MCQ on single phase motor 120-140

120. 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

121. 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 immediately connect it to supply

122. 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✔

123. 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

124. A shaded pole motor does not possess
(a) centrifugal switch
(b) capacitor
(c) commutator
(d) all of the above✔

125. In a A.C. series motor armature coils are usually connected to commutator
(a) through resistance✔
(b) through reactances
(c) through capacitors
(d) solidly

126. 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 between stator and rotor

127. 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

128. A repulsion motor is equipped with
(a) slip rings
(b) commutator✔
(c) both (a) and (b)
(d) none of the above

129. The capacitors used in single-phase capacitor motors have no
(a) voltage rating
(b) dielectric medium
(c) polarity marking✔
(d) definite value

130. 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✔

131. 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

132. 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

133. 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✔

134. 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 curren✔
(d) several times the full load current

135. 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✔

136. 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 up to 1 W output
(d) it develops hysteresis torque which is extremely steady both in amplitude and phase✔

137. 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

138. 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✔

139. The starting winding of a single-phase motor is placed in
(a) armature
(b) field
(c) rotor
(d) stator✔

140. The speed of a universal motor is usually reduced by using
(a) gearing✔
(b) belts
(c) brakes
(d) chains

MCQ on single phase motor101-119

101. 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

102. The shaded pole motor is used for
(a) high starting torque
(b) low starting torque✔
(c) medium starting torque
(d) very high starting torque

103. 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

104. 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

105. 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

106. Which of the following motors is used for unity power factor ?
(a) Hysteresis motor
(b) Schrage motor✔
(c) Universal motor
(d) Reluctance motor

107. 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

108. 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

109. 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)✔

110. 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

111. 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

112. 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

113. Which of the following motors is used in tape-recorders ?
(a) Hysteresis motor✔
(b) Reluctance motor
(c) Capacitor-run motor
(d) Universal motor

114. 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 rushing currents
(d) It has high starting torque

115. 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

116. If the centrifugal switch of a two-value capacitor motor using two capacitors fails to open then
(a) motor will not come up to 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✔

117. 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✔

118. 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

119. Most of the fractional horsepower motors have either
(a) hard and annealed bearings
(b) ball or roller bearings
(c) soft and porous bearing
(d) plain and sleeve bearing✔

MCQ on single phase motor 81-100

81. 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

82. 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✔

83. The speed of a universal motor is generally reduced by using
(a) gear trains✔
(b) V-belts
(c) brakes
(d) chains

84. 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✔

85. 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

86. 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

87. 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

88. Which motor is normally free from mechanical and magnetic vibrations ?
(a) Split phase motor
(b) Universal motor
(c) Hysteresis motor✔
(d) Shaded pole motor

89. 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

90. A reluctance motor
(a) is self-starting
(b) is constant speed motor
(c) needs no D.C. excitation
(d) all of the above✔

91. In a hysteresis motor, the rotor must have
(a) retentivity✔
(b) resistivity
(c) susceptibility
(d) none of the above

92. The rotor of a hysteresis motor is made of
(a) aluminium
(b) cast iron
(c) chrome steel✔
(d) copper

93. The electric motor used in portable drills is
(a) capacitor run motor
(b) hysteresis motor
(c) universal motor✔
(d) repulsion motor

94. 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

95. 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

96. Torque developed by a single phase induction motor at starting is
(a) pulsating
(b) uniform
(c) none of the above
(d) nil✔

97. 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

98. 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

99. 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

100. 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

MCQ on single phase motor 61 to 80

61. For which of the applications a reluctance motor is preferred ?
(a) Electric shavers
(b) Refrigerators
(c) Signalling and timing devices✔
(d) Lifts and hoists

62. 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

63. 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

64. 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

65. A schrage motor can run on
(a) zero slip
(b) negative slip
(c) positive slip
(d) all of the above✔

66. 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

67. 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

68. 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

69. In split-phase motor auxiliary 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

70. 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✔

71. In a two value capacitor motor, the capacitor used for running purposes is
(a) air capacitor
(b) paper spaced oil filled type✔
(c) ceramic type
(d) a.c. electrolytic type

72. 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

73. 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

74. 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

75. Which of the following motors has highest starting torque ?
(a) Repulsion motor
(b) Shaped pole motor
(c) Capacitor-start motor✔
(d) Split-phase motor

76. The repulsion-start induction-run motor is used because of
(a) good power factor
(b) high efficiency
(c) minimum cost
(d) high starting torque✔

