1. 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?
Correct : B. 210v
2. 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?
Correct : A. 190v
3. 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?
Correct : C. 134nm
4. 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?
Correct : B. 122.5nm
5. 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__.
Correct : A. 502w
6. 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___.
Correct : D. 250rpm
7. 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.
Correct : A. 14.08hp
8. Which motor should not be used for centrifugal pumps?
Correct : B. series
9. If the applied voltage to a DC machine is 230V, then back emf for maximum power developed is ___.
Correct : C. 115v
10. A DC motor runs at 1725rpm at full load and 1775rpm at no load. The speed regulation is _____.
Correct : B. 0.029
11. 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?
Correct : D. 486v
12. 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?
Correct : A. 675rpm
13. 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 _____.
Correct : D. 218nm
14. The resistance of the shunt field winding as compared to series field winding is ____.
Correct : B. more
15. The field winding of a machine designed for separate excitation is
Correct : A. of the shunt field type
16. 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.
Correct : D. 2.47Ω
17. 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.
Correct : A. 2.16Ω
18. In a DC compound machine,
Correct : A. shunt field winding plays dominent role
19. A DC shunt motor is rotating at 267 rad/sec and developing 57.2Nm of torque. How many kilowatts of mechanical power are developed?
Correct : B. 15.3kw
20. A 20HP DC motor has 89.3% efficiency at rated power. What are its total losses?
Correct : A. 1787w
21. By flux control method of speed control of a dc shunt motor, we can obtain speeds.
Correct : A. above the normal speed only
22. By putting controller resistance in series with the armature of a DC motor, we can obtain speeds
Correct : B. below the normal speed only
23. Motor starters are essential for
Correct : C. avoiding excessive starting current
24. The only disadvantage of field control method for controlling the speed of a dc shunt motor is that it
Correct : D. adversely affects commutation
25. When quick speed reversal is a consideration, the motor preffered is
Correct : D. dc motor
26. The range of horse power of electric motor drives for rolling mills is of the order of
Correct : D. 100 to 500 hp
27. Motors preferred for rolling mill drive is
Correct : C. any of the above
28. Cumulatively compounded motors are used where we require _____.
Correct : C. heavy duty excavators
29. Which type of motors are preferred in lifts?
Correct : A. dc compound motors.
