inversely proportional to slip
(c) proportional to the square of the slip
(d) none of the above
Ans: a
99. The rotor of an induction motor runs at
(a) synchronous speed
(b) below synchronous speed
(c) above synchronous speed
(d) any of the above
Ans: b

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 MCQ Electrical power (induction motors)

100. The starting torque of a three phase induction motor can be increased by
(a) increasing slip
(b) increasing current
(c) both (a) and (b)
(d) none of the above
Ans: c
101. Insertion of resistance in the stator of an induction motor
(a) increases the load torque
(b) decreases the starting torque
(c) increases the starting torque
(d) none of the above
Ans: b

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 MCQ Electrical power (induction motors)

- 3. B. SINGLE PHASE INDUCTION MOTORS

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 inductiance
Ans: b
2. If the capacitor of a single-phase motor is short-circuited
(a) the motor will not start (b) the motor will run
(c) the motor will run in reverse direction
(d) the motor will run in the same direction at reduced r.p.m.
Ans: a
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
Ans: a
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
Ans: a
5. In a capacitor start motor, the phase displacement between starting and
running winding can be nearly
(a) 10° (b) 30°
(c) 60° (d) 90°
Ans: d

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 MCQ Electrical power (induction motors)

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
Ans: a
7. The rotor developed by a single-phase motor at starting is
(a) more than i.he rated torque
(b) rated torque
(c) less than the rated torque
(d) zero
Ans: d
8. Which of the following motor will give relatively high starting torque ?
(a) Capacitor start motor
(b) Capacitor run motor
(c) Split phase motor
(d) Shaded pole motor
Ans: a
9. Which of the following motor will have relatively higher power factor ?
(a) Capacitor run motor
(b) Shaded pole motor
(c) Capacitor start motor
(d) Split phase motor
Ans: a
10. 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
Ans: b

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 MCQ Electrical power (induction motors)

11. 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
Ans: d
12.A centrifugal switch is used to dis- connect '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
Ans: c
13. If a particular application needs high speed and high starting torque, then
which of the following motor will be preferred ?
(a) Universal motor
(b) Shaded pole type motor
(c) Capacitor start motor
(d) Capacitor start and run motor
Ans: a
14. The value of starting capacitor of a fractional horse power motor will be
(a) 100 uF (6) 200 uF
(c) 300 uF (d) 400 uF
Ans: c
15. In repulsion motor direction of rotation of motor
(a) is opposite to that of brush shift
(b) is the same as that of brush shift
(c) is independent of brush shift
Ans: b

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 MCQ Electrical power (induction motors)

16. In a single phase motor the centrifugal switch

(a) disconnects auxiliary winding of the motor
(b) disconnects main winding of the motor
(c) reconnects the main winding the motor
(d) reconnects the auxiliary winding of the motor
Ans: a
17. The running winding of a single phase motor on testing with meggar is
found to be ground. Most probable location of the ground will be
(a) at the end connections
(b) at the end terminals
(c) anywhere on the winding inside a slot
(d) at the slot edge where coil enters or comes out of the slot
Ans: d
18. A capacitor-start single phase induction motor is switched on to supply
with its capacitor replaced by an inductor of equivalent reactance value. It will
(a) start and then stop
(b) start and run slowly
(c) start and run at rated speed
(d) not start at all
Ans: d
19. Which of the following motors is used in mixies ?
(a) Repulsion motor (b) Reluctance motor
(c) Hysteresis motor (d) Universal motor
Ans: d
20. Which of the following motors is inherently self starting ?
(a) Split motor
(b) Shaded-pole motor
(c) Reluctance motor
(d) None of these
Ans: b

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 MCQ Electrical power (induction motors)

