Electrical and Electronics Engineering Multiple Choice Questions EEE
1. With the increase in the speed of a dc motor:
A. both back emf as well as line current increases
B. both back emf and line current falls
C. back emf increases but the line current falls
D. back emf falls and line current increases
Answer: C.back emf increases but the line current falls
2. The output indicated on the name plate of any motor is always the:
A. gross power
B. power drawn in volt amperes
C. power drawn in watts
D. output power at the shaft
Answer: D.output power at the shaft
3. The direction of rotation of dc shunt motor can be reversed by interchanging:
A. the supply terminals
B. the field terminals
C. the armature terminals only
D. either field or armature terminals
Answer: D.either field or armature terminals
4. The output power of any electrical motor is taken from the:
A. armature
B. field
C. coupling mounted on the shaft
D. motor frame
Answer: C.coupling mounted on the shaft
5. If the back emf in a dc motor varnishes suddenly, then the motor:
A. run at very high speeds
B. start hunting
C. burn
D. come to stall
Answer: C.burn
6. The direction of the armature current in a dc motor is:
A. the same as the generated emf
B. opposite to that of generated emf
C. not dependent upon the direction of the armature emf
D. none of the above
Answer: B.opposite to that of generated emf
7. When a dc machine is connected to the dc supply main it will produce:
A. emf in opposition to the applied voltage
B. emf in phase with the applied voltage
C. emf decreases with time
D. none of the above
Answer: A.emf in opposition to the applied voltage
8. The direction of rotation of a dc motor can be determined by:
A. fleming\s right hand rule
B. fleming\s left hand rule
C. lenz\s law
D. ampere\s law
Answer: B.fleming\s left hand rule
9. A thick wire is used in dc series motor field winding than that in dc shunt motor:
A. to create more flux
B. to reduce the resistance
C. to carry large load current
D. both (b) and ©
Answer: D.both (b) and ©
10. An electrical train employing a dc series motor is running at the fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in:
A. drop in the speed and rise in the current
B. rise in the speed and drop in the current
C. rise in the speed and rise in the current
D. drop in speed with current unaltered
Answer: A.drop in the speed and rise in the current
11. A DC shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will:
A. remains unchanged
B. increases
C. decreases
D. be zero
Answer: C.decreases
12. A DC series motor is best suited for electrical traction because:
A. it develops high starting torque
B. it runs at very high speed
C. it is cheaper in cost
D. it is more rugged in construction like induction motor
Answer: A.it develops high starting torque
13. Which of the following dc motor has maximum self relieving property:
A. shunt
B. series
C. cumulative compound
D. differential compound
Answer: B.series
14. When the direction of power flow in a differential compounded motor reverses, it will operate as a:
A. cumulative compound generator
B. differential compound generator
C. series motor
D. shunt motor
Answer: A.cumulative compound generator
15. A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be:
A. level compound
B. differential compound
C. cumulative compound
D. none of the above
Answer: C.cumulative compound
16. The output voltage of a DC generator is
A. e = v + iara
B. e = v – iara
C. e = v + ia
D. e = v + ra
Answer: A.e = v + iara
17. The material used for commutator brushes is mostly
A. copper
B. carbon
C. mica
D. cast iron
Answer: B.carbon
18. A 4 pole DC generator rotates at 1500 rpm. How many times in a second, will the emf induced in each armature conductor changes its direction?
A. 750
B. 100
C. 500
D. 200
Answer: B.100
19. Magnetic field of a DC generator is produced by what?
A. permanent magnets
B. electromagnets
C. both option b & c
D. none of the options
Answer: B.electromagnets
20. In a DC generator the emf generated by the armature is maximum when
A. rate of change of flux is maximum
B. rate of change of flux is minimum
C. induced voltage is high
D. shaft rotation is high
Answer: A.rate of change of flux is maximum
21. What is the actual arrangement of series wound generator?
A. armature and field both are parallel
B. armature and field both are connected
C. increase the speed of shaft rotation
D. armature and field both are in series with the load
Answer: D.armature and field both are in series with the load
22. What is the effect of armature reaction?
A. armature flux weakens the main field flux
B. armature flux distorts the main field flux
C. both option b & a
D. none of the options
Answer: C.both option b & a
23. In DC machine, brushes are always placed along
A. magnetic neutral axis
B. geometrical neutral axis
C. armature axis
D. load axis
Answer: A.magnetic neutral axis
24. What type of connection is made in between the interpole & the field winding?
A. series
B. parallel
C. compound
D. none of the options
Answer: B.parallel
25. In DC machine, lap winding is used in
A. high current and low voltage applications
B. high voltage and low current applications
C. where constant speed is required
D. where greater load is connected
Answer: A.high current and low voltage applications
26. The basic requirement of a dc armature winding is that it must be
A. a closed one
B. a lap winding
C. a wave winding
D. either b or c
Answer: A.a closed one
27. The sole purpose of a commutator in a dc generator is to
A. increase output voltage
B. reduce sparking at brushes
C. provide smoother output
D. convert the induced ac into dc
Answer: D.convert the induced ac into dc
28. In a dc generator, the generator, the generated emf is directly proportional to the
A. field current
B. pole flux
C. number of armature parallel paths
D. number of dummy coils
Answer: B.pole flux
29. Voltage equation of a dc motor is
A. v = eb + iara
B. eb = v + iara
C. v = eb/iara
D. v = eb + ia2ra
Answer: A.v = eb + iara
30. which of the following motor has the constant speed?
A. series motor
B. shunt motor
C. cumulatively compound motor
D. all of the above
Answer: B.shunt motor
31. The usual test to find the efficiency of the traction motor is
A. field\s test
B. retardation test
C. hopkinson\s test
D. swinburn\s test
Answer: A.field\s test
32. A DC series motor is best for driving
A. lathes
B. cranes and hoists
C. shears and punches
D. machine tools
Answer: B.cranes and hoists
33. In a DC series motor increasing the load current will
A. decrease the speed
B. increase the speed
C. better commutation
D. increase the back emf
Answer: A.decrease the speed
34. The DC motor, which can provide zero speed regulation at full load without any controller is
A. series
B. shunt
C. cumulative compound
D. differential compound
Answer: B.shunt
35. In 8 – pole wave connected motor armature, the number of parallel paths are
A. 8
B. 4
C. 2
D. 1
Answer: C.2
36. The speed of a dc motor can be controlled by varying
A. its flux per pole
B. resistance of armature circuit
C. applied voltage
D. all of the above
Answer: D.all of the above
37. The d.c. series motor should always be started with load because
A. at no load, it will rotate at dangerously high speed.
B. it will fail to start.
C. it will not develop high starting torque.
D. all are true.
Answer: A.at no load, it will rotate at dangerously high speed.
38. In a d.c. machine, the armature mmf is
A. stationary w.r.t. armature.
B. rotating w.r.t. field.
C. stationary w.r.t. field.
D. rotating w.r.t. brushes.
Answer: C.stationary w.r.t. field.
