McqMate
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 |
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