1. Laminations of core are generally made of (c) silicon steel
2. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine?
2. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine?
(c) 0.5m
3. The armature of D.C. generator is laminated to (d) reduce eddy current loss
4. The resistance of armature winding depends on (a)length of conductor (b) cross-sectional area of the conductor (c) number of conductors
5. The field coils of D.C. generator are usually made of (b) copper
6. The commutator segments are connected to the armature conductors by means of (a) copper lugs
7. In a commutator (c) mica is harder than copper
8. In D.C. generators the pole shoes are fastened to the pole core by (b) counter sunk screws
9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of (b) lines of force
10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates (b) magnetic flux, direction of motion and the direction of e.m.f. induced
11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
(d) direction of motion of conductor, if forefinger points along the lines of flux
12. The bearings used to support the rotor shafts are generally (a)ball bearings
13. In D.C. generators, the cause of rapid brush wear may be (a) severe sparking
(b) rough commutator surface (c) imperfect contact
14. In lap winding, the number of brushes is always (b) same as the number of poles
15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ? (b) Wave winding
16. In a four-pole D.C. machine (b) alternate poles are north and south
17. Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved
18. A separately excited generator as compared to a self-excited generator (a) is amenable to better voltage control (b) is more stable (c) has exciting current independent of load current
19. In case of D.C. machines, mechanical losses are primary function of (c) speed
20. Iron losses in a D.C. machine are independent of variations in (b) load
21. In D.C. generators, current to the external circuit from armature is given through (a) commutator
23. Brushes of D.C. machines are made of (a) carbon
24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by (a)Blv
25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be (b) 8
26. The material for commutator brushes is generally (d) carbon
27. The insulating material used between the commutator segments is normally (c) mica
28. In D.C. generators, the brushes on commutator remain in contact with conductors which
3. The armature of D.C. generator is laminated to (d) reduce eddy current loss
4. The resistance of armature winding depends on (a)length of conductor (b) cross-sectional area of the conductor (c) number of conductors
5. The field coils of D.C. generator are usually made of (b) copper
6. The commutator segments are connected to the armature conductors by means of (a) copper lugs
7. In a commutator (c) mica is harder than copper
8. In D.C. generators the pole shoes are fastened to the pole core by (b) counter sunk screws
9. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of (b) lines of force
10. Fleming's right-hand rule regarding direction of induced e.m.f., correlates (b) magnetic flux, direction of motion and the direction of e.m.f. induced
11. While applying Fleming's right-hand rule to And the direction of induced e.m.f., the thumb points towards
(d) direction of motion of conductor, if forefinger points along the lines of flux
12. The bearings used to support the rotor shafts are generally (a)ball bearings
13. In D.C. generators, the cause of rapid brush wear may be (a) severe sparking
(b) rough commutator surface (c) imperfect contact
14. In lap winding, the number of brushes is always (b) same as the number of poles
15. For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ? (b) Wave winding
16. In a four-pole D.C. machine (b) alternate poles are north and south
17. Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved
18. A separately excited generator as compared to a self-excited generator (a) is amenable to better voltage control (b) is more stable (c) has exciting current independent of load current
19. In case of D.C. machines, mechanical losses are primary function of (c) speed
20. Iron losses in a D.C. machine are independent of variations in (b) load
21. In D.C. generators, current to the external circuit from armature is given through (a) commutator
23. Brushes of D.C. machines are made of (a) carbon
24. If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by (a)Blv
25. In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be (b) 8
26. The material for commutator brushes is generally (d) carbon
27. The insulating material used between the commutator segments is normally (c) mica
28. In D.C. generators, the brushes on commutator remain in contact with conductors which
(c) lie under interpolar region
29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be (c) cross magnetisation as well as demagnetising
30. Armature reaction of an unsaturated D.C. machine is (a) cross magnetising
31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover (b) to avoid mechanicaljerk to the shaft
29. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be (c) cross magnetisation as well as demagnetising
30. Armature reaction of an unsaturated D.C. machine is (a) cross magnetising
31. D.C. generators are connected to the busbars or disconnected from them only under the floating condition
(a) to avoid sudden loading of the primemover (b) to avoid mechanicaljerk to the shaft
(c) to avoid burning of switch contacts
32. Eddy currents are induced in the pole shoes of a D.C. machine due to
32. Eddy currents are induced in the pole shoes of a D.C. machine due to
(c) relative rotation between field and armature
34. Equilizer rings are required in case armature is (b) lap wound
35. Welding generator will have (a) lap winding
36. In case of D.C. machine winding, number of commutator segments is equal to (a) number of armature coils
37. For a D.C. machines laboratory following type of D.C. supply will be suitable (c) induction motor D.C. generator set
38. The function of pole shoes in the case of D.C. machine is (a) to reduce the reluctance of the mag¬netic path
(b) to spread out the flux to achieve uniform flux density (c) to support the field coil
39. In the case of lap winding resultant pitch is (d) difference of front and back pitches
40. A D.C. welding generator has (a) lap winding
34. Equilizer rings are required in case armature is (b) lap wound
35. Welding generator will have (a) lap winding
36. In case of D.C. machine winding, number of commutator segments is equal to (a) number of armature coils
37. For a D.C. machines laboratory following type of D.C. supply will be suitable (c) induction motor D.C. generator set
38. The function of pole shoes in the case of D.C. machine is (a) to reduce the reluctance of the mag¬netic path
(b) to spread out the flux to achieve uniform flux density (c) to support the field coil
39. In the case of lap winding resultant pitch is (d) difference of front and back pitches
40. A D.C. welding generator has (a) lap winding
41. Which of the following statement about D.C. generators is
false ?