39. In a DC motor, unidirectional torque is produced with the help of
A. brushes
B. commutator
C. end-plates
D. both a and b
Answer: D. both a and b
40. The counter emf of dc motor
A. often exceeds the supply voltage
B. aids the applied voltage
C. helps in energy conversion
D. regulates its armature voltage
Answer: C.helps in energy conversion
41. The Eb/V ratio of a dc motor is an indication of its
A. efficiency
B. speed regulation
C. starting torque
D. running torque
Answer: A.efficiency
42. The induced emf in the armature conductors of a dc motor is
A. sinusoidal
B. trapezoidal
C. rectangular
D. alternating
Answer: A.sinusoidal
43. A dc motor can be looked upon as dc generator with the power flow
A. reduced
B. reversed
C. increased
D. modified
Answer: B.reversed
44. The Ta/Ia graph of a dc series motor is a
A. parabola from no load to overload
B. straight line throughout
C. parabola throughout
D. parabola upto full load and a straight line at overloads
Answer: D.parabola upto full load and a straight line at overloads
45. When load is removed, …….motor will run at the highest speed.
A. shunt
B. cumulative – compound
C. differential compound
D. series
Answer: D.series
46. In Fleming’s right-hand rule, the thumb point towards
A. direction of flux
B. direction of induced e.m.f.
C. direction of motion of conductor, if fore finger points along the lines of flux
D. direction of motion of the conductor\ if fore finger point in the direction of generated e.m.f.
Answer: C.direction of motion of conductor, if fore finger points along the lines of flux
47. . The armature of a dc machine is made of____.
A. silicon steel
B. wrought iron
C. cast steel
D. soft iron
Answer: A.silicon steel
48. The yoke of a d.c. machine is made of ____.
A. silicon steel
B. soft iron
C. aluminum
D. cast steel
Answer: D.cast steel
49. . The coupling field electrical and mechanical systems of dc machine is____.
A. electric field
B. magnetic field
C. both electric and magnetic fields
D. mechanical field
Answer: B.magnetic field
50. The real working part of a dc machine is the ___.
A. commutator
B. field winding
C. armature winding
D. none of the above
Answer: C.armature winding
51. ____ dc machine are most common.
A. 2-pole
B. 4-pole
C. 6-pole
D. 8-pole
Answer: B.4-pole
52. The armature winding of a dc machine is place on rotor to_____.
A. save iron
B. reduce losses
C. improve commutation
D. reduce armature reaction
Answer: C.improve commutation
53. The yoke of a dc machine carries ____pole flux.
A. the
B. one-half of
C. two times the
D. none of the above
Answer: B.one-half of
54. A 4-pole dc machine has ____ magnetic circuits.
A. 2
B. 8
C. 4
D. none of above
Answer: C.4
55. The field structure of a dc machine uses ____.
A. salient pole arrangement
B. non-salient pole arrangement
C. both a and b
D. none of the above
Answer: A.salient pole arrangement
56. ____ together are called stray losses
A. copper and iron losses
B. iron and mechnical losses
C. field copper and iron losses
D. frictional and copper losses
Answer: B.iron and mechnical losses
57. The armature conductors of 6 pole, lap wound D.C. generator are divided into
A. 2 parallel paths
B. 4 parallel paths
C. 3 parallel paths
D. 6 parallel paths
Answer: D.6 parallel paths
58. A 30W, 300V D.C. shunt genrator has armature and field resistances of 0.05Ω and 100Ω respectively. What is generated e.m.f.?
A. 295.25v
B. 311.25v
C. 305.15v
D. none of the above
Answer: C.305.15v
59. The commutator of D.C. geenrator acts as ___
A. an amplifier
B. a rectifier
C. a load
D. none of the above
Answer: B.a rectifier
60. A 4 pole , lap wound D.C. shunt generator has an armature winding consisting of 220 turns each of 0.004Ω. The armature resistance is ___
A. 0.5Ω
B. 1Ω
C. 0.025Ω
D. 0.055Ω
Answer: D.0.055Ω
61. Wave wound genrators provide
A. less current but more voltage
B. more current but less voltage
C. more current but less voltage
D. none of the above
Answer: A.less current but more voltage
62. A D.C. motor is still used in industrial applications because it____.
A. is cheap
B. is simple in construction
C. provides fine speed control
D. none of the above
Answer: C.provides fine speed control
63. The field poles and armature of a D.C. machine are laminated to___.
A. reduce the weight of the machine
B. decrease the speed
C. reduce eddy currents
D. reduce armature reaction
Answer: C.reduce eddy currents
64. The value of back EMF in a DC motor is maximum at ____.
A. no load
B. full load
C. half of full load
D. none of the above
Answer: A.no load
65. The mechanical power developed in a dc motor is maximum when back emf (Eb) is equal to ——the applied voltage (V)
A. twice
B. half
C. one third
D. none of the above
Answer: B.half
66. When the speed of dc motor increases , its armature current —-
A. increases
B. decreases
C. remains constant
D. none of the above
Answer: B.decreases
67. The amount of back emf of a shunt motor will increase when
A. the load is increased
B. the field is weakened
C. the field is strengthened
D. none of the above
Answer: C.the field is strengthened
68. The speed of a dc motor is
A. directly propotional to flux per pole
B. inversely propotional to flux per pole
C. inversely propotional to applied voltage
D. none of the above
Answer: B.inversely propotional to flux per pole
69. The torque developed by a dc motor is directly propotional to—
A. flux per pole x armature current
B. armature resistance x applied voltage
C. armature resistancex armature current
D. none of the above
Answer: A.flux per pole x armature current
70. The shaft torque in a DC motor is less than total armature torque because of ____in the motor
A. cu losses
B. field losses
C. iron and friction lossees
D. none of the above
Answer: C.iron and friction lossees
71. In a DC motor the brushes shifted from the mechanical nuetral plane in a direction opposite to the rotation to _____.
A. decrease the speed
B. increase the speed
C. reduce sparking
D. produce flat characteristics
Answer: C.reduce sparking
72. The speed of a ____ motor is practically constant
A. cumulative compound
B. series
C. differential compound
D. shunt motor
Answer: D.shunt motor
73. ____ motor is a variable speed motor.
A. series
B. shunt
C. cumulatively compounded
D. differetial compounded
Answer: A.series
74. The most commonly used method of speed control of a DC motor is by varying ____.
A. voltage applied to a motor
B. field control
C. effective number of conductors in series
D. armature circuit resistance
Answer: B.field control
75. The running speed of a DC series motor is basically determined by _____.
A. field excitation
B. load
C. armature resistance
D. none of the above
Answer: B.load
76. ____ motor has the best speed regulation
A. series
B. cumulatively compounded
C. shunt
D. differentially compounded
Answer: C.shunt
77. The deciding factor in the selection of a dc motor for a particular application is its ____ characteristics
A. speed-torque
B. speed-armature current
C. torque-armature current
D. none of the above
Answer: A.speed-torque
78. A series motor will over speed when ____.
A. the load is increased
B. the field is opened
C. the armature circuit is opened
D. laod is removed
Answer: D.laod is removed
79. A cumulatively compounded motor does not run at dangerous speed at light loads because of the presence of ______.
A. shunt winding
B. series winding
C. interpoles
D. compensating windings
Answer: A.shunt winding
80. DC shunt motor are used in those applications where____ is required.
A. high statring torque
B. practically constant speed
C. high no load speed
D. variable speed
Answer: B.practically constant speed
81. DC series motor are used in those applications where ____ is required.
A. high statring torque
B. constant speed
C. low no load speed
D. none of the above
Answer: A.high statring torque
82. Cumulatively compounded motors are used where we require _____.
A. variable speed
B. poor speed regulation
C. sudden heavy loads for short duration
D. none of the above
Answer: C.sudden heavy loads for short duration
83. ____ motors never use belt- connected loads.