21. The direction of rotation of an hysteresis motor is determined by

(a) interchanging the supply leads
(b) position of shaded pole with respect to main pole
(c) retentivity of the rotor material
(d) none of these
Ans: b
22. Burning out of windings is due to
(a) short circuited capacitor
(b) capacitor value hiving changed
(c) open circuiting of capacitor
(d) none of the above
Ans: a
23. Direction of rotation of a split phase motor can be reversed by reversing
the connection of
(a) running winding only
(b) starting winding only
(c) either (a) or (b)
(d) both (a) and (b)
Ans: c
24. Short-circuiter is used in
(a) repulsion induction motor
(b) repulsion motor
(c) repulsion start induction run motor
(d) none of the above
Ans: c
25. The range of efficiency for shaded pole motors is (a) 95% to 99%
(b) 80% to 90%
(c) 50% to 75%
(d) 5% to 35%
Ans: d

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 MCQ Electrical power (induction motors)

26. 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
Ans: d
27. The power factor of a single-phase induction motor is usually
(a) lagging
(b) always leading
(c) unity
(d) unity to 0.8 leading
Ans: a
28. A shaded pole motor can be used for
(a) toys
(b) hair dryers
(c) circulators
(d) any of the above
Ans: d
29. A hysteresis motor works on the principle of
(a) hysteresis loss
(b) magnetisation of rotor
(c) eddy current loss
(d) electromagnetic induction
Ans: a
30. Which of the following motor will give the highest starting torque ?
(a) D.C. shunt motor
(b) Schrage motor
(c) Repulsion start and induction run motor
(d) Universal motor
Ans: b

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 MCQ Electrical power (induction motors)

31. For which of the applications a reluctance motor is preferred ?

(a) Electric shavers
(b) Refrigerators
(c) Signalling and timing devices
(d) Lifts and hoists
Ans: c
32. 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
Ans: c
33. 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
Ans: b
34. 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
Ans: c
35. A schrage motor can run on
(a) zero slip
(b) negative slip
(c) positive slip
(d) all of the above
Ans: d

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 MCQ Electrical power (induction motors)

36. A universal motor can run on

(a) A.C. only
(6) D.C. only
(c) either A.C. or D.C.
(d) none of the above
Ans: c
37. 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
Ans: a
38. Single phase induction motor usually operates on
(a) 0.6 power factor lagging
(b) 0.8 power factor lagging
(c) 0.8 power factor leading
(d) unity power factor
Ans: a
39. In split-phase motor iauxiliary winding is of
(a) thick wire placed at the bottom of the slots
(b) thick wire placed at the top of the slots
(c) thin wire placed at the top of the slots
(d) thin wire placed at the bottom of the slots
Ans: c
40. Which of the following motors will operate at high power factor ?
(a) Shaped pole motor
(b) Split phase motor
(c) Capacitor start motor
(d) Capacitor run motor
Ans: d

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 MCQ Electrical power (induction motors)

41. In a two value capacitor motor, the capacitor used for running purposes is
(a) air capacitor
(b) paper spaced oilfilled type
(c) ceramic type
(d) a.c. electrolytic type
Ans: b
42. Which of the following motors can be run on AC. as well as D.C. supply ?
(a) Universal motor
(b) Repulsion motor
(c) Synchronous motor
(d) Reluctance motor
Ans: a
43. In A.C. series motor compensating winding is employed to
(a) reduce the effects of armature reaction
(b) increase the torque
(c) reduce sparking at the brushes
(d) none of the above
Ans: c
44. Which of the following single-phase induction motors is generally used in
time phonographs?
(a) Resistance start
(b) Capacitor start capacitor run
(c) Shaded pole
(d) Universal
Ans: c
45. Which of the following motors has highest starting torque ?
(a) Repulsion motor
(b) Shaped pole motor
(c) Capacitor-start motor
(d) Split-phase motor
Ans: c

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 MCQ Electrical power (induction motors)

46. The repulsion-start induction-run motor is used because of

(a) good power factor
(b) high efficiency
(c) minimum cost
(d) high starting torque
Ans: d
47. 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
Ans: a
48. 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
Ans: d
49. The wattage rating for a ceiling fan motor will be in the range
(a) 200 to 250 W
(b) 250 to 500 W
(c) 50 to 150 W
(d) 10 to 20 W
Ans: c
50. 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
Ans: a