(d) Equilizing bus bars are used with parallel running of D.C. shunt gen¬erators
42. The demagnetising component of armature reaction in a D.C. generator (a) reduces generator e.m.f.
43. Magnetic field in a D.C. generator is produced by (a) electromagnets
44. The number of brushes in a commutator depends on (d) amount of current to be collected
45. Compensating windings are used in D.C. generators
(c) to neutralise the cross-magnetising effect of the armature reaction
46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ? (b) Commutator
47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(d) Equilizing bus bars are used with parallel running of D.C. shunt gen¬erators
42. The demagnetising component of armature reaction in a D.C. generator (a) reduces generator e.m.f.
43. Magnetic field in a D.C. generator is produced by (a) electromagnets
44. The number of brushes in a commutator depends on (d) amount of current to be collected
45. Compensating windings are used in D.C. generators
(c) to neutralise the cross-magnetising effect of the armature reaction
46. Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ? (b) Commutator
47. In a D.C. generator the ripples in the direct e.m.f. generated are reduced by
(c) using carbon brushes of superior quality
48. In D.C. generators, lap winding is used for (b) low voltage, high current
49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be (b) 3 : 1
50. The voltage drop for which of the following types of brush can be expected to be least ? (c) Metal graphite brushes
51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be (b) 2E
53. The armature core of a D.C. generator is usually made of (a) silicon steel
9.63. Satisfactory commutation of D.C. machines requires (a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders (c) smooth, concentric commutator properly undercut
54. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is connected
(b) indicated by a spark completely around the commutator
56. For the parallel operation of two or more D.C. compound generators, we should ensure that
(d) series fields of all generators should be either on positive side or negative side of the armature
57. D.C. series generator is used (c) voltage at the toad end of the feeder
58. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
(d) self-excited generator
59. Interpole flux should be sufficient to (c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
60. D.C. generator generally preferred for charging automobile batteries is (c) long shunt compound generator
61. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
(d) number of poles is 2
62. Permeance is the reciprocal of (b) reluctance
63. In D.C. generators the polarity of the interpoles (a) is the same as that of the main pole ahead
64. The e.m.f. generated in a D.C. generator is directly proportional to (b) speed of armature
65. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when
(a) there is no load on|he generator
66. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except (b) dummy coils
67. In D.C. generators on no-load, the air gap flux distribution in space is (d) flat topped
68. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly (c) 240 V
69. The purpose of providing dummy coils in a generator is (d) to provide mechanical balance for the rotor
71. If a D.C. generator fails to build up the probable cause could not be
48. In D.C. generators, lap winding is used for (b) low voltage, high current
49. Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generator A and B will be (b) 3 : 1
50. The voltage drop for which of the following types of brush can be expected to be least ? (c) Metal graphite brushes
51. The e.m.f. generated by a shunt wound D.C. generator isE. Now while pole flux remains constant, if the speed of the generator is doubled, the e.m.f. generated will be (b) 2E
53. The armature core of a D.C. generator is usually made of (a) silicon steel
9.63. Satisfactory commutation of D.C. machines requires (a) brushes should be of proper grade and size
(b) brushes should smoothly run in the holders (c) smooth, concentric commutator properly undercut
54. Open circuited armature coil of a D.C. machine is
(a) identified by the scarring of the commutator segment to which open circuited coil is connected
(b) indicated by a spark completely around the commutator
56. For the parallel operation of two or more D.C. compound generators, we should ensure that