A. series
B. shunt
C. cumulatively compounded
D. differential compound
Answer: A.series
84. For 20% increase in current, the motor that will give the greastest increase in torque is ___ motor
A. shunt
B. series
C. cumulatively compounded
D. differnetially compounded
Answer: B.series
85. Each commutator segment is connected to armature conductor by means of ___
A. insulator
B. dielectric
C. copper lug
D. resistance wire
Answer: C.copper lug
86. In a 4 pole machine___
A. alternate poles are north and south
B. two north poles follow two south poles
C. in all there are north poles
D. in all there are south poles
Answer: A.alternate poles are north and south
87. If the applied voltage of dc motor is reduced to half with load torque doubled the armature current will be____
A. unaltered
B. zero
C. doubled
D. half
Answer: C.doubled
88. Back EMF of DC motor depends on
A. field flux
B. shape of conductor
C. type of sliprings
D. brush material
Answer: A.field flux
89. A DC motor develops torque of the 100Nm at 400 rpm, at 300 rpm a motor will develop torque of___.
A. 133nm
B. 100nm
C. 67nm
D. 180nm
Answer: B.100nm
90. A DC series motor is most suitable for _____.
A. cranes
B. pump
C. lathes
D. punch presses
Answer: A.cranes
91. ____ motor is most suitable for punch presses
A. shunt
B. series
C. differential compound
D. cumulative compound
Answer: D.cumulative compound
92. In a vaccum cleaner, we generally use ____ motor
A. shunt
B. cumulative – compound
C. series motor
D. differetial compounded
Answer: C.series motor
93. The most suitable motor for elevators is the ___ motor.
A. series
B. shunt
C. differential compound
D. cumulative compound
Answer: D.cumulative compound
94. The friction and windage losses in a DC motor depends upon ____.
A. speed
B. flux
C. armature current
D. field and armature resistance
Answer: A.speed
95. A motor takes a large starting currents because _____.
A. the armature resistance is high
B. back emf is low
C. shunt field is produce weak field
D. none of the above
Answer: B.back emf is low
96. Excessive sparking at the brushes may be caused due to _____.
A. dirt on the commutator
B. loose coupling
C. misalignment of machine
D. worn bearing
Answer: A.dirt on the commutator
97. A 440V shunt motor has an armature resistance of 0.8Ω field reistnace of 200Ω . Find the back emf when giving an output of 7.46kW at 85 % efficiency?
A. 222.4v
B. 425.8v
C. 312.6v
D. 392.7v
Answer: B.425.8v
98. A 250V DC shunt motor takes a total current of 20A. Resistance of shunt field winding is 200Ω and that of armature is 0.3Ω . What is the current in the armature?
A. 9.65a
B. 11.25a
C. 18.75a
D. 16.62a
Answer: C.18.75a
99. A 220V DC shunt motor takes a total current of 80A and runs at 800 rpm. Resistnace of a shunt field is 50Ω and that of armature 0.1Ω. The iron and friction losses amount to 1600W. What is the armture torque?
A. 212nm
B. 176nm
C. 192nm
D. 242nm
Answer: C.192nm
100. A 220V DC shunt motor takes a total current of 80A and runs at 800 rpm. Resistnace of a shunt field is 50Ω and that of armature 0.1Ω. The iron and friction losses amount to 1600W. What is the lost torque?
A. 11nm
B. 19nm
C. 22nm
D. 34nm
Answer: B.19nm
101. A 220V DC series motor is taking a current of 40A. Resistance of armature is 0.5Ω and series field is 0.25Ω. What is the voltage at the brushes?
A. 190v
B. 210v
C. 180v
D. none of the above
Answer: B.210v
102. A 220V DC series motor is taking a current of 40A. Resistance of armature is 0.5Ω and series field is 0.25Ω. What is the back emf?
A. 190v
B. 210v
C. 170v
D. none of the above
Answer: A.190v
103. A 220V series motor takes a current of 35A and runs at 500rpm. Armature resistance of 0.25Ω and series field resistance 0.3Ω. If iron and frictional losses amount of 600W, what is the armature torque?
A. 122.5nm
B. 118.5nm
C. 134nm
D. 117nm
Answer: C.134nm
104. A 220V series motor takes a current of 35A and runs at 500rpm. Armature resistance of 0.25Ω and series field resistance 0.3Ω. If iron and frictional losses amount of 600W, what is the shaft torque?
A. 134nm
B. 122.5nm
C. 117nm
D. none of the above
Answer: B.122.5nm
105. The armature torque of a DC motor running of 800rpm is 99.3Nm and shaft torque is 93.3Nm. The iron and friction losses are__.
A. 502w
B. 400w
C. 200w
D. 300w
Answer: A.502w
106. A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the speed of the motor___.
A. 200rpm
B. 225rpm
C. 175rpm
D. 250rpm
Answer: D.250rpm
107. A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the output power in H.P.
A. 14.08hp
B. 21.67hp
C. 9.48hp
D. 11.72hp
Answer: A.14.08hp
108. Which motor should not be used for centrifugal pumps?
A. shunt
B. series
C. cumulatively compound
D. differenctially compound
Answer: B.series
109. If the applied voltage to a DC machine is 230V, then back emf for maximum power developed is ___.
A. 200v
B. 230v
C. 115v
D. 460v
Answer: C.115v
110. A DC motor runs at 1725rpm at full load and 1775rpm at no load. The speed regulation is _____.
A. 0.047
B. 0.029
C. 0.076
D. 0.015
Answer: B.0.029
111. A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb. The armature resistance is 0.2Ω and contact drop per brush is 1V. What is the back emf?
A. 352v
B. 408v
C. 474v
D. 486v
Answer: D.486v
112. A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb. The armature resistance is 0.2Ω and contact drop per brush is 1V. What is the full load speed of the motor?
A. 675rpm
B. 522rpm
C. 484rpm
D. 576rpm
Answer: A.675rpm
113. The armature of a 4 pole shunt motor has a lap winding accomodated in 60 slots, each containing 20 conductors, if the useful flux per pole is 23mWb, the armature torque developed when the armature current is 50A is _____.
A. 176nm
B. 192nm
C. 256nm
D. 218nm
Answer: D.218nm
114. The resistance of the shunt field winding as compared to series field winding is ____.
A. less
B. more
C. the same
D. none of the above
Answer: B.more
115. The field winding of a machine designed for separate excitation is
A. of the shunt field type
B. of the series field type
C. either of the two
D. none of the above
Answer: A.of the shunt field type
116. A shunt motor runs at 500rpm on a 200V circuit. Its armature resistance is 0.5Ω and the current taken is 30A in addition to field current. What resistance must be placed in series with armature circuit to reduce to speed to 300 rpm; the current in armature remains same.
A. 4.24Ω
B. 3.78Ω
C. 6.74Ω
D. 2.47Ω
Answer: D.2.47Ω
117. A 200V DC series motor runs at 500rpm when taking a line current of 25A.The resistance of the armature is 0.3Ω and that of the series field is 0.5Ω. If current taken remains constant, calculate the resistance necessary to reduce the speed to 350rpm.
A. 2.16Ω
B. 3.42Ω
C. 1.56Ω
D. 4.83Ω
Answer: A.2.16Ω
118. In a DC compound machine,
A. shunt field winding plays dominent role
B. series field winding plays dominent role
C. either can play dominent role
D. both play equally dominent role
Answer: A.shunt field winding plays dominent role
119. A DC shunt motor is rotating at 267 rad/sec and developing 57.2Nm of torque. How many kilowatts of mechanical power are developed?