77. 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

78. 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✔

79. 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

80. 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

MCQ on single phase motor 49-60

49. Which of the following motors is used in mixies ?
(a) Repulsion motor
(b) Reluctance motor
(c) Hysteresis motor
(d) Universal motor✔

50. Which of the following motors is inherently self starting ?
(a) Split motor
(b) Shaded-pole motor✔
(c) Reluctance motor
(d) None of these

51. 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

52. Burning out of winding is due to
(a) short circuited capacitor✔
(b) capacitor value hiving changed
(c) open circuiting of capacitor
(d) none of the above

53. 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)

54. Short-circuiter is used in
(a) repulsion induction motor
(b) repulsion motor
(c) repulsion start induction run motor✔
(d) none of the above

55. 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%✔

56. 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✔

57. The power factor of a single-phase induction motor is usually
(a) lagging✔
(b) always leading
(c) unity
(d) unity to 0.8 leading

58. A shaded pole motor can be used for
(a) toys
(b) hair dryers
(c) circulators
(d) any of the above✔

59. A hysteresis motor works on the principle of
(a) hysteresis loss✔
(b) magnetisation of rotor
(c) eddy current loss
(d) electromagnetic induction

60. 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

MCQ on Single Phase Motor 19-48

19. A capacitor start single phase induction motor will usually have a power factor of
(A) unity
(B) 0.8 leading
(C) 0.6 leading
(D) 0.6 lagging.✔

20. A capacitor start, capacitor run single phase induction motor is basically a
(A) ac series motor
(B) dc series motor
(C) 2 phase induction motor✔
(D) 3 phase induction motor.

21. The starting torque of a capacitor start motor is
(A) zero
(B) low✔
(C) same as rated torque
(D) more than rated torque.

22. The torque developed by a split phase motor is proportional to
(A) Sine of angle between lm and ls✔
(B) Cosine of angle between lm and Is
(C) Main winding current, Im
(D) Auxiliary winding current,Is

23. A capacitor start single phase induction motor is switched on the supply with its capacitor replaced by an inductor of equivalent reactance value. It will
(A) not start✔
(B) start and run
(C) start and then stall
(D) none of the above.

24. The starting capacitor of a single phase motor is
(A) Electrolytic capacitor✔
(B) Ceramic capacitor
(C) Paper capacitor
(D) None of the above.

25. Which of the following is the most economical method of starting a single phase motor ?
(A) Resistance start method
(B) Inductance start method
(C) Capacitance start method✔
(D) Split-phase method.

26. The number of turns in the starting winding of a capacitor start motor as compared to that for split phase motor is
(A) same
(B) more✔
(C) less
(D) none of the above.

27. In a split phase motor, the ratio of number of turns for starting winding to that for running winding is
(A) 2.0
(B) more than 1
(C) 1.0
(D) less than 1.✔

28. A single phase motor generally used for small air compressor is
(A) capacitor start capacitor run motor✔
(B) reluctance motor
(C) universal motor
(D) shaded pole motor.

29. Out of the following motors, which will give the highest starting torque ?
(A) Universal motor
(B) Capacitor start motor✔
(C) Shaded pole motor
(D) All have zero starting torque.

30. Which single phase ac motor will you select for record players and tape recorders ?
(A) Hysteresis motor✔
(B) Shaded pole motor
(C) Reluctance motor
(D) Two value capacitor motor.

31. A universal motor is one
(A) which can run on any value of supply voltage
(B) which has infinitely varying speed
(C) which can operate on ac as well as dc voltage✔
(D) which can work as single phase or three phase motor.

32. Under normal operating conditions which motor can run at 5000 rpm ?
(A) Synchronous motor
(B) Induction motor
(C) Universal motor✔
(D) No motor can give 5000 rpm.

33.The motor used in household refrigerator is
(A) dc series motor
(B) dc shunt motor
(C) universal motor
(D) single phase induction motor.✔

34. The direction of rotation of universal motor can be reversed by
(A) reversing the supply terminals
(B) switching over from ac to dc
(C) interchanging the brush leads✔
(D) any of the above.

35. A universal motor operates on
(A) constant speed and varying load
(B) constant load and varying speed
(C) approximately constant speed and load✔
(D) synchronous speed with varying load.

36. Which of the following single phase motors will operate at high power factor ?
(A) shaded pole motor
(B) capacitor run motor✔
(C) split phase motor
(D) capacitor start motor.

37. A motor suitable for signaling device is
(A) induction motor
(B) dc shunt motor
(C) dc series motor
(D) reluctance motors.✔

38. Which capacitor is preferred in case of single phase motor
(A) Paper capacitor
(B) Ceramic capacitor
(C) Mica capacitor
(D) Electrolytic capacitor.✔

39. The motor used for driving the record player deck is
(A) dc series motor
(B) synchronous motor
(C) hysteresis motor✔
(D) dc shunt motor.