(d) series fields of all generators should be either on positive side or negative side of the armature
57. D.C. series generator is used (c) voltage at the toad end of the feeder
58. Following D.C. generator will be in a position to build up without any residual magnetism in the poles
(d) self-excited generator
59. Interpole flux should be sufficient to (c) neutralise both the armature reaction flux as well as commutating e.m.f. induced in the coil
60. D.C. generator generally preferred for charging automobile batteries is (c) long shunt compound generator
61. In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when
(d) number of poles is 2
62. Permeance is the reciprocal of (b) reluctance
63. In D.C. generators the polarity of the interpoles (a) is the same as that of the main pole ahead
64. The e.m.f. generated in a D.C. generator is directly proportional to (b) speed of armature
65. In a D.C. generator the magnetic neutral axis coincides with the geometrical neutral axis, when
(a) there is no load on|he generator
66. In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except (b) dummy coils
67. In D.C. generators on no-load, the air gap flux distribution in space is (d) flat topped
68. A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If the speed increases to 1200 r.p.m., the generated e.m.f. will be nearly (c) 240 V
69. The purpose of providing dummy coils in a generator is (d) to provide mechanical balance for the rotor
71. If a D.C. generator fails to build up the probable cause could not be
(b) field resistance less than the critical resistance
72. Flashing the field of D.C. generator means (b) creating residual magnetism by a D.C. source
73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be (d) 580 V
74. In a D.C. generator the critical resistance refers to the resistance of (b) field
75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
76. Armature coil is short circuited by brushes when it lies (a) along neutral axis
77. A cumulatively compounded long shunt generator when operating as a motor would be
72. Flashing the field of D.C. generator means (b) creating residual magnetism by a D.C. source
73. The e.m.f. induced in the armature of a shunt generator is 600 V. The armature resistance is 0.1 ohm. If the armature current is 200 A, the terminal voltage will be (d) 580 V
74. In a D.C. generator the critical resistance refers to the resistance of (b) field
75. To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead so as to bring them
(a) just ahead of magnetic neutral axis
76. Armature coil is short circuited by brushes when it lies (a) along neutral axis
77. A cumulatively compounded long shunt generator when operating as a motor would be
(b) differentially compounded long shunt
78. To avoid formation of grooves in the commutator of a D.C.
machine (a) the brushes of opposite polarity should track each other
79. The following constitute short-circuit in the armature winding. (a) Insulation failure between two commutator bars (6) Insulation failure between two turns of a coil (c) Two of more turns of the same coil getting grounded
80. The rapid wear of brushes takes place due to (a) abrasion from dust (b) excessive spring pressure (c) rough commutator bars (d) high mica insulation between com-mutation bars
81. Number of tappings for each equilizer ring is equal to (a) number of pole pairs
82. A D.C. generator can be considered as (c) rotating amplifier
83. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called (d) armature
84. In a D.C. machine stray loss is the sum of (d) iron loss and mechanical loss
85. Lap winding is composed of (a) any even number of conductors
86. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will (b) decrease
87. An exciter for a turbo generator is a (b) shunt generator
88. In case of a flat compounded generator (c) voltage remains constant irrespective of the load
89. Which of the following generator will have negligible terminal voltage while running on no-load ?
79. The following constitute short-circuit in the armature winding. (a) Insulation failure between two commutator bars (6) Insulation failure between two turns of a coil (c) Two of more turns of the same coil getting grounded
80. The rapid wear of brushes takes place due to (a) abrasion from dust (b) excessive spring pressure (c) rough commutator bars (d) high mica insulation between com-mutation bars