A. 9.8kw
B. 15.3kw
C. 17.8kw
D. 11.2kw
Answer: B.15.3kw
120. A 20HP DC motor has 89.3% efficiency at rated power. What are its total losses?
A. 1787w
B. 1232w
C. 2184w
D. 1572w
Answer: A.1787w
121. By flux control method of speed control of a dc shunt motor, we can obtain speeds.
A. above the normal speed only
B. below the normal speed only
C. above as well as below the normal speed
D. none of the above
Answer: A.above the normal speed only
122. By putting controller resistance in series with the armature of a DC motor, we can obtain speeds
A. above the normal speed only
B. below the normal speed only
C. above as well as below the normal speed
D. none of the above
Answer: B.below the normal speed only
123. Motor starters are essential for
A. accelerating the motor
B. starting the motor
C. avoiding excessive starting current
D. preventing fuse blowing
Answer: C.avoiding excessive starting current
124. The only disadvantage of field control method for controlling the speed of a dc shunt motor is that it
A. gives speeds lower than the normal speed
B. is wasteful
C. needs a large rheostat
D. adversely affects commutation
Answer: D.adversely affects commutation
125. When quick speed reversal is a consideration, the motor preffered is
A. synchronous motor
B. squirrel cage induction motor
C. wound rotor induction motor
D. dc motor
Answer: D.dc motor
126. The range of horse power of electric motor drives for rolling mills is of the order of
A. 1 to 10 hp
B. 15 to 25 hp
C. 50 to 100 hp
D. 100 to 500 hp
Answer: D.100 to 500 hp
127. Motors preferred for rolling mill drive is
A. dc motors
B. ac slip ring motors with speed control
C. any of the above
D. none of the above.
Answer: C. any of the above
128. Cumulatively compounded motors are used where we require _____.
A. light duty excavators
B. medium duty excavators
C. heavy duty excavators
D. all of the above
Answer: C. heavy duty excavators
129. Which type of motors are preferred in lifts?
A. a. dc compound motors.
B. b. dc series motors.
C. c. dc shunt motors.
D. d. none of the above.
Answer: A.a. dc compound motors.
130. In cloth washing machines and refrigerators which motors are preferred?
A. a. dc cumulative compound motors
B. b. slip ring im
C. c. stepper motor
D. d. universal motors
Answer: D.d. universal motors
131. In lathes, milling and grinding machines which motor will preferred?
A. a. dc shunt motors
B. b. cage induction motor
C. c. synchronous motor
D. d. either a or b
Answer: D.d. either a or b
132. In planners which of following motors are preferred?
A. a. dc shunt motor
B. b. dc compound motor
C. c. any of above
D. none
Answer: C.c. any of above
133. In iron and steel industry which motors are preferred?
A. a. induction motors
B. b. synchronous motors
C. c. dc shunt wound motors
D. d. pipe motors
Answer: C.c. dc shunt wound motors
134. A sinusoidal voltage of frequency 1 Hz is applied to the field of a d.c generator. The armature voltage will be
A. 1 hz square wave
B. 1 hz sine wave
C. d. c voltage
D. zero
Answer: B.1 hz sine wave
135. In wave winding, the number of parallel paths of armature winding is
A. p
B. 2
C. 4
D. p/2
Answer: B.2
136. The emf equation of dc generator is E=
A. Øp/nza
B. Øp60/nza
C. Øpa/60nz
D. Øpnz/60a
Answer: D.Øpnz/60a
137. If number of conductors in a dc generator is Z then total number of turns are
A. z
B. 2z
C. z/2
D. 4z
Answer: C.z/2
138. What is the flux in the armature core section of a dc machine if the air gap flux be ø Wb?
A. ø
B. 0.1 ø
C. 1.5 ø
D. ø /2
Answer: A.ø
139. The flux leakage coefficient in dc machine is usually
A. 0.6 to 0.8
B. 1.05
C. 1.2 to 1.3
D. 2 to 2.5
Answer: C.1.2 to 1.3
140. Armature resistance of a d.c. machine is about
A. 25
B. 200
C. 100
D. 0.1
Answer: D.0.1
141. The electrical equivalent of gross mechanical power developed in a dc motor is
A. vil
B. ebil
C. ebia
D. ebish
Answer: C.ebia
142. The armature torque is —— that of shaft torque
A. less than
B. same as
C. greater than
D. none of these
Answer: C.greater than
143. If the voltage equation of a dc motor is multiplied by —– on both sides, we get power equation of dc motor
A. ra
B. v
C. n
D. ia
Answer: D.ia
144. The torque equation of a dc motor is —
A. ta = 0.159Ø ia/2πpza
B. ta = 0.159Øia/2πza
C. ta = 0.159Øiaz/2πa
D. ta = 0.159Øiapz/a
Answer: D.ta = 0.159Øiapz/a
145. The speed of dc motor is highest on
A. no load
B. 70% of full load
C. 10% of full load
D. 100% of full load
Answer: A.no load
146. With given power rating for lower current and higher voltage rating of a d.c. machine, one should prefer_________.
A. lap winding
B. wave winding
C. none of these
D. any of these
Answer: B.wave winding
147. If the number of poles in a lap wound generator be doubled, then the generated e.m.f will_________.
A. become half
B. become double
C. increase to four times
D. remains constant
Answer: B.become double
148. The counter emf of dc motor__________
A. often exceeds the supply voltage
B. aids the applied voltage
C. helps in energy conversion
D. regulates its armature voltage
Answer: C.helps in energy conversion
149. In a DC series motor increasing the load current will
A. decrese the speed
B. increase the speed
C. better commutation
D. increase the back emf
Answer: A.decrese the speed
150. The generator works on the principle of
A. statically induced emf
B. dynamically induced emf
C. mutul induction
D. kirchhoff\s law
Answer: B.dynamically induced emf
151. Air ducts are provided in armature core to
A. increase the core area
B. cool the armature
C. to accommodate the windins
D. none of these
Answer: B.cool the armature
152. Due to which of the following reasons, copper brushes in D.C. machine are used?
A. when high voltage and small currents are involved
B. when low voltage and high currents are involved
C. in both of the above cases
D. in none of the above cases
Answer: C.in both of the above cases
153. The magnitude of induced emf in a dc generator is given by
A. blv
B. bil
C. bv/l
D. bi/l
Answer: A.blv
154. In a dc generator, the eddy current power loss is
A. directly proportional to thickness of each lamination
B. inversely proportional to thickness of each lamination
C. directly proportional to square of thickness of each lamination
D. none of the above
Answer: A.directly proportional to thickness of each lamination
155. In a 240v dc motor, back emf is 220v and Ra= 0.5Ω then its armature current is
A. 20a
B. 10a
C. 80a
D. 40a
Answer: D.40a
156. —– is the power equation of dc motor
A. via = ebia + ia2 ra
B. via = ebia + ia ra2
C. vn = eb n + nia ra
D. via = eb2ia + ia2 ra
Answer: A.via = ebia + ia2 ra
157. A 4 pole 1500 rpm,dc generator has a lap wound armature having 24 slots with 10 conductors/slot.If flux/pole is 0.04Wb then emf generator in armature is —–V
A. 480v
B. 240v
C. 960v
D. 120v
Answer: B.240v
158. A 8 pole dc generator has a lap wound armature having 400 armature turns. If flux/pole is 10mWb and emf generated in armature is 200v then speed is —–rpm
A. 2000 rpm
B. 1500 rpm
C. 500 rpm
D. 1000rpm
Answer: B.1500 rpm
159. A 4 pole 1200 rpm, dc generator has lap wound armature producing 240v emf in the armature with flux/pole as 0.02Wb,then total number of armature conductors are
A. 2400
B. 1000
C. 600
D. 1200
Answer: C.600
160. The stator of I.M. motor is made up off———- laminations.
A. cast iron
B. cast steel
C. silicon steel
D. steel
Answer: C.silicon steel
161. Stator part of I.M. has slots to hold ——-
A. rotor winding
B. stator winding
C. shaft
D. brush
Answer: B.stator winding
162. Stator windings are insulated from core with the help of
A. slot insulator
B. epoxy coating
C. a or b
D. none
Answer: B.epoxy coating
163. 3 phase I.M. are classified as — and—- based on rotor construction.
