McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
Chapters
| 51. |
Which D.C. motor is generally preferred for cranes and hoists ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded motor |
| D. | Differentially compounded motor |
| Answer» A. Series motor | |
| 52. |
Three point starter can be used for |
| A. | series motor only |
| B. | shunt motor only |
| C. | compound motor only |
| D. | both shunt and compound motor |
| Answer» D. both shunt and compound motor | |
| 53. |
Sparking, is discouraged in a D.C. motor because |
| A. | it increases the input power con-sumption |
| B. | commutator gets damaged |
| C. | both (a) and (b) |
| D. | none of the above |
| Answer» B. commutator gets damaged | |
| 54. |
Speed control by Ward Leonard method gives uniform speed variation |
| A. | in one direction |
| B. | in both directions |
| C. | below normal speed only |
| D. | above normal speed only. |
| Answer» B. in both directions | |
| 55. |
Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be |
| A. | level compounded |
| B. | under compounded |
| C. | cumulatively compounded |
| D. | differentially compounded |
| Answer» C. cumulatively compounded | |
| 56. |
Following motor is used where high starting torque and wide speed range control is required. |
| A. | Single phase capacitor start |
| B. | Induction motor |
| C. | Synchronous motor |
| D. | D.C. motor |
| Answer» D. D.C. motor | |
| 57. |
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 |
| B. | the motor will work as series motor and run at slow speed in the same direction |
| C. | the motor will work as series motor and run at high speed in the samedirection |
| D. | the motor will not work and come to stop |
| Answer» A. the motor will first stop and then run in opposite direction as series motor | |
| 58. |
Which of the following motor has the poorest speed regulation ? |
| A. | Shunt motor |
| B. | Series motor |
| C. | Differential compound motor |
| D. | Cumulative compound motor |
| Answer» B. Series motor | |
| 59. |
Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | induction motor |
| D. | all of above motors |
| Answer» A. D.C. series motor | |
| 60. |
As -the load is increased the speed of D.C. shunt motor will |
| A. | reduce slightly |
| B. | increase slightly |
| C. | increase proportionately |
| D. | remains unchanged |
| Answer» A. reduce slightly | |
| 61. |
The armature torque of the D.C. shunt motor is proportional to |
| A. | field flux only |
| B. | armature current only |
| C. | both (a) and (b) |
| D. | none of the above |
| Answer» B. armature current only | |
| 62. |
Which of the following method of speed control of D.C. machine will offer minimum efficiency ? |
| A. | Voltage control method |
| B. | Field control method |
| C. | Armature control method |
| D. | All above methods |
| Answer» C. Armature control method | |
| 63. |
Usually wide and sensitive speed control is desired in case of |
| A. | centrifugal pumps |
| B. | elevators |
| C. | steel rolling mills |
| D. | colliery winders |
| Answer» D. colliery winders | |
| 64. |
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 |
| A. | 2.36% |
| B. | 4.76% |
| C. | 6.77% |
| D. | 8.84% |
| Answer» B. 4.76% | |
| 65. |
The armature voltage control of D.C. motor provides |
| A. | constant torque drive |
| B. | constant voltage drive |
| C. | constant current drive |
| D. | none of the above |
| Answer» A. constant torque drive | |
| 66. |
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 |
| B. | a resistance is connected parallel to the armature |
| C. | armature is temporarily open circuited |
| D. | a high value resistor is connected across the fieldwinding |
| Answer» A. a resistance is connected in series with armature | |
| 67. |
The speed of a D.C. shunt motor can be increased by |
| A. | increasing the resistance in armature circuit |
| B. | increasing the resistance in field circuit |
| C. | reducing the resistance in the field circuit |
| D. | reducing the resistance in the armature circuit |
| Answer» B. increasing the resistance in field circuit | |
| 68. |
If I2 be the armature current, then speed of a D.C. shunt motor is |
| A. | independent of Ia |
| B. | proportional to la |
| C. | varies as (Ia) |
| D. | varies as la |
| Answer» A. independent of Ia | |
| 69. |
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 |
| B. | reduce to one-fourth value |
| C. | increase four folds |
| D. | be doubled |
| Answer» A. remain unchanged | |
| 70. |
At the instant of starting when a D.C. motor is put on supply, it behaveslike |
| A. | a highly resistive circuit |
| B. | a low resistance circuit |
| C. | a capacitive circuit |
| D. | none of the above |
| Answer» B. a low resistance circuit | |
| 71. |
The speed of a D.C. motor can be varied by varying |
| A. | field current |
| B. | applied voltage |
| C. | resistance in series with armature |
| D. | any of the above |
| Answer» D. any of the above | |
| 72. |
Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ? |
| A. | Low cost |
| B. | Wide speed range |
| C. | Stability |
| D. | High starting torque. |
| Answer» A. Low cost | |
| 73. |
For a D.C. shunt motor if the excitation is changed |
| A. | torque will remain constant |
| B. | torque will change but power will remain constant |
| C. | torque and power both will change |
| D. | torque, power and speed, all will change |
| Answer» B. torque will change but power will remain constant | |
| 74. |
Which motor has the poorest speed control? |
| A. | Differentially compounded motor |
| B. | Cumulatively compoundedmotor |
| C. | Shunt motor |
| D. | Series motor |
| Answer» D. Series motor | |
| 75. |
The plugging gives the |
| A. | zero torque braking |
| B. | smallest torque braking |
| C. | highest torque braking |
| D. | none of the above |
| Answer» C. highest torque braking | |
| 76. |
The armature voltage control of D.C. motor provides |
| A. | constant voltage drive |
| B. | constant current drive |
| C. | constant torque drive |
| D. | none of the above |
| Answer» C. constant torque drive | |
| 77. |
If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor |
| A. | of lower H.P. should be selected |