40. When a motor speed of 5000 rpm is required, which motor will you select ?
(A) Capacitor start motor
(B) Shaded pole motor
(C) Hysteresis motor
(D) Universal motor✔

41. As compared to other single phase ac motors a universal motor has
(A) speed ratio of 2: 1 on ac/dc
(B) highest efficiency on 50 Hz supply
(C) high horse power/kg ratio✔
(D) all of the above.

42. When a universal motor is operated on no load, its speed is limited by
(A) armature reaction
(B) armature weight
(C) windage and friction✔
(D) supply voltage frequency.

43. Which of the following applications make use of a universal motor ?
(A) Floor polishing machine
(B) Oil expeller
(C) Portable tools✔
(D) Lathe machines.

44. In portable tools the speed of the driven shaft is reduced by
(A) Gearing✔
(B) Belt drive
(C) Chain drive
(D) Fluid drive

45. For ceiling fans generally the single phase motor used is
(A) split phase type
(B) capacitor start type
(C) capacitor start and run type
(D) permanent capacitor type.✔

46. In case of split phase motors the phase shift is usually limited to
(A) 3 degrees✔
(B) 60 degrees
(C) 90 degrees
(D) 150 degrees.

47. The capacitance of a small single phase motor will be of the order of
(A) Kilo farads
(B) Few hundred farads
(C) Farads
(D) Micro or pico farads.✔

48. the single Ф motor commercially Manufactured up to
(a) 1HP
(b) 2 HP✔
(c) 5 HP
(c) 10HP

MCQ on Single Phase Motor 1 - 18

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

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.

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) 10°
(b) 30°
(c) 60°
(d) 90°✔

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 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✔

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

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

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

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✔

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

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

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

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

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

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✔

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
(d) All of above✔

Basic electrical Mcq 101-120

101. If/, R and t are the current, resistance and time respectively, then according to Joule’s law heat produced will be proportional to
(a) I2Rt✔
(b) I2Rf
(c) I2R2t
(d) I2R2t*

102. Nichrome wire is an alloy of
(a) lead and zinc
(b) chromium and vanadium
(c) nickel and chromium✔
(d) copper and silver

103. When a voltage of one volt is applied, a circuit allows one micro ampere current to flow through it. The conductance of the circuit is
(a) 1 n-mho✔
(b) 106 mho
(c) 1 milli-mho
(d) none of the above

104. Which of the following can have negative temperature coefficient ?
(a) Compounds of silver
(6) Liquid metals
(c) Metallic alloys
(d) Electrolytes✔

105. Conductance : mho ::
(a) resistance : ohm✔
(b) capacitance : henry
(c) inductance : farad
(d) lumen : steradian

106. 1 angstrom is equal to
(a) 10-8 mm
(6) 10″6 cm
(c) 10″10 m✔
(d) 10~14 m

107. One newton meter is same as
(a) one watt
(b) one joule✔
(c) five joules
(d) one joule second

108. Active materials of a lead-acid cell are :
(a) lead peroxide
(b) sponge lead
(c) dilute sulphuric acid
(d) all the above✔

109. During the charging of a lead-acid cell :
(a) its cathode becomes dark chocolate brown in colour
(b) its voltage increases✔
(c) it gives out energy
(d) specific gravity of H2SO4 is decreased

110. The ratio of Ah efficiency to Wh efficiency of a lead-acid cell is :
(a) always less than one
(b) just one
(c) always greater than one✔
(d) either (a) or (b)

111. The capacity of a cell is measured in :
(a) watt-hours
(b) watts
(c) amperes
(d) ampere-hours✔

112. The capacity of a lead-acid cell does NOT depend on its :

(a) rate of charge✔
(b) rate of discharge
(c) temperature
(d) quantity of active material

113. As compared to constant-current system, the constant-voltage system of charging a lead-acid cell has the advantage of :
(a) avoiding excessive gassing
(b) reducing time of charging
(c) increasing cell capacity
(d) both (b) and (c)✔

114. Sulphation in a lead-acid battery occurs due to :
(a) trickle charging
(b) incomplete charging✔
(c) heavy discharging
(d) fast charging

115. The active materials of a nickel-iron battery are :
(a) nickel hydroxide
(b) powdered iron and its oxides
(c) 21% solution of caustic potash
(d) all of the above✔