A. slip ring & squirrel cage
B. split phase &squirrel cage
C. capacitor start motor& slip ring
D. shaded pole& capacitor start
Answer: A.slip ring & squirrel cage
164. When a induction motor is switched on a rotor frequency is
A. 60
B. same as supply frequency
C. same as slip frequency
D. zero
Answer: B.same as supply frequency
165. when the rotor of induction motor is standstill the value of slip is
A. zero
B. 1
C. 100
D. infinite
Answer: B.1
166. Squirrel cage I.M.motor has skewed rotor bar to help to produce constant — .
A. voltage
B. torque
C. frequency
D. magnetic field
Answer: B.torque
167. The effect of increasing the length of the air gap in an induction motor will increase
A. power factor
B. speed
C. magnetizing current
D. air-gap flux
Answer: C.magnetizing current
168. the difference between the synchronous speed and the actual speed of an induction motor is known as
A. regulation
B. back lash
C. slip
D. lag
Answer: C.slip
169. Rotating magnetic field is produced in a….
A. single – phase induction motor
B. three phase induction motor
C. dc series motor
D. ac series motor
Answer: B.three phase induction motor
170. Star- delta starter of an induction motor
A. inserts resistance in rotor circuit
B. inserts resistance in stator circuit
C. applies reduced voltage to rotor
D. applies reduced voltage to stator
Answer: D.applies reduced voltage to stator
171. Star- delta starter of an induction motor
A. applies voltage of √3 times of rated voltage to stator
B. applies reduced voltage of 1/√3 times of rated voltage to stator
C. applies reduced voltage of 1/√3 times of rated voltage to rotor
D. applies voltage of √3 times of rated voltage to rotor
Answer: B. applies reduced voltage of 1/√3 times of rated voltage to stator
172. The speed of an induction motor
A. decreases too much with the increase of load
B. increase with the increase of load
C. decreases slightly with the increase of load
D. remains constant with the increase of load
Answer: C.decreases slightly with the increase of load
173. The stator of I.M produces —- magnetic field.
A. steady
B. rotating
C. alternating
D. pulsating
Answer: B.rotating
174. If the frequency of 3-phase supply to stator of 3-phase I.M. is increased,then synchronous speed—-
A. is decreased
B. is increased
C. remains unchanged
D. none
Answer: B.is increased
175. An I.M. moror is preferred to a D.C. motor because of its—–
A. high starting torque
B. fine speed control
C. simple and rugged construction
D. none
Answer: C.simple and rugged construction
176. The starting torque of 3 phase I.M. motor is——-Supply voltage.
A. independent of
B. directly proportional to
C. directly proportional to squre of
D. none
Answer: C.directly proportional to squre of
177. Squirrel cage I.M. motor suffers from disadvantage of — starting torque.
A. low
B. high
C. pulsating
D. none
Answer: A.low
178. Rotor winding of 3 phase I.M. is generally——
A. star connected
B. delta connected
C. series connected
D. parallel connected
Answer: A.star connected
179. the direction of rotating magnetic field depends upon
A. the direction of rotating magnetic field depends upon
B. phase sequence of supply voltage
C. supply current
D. supply voltage
Answer: B.phase sequence of supply voltage
180. The relation among synchronous speed(Ns),rotor speed(Ns),slip(s)
A. n=(s-1)ns
B. n=(1-s)ns
C. n=(1+s)ns
D. n=s xns
Answer: B.n=(1-s)ns
181. slip of I.M. is given by the formula
A. (ns-n)/ns
B. ns/(ns-n)
C. ns/n
D. (ns-n)
Answer: A.(ns-n)/ns
182. when rotor of 3-phase I.M.motor is blocked stopped forcibly, the slip is —
A. 0
B. 0.5
C. 0.1
D. 1
Answer: D.1
183. The quantity (Ns-N) with respect to I.M. motor is called—-
A. slip
B. frequency
C. relative speed
D. speed of rotor
Answer: C.relative speed
184. frequency( fr) of induced emf in rotor of I.M. is given by —
A. s2.f
B. f2.s
C. s/f
D. s.f
Answer: D.s.f
185. At any given slip s the rotor induced emf (E2r) is —-
A. f/e2
B. f.e2
C. s.e2
D. s/e2
Answer: C.s.e2
186. Rotor induced emf is maximum when slip is —
A. 0
B. 1
C. 0.5
D. 0.05
Answer: B.1
187. At any given slip s the rotor reactance is —-
A. s.x2
B. s/x2
C. fr.x2
D. f.x2
Answer: A.s.x2
188. The reactance of the rotor circuit of 3-phase I.M. is maxium at
A. no-load
B. full-load
C. half of full load
D. start
Answer: D.start
189. which mathematical expression represents correct formula to find rotor current (I2)during starting
A. e2. √(r2+x2)
B. s.e2 / √(r22+x22)
C. e2/ √(r22+x22)
D. s.e2. √(r2+x2)
Answer: C.e2/ √(r22+x22)
190. which mathematical expression represents correct formula to find rotor current when running at slip s.(I2r)
A. e2. √(r2+x2)
B. s.e2/ √(r22+x22)
C. e2. √(r2+x2)
D. s.e2/ √(r22+s2x22)
Answer: D.s.e2/ √(r22+s2x22)
191. The rotor current in 3-phase I.M. is—–slip
A. inversely proportional to slip
B. directly proportional to slip
C. independent of
D. directly proportional to square of slip
Answer: B.directly proportional to slip
192. If slip of a 3-phase I.M. increases, the power factor of rotor circuit
A. is decreased
B. is increased
C. remains unchanged
D. none
Answer: B.is increased
193. The slip ring I.M. has high starting —-with ——starting current.
A. low, high
B. low, low
C. high, low
D. high, high
Answer: C.high, low
194. the squirrel cage I.M. has ——- starting torque.