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 MCQ Electrical power (induction motors)

51. 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
Ans: c
52. 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
Ans: d
53. The speed of a universal motor is generally reduced by using
(a) gear trains (b) V-belts
(c) brakes (d) chains
Ans: a
54. 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
Ans: d
55. 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 of flux
(c) fine copper wire winding
(d) none of the above
Ans: a

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 MCQ Electrical power (induction motors)

56. The direction of rotation of universal motor can be reversed the 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
Ans: c
57. 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
Ans: c
58. Which motor is normally free from mechanical and magnetic vibrations ?
(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor
(d) Shaded pole motor
Ans: c
59. 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
Ans: c
60. A reluctance motor
(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above
Ans: d

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 MCQ Electrical power (induction motors)

61. In a hysteresis motor, the rotor must have

(a) retentivity (b) resistivity
(c) susceptibility
(d) none of the above
Ans: a
62. The rotor of a hysteresis motor is made of
(a) aluminium
(b) cast iron
(c) chrome steel
(d) copper
Ans: c
63. The electric motor used in portable drills is
(a) capacitor run motor
(b) hysteresis motor
(c) universal motor
(d) repulsion motor
Ans: c
64. Which of the following applications always have some load whenever
switched on ?
(a) Vacuum cleaners
(b) Fan motors
(c) Pistol drills
(d) All of the above
Ans: c
65. 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
Ans: b

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 MCQ Electrical power (induction motors)

66. Torque developed by a single phase induction motor at starting is

(a) pulsating
(b) uniform
(c) none of the above
(d) nil
Ans: d
67. In split phase motor main winding is of
(a) thin wire placed at the top of the slots
(b) thin wire placed at the bottom of the slots
(c) thick wire placed at the bottom of the slots
(d) thick wire placed at the top of the" slots
Ans: c
68. In repulsion motor, maximum torque is developed when
(a) brush axis is at 45° electrical to the field axis
(b) brush axis coincides with the field axis
(c) brush axis is at 90° electrical to the field axis
(d) none of the above
Ans: a
69. If the centrifugal switch does not open at 70 to 80 percent of synchronous
speed of motor, it would result in
(a) damage to the starting winding
(b) damage to the centrifugal switch
(c) overloading of running winding
(d) none of the above
Ans: a
70. Speed torque characteristic of a repulsion induction motor is similar to
that of a D.C.
(a) shunt motor (b) series motor
(c) compound motor
(d) separately excited motor
Ans: c

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 MCQ Electrical power (induction motors)

71. In a ceilingfan employing capacitor run motor

(a) secondary winding surrounds the primary winding
(b) primary winding surrounds the secondary winding
(c) both are usual arrangements
(d) none of the above
Ans: a
72. The shaded pole motor is used for
(a) high starting torque
(b) low starting torque
(c) medium starting torque
(d) very high starting torque
Ans: b
73. The rotor slots, in an induction motor, are usually not quite parallel to the
shaft because it
(a) improves the efficiency
(b) helps the rotor teeth to remain under the stator teeth
(c) helps in reducing the tendency of the rotor teeth to remain under the
stator teeth
(d) improves the power factor
Ans: c
74. The speed/load characteristics of a universal motor is same as that of
(a) A.C. motor (b) D.C. shunt motor
(c) D.C. series motor
(d) none of the above
Ans: c
75. The purpose of stator winding in the compensated repulsion motor is to
(a) provide mechanical balance
(b) improve power factor and provide better speed regulation
(c) prevent hunting in the motor
(d) eliminate armature reaction
Ans: b

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 MCQ Electrical power (induction motors)