116. During the charging and discharging of a nickel
iron cell :
(a) its e.m.f. remains constant
(b) water is neither formed nor absorbed✔
(c) corrosive fumes are produced
(d) nickel hydroxide remains unspoilt

117. As compared to a lead-acid cell, the efficiency of a nickel-iron cell is less due to its :
(a) lower e.m.f.
(b) smaller quantity of electrolyte used
(c) higher internal resistance✔
(d) compactness

118. The period of a wave is :
(a) the same as frequency
(b) time required to complete one cycle✔
(c) expressed in amperes
(d) none of the above

119. The form factor is the ratio of :
(a) peak value to r.m.s. value
(b) r.m.s. value to average value✔
(c) average value to r.m.s. value
(d) none of the above

120. The r.m.s. value and mean value is the same in the case of :
(a) triangular wave
(b) sine wave
(c) square wave✔
(d) half wave rectified sine wave

Basic electrical mcq 81-100

81. Three 6 ohm resistors are connected to form a triangle. What is the resistance between any two corners ?
(a) 3/2 Q
(b 6 Q
(c) 4 Q✔
(d) 8/3 Q

82. Ohm’s law is not applicable to
(a) semi-conductors✔
(b) D.C. circuits
(c) small resistors
(d) high currents

83. Two copper conductors have equal length. The cross-sectional area of one conductor is four times that of the other. If the conductor having smaller cross-sectional area has a resistance of 40 ohms the resistance of other conductor will be
(a) 160 ohms
(b) 80 ohms
(c) 20 ohms
(d) 10 ohms✔

84. A nichrome wire used as a heater coil has the resistance of 2 £2/m. For a heater of 1 kW at 200 V, the length of wire required will be
(a) 80 m✔
(b) 60 m
(c) 40 m
(d) 20 m

85. Temperature co-efficient of resistance is expressed in terms of
(a) ohms/°C
(b) mhos/ohm°C
(e) ohms/ohm°C✔
(d) mhos/°C

86. Which of the following materials has the least resistivity ?
(a) Zinc
(b) Lead
(c) Mercury
(d) Copper✔

87. When current flows through heater coil it glows but supply wiring does not glow because
(a) current through supply line flows at slower speed
(b) supply wiring is covered with insulation layer
(c) resistance of heater coil is more than the supply wires✔
(d) supply wires are made of superior material

88. The condition for the validity under Ohm’s law is that
(a) resistance must be uniform✔
(b) current should be proportional to the size of the resistance
(c) resistance must be wire wound type
(d) temperature at positive end should be more than the temperature at negative end

89. Which of the following statement is correct ?
(a) A semi-conductor is a material whose conductivity is same as between that of a conductor and an insulator✔
(b) A semi-conductor is a material which has conductivity having average value of conductivity of metal and insulator
(c) A semi-conductor is one which con¬ducts only half of the applied voltage
(d) A semi-conductor is a material made of alternate layers of conducting material and insulator

90. A rheostat differs from potentiometer in the respect that it
(a) has lower wattage rating
(b) has higher wattage rating✔
(c) has large number of turns
(d) offers large number of tapping

91. The weight of an aluminium conductor as compared to a copper conductor of identical cross-section, for the same electrical resistance, is
(a) 50%✔
(b) 60%
(c) 100%
(d) 150%

92. An open resistor, when checked with an ohm-meter reads
(a) zero
(b) infinite✔
(c) high but within tolerance
(d) low but not zero

93. are the materials having electrical conductivity much less than most of the metals but much greater than that of typical insulators.
(a) Varistors
(b) Thermistor
(c) Semi-conductors✔
(d) Variable resistors

94. All good conductors have high
(a) conductance✔
(b) resistance
(c) reluctance
(d) thermal conductivity

95. Voltage dependent resistors are usually made from
(a) charcoal
(b) silicon carbide
(c) nichrome✔
(d) graphite

96. Voltage dependent resistors are used
(a) for inductive circuits
(6) to supress surges✔
(c) as heating elements
(d) as current stabilizers

97. The ratio of mass of proton to that of electron is nearly
(a) 1840✔
(b) 1840
(c) 30
(d) 4

98. The number of electrons in the outer most orbit of carbon atom is
(a) 3
(b) 4✔
(c) 6
(d) 7

99. With three resistances connected in parallel, if each dissipates 20 W the total power supplied by the voltage source equals
(a) 10 W
(b) 20 W
(c) 40 W
(d) 60 W✔

100. A thermistor has
(a) positive temperature coefficient
(b) negative temperature coefficient
(c) zero temperature coefficient
(d) variable temperature coefficient✔