A. high
B. low
C. moderate
D. very high
Answer: C.moderate
195. External resistance is added to rotor winding of slip ring I.M to ——–starting torque
A. increase
B. decrease
C. to keep constant
D. none of the above
Answer: A.increase
196. For 6 pole 50Hz I.M, sychronous speed of rotating magnetic field is———
A. 1200rpm
B. 1000rpm
C. 500rpm
D. 50rpm
Answer: B.1000rpm
197. For 2 pole 50Hz I.M,sychronous speed of rotating magnetic field is———rpm
A. 3000
B. 1000
C. 1500
D. 500
Answer: A.3000
198. For sychronous speed of rotating magnetic field 1000rpm, for 50 Hz supply,required no of poles =——–
A. 6
B. 2
C. 4
D. 8
Answer: A.6
199. for given no. of poles and if supply frequency reduces, sychronous speed of rotating magnetic field
A. remains same
B. decreases
C. increases
D. decreases to half value
Answer: B.decreases
200. For 3phase I.M,The synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 960 rpm ,then slip is
A. 0.04
B. 0.02
C. 0.01
D. 0.021
Answer: A.0.04
201. For 3phase I.M,the synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 970 rpm ,then slip is
A. 0.01
B. 0.06
C. 0.03
D. 0.05
Answer: C.0.03
202. For 3phase I.M,the synchronous speed of rotating magnetic field is 1500 rpm,speed of rotor is 1440 rpm ,then slip is
A. 0.01
B. 0.06
C. 0.03
D. 0.04
Answer: D.0.04
203. For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, speed of rotor is 731.25 rpm ,then slip is
A. 0.025
B. 0.06
C. 0.03
D. 0.04
Answer: A.0.025
204. For 3phase I.M.,the synchronous speed of rotating magnetic field is 1000 rpm, slip is 3% ,speed of rotor is———-
A. 970rpm
B. 1000
C. 250
D. 500
Answer: A.970rpm
205. For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, slip is 2.5% ,speed of rotor is———-
A. 500rpm
B. 731.25rpm
C. 1150rpm
D. 300
Answer: B. 731.25rpm
206. For I.M. running with 731.25rpm with slip of 2.5%, the synchronous speed of rotating magnetic field
A. 750
B. 1000
C. 500
D. 1500
Answer: A.750
207. For I.M. running with 1440rpm with slip of 4% the synchronous speed of rotating magnetic field
A. 750
B. 1000
C. 1500
D. 500
Answer: C.1500
208. For I.M. running with 970rpm with slip of 3%, the synchronous speed of rotating magnetic field
A. 750
B. 1000
C. 1500
D. 500
Answer: B.1000
209. A 6pole ,3 phase 50Hz I.M is running with 970 rpm. The slip of I.M is
A. 0.03
B. 0.05
C. 0.02
D. 0.01
Answer: A.0.03
210. A 8 pole ,50Hz ,3phase I.M ,If full load slip is 2.5%. Rotor speed is
A. 200
B. 731
C. 600
D. 1000
Answer: B.731
211. A 8pole ,3 phase 50Hz I.M is running with 731.25 rpm. The slip of I.M is
A. 0.0256
B. 1.975
C. 0.025
D. none of the above
Answer: C.0.025
212. A 6pole ,3 phase 50Hz I.M is running with s=3%,runs with
A. 200
B. 600
C. 1000
D. 970
Answer: D.970
213. A 3-phase slip-ring induction motor has ……………… rotor.
A. short circuited
B. wound
C. squirrel cage
D. double cage
Answer: B.wound
214. A wound rotor induction motor can be distinguished from a squirrel cage induction motor by
A. presence of slip-rings.
B. frame size
C. shaft diameter
D. any of the above
Answer: A.presence of slip-rings.
215. The operation of an induction motor is based on
A. len\s law
B. ampere law
C. principle of mutual induction
D. principle of self induction
Answer: C.principle of mutual induction
216. The rotating magnetic field produced by stator currents rotates at
A. synchronous speed , ns
B. rotor speed n
C. speed = ns – n
D. a speed higher than synchronous speed
Answer: A.synchronous speed , ns
217. The relative speed between stator flux and rotor is equal to
A. synchronous speed , ns
B. rotor speed n
C. zero
D. ns – n
Answer: D.ns – n
218. Two of the supply terminals to a 3-phase induction motor get interchanged during reconnection after normal maintenance. When switched on to supply, the motor will
A. rotate in the same direction as before maintenance.
B. rotate in a direction opposite to that before maintenance.
C. not start at all.
D. get heated and damaged.
Answer: B.rotate in a direction opposite to that before maintenance.
219. The direction of rotation of a 3-phase induction motor can be reversed by
A. interchanging any two leads from supply.
B. interchanging any two leads from slip-rings.
C. interchanging all the three leads from the supply
D. disconnecting any one phase
Answer: A.interchanging any two leads from supply.
220. The speed of rotor of an induction motor is always ………………… synchronous speed.
A. equal to
B. more than
C. less than
D. half of
Answer: C.less than
221. Synchronous speed is defined as the speed at which the
A. stator magnetic field rotates.
B. rotor rotates on no-load.
C. rotor rotates on full load.
D. none of the above.
Answer: A.stator magnetic field rotates.
222. A 3-phase, 4-pole induction motor has a no-load slip of 2% when connnected to a 25 Hz source, the no-load speed in rpm is
A. 730
B. 735
C. 765
D. 1430
Answer: B.735
223. A 4-pole, 3-phase induction motor is running at 4 percent slip at full load. If the speed of the motor is 720 rpm, the supply frequency is
A. 16hz
B. 25hz
C. 16
D. 20
Answer: B.25hz
224. The speed of rotating field due to rotor currents relative to rotor surface in an induction motor is
A. n
B. s.n
C. ns
D. s.ns
Answer: B.s.n
225. The speed of rotating field due to rotor currents relative to stator core in an induction motor is
A. s
B. ns
C. sn
D. sns
Answer: B.ns
226. A 3-phase ,400 V, 4-pole induction motor is fed from a 3-phase, 400V, 50 Hz supply and runs at 1440 rpm. The frequency of rotor emf is