76. Which of the following motors is used for unity power factor ?
(a) Hysteresis motor (b) Schrage motor
(c) Universal motor (d) Reluctance motor
Ans: b
77. The motor used for the compressors is
(a) d.c. series motor
(b) shaded pole motor
(c) capacitor-start capacitor-run motor
(d) reluctance motor
Ans: c
78. Which of the following motors is used in a situation where load increases
with speed ?
(a) Induction motor
(b) Three-phase series motor
(c) Schrage motor
(d) Hysteresis motor
Ans: b
79. In repulsion motor, zero torque is developed when
(a) brush axis is 45° electrical to field axis
(b) brush axis coincides with the field axis
(c) brush axis is 90° electrical to field axis
(d) both (b) and (c)
Ans: d
80. Centrifugal switch disconnects the auxiliary winding of the motor at about
percent of synchronous speed
(a) 30 to 40
(b) 70 to 80
(c) 80 to 90
(d) 100
Ans: b

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 MCQ Electrical power (induction motors)

81. Starting winding of a single phase motor of a refrigerator is disconnected

from the circuit by means of a
(a) magnetic relay
(b) thermal relay
(c) centrifugal switch
(d) none of the above
Ans: a
82. If a single phase induction motor runs slower than normal, the most likely
defect is
(a) worn bearings
(b) short-circuit in the winding
(c) open-circuit in the winding
(d) none of the above
Ans: a
83. Which of the following motors is used in tape-recorders ?
(a) Hysteresis motor
(b) Reluctance motor
(c) Capacitor-run motor
(d) Universal motor
Ans: a
84. Which of the following statements regarding two value capacitor motor is
incorrect ?
(a) It is a reversing motor
(b) It is preferred to permanent-split single-value capacitor motor where
frequent reversals are required
(c) It has low starting as well as rush¬ing currents
(d) It has high starting torque
Ans: b

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 MCQ Electrical power (induction motors)

85. Two-value capacitor motor finds increased application as compressor

motor in small home air-conditioners because
(a) it is comparatively cheaper
(b) it has almost non-destructible capacitor
(c) it has low starting as well as running currents at relatively high power
factor
(d) it is quiet in operation
Ans: c
86. If the centrifugal switch of a two-value capacitor motor using two
capacitors fails to open then
(a) motor will not come upto speed
(b) motor will not carry the load
(c) current drawn by the motor will be excessively high
(d) electrolytic capacitor will, in all probability, suffer break down
Ans: d
87. In a universal motor, the most common cause of brush sparking is
(a) open armature winding
(b) shorted armature winding
(c) shorted field winding"
(d) high commutator mica
(e) all of the above
Ans: e
88. If starting winding of a single-phase induction motor is left in the circuit, it
will
(a) run faster
(b) spark at light loads
(c) draw excessive current and overheat
(d) run slower
Ans: c

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 MCQ Electrical power (induction motors)

89. Most of the fractional horsepower motors have either

(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearings
(d) plain or sleeve bearings
Ans: d
90. Which of the following statements regarding reluctance-start motor is
incorrect ?
(a) It is similar to reluctance motor
(b) It is basically an induction motor and not a synchronous one
(c) So far as its basic working principle is concerned, it is similar to shaded pole motor
(d) the air-gap between rotor and salient poles is non- uniform
Ans: a
91. To reverse the direction of rotation of acapacitor start motor while it is
running we should
(a) disconnect motor from the supply till it stops then reconnect it to supply
with reversed connection of main or auxiliary winding
(b) disconnect motor from supply and immediately reconnect it to supply
with reversed connections of the main winding
(c) reverse the direction of connection of the auxiliary winding and after
motor comes to rest then connect auxiliary winding to the supply
(d) reverse the direction of connections of the auxiliary winding and im-
mediately connect it to supply
Ans: a
92. In case of a reluctance motor, when the load is increased so that it cannot
maintain synchronous speed the motor will
(a) become unstable
(b) draw excessive armature current and may burn out
(c) fall out of synchronism and come to stand still
(d) run as induction motor
Ans: d

