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:
Correct : 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:
Correct : C. decreases
12. A DC series motor is best suited for electrical traction because:
Correct : A. it develops high starting torque
13. Which of the following dc motor has maximum self relieving property:
Correct : B. series
14. When the direction of power flow in a differential compounded motor reverses, it will operate as a:
Correct : A. cumulative compound generator
15. A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be:
Correct : C. cumulative compound
16. The output voltage of a DC generator is
Correct : A. e = v + iara
17. The material used for commutator brushes is mostly
Correct : 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?
Correct : B. 100
19. Magnetic field of a DC generator is produced by what?
Correct : B. electromagnets
20. In a DC generator the emf generated by the armature is maximum when
Correct : A. rate of change of flux is maximum
21. What is the actual arrangement of series wound generator?
Correct : D. armature and field both are in series with the load
22. What is the effect of armature reaction?
Correct : C. both option b & a
23. In DC machine, brushes are always placed along
Correct : A. magnetic neutral axis
24. What type of connection is made in between the interpole & the field winding?
Correct : B. parallel
25. In DC machine, lap winding is used in
Correct : A. high current and low voltage applications
26. The basic requirement of a dc armature winding is that it must be
Correct : A. a closed one
27. The sole purpose of a commutator in a dc generator is to
Correct : D. convert the induced ac into dc
28. In a dc generator, the generator, the generated emf is directly proportional to the
Correct : B. pole flux
29. Voltage equation of a dc motor is
Correct : A. v = eb + iara
30. which of the following motor has the constant speed?
Correct : B. shunt motor
31. The usual test to find the efficiency of the traction motor is
Correct : A. field\s test
32. A DC series motor is best for driving
Correct : B. cranes and hoists
33. In a DC series motor increasing the load current will
Correct : A. decrease the speed
34. The DC motor, which can provide zero speed regulation at full load without any controller is
Correct : B. shunt
35. In 8 - pole wave connected motor armature, the number of parallel paths are
Correct : C. 2
36. The speed of a dc motor can be controlled by varying
Correct : D. all of the above
37. The d.c. series motor should always be started with load because
Correct : A. at no load, it will rotate at dangerously high speed.
38. In a d.c. machine, the armature mmf is
Correct : C. stationary w.r.t. field.
39. In a DC motor, unidirectional torque is produced with the help of
Correct : D. both a and b
40. The counter emf of dc motor
Correct : C. helps in energy conversion
41. The Eb/V ratio of a dc motor is an indication of its
Correct : A. efficiency
42. The induced emf in the armature conductors of a dc motor is
Correct : A. sinusoidal
43. A dc motor can be looked upon as dc generator with the power flow
Correct : B. reversed
44. The Ta/Ia graph of a dc series motor is a
Correct : D. parabola upto full load and a straight line at overloads
45. When load is removed, .......motor will run at the highest speed.
Correct : D. series
46. In Fleming's right-hand rule, the thumb point towards
Correct : 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____.
Correct : A. silicon steel
48. The yoke of a d.c. machine is made of ____.
Correct : D. cast steel
49. . The coupling field electrical and mechanical systems of dc machine is____.
Correct : B. magnetic field
50. The real working part of a dc machine is the ___.
Correct : C. armature winding
51. ____ dc machine are most common.
Correct : B. 4-pole
52. The armature winding of a dc machine is place on rotor to_____.
Correct : C. improve commutation
53. The yoke of a dc machine carries ____pole flux.
Correct : B. one-half of
54. A 4-pole dc machine has ____ magnetic circuits.
Correct : C. 4
55. The field structure of a dc machine uses ____.
Correct : A. salient pole arrangement
56. ____ together are called stray losses
Correct : B. iron and mechnical losses
57. The armature conductors of 6 pole, lap wound D.C. generator are divided into
Correct : 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.?
Correct : C. 305.15v
59. The commutator of D.C. geenrator acts as ___
Correct : 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 ___
Correct : D. 0.055Ω
61. Wave wound genrators provide
Correct : A. less current but more voltage
62. A D.C. motor is still used in industrial applications because it____.
Correct : C. provides fine speed control
63. The field poles and armature of a D.C. machine are laminated to___.
Correct : C. reduce eddy currents
64. The value of back EMF in a DC motor is maximum at ____.
Correct : 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)
Correct : B. half
66. When the speed of dc motor increases , its armature current ----
Correct : B. decreases
67. The amount of back emf of a shunt motor will increase when
Correct : C. the field is strengthened
68. The speed of a dc motor is
Correct : B. inversely propotional to flux per pole
69. The torque developed by a dc motor is directly propotional to---
Correct : 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
Correct : 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 _____.
Correct : C. reduce sparking
72. The speed of a ____ motor is practically constant
Correct : D. shunt motor
73. ____ motor is a variable speed motor.
Correct : A. series
74. The most commonly used method of speed control of a DC motor is by varying ____.
Correct : B. field control
75. The running speed of a DC series motor is basically determined by _____.
Correct : B. load
76. ____ motor has the best speed regulation
Correct : C. shunt
77. The deciding factor in the selection of a dc motor for a particular application is its ____ characteristics
Correct : A. speed-torque
78. A series motor will over speed when ____.
Correct : D. laod is removed
79. A cumulatively compounded motor does not run at dangerous speed at light loads because of the presence of ______.
Correct : A. shunt winding
80. DC shunt motor are used in those applications where____ is required.
Correct : B. practically constant speed
81. DC series motor are used in those applications where ____ is required.
Correct : A. high statring torque
82. Cumulatively compounded motors are used where we require _____.
Correct : C. sudden heavy loads for short duration
83. ____ motors never use belt- connected loads.
Correct : A. series
84. For 20% increase in current, the motor that will give the greastest increase in torque is ___ motor
Correct : B. series
85. Each commutator segment is connected to armature conductor by means of ___
Correct : C. copper lug
86. In a 4 pole machine___
Correct : 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____
Correct : C. doubled
88. Back EMF of DC motor depends on
Correct : A. field flux
89. A DC motor develops torque of the 100Nm at 400 rpm, at 300 rpm a motor will develop torque of___.
Correct : B. 100nm
90. A DC series motor is most suitable for _____.
Correct : A. cranes
91. ____ motor is most suitable for punch presses
Correct : D. cumulative compound
92. In a vaccum cleaner, we generally use ____ motor
Correct : C. series motor
93. The most suitable motor for elevators is the ___ motor.
Correct : D. cumulative compound
94. The friction and windage losses in a DC motor depends upon ____.
Correct : A. speed
95. A motor takes a large starting currents because _____.
Correct : B. back emf is low
96. Excessive sparking at the brushes may be caused due to _____.
Correct : 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?
Correct : 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?
Correct : 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?
Correct : 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?