A. 2hz
B. 50hz
C. 4hz
D. 0hz
Answer: A.2hz
227. In a 3-phase induction motor, the mechanical power developed, in terms of air rotor input P2 is
A. (s – 1) p2
B. p2 / (1-s)
C. 1/(s p2)
D. (1 – s) p2
Answer: D.(1 – s) p2
228. An induction motor employs a starting device to restrict………….. at start
A. line voltage
B. line current
C. torque
D. power
Answer: B.line current
229. High starting torque can be produced by induction motor if
A. a squirrel cage motor is started with auto-transformer starter
B. a slip-ring induction motor is started with star-delta starter
C. a squirrel cage motor is started by direct-on-line starter.
D. a slip-ring induction motor is started with rotor resistance starter
Answer: D.a slip-ring induction motor is started with rotor resistance starter
230. A squirrel cage induction motor is favoured when ……………….. is the main consideration.
A. initial cost
B. rotor core and rotor teeth
C. stator core and stator teeth
D. stator winding
Answer: C.stator core and stator teeth
231. The torque developed by a 3-phase induction motor during starting
A. depends on rotor induced emf during starting
B. rotor induced emf during running condition
C. does not depend on rotor induced emf
D. none of these
Answer: A.depends on rotor induced emf during starting
232. Condition for maximum torque developed during starting by a three phase induction motor is
A. r2 = x2
B. r2 =s x2
C. r2 /s x2
D. x2/r2
Answer: A.r2 = x2
233. Condition for maximum torque developed during running by a three phase induction motor is
A. r2 = x2
B. r2 =s x2
C. r2 /s x2
D. x2/r2
Answer: B.r2 =s x2
234. Starting torque depends on
A. rotor resistance and rotor reactance during starting
B. supply voltage
C. both 1 and 2
D. none of these
Answer: C.both 1 and 2
235. Torque developed by three phase induction motor
A. depends on power factor of rotor
B. depends on power factor of stator
C. does not depend on on power factor of rotor or stator
D. both 1 and 2
Answer: D.both 1 and 2
236. The power factor of induction motor is during running condition
A. depend on slip
B. is independent of slip
C. rotor reactance
D. both b and c
Answer: D.both b and c
237. The torque developed by three phase induction motor depends on following three factors
A. speed, frequency, number of poles
B. voltage, current and stator impedance
C. synchronous speed, rotor speed and frequency
D. rotor emf, rotor current and rotor p.f
Answer: D.rotor emf, rotor current and rotor p.f
238. When load is placed in three phase induction motor, its speed
A. decreases
B. increases
C. remains unchanged
D. becomes zero
Answer: A.decreases
239. When load is connected to three phase induction motor is increased, then its slip
A. decreases
B. increases
C. remains unchanged
D. becomes zero
Answer: B.increases
240. When load is connected to three phase induction motor is increased, then its rotor induced emf
A. decreases
B. increases
C. remains unchanged
D. becomes zero
Answer: B.increases
241. When load is placed in three phase induction motor its current
A. decreases
B. increases
C. remains unchanged
D. becomes zero
Answer: B.increases
242. When load is placed in three phase induction motor, its torque
A. decreases
B. increases
C. remains unchanged
D. becomes zero
Answer: B.increases
243. Maximum torque during running condition developed by three phase induction motor can be obtained by changing rotor resistance
A. in squirrel cage type motor
B. in slip ring type motor
C. in both 1 and 2
D. none of these
Answer: B.in slip ring type motor
244. There is no electrical connection between stator and rotor, still power is transffered from stator to rotor through
A. magnetic flux
B. air
C. water
D. conductor
Answer: A.magnetic flux
245. At start , the slip of induction motor is
A. zero
B. 0.5
C. one
D. infinite
Answer: C.one
246. Under running condition, the rotor reactance is proportional to
A. induced emf
B. rotor current
C. slip
D. supply voltage
Answer: C.slip
247. Under running condition , the rotor resistance is proportional to
A. induced emf
B. rotor current
C. slip
D. none of these
Answer: D.none of these
248. At start the rotor power factor is
A. very high
B. very low
C. unity
D. zero
Answer: B.very low
249. Power factor of rotor of three phase induction motor depends on
A. rotor resistance
B. speed of rotor
C. rotor reactance
D. all of these
Answer: D.all of these
250. The function of starter is
A. to start the motor
B. to start and stop the motor
C. to limit the starting current
D. to limit the applied the voltage
Answer: C.to limit the starting current
251. When three phase induction motor is started with star-delta starter, during starting stator is connected
A. in star
B. in delta
C. in star or delta
D. none of these
Answer: A.in star
252. When three phase induction motor is started with star-delta starter, during normal running condition, stator is connected
A. in star
B. in delta
C. in star or delta
D. none of these
Answer: B.in delta
253. The torque developed by three phase induction motor is approximately proportional to
A. square of applied voltage
B. applied voltage
C. half of applied voltage
D. double of appled voltage
Answer: A.square of applied voltage
254. The rotor of an induction motor can’t run at synchronous speed, if it did so then
A. rotor emf would be zero
B. rotor current would be zero
C. rotor torque would be zero
D. all of these
Answer: D. all of these
255. A 3-phase , 50 Hz , 4-pole squirrel cage induction motor has its stator rewound for 6 poles without any alternations in the rotor. The motor would now run at a speed
A. less than 1000 rpm
B. less than 1500 rpm
C. less than 3000 rpm
D. zero rpm
Answer: A.less than 1000 rpm
256. If the input voltage and the frequency of supply is halved, to the 3-phase induction motor
A. the maximum torque is halved
B. the maximum torque remains the same
C. the air-gap flux is halved
D. none of these
Answer: A.the maximum torque is halved
257. The speed of the slip ring induction motor can be easily controlled by
A. changing supply frequency
B. changing number of poles
C. changing the resistance of the rotor winding
D. all of these
Answer: D.all of these
258. A 440V, 20HP, 3phase motor operates at full load, 88% efficiency and 0.65 power factor lagging, the current drawn by motor is
A. 59.28a
B. 0.0458a
C. 34.22 a
D. 26.50a
Answer: C.34.22 a
259. A6 pole 3 phase 50Hz induction motor develops mechanical power of 40Hp and has mechanical losses of 1500W at a speed of 960rpm when connected to 500V. The output available at the shaft is (Take 1HP=746W)
A. 27kw
B. 31340w
C. 29840w
D. 28340w
Answer: D.28340w
260. DOL starter is used for 3 phase I.M. motor having rating of
A. ≤5 h.p.
B. > 5 h.p.
C. 5 to 10 h.p.
D. >10h.p.
Answer: A.≤5 h.p.
261. Thermal relays are used in DOL starter of Three Phase I.M. to
A. protect the motor from high temperature
B. protect the motor from overloading
C. protect the motor from short circuit
D. none of the above
Answer: B.protect the motor from overloading
262. No. of contacts used in a contactor of DOL starter
A. 2
B. 3
C. 4
D. 1
Answer: C.4
263. Q. In DOL starter NO(Normally open) contact is used as
A. start push button
B. stop push button
C. a and b
D. none of the above
Answer: A.start push button
264. In DOL starter NC(Normally closed) contact is used as
A. start push button
B. stop push button
C. a and b
D. none of the above
Answer: B.stop push button
265. The advantage of Autotransformer starter over stator resistance starter is
A. produces more torque
B. produces less losses
C. smooth variation of speed
D. none of the above
Answer: B.produces less losses
266. The rotor speed of a 6 pole 50Hz induction motor is 960 r.p.m. The percentage slip is ____.
A. 0.03
B. 0.04
C. 0.05
D. 0.02
Answer: B.0.04
267. A 3 phase induction motor connected from a 3 pjhase, 50Hz AC supply runs at 720rpm and has slip 4%. The number of poles in motor are _____.
A. 4
B. 6
C. 8
D. 16
Answer: C.8
268. The torque developed in an induction motor is nearly proportional to
A. 1/v
B. v
C. v^2
D. none of these
Answer: C.v^2
269. The air gap between the stator and rotor of a 3 phase induction motor ranges from
A. 2 cm to 4 cm
B. 0.4mm to 4mm
C. 1cm to 2cm
D. 4cm to 6cm
Answer: B.0.4mm to 4mm
270. An induction motor under full load has slip of about____.
A. 0.03
B. 0.1
C. 0.3
D. zero
Answer: A.0.03
271. A 4 pole, 440V, 50Hz induction motor is running at a slip of 4%. The speed of motor is ____.
A. 1260 rpm
B. 1440rpm
C. 1500rpm
D. 1560rpm
Answer: B.1440rpm
272. A 4 pole, 50Hz induction motor runs at a speed of 1440rpm. The frequency of the rotor induced emf is _____.
A. 3hz
B. 2.5hz
C. 2hz
D. 1hz
Answer: C.2hz
273. The value of slip is ___ at start.
A. zero
B. infinite
C. 100
D. 1
Answer: D.1
274. Slip rings are usually made up of ___.
A. copper
B. iron
C. carbon
D. phosphor-bronze
Answer: D.phosphor-bronze
275. The rotor standstill resistance and reactance of an induction motor are 0.5Ω and 2.5Ω hence the rotor impedance at 5% slip is____.
A. 0.5Ω
B. 0.025Ω
C. 0.5154Ω
D. 0.125Ω
Answer: C.0.5154Ω
276. The torque of 3 phase induction motor depends on__.
A. part of rotating magnetic field reacting with stator
B. rotor current is running condition
C. rotor power factor in running condition
D. all of these
Answer: D.all of these
277. The constant ‘k’ in the torque equation of a 3 phase induction motor depends
A. supply voltage
B. rotor current in running condition
C. synchronous speed
D. all of these
Answer: C.synchronous speed
278. A 3 phase indution motor is running with slip of 4% hving synchronous speed of 1500rpm. If rotor induced emf per phase in standstill condition is 115.47V and rotor impedance in standstill condition is 0.1+j1 Ω then torque developed ia____.
