McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 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 | |
Done Studing? Take A Test.
Great job completing your study session! Now it's time to put your knowledge to the test. Challenge yourself, see how much you've learned, and identify areas for improvement. Don’t worry, this is all part of the journey to mastery. Ready for the next step? Take a quiz to solidify what you've just studied.