81. Number of tappings for each equilizer ring is equal to (a) number of pole pairs
82. A D.C. generator can be considered as (c) rotating amplifier
83. In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called (d) armature
84. In a D.C. machine stray loss is the sum of (d) iron loss and mechanical loss
85. Lap winding is composed of (a) any even number of conductors
86. In a D.C. generator in case the resistance of the field winding is increased, then output voltage will (b) decrease
87. An exciter for a turbo generator is a (b) shunt generator
88. In case of a flat compounded generator (c) voltage remains constant irrespective of the load
89. Which of the following generator will have negligible terminal voltage while running on no-load ?
(a) Series generator
91. In over compounded generator, full load terminal voltage is (c) more than no load terminal voltage
92. In a level compounded D.C. generator, full load terminal voltage is (b) equal to no-load terminal voltage
93. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(d) commutation
94. In a D.C. generator (c) external characteristic= magnetisation characteristic- ohmic drop - armature reaction
95. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
(b) will be of 5 Hz
96. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(b) about 2 V
97. In a separately excited generator supplying rated load the armature reaction , (a) is always present
98. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be (a) zero
99. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip
101. Wave winding is composed of (c) that even number which is exact multiple of poles + 2
102. The critical resistance of the D.C. generator is the resistance of (a) field
103. When two D.C. series generators are running in parallel, an equilizer bar is used
(c) so that two similar machines will pass approximately equal currents to the load
104. Which of the following generating machine will offer constant voltage on all loads ?
91. In over compounded generator, full load terminal voltage is (c) more than no load terminal voltage
92. In a level compounded D.C. generator, full load terminal voltage is (b) equal to no-load terminal voltage
93. The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except
(d) commutation
94. In a D.C. generator (c) external characteristic= magnetisation characteristic- ohmic drop - armature reaction
95. A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave
(b) will be of 5 Hz
96. A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be
(b) about 2 V
97. In a separately excited generator supplying rated load the armature reaction , (a) is always present
98. If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speed will be (a) zero
99. Armature reaction in a generator results in
(a) demagnetisation of leading pole tip and magnetisation of trailing pole tip
101. Wave winding is composed of (c) that even number which is exact multiple of poles + 2
102. The critical resistance of the D.C. generator is the resistance of (a) field
103. When two D.C. series generators are running in parallel, an equilizer bar is used
(c) so that two similar machines will pass approximately equal currents to the load
104. Which of the following generating machine will offer constant voltage on all loads ?
(c) Level compounded generator .
105. Which of the following generators will be preferred if they are required to be run in parallel ?
105. Which of the following generators will be preferred if they are required to be run in parallel ?
(a) Shunt generators
106. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ? (d) That generator takes large share of loads
107. A D.C. generator works on the principle of (c) Faraday's law of electromagnetic induction
108. A series generator can self-excite (b) only if the load current is not zero
109. A shunt generator can self-excite (a) only if the resistance of the field circuit is less than critical value
110. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be (c) greater than 150 V
111. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(c) may be greater or less than 250 V
112. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be (b) 267.5 V
113. The essential condition for parallel operation of two D.C. generators is that they have '
106. Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ? (d) That generator takes large share of loads
107. A D.C. generator works on the principle of (c) Faraday's law of electromagnetic induction
108. A series generator can self-excite (b) only if the load current is not zero
109. A shunt generator can self-excite (a) only if the resistance of the field circuit is less than critical value
110. The terminal voltage of a series generator is 150 V when the load current is 5 A. If the load current is increased to 10 A, the terminal voltage will be (c) greater than 150 V
111. The open circuit voltage of a compound generator is 250 V. At full load the terminal voltage
(c) may be greater or less than 250 V
112. Two D.C. shunt generators, each with armature resistance of 0.02 ohm and field resistance of 50 ohm run in parallel and supply a total current of 1000 amperes to the load circuit. If their e.m.fs. are 270 V and 265 V, their bus bar voltage will be (b) 267.5 V
113. The essential condition for parallel operation of two D.C. generators is that they have '
(c) the same drooping voltage characteristics