| B. | of higher H.P. should be selected |
| C. | can be used for 50°C ambient temperature also |
| D. | is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor |
| Answer» D. is to be derated by a factor recom-mended by manufacturer and select the next higher H.P. motor | |
| 78. |
If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking |
| A. | regenerative |
| B. | plugging |
| C. | dynamic braking |
| D. | none of the above |
| Answer» B. plugging | |
| 79. |
Which of the following motors one will choose to drive the rotary compressor ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | Universal motor |
| D. | Synchronous motor |
| Answer» D. Synchronous motor | |
| 80. |
If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will |
| A. | increase |
| B. | decrease |
| C. | remain same |
| D. | become zero |
| Answer» A. increase | |
| 81. |
Why are the D.C. motors preferred for traction applications ? |
| A. | Torque and speed are inversely proportional to armature current |
| B. | Torque is proportional to armature current |
| C. | Torque is proportional to square root of armature current |
| D. | The speed is inversely proportional to the torque and the torque is proportional to square of armature current |
| Answer» D. The speed is inversely proportional to the torque and the torque is proportional to square of armature current | |
| 82. |
Which of the following motors is usually used in house-hold refrigerators ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | Single phase induction motor (split phase start or induction run motor) |
| D. | Reluctance motor |
| Answer» C. Single phase induction motor (split phase start or induction run motor) | |
| 83. |
Which of the following motors is most suitable for signalling devices and many kinds of timers ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» D. Reluctance motor | |
| 84. |
Which motor should not be started on no-load ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded motor |
| D. | Differentially compounded motor. |
| Answer» A. Series motor | |
| 85. |
Ward-Leonard control is basically a |
| A. | voltage control method |
| B. | field divertor method |
| C. | field control method |
| D. | armature resistance control method |
| Answer» A. voltage control method | |
| 86. |
For constant torque drive which speed control method is preferred ? |
| A. | Field control |
| B. | Armature voltage control |
| C. | Shunt armature control |
| D. | Mechanical loading system |
| Answer» B. Armature voltage control | |
| 87. |
In Ward-Leonard control the lower limit of speed is imposed by |
| A. | residual magnetism of the generator |
| B. | core losses of motor |
| C. | mechanical losses of motor and gen¬erator together |
| D. | all of the above |
| Answer» A. residual magnetism of the generator | |
| 88. |
The main disadvantage of the Ward-Leonard control method is |
| A. | high initial cost |
| B. | high maintenance cost |
| C. | low efficiency at Hght loads |
| D. | all of the above |
| Answer» D. all of the above | |
| 89. |
Regenerative method of braking is based on that |
| A. | back e.m.f. is less than the applied voltage |
| B. | back e.m.f. is equal to the applied voltage |
| C. | back e.m.f. of rotor is more than the applied voltage |
| D. | none of the above |
| Answer» B. back e.m.f. is equal to the applied voltage | |
| 90. |
The hysteresis loss in a D.C. machine least depends on |
| A. | Frequency of magnetic reversals |
| B. | Maximum value of flux density |
| C. | Volume and grade of iron |
| D. | Rate of flow of ventilating air |
| Answer» D. Rate of flow of ventilating air | |
| 91. |
In a D.C. generator all of the following could be the effects of iron losses except |
| A. | Loss of efficiency |
| B. | Excessive heating of core |
| C. | Increase in terminal voltage |
| D. | Rise in temperature of ventilating air |
| Answer» C. Increase in terminal voltage | |
| 92. |
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 ? |
| A. | hysteresis loss |
| B. | field copper loss |
| C. | armature copper loss |
| D. | eddy current loss |
| Answer» C. armature copper loss | |
| 93. |
Which of the following loss in a D.C. generator varies significantly with the load current ? |
| A. | Field copper loss |
| B. | Windage loss |
| C. | Armature copper loss |
| D. | None of the above |
| Answer» C. Armature copper loss | |
| 94. |
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. | all above factors |
| Answer» D. all above factors | |
| 95. |
D.C. shunt motors are used for driving |
| A. | trains |
| B. | cranes |
| C. | hoists |
| D. | machine tools |
| Answer» D. machine tools | |
| 96. |
In a manual shunt motor starter |
| A. | over load relay is connected in series and no volt relay in parallel with the load |
| B. | over load relay is connected in paral¬lel and no volt relay in series with the load |
| C. | over load relay and no volt relay are both connected in series with the load |
| D. | over load relay and no volt relay are both connected in parallel with the load |
| Answer» A. over load relay is connected in series and no volt relay in parallel with the load | |
| 97. |
Which of the following steps is likely to result in reduction of hysteresis loss in a D.C. generator ? |
| A. | Providing laminations in armature core |
| B. | Providing laminations in stator |
| C. | Using non-magnetic material for frame |
| D. | Using material of low hysteresis co-efficient for armature corematerial |
| Answer» D. Using material of low hysteresis co-efficient for armature corematerial | |
| 98. |
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 |
| D. | All of the above |
| Answer» D. All of the above | |
| 99. |
Which of the following losses are significantly reduced by laminating the core of a D.C. generator ? |
| A. | Hysteresis losses |
| B. | Eddy current losses |
| C. | Copper losses |
| D. | Windage losses |
| Answer» B. Eddy current losses | |
| 100. |
The total losses in a well designed D.C. generator of 10 kW will be nearly |
| A. | 100 W |
| B. | 500 W |
| C. | 1000 W |
| D. | 1500 W |
| Answer» B. 500 W | |
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