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 MCQ Electrical power (induction motors)

93. Which of the following motors has two separate windings on the motor ?
(a) Repulsion motor
(b) Repulsion induction motor
(c) Repulsion start induction run motor
(d) None of the above
Ans: b
94. A shaded pole motor does not possess
(a) centrifugal switch
(b) capacitor
(c) commutator
(d) all of the above
Ans: d
95. In a A.C. series motor armature coils are usually connected to commutator
(a) through resistance (b) through reactances
(c) through capacitors (d)solidly
Ans: a
96. Which of the following statements regarding a reluctance motor is
incorrect ?
(a) It cannot be reversed, ordinarily
(b) It requires no D.C. field excitation for its operation
(c) It is nothing else but a single-phase, salient pole synchronous-induction motor
(d) Its squirrel cage-rotor is of unsym-metrical magnetic construction in order
to vary reluctance path bet¬ween stator and rotor
Ans: a
97. A universal motor is one which
(a) can be operated either on D.C. or A.C. supply at approximately the same
speed and output
(b) can be marketed internationally
(c) runs at dangerously high speed on no-load
Ans: a

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 MCQ Electrical power (induction motors)

98. A repulsion motor is equipped with

(a) slip rings
(b) commutator
(c) both (a) and (b)
(d) none of the above
Ans: b
99. The capacitors used in single-phase capacitor motors have no
(a) voltage rating (b) dielectric medium
(c) polarity marking (d) definite value
Ans: c
100. If a D.C. series motor is operated on A.C. supply, it will
(a) spark excessively
(b) have poor efficiency
(c) have poor power factor
(d) all of the above
Ans: d
101. After the starting winding of a single phase induction motor is
disconnected from supply, it continues to run only on
(a) running winding
(b) rotor winding
(c) field winding
(d) compensating winding
Ans: a
102. Which of the following statements regarding repulsion-start induction
motor is incorrect ?
(a) It requires more maintenance of commutator and other mechanical devices
(b) It makes quite a bit of noise on starting
(c) In fractional horse power motors, it has replaced the capacitor motors
(d) It is not easily reversed
Ans: c

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 MCQ Electrical power (induction motors)

103. A.C. series motor as compared to D.C. series motor has

(a) smaller brush width
(b) less number of field turns
(c) more number of armature turns
(d) less air gap
(e) all of the above
Ans: e
104. Locked rotor current of a shaded pole motor is
(a) equal to full load current
(b) less than full load current
(c) slightly more than full load current
(d) several times the full load current
Ans: c
105. Speed control of a universal motor is achieved by
(a) varying field flux with tapped field windings
(b) connecting rheostat in series
(c) applying variable voltage by means of silicon controlled rectifier
(d) applying variable voltage by means of variable auto-transformer
(e) all of the above methods
Ans: e
106. Hysteresis motor is particularly useful for high-quality record players and
tape- recorders because
(a) it revolves synchronously
(b) it is not subject to any magnetic or mechanical vibrations
(c) it can be easily manufactured in extremely small sizes of upto 1 W output
(d) it develops hysteresis torque which is extremely steady both in amplitude
and phase
Ans: d

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 MCQ Electrical power (induction motors)

107. Which of the following statements regarding hysteresis motor is in

incorrect ?
(a) It is extremely sensitive to fluctuations in supply voltage
(b) Its high starting torque is due to its high rotor hysteresis loss
(c) It is extremely quiet in operation
(d) It accelerates from rest to full-speed almost instantaneously
Ans: a
108. Which of the following statements regarding single-phase induction
motoris correct ?
(a) It requires only one winding
(b) It can rotate in one direction only
(c) It is self-starting
(d) It is not self-starting
Ans: d
109. The starting winding of a single-phase motor is placed in
(a) armature
(b) field
(c) rotor
(d) stator
Ans: d
110. The speed of a universal motor is usually reduced by using
(a) gearing
(b) belts
(c) brakes
(d) chains
Ans: a

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