114. When two D.C. generators are running in parallel an equilizer bar is used
(d) so that the two identical machines will pass approximately equal cur¬rents to the load
114. When two D.C. generators are running in parallel an equilizer bar is used
(d) so that the two identical machines will pass approximately equal cur¬rents to the load
115. With a D.C. generator which of the following regulation is
preferred ? (d) 1% regulation
116. Which generator would you prefer for feeding long D.C. transmission lines ? (c) Over compound generator
117. In a D.C. generator the critical resistance can be increased by (c) increasing its speed
118. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is (b) 4
119. For both lap and wave windings, there are as many commutator bars as the number of (c) winding elements
120. The series field of a short-shunt D.C. generator is excited by (d) load current
121. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately (d) 5 percent
122. Shunt generators are most suited for stable parallel operation because of their (c) drooping voltage characteristics
123. The main factor which leads to unstable parallel operation of flat and over compounded generators is
(a) their rising voltage characteristics
124. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to (a) reverse the field connections
116. Which generator would you prefer for feeding long D.C. transmission lines ? (c) Over compound generator
117. In a D.C. generator the critical resistance can be increased by (c) increasing its speed
118. The number of armature parallel paths in a two-pole D.C. generator having duplex lap winding is (b) 4
119. For both lap and wave windings, there are as many commutator bars as the number of (c) winding elements
120. The series field of a short-shunt D.C. generator is excited by (d) load current
121. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately (d) 5 percent
122. Shunt generators are most suited for stable parallel operation because of their (c) drooping voltage characteristics
123. The main factor which leads to unstable parallel operation of flat and over compounded generators is
(a) their rising voltage characteristics
124. If a self excited D.C. generator after being installed, fails to build up on its first trial run, the first thing to do is to (a) reverse the field connections
D.C. Motors - Electrical Engineering Multiple Choice
Questions and Answers
1. No-load speed of which of the following motor will be highest ? (b) Series motor
2. The direction of rotation of a D.C. series motor can be changed by
(b) interchanging field terminals
3. Which of the following application requires high starting torque ? (c) Locomotive
4. If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ? (a) Series motor
5. Which D.C. motor will be preferred for machine tools ? (b) Shunt motor
6. Differentially compound D.C. motors can find applications requiring (b) low starting torque
7. Which D.C. motor is preferred for elevators ? (d) Cumulative compound motor
8. According to Fleming's left-hand rule, when the forefinger points in the direction of the field or flux, the middle finger will point in the direction of (a) current in the conductor aovtaat of conductor
9. If the field of a D.C. shunt motor gets opened while motor is running (c) the motor will attain dangerously high speed 1
10. Starters are used with D.C. motors because
(d) to restrict armature current as there is no back e.m.f.
while starting
11. In D.C. shunt motors as load is reduced (c) the speed will remain almost/constant
12. A D.C. series motor is that which (a) has its field winding consisting of thick wire and less turns
13. For starting a D.C. motor a starter is required because (b) it limits the starting current to a safe value
14. The type of D.C. motor used for shears and punches is (d) cumulative compound D.C. motor
15. If a D.C. motor is connected across the A.C. supply it will
(d) burn due to heat produced in the field winding by .eddy currents
16. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
11. In D.C. shunt motors as load is reduced (c) the speed will remain almost/constant
12. A D.C. series motor is that which (a) has its field winding consisting of thick wire and less turns
13. For starting a D.C. motor a starter is required because (b) it limits the starting current to a safe value
14. The type of D.C. motor used for shears and punches is (d) cumulative compound D.C. motor
15. If a D.C. motor is connected across the A.C. supply it will
(d) burn due to heat produced in the field winding by .eddy currents
16. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
(a) Ward Leonard control
17. When two D.C. series motors are connected in parallel, the resultant speed is (c) normal speed
18. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
17. When two D.C. series motors are connected in parallel, the resultant speed is (c) normal speed
18. The speed of a D.C. shunt motor more than its full-load speed can be obtained by
(a) decreasing the field current
19. In a D.C. shunt motor, speed is (a) independent of armature current
20. A direct on line starter is used: for starting motors (a) up to 5 H.P.
21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? (c) The armature may burn
22. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because (d) flux is practically constant in D:C. shunt motors
23. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
19. In a D.C. shunt motor, speed is (a) independent of armature current
20. A direct on line starter is used: for starting motors (a) up to 5 H.P.
21. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? (c) The armature may burn
22. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because (d) flux is practically constant in D:C. shunt motors
23. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(d) more than full-load current
24. These days D.C. motors are widely used in (c) electric traction
25. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
24. These days D.C. motors are widely used in (c) electric traction
25. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(c) Commutator
26. In which of the following applications D.C. series motor is invariably tried? (a) Starter for a car
27. In D.C. machines fractional pitch winding is used (d) to reduce the sparking
28. A three point starter is considered suitable for (b) shunt as well as compound motors
26. In which of the following applications D.C. series motor is invariably tried? (a) Starter for a car
27. In D.C. machines fractional pitch winding is used (d) to reduce the sparking
28. A three point starter is considered suitable for (b) shunt as well as compound motors
29. In case-the conditions for maximum power for a D.C. motor
are established, the efficiency of the motor will be (d) less than 50%
30. The ratio of a) series motors (b) shunt motors
32. In D.C. motor which of the following can sustain the maximum temperature rise? (c) Field winding
33. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
30. The ratio of a) series motors (b) shunt motors
32. In D.C. motor which of the following can sustain the maximum temperature rise? (c) Field winding
33. Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
(d) Fleming's left-hand rule
34. Which of the following load normally needs starting torque more than the rated torque? (b) Conveyors
35. The starting resistance of a D.C. motor is generally (a) low
36. The speed of a D.C. series motor is (d) inversely proportional to the armature current
37. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
34. Which of the following load normally needs starting torque more than the rated torque? (b) Conveyors
35. The starting resistance of a D.C. motor is generally (a) low
36. The speed of a D.C. series motor is (d) inversely proportional to the armature current
37. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
(c) 25% of the previous value
38. The current drawn by the armature of D.C. motor is directly proportional to (a) the torque required
39. The power mentioned on the name plate of an electric motor indicates
38. The current drawn by the armature of D.C. motor is directly proportional to (a) the torque required
39. The power mentioned on the name plate of an electric motor indicates
(d) the output power available at the shaft
40. Which D.C. motor has got maximum self loading property? (d) Differentially compounded motor
41. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
40. Which D.C. motor has got maximum self loading property? (d) Differentially compounded motor
41. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
(c) Cumulatively compounded motor
42. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens (c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
43. D.C. series motors are used (d) in none of the above situations.
44. For the same H.P. rating and full load speed, following motor has poor starting torque (c) differentially compounded
45. In case of conductively compensated D.C. series motors, the compensating winding is provided (c) in series with armature winding
46. Sparking at the commutator of a D.C. motor may result in (a) damage to commutator segments
42. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens (c) this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
43. D.C. series motors are used (d) in none of the above situations.
44. For the same H.P. rating and full load speed, following motor has poor starting torque (c) differentially compounded
45. In case of conductively compensated D.C. series motors, the compensating winding is provided (c) in series with armature winding
46. Sparking at the commutator of a D.C. motor may result in (a) damage to commutator segments
(b) damage to commutator insulation (c) increased power
consumption
47. Which of the following motor is preferred for operation in highly explosive atmosphere ? (c) Air motor
48. If the supply voltage for a D.C. motor is increased, which of the following will decrease ? (c) Full-load current
49. Which one of the following is not the function of pole shoes in a D.C. machine ? (a) To reduce eddy current loss
50. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is (d) 0.5
51. The condition for maximum power in case of D.C. motor is (b) back e.m.f. = | x supply voltage
52. For which of the following applications a D.C. motor is preferred over an A.C. motor ? (c) Variable speed operation
53. In D.C. machines the residual magnetism is of the order of (a) 2 to 3 per cent
54. Which D.C. motor is generally preferred for cranes and hoists ? (a) Series motor
55. Three point starter can be used for (d) both shunt and compound motor
56. Sparking, is discouraged in a D.C. motor because (b) commutator gets damaged
57. Speed control by Ward Leonard method gives uniform speed variation (b) in both directions
58. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be (c) cumulatively compounded
60. In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor
61. Which of the following motor has the poorest speed regulation ? (b) Series motor
62. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
47. Which of the following motor is preferred for operation in highly explosive atmosphere ? (c) Air motor
48. If the supply voltage for a D.C. motor is increased, which of the following will decrease ? (c) Full-load current
49. Which one of the following is not the function of pole shoes in a D.C. machine ? (a) To reduce eddy current loss
50. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is (d) 0.5
51. The condition for maximum power in case of D.C. motor is (b) back e.m.f. = | x supply voltage