30. In cloth washing machines and refrigerators which motors are preferred?
Correct : D. universal motors
31. In lathes, milling and grinding machines which motor will preferred?
Correct : D. either a or b
32. In planners which of following motors are preferred?
Correct : C. any of above
33. In iron and steel industry which motors are preferred?
Correct : C. dc shunt wound motors
34. A sinusoidal voltage of frequency 1 Hz is applied to the field of a d.c generator. The armature voltage will be
Correct : B. 1 hz sine wave
35. In wave winding, the number of parallel paths of armature winding is
Correct : B. 2
36. The emf equation of dc generator is E=
Correct : D. Øpnz/60a
37. If number of conductors in a dc generator is Z then total number of turns are
Correct : C. z/2
38. What is the flux in the armature core section of a dc machine if the air gap flux be ø Wb?
Correct : A. ø
39. The flux leakage coefficient in dc machine is usually
Correct : C. 1.2 to 1.3
40. Armature resistance of a d.c. machine is about
Correct : D. 0.1
41. The electrical equivalent of gross mechanical power developed in a dc motor is
Correct : C. ebia
42. The armature torque is ------ that of shaft torque
Correct : C. greater than
43. If the voltage equation of a dc motor is multiplied by ----- on both sides, we get power equation of dc motor
Correct : D. ia
44. The torque equation of a dc motor is --
Correct : D. ta = 0.159Øiapz/a
45. The speed of dc motor is highest on
Correct : A. no load
46. With given power rating for lower current and higher voltage rating of a d.c. machine, one should prefer_________.
Correct : B. wave winding
47. If the number of poles in a lap wound generator be doubled, then the generated e.m.f will_________.
Correct : B. become double
48. The counter emf of dc motor__________
Correct : C. helps in energy conversion
49. In a DC series motor increasing the load current will
Correct : A. decrese the speed
50. The generator works on the principle of
Correct : B. dynamically induced emf
51. Air ducts are provided in armature core to
Correct : B. cool the armature
52. Due to which of the following reasons, copper brushes in D.C. machine are used?
Correct : C. in both of the above cases
53. The magnitude of induced emf in a dc generator is given by
Correct : A. blv
54. In a dc generator, the eddy current power loss is
Correct : A. directly proportional to thickness of each lamination
55. In a 240v dc motor, back emf is 220v and Ra= 0.5Ω then its armature current is
Correct : D. 40a
56. ----- is the power equation of dc motor
Correct : A. via = ebia + ia2 ra
57. 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
Correct : B. 240v
58. 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
Correct : B. 1500 rpm
59. 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
Correct : C. 600
60. The stator of I.M. motor is made up off---------- laminations.
Correct : C. silicon steel
61. Stator part of I.M. has slots to hold -------
Correct : B. stator winding
62. Stator windings are insulated from core with the help of
Correct : B. epoxy coating
63. 3 phase I.M. are classified as --- and---- based on rotor construction.
Correct : A. slip ring & squirrel cage
64. When a induction motor is switched on a rotor frequency is
Correct : B. same as supply frequency
65. when the rotor of induction motor is standstill the value of slip is
Correct : B. 1
66. Squirrel cage I.M.motor has skewed rotor bar to help to produce constant --- .
Correct : B. torque
67. The effect of increasing the length of the air gap in an induction motor will increase
Correct : C. magnetizing current
68. the difference between the synchronous speed and the actual speed of an induction motor is known as
Correct : C. slip
69. Rotating magnetic field is produced in a....
Correct : B. three phase induction motor
70. Star- delta starter of an induction motor
Correct : D. applies reduced voltage to stator
71. Star- delta starter of an induction motor
Correct : B. applies reduced voltage of 1/√3 times of rated voltage to stator
72. The speed of an induction motor
Correct : C. decreases slightly with the increase of load
73. The stator of I.M produces ---- magnetic field.
Correct : B. rotating
74. If the frequency of 3-phase supply to stator of 3-phase I.M. is increased,then synchronous speed----
Correct : B. is increased
75. An I.M. moror is preferred to a D.C. motor because of its-----
Correct : C. simple and rugged construction
76. The starting torque of 3 phase I.M. motor is-------Supply voltage.
Correct : C. directly proportional to squre of
77. Squirrel cage I.M. motor suffers from disadvantage of -- starting torque.
Correct : A. low
78. Rotor winding of 3 phase I.M. is generally------
Correct : A. star connected
79. the direction of rotating magnetic field depends upon
Correct : B. phase sequence of supply voltage
80. The relation among synchronous speed(Ns),rotor speed(Ns),slip(s)
Correct : B. n=(1-s)ns
81. slip of I.M. is given by the formula
Correct : A. (ns-n)/ns
82. when rotor of 3-phase I.M.motor is blocked stopped forcibly, the slip is ---
Correct : D. 1
83. The quantity (Ns-N) with respect to I.M. motor is called----
Correct : C. relative speed
84. frequency( fr) of induced emf in rotor of I.M. is given by --
Correct : D. s.f
85. At any given slip s the rotor induced emf (E2r) is ----
Correct : C. s.e2
86. Rotor induced emf is maximum when slip is --
Correct : B. 1
87. At any given slip s the rotor reactance is ----
Correct : A. s.x2
88. The reactance of the rotor circuit of 3-phase I.M. is maxium at
Correct : D. start
89. which mathematical expression represents correct formula to find rotor current (I2)during starting
Correct : C. e2/ √(r22+x22)
90. which mathematical expression represents correct formula to find rotor current when running at slip s.(I2r)
Correct : D. s.e2/ √(r22+s2x22)
91. The rotor current in 3-phase I.M. is-----slip
Correct : B. directly proportional to slip
92. If slip of a 3-phase I.M. increases, the power factor of rotor circuit
Correct : B. is increased
93. The slip ring I.M. has high starting ----with ------starting current.
Correct : C. high, low
94. the squirrel cage I.M. has ------- starting torque.
Correct : C. moderate
95. External resistance is added to rotor winding of slip ring I.M to --------starting torque
Correct : A. increase
96. For 6 pole 50Hz I.M, sychronous speed of rotating magnetic field is---------
Correct : B. 1000rpm
97. For 2 pole 50Hz I.M,sychronous speed of rotating magnetic field is---------rpm
Correct : A. 3000
98. For sychronous speed of rotating magnetic field 1000rpm, for 50 Hz supply,required no of poles =--------
Correct : A. 6
99. for given no. of poles and if supply frequency reduces, sychronous speed of rotating magnetic field
Correct : B. decreases
100. For 3phase I.M,The synchronous speed of rotating magnetic field is 1000 rpm,speed of rotor is 960 rpm ,then slip is