A. 118.54
B. 87.81
C. 225.45
D. 67.29
Answer: B.87.81
279. A 3 phase induction motor running with full load slip of 1.2% and its rotor impedance per phase on standstill is 0.016+j0.265Ω then the ratio of full load torque to maximum torque is
A. 0.382
B. 3.16
C. 0.1203
D. 0.556
Answer: A.0.382
280. A 3 phase induction motor is running with full load slip of 1.2% and its rotor impedance per phase is 0.06+j0.265Ω then ratio of starting torque to maximum torque is
A. 0.382
B. 3.16
C. 0.123
D. 0.556
Answer: C.0.123
281. A 3 phase I.M. is running with full load slip of 1.2% and its rotor impedance per phase on standstill is 0.016+j0.265Ω then ratio of full load torque to starting torque is _____.
A. 0.382
B. 3.16
C. 0.123
D. 0.556
Answer: B.3.16
282. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. If voltage between the slip rings on open circuit is 520V then the torque developed on full load is ___ Nm.
A. 202.52
B. 165.53
C. 430.36
D. 514.21
Answer: A.202.52
283. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. If voltage between the slip rings on open circuit is 520V then the maximum torque developed is ___ Nm.
A. 202.52
B. 165.53
C. 430.36
D. 514.21
Answer: C.430.36
284. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. The ratio of full load torque to maximum torque is ___.
A. 0.817
B. 1.223
C. 0.384
D. 0.4705
Answer: D.0.4705
285. A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. The external resistance required in the rotor per phase to get maximum torque at start is ___.
A. 0.2
B. 1.6
C. 0.8
D. 0.4
Answer: B.1.6
286. A 3 phase I.M. has rotor impedance on standstill as 0.8+j3.8Ω. Then the maximum torque will occur at slip of ____%
A. 21.05
B. 20
C. 30
D. 35.26
Answer: A.21.05
287. A 50Hz, 8 pole, 3 phase I.M. has a full load slip of 4%. Its rotor impedance per phase on standstill is 0.01+j0.005 ohms. Then the speed at maximum torque is ____.
A. 200
B. 300
C. 750
D. 600
Answer: D.600
288. A 50Hz 20 poles 3 phase I.M. has a full load slip 1.33%. Its rotor impedance per phase on standstill is 0.02+j0.3ohms. Then the ratio of starting torque to the maximum torque is____.
A. 0.384
B. 0.527
C. 0.132
D. 0.854
Answer: C.0.132
289. The external resistance added in the rotor circuit at start _____.
A. increase the starting torque
B. acts as starter
C. prevents inrush current
D. all of these
Answer: D.all of these
290. A 3 phase induction motor is running with 4% slip. Its rotor input is 10kW then rotor copper losses are
A. 1kw
B. 4kw
C. 400w
D. 0.04kw
Answer: C.400w
291. A 3 phase I.M. is running with slip 5%. Its air gap power is 12kW then total mechanical power developed is____.
A. 11.4kw
B. 12kw
C. 11.25kw
D. 16.6kw
Answer: A.11.4kw
292. A 3 phase I.M. running with slip 5%. Its rotor input is 20kW then its power output is ____ if frictional losses are 1kW.
A. 19.75kw
B. 1.8kw
C. 18kw
D. 21kw
Answer: C.18kw
293. A 3 phase I.M. is running with 5% slip. Its rotor input is 20kW and its synchronous speed is 1500rpm then its shaft torque is ___ if frictional losses are 1kW.
A. 226.89nm
B. 120.62nm
C. 135.48nm
D. 214.7nm
Answer: B.120.62nm
294. A 3 phase I.M. is running with 5% slip. Its rotor input is 20kW then its rotor efficiency is ____.
A. 0.95
B. 0.65
C. 0.75
D. insufficient data
Answer: A.0.95
295. A 25kW, 3 phase I.M. is running with 6% slip. Its rotor copper losses are ____ if frictional losses are 850W.
A. 1700
B. 1650
C. 1550
D. 1400
Answer: B.1650
296. A 25kW, 3 phase I.M. is running with 6% slip. Its rotor resistance per phase is____ if frictional losses are 850W and rotor current per phase is 65A.
A. 0.39
B. 0.165
C. 0.13
D. 0.215
Answer: C.0.13
297. A 4 pole, 3 phase I.M. is running with a slip of 4% producing shaft torque of 300Nm then its output power is ____ kW.
A. 46.89
B. 28.54
C. 52.12
D. 45.23
Answer: D.45.23
298. For a 3 phase I.M. running at 1440 rpm the torque lost in friction is 50Nm then its frictional losses are____.
A. 7.54
B. 4.23
C. 6.25
D. 8.45
Answer: A.7.54
299. A 3 phase I.M. is running with speed 1455 rpm on full load then its synchronous speed must be ____ rpm.
A. 1600
B. 1500
C. 2000
D. 1000
Answer: B.1500
300. An induction motor is
A. self starting with zero torque
B. self starting with high torque
C. self starting with small torque as compared to rated torque
D. assisted starting with zero torque
Answer: C.self starting with small torque as compared to rated torque
301. Various methods for starting a three phase induction motor are given, which method will required six stator terminals
A. dol
B. auto transformer
C. start delta
D. rheostat
Answer: C.start delta
302. Which of the following parameters of induction motor varies inversely as the supply freq
A. full load speed
B. starting current
C. slip
D. maximum running torque
Answer: B.starting current
303. When the supply voltage for an induction motor is reduced by 10%, the maximum running torque will be
A. decrease by 10%
B. decrease by 20%
C. increase by 10%
D. increase by 20%
Answer: B.decrease by 20%
304. If the supply freq of an induction motor is increased by 5%, the synchronous speed will
A. decrease by 10%
B. decrease by 5%
C. increase by 5%
D. increase by 10%
Answer: C.increase by 5%
305. The direction of rotation of field in a 3-ph induction motor depends upon
A. number of poles
B. magnitude of supply voltage
C. supply freq
D. phase sequence of supply voltage
Answer: D.phase sequence of supply voltage
306. The maximum voltage is induced in the rotor of 3-ph induction motor when it—-
A. runs at no load
B. runs at full load
C. is blocked
D. none of the above
Answer: A.runs at no load
307. When an induction motor is running at full load, rotor reactance is ——rotor resistance
A. low comparable to
B. very large compared to
C. large compared to
D. none of the above
Answer: A.low comparable to
308. If an induction motor is running at slip s ( in decimal) the rotor output is
A. (1+s) x rotor input
B. (s-1) x rotor input
C. s x rotor input
D. (1-s) x rotor input
Answer: D.(1-s) x rotor input
309. The conditions of induction motor at no load resembles those of transformer whose secondary is……
A. short circuited
B. open circuited
C. supplying a variable resistive load
D. none of the above
Answer: A.short circuited
310. The input to a 3-ph induction motor is 50KW. The stator losses amount to 800W. The rotor cu loss per phase is (slip = 3%)
A. 576w
B. 492w
C. 1050w
D. 728w
Answer: B.492w
311. The input to a 3-ph induction motor is 50KW. The stator losses amount to 800W. The mechanical power developed (slip = 3%)
A. 59hp
B. 69hp
C. 47hp
D. 64hp
Answer: D.64hp
312. An 8-pole , 50Hz,3-ph indduction motor running with a slip of 4% is taking 20KW. Stator losses amount 0.5KW. The total torque develped is
A. 248nm
B. 312nm
C. 195nm
D. 214nm
Answer: A.248nm
313. A 6pole, 3-ph induction motor is runs at a speed of 960rpm & the shaft torque is 135.7Nm. Calculate the rotor cu loss if the friction and windage losses amount to 150W. The suppy freq is 50Hz.
A. 625w
B. 785w
C. 425w
D. 574w
Answer: D.574w