52. For which of the following applications a D.C. motor is preferred over an A.C. motor ? (c) Variable speed operation
53. In D.C. machines the residual magnetism is of the order of (a) 2 to 3 per cent
54. Which D.C. motor is generally preferred for cranes and hoists ? (a) Series motor
55. Three point starter can be used for (d) both shunt and compound motor
56. Sparking, is discouraged in a D.C. motor because (b) commutator gets damaged
57. Speed control by Ward Leonard method gives uniform speed variation (b) in both directions
58. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be (c) cumulatively compounded
60. In a differentially compounded D.C. motor, if shunt field suddenly opens
(a) the motor will first stop and then run in opposite direction as series motor
61. Which of the following motor has the poorest speed regulation ? (b) Series motor
62. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
(a) D.C. series motor
63. As -the load is increased the speed of D.C. shunt motor will (a) reduce slightly
64. The armature torque of the D.C. shunt motor is proportional to (b) armature current only
65. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
63. As -the load is increased the speed of D.C. shunt motor will (a) reduce slightly
64. The armature torque of the D.C. shunt motor is proportional to (b) armature current only
65. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
(c) Armature control method
66. Usually wide and sensitive speed control is desired in case of (d) colliery winders
67. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is (b) 4.76%
68. The armature voltage control of D.C. motor provides (a) constant torque drive
66. Usually wide and sensitive speed control is desired in case of (d) colliery winders
67. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is (b) 4.76%
68. The armature voltage control of D.C. motor provides (a) constant torque drive
69. As there is no back e.m.f. at the instant of starting a
D.C. motor, in order to prevent a heavy current from flowing though the
armature circuit (a) a resistance is
connected in series with armature
70. The speed of a D.C. shunt motor can be increased by (b) increasing the resistance in field circuit
71. If I2 be the armature current, then speed of a D.C. shunt motor is (a) independent of Ia
72. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
70. The speed of a D.C. shunt motor can be increased by (b) increasing the resistance in field circuit
71. If I2 be the armature current, then speed of a D.C. shunt motor is (a) independent of Ia
72. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
(a) remain unchanged
73. At the instant of starting when a D.C. motor is put on supply, it behaves like (b)a low resistance circuit
74. The speed of a D.C. motor can be varied by varying (a) field current
(b) applied voltage (c) resistance in series with armature
75. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ? (a) Low cost
76. For a D.C. shunt motor if the excitation is changed (b) torque will change but power will remain constant
77. Which motor has the poorest speed control? (d) Series motor
78. The plugging gives the (c) highest torque braking
79. The armature voltage control of D.C. motor provides (c) constant torque drive
80. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor (d) is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor
81. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking (b) plugging
82. Which of the following motors one will choose to drive the rotary compressor ? (d) Synchronous motor
83. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will (a) increase
84. Why are the D.C. motors preferred for traction applications ?
(d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current
85. Which of the following motors is usually used in house-hold refrigerators ?
(c) Single phase induction motor (split phase start or induction run motor)
86. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
73. At the instant of starting when a D.C. motor is put on supply, it behaves like (b)a low resistance circuit
74. The speed of a D.C. motor can be varied by varying (a) field current
(b) applied voltage (c) resistance in series with armature
75. Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ? (a) Low cost
76. For a D.C. shunt motor if the excitation is changed (b) torque will change but power will remain constant
77. Which motor has the poorest speed control? (d) Series motor
78. The plugging gives the (c) highest torque braking
79. The armature voltage control of D.C. motor provides (c) constant torque drive
80. If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor (d) is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor
81. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking (b) plugging
82. Which of the following motors one will choose to drive the rotary compressor ? (d) Synchronous motor
83. If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will (a) increase
84. Why are the D.C. motors preferred for traction applications ?
(d) The speed is inversely proportional to the torque and the torque is proportional to square of armature current
85. Which of the following motors is usually used in house-hold refrigerators ?
(c) Single phase induction motor (split phase start or induction run motor)
86. Which of the following motors is most suitable for signalling devices and many kinds of timers ?
(d) Reluctance motor
87. Which motor should not be started on no-load ? (a) Series motor
88. Ward-Leonard control is basically a (a) voltage control method
89. For constant torque drive which speed control method is preferred ? (b) Armature voltage control
90. In Ward-Leonard control the lower limit of speed is imposed by
(a) residual magnetism of the generator
91. The main disadvantage of the Ward-Leonard control method is
(a) high initial cost (b) high maintenance cost (c) low efficiency at Hght loads
92. Regenerative method of braking is based on that (b) back e.m.f. is equal to the applied voltage
93. The hysteresis loss in a D.C. machine least depends on (d) Rate of flow of ventilating air
94. In a D.C. generator all of the following could be the effects of iron losses except (c) Increase in terminal voltage
95. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ? (c) armature copper loss
96. Which of the following loss in a D.C. generator varies significantly with the load current ?
87. Which motor should not be started on no-load ? (a) Series motor
88. Ward-Leonard control is basically a (a) voltage control method
89. For constant torque drive which speed control method is preferred ? (b) Armature voltage control
90. In Ward-Leonard control the lower limit of speed is imposed by
(a) residual magnetism of the generator
91. The main disadvantage of the Ward-Leonard control method is
(a) high initial cost (b) high maintenance cost (c) low efficiency at Hght loads
92. Regenerative method of braking is based on that (b) back e.m.f. is equal to the applied voltage
93. The hysteresis loss in a D.C. machine least depends on (d) Rate of flow of ventilating air
94. In a D.C. generator all of the following could be the effects of iron losses except (c) Increase in terminal voltage
95. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ? (c) armature copper loss
96. Which of the following loss in a D.C. generator varies significantly with the load current ?
(c) Armature copper loss
97. Torque developed by a D.C. motor depends upon (a) magnetic field
(b) active length of the conductor (c) current flow through the conductors
(d) number of conductors (e) radius of armature
98. D.C. shunt motors are used for driving (d) machine tools
99. In a manual shunt motor starter (a) over load relay is connected in series and no volt relay in parallel with the load
100. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ? (d) Using material of low hysteresis co-efficient for armature core material
101. Which of the following loss in a D.C. generator is dissipated in the form of heat? (a) Mechanical loss
97. Torque developed by a D.C. motor depends upon (a) magnetic field
(b) active length of the conductor (c) current flow through the conductors
(d) number of conductors (e) radius of armature
98. D.C. shunt motors are used for driving (d) machine tools
99. In a manual shunt motor starter (a) over load relay is connected in series and no volt relay in parallel with the load
100. Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ? (d) Using material of low hysteresis co-efficient for armature core material
101. Which of the following loss in a D.C. generator is dissipated in the form of heat? (a) Mechanical loss
(b) Core loss (c) Copper
loss
102. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
102. Which of the following losses are significantly reduced by laminating the core of a D.C. generator ?
(b) Eddy current
losses
103. The total losses in a well designed D.C. generator of 10 kW will be nearly (b) 500 W
104. The condition for maximum efficiency for a D.C. generator is (d) variable losses = constant losses
103. The total losses in a well designed D.C. generator of 10 kW will be nearly (b) 500 W
104. The condition for maximum efficiency for a D.C. generator is (d) variable losses = constant losses
105. D.C. generators are normally designed for maximum
efficiency around (a) full-load
106. In a D.C. generator, the iron losses mainly take place in (d) armature rotor
107. D.C. generators are installed near the load centres to reduce (b) line losses
108. The purpose of retardation test on D.C. shunt machines is to find out (a) stray losses
109. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? (c) Field test
110. Hopkinson's test on D.C. machines is conducted at (c) full-load
111. During rheostat braking of D.C. series motors (a) motor is run as a generator
112. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors (b) Series motors (c) Compound motors
113. Which method of braking is generally used in elevators ? (a) Plugging
114. In variable speed motor (b) a weaker commutating field is needed at low speed than at high speed
115. When the armature of a D.C. motor rotates, e.m.f. induced is (c) back e.m.f.
116. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
106. In a D.C. generator, the iron losses mainly take place in (d) armature rotor
107. D.C. generators are installed near the load centres to reduce (b) line losses
108. The purpose of retardation test on D.C. shunt machines is to find out (a) stray losses
109. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? (c) Field test
110. Hopkinson's test on D.C. machines is conducted at (c) full-load
111. During rheostat braking of D.C. series motors (a) motor is run as a generator
112. For which types of D.C. motor, dynamic braking is generally used ?
(a) Shunt motors (b) Series motors (c) Compound motors
113. Which method of braking is generally used in elevators ? (a) Plugging
114. In variable speed motor (b) a weaker commutating field is needed at low speed than at high speed
115. When the armature of a D.C. motor rotates, e.m.f. induced is (c) back e.m.f.
116. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
(a) drum type controller is used
117. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it
118. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the (a) series motor
119. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this (c) compound motor
120. Which D.C. motor has got maximum self relieving property ? (a) Series motor
121. In the D.C. motor the iron losses occur in (b) the armature
122. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
117. If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
(a) this will make armature to take heavy current, possibly burning it
118. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the (a) series motor
119. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this (c) compound motor
120. Which D.C. motor has got maximum self relieving property ? (a) Series motor
121. In the D.C. motor the iron losses occur in (b) the armature
122. The speed of a D.C. shunt motor is required to be more than full load speed. This is possible by
(a) reducing the field current
123. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
123. One D.C. motor drives another D.C. motor. The second D.C. motor when excited and driven
(a) runs as a generator