MCQOPTIONS
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MCQOPTIONS
This section includes 100 Mcqs, each offering curated multiple-choice questions to sharpen your NTPC (Technical Ability) knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Which of the following motors is most suitable for signalling devices and many kinds oftimers ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» E. | |
| 52. |
Which of the following is not the standard voltage for power supply in India ? |
| A. | llkV |
| B. | 33kV |
| C. | 66 kV |
| D. | 122 kV |
| Answer» E. | |
| 53. |
The degree of mechanical vibrations produced by the laminations of a transformerdepends on |
| A. | tightness of clamping |
| B. | gauge of laminations |
| C. | size of laminations |
| D. | all of the above |
| Answer» E. | |
| 54. |
Differentially compound D.C. motors can find applicationsrequiring |
| A. | high starting torque |
| B. | low starting torque |
| C. | variable speed |
| D. | frequent on-off cycles |
| Answer» C. variable speed | |
| 55. |
By looking at which part of the motor, it can be easily confirmedthat a particularmotor is D.C. motor? |
| A. | Frame |
| B. | Shaft |
| C. | Commutator |
| D. | Stator |
| Answer» D. Stator | |
| 56. |
Which of the following is not a part of transformer installation ? |
| A. | Conservator |
| B. | Breather |
| C. | Buchholz relay |
| D. | Exciter |
| Answer» E. | |
| 57. |
To get the speed of D.C, motor below the normal without wastage of electrical energy isused. |
| A. | Ward Leonard control |
| B. | rheostatic control |
| C. | any of the above method |
| D. | none of the above method |
| Answer» B. rheostatic control | |
| 58. |
Which of the following properties is not necessarily desirable for the material fortransformer core ? |
| A. | Low hysteresis loss |
| B. | High permeability |
| C. | High thermal conductivity |
| D. | Adequate mechanicalstrength |
| Answer» D. Adequate mechanicalstrength | |
| 59. |
Reduction in core losses and increase in permeability are obtained with transformeremploying |
| A. | core built-up of laminations of cold rolled grain oriented steel |
| B. | core built-up of laminations of hot rolled sheet |
| C. | either of the above |
| D. | none of the above |
| Answer» B. core built-up of laminations of hot rolled sheet | |
| 60. |
Two generators A and B have 6-poles each. Generator A has wave wound armature while generator B has lap wound armature. The ratio of the induced e.m.f. is generatorA and B will be |
| A. | 2 : 3 |
| B. | 3 : 1 |
| C. | 3 : 2 |
| D. | 1 :3 |
| Answer» C. 3 : 2 | |
| 61. |
In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be |
| A. | 4 |
| B. | 8 |
| C. | 16 |
| D. | 32 |
| Answer» C. 16 | |
| 62. |
If R2 is the resistance of secondary winding of the transformer and K is thetransformation ratio then the equivalent secondary resistance referred to primary will be |
| A. | R2/VK |
| B. | R2IK2 |
| C. | R22!K2 |
| D. | R22/K |
| Answer» C. R22!K2 | |
| 63. |
In any rotating machine that part which houses the conductors and inwhich e.m.f. induced is to be utilised is called |
| A. | rotor |
| B. | stator |
| C. | field |
| D. | armature |
| Answer» E. | |
| 64. |
Which of the following property is not necessarily desirable in the material fortransformer core ? |
| A. | Mechanical strength |
| B. | Low hysteresis loss |
| C. | High thermal conductivity |
| D. | High permeability |
| Answer» D. High permeability | |
| 65. |
The voltage drop for which of the following types of brush can be expected to beleast? |
| A. | Graphite brushes |
| B. | Carbon brushes |
| C. | Metal graphite brushes |
| D. | None of the above |
| Answer» D. None of the above | |
| 66. |
Which of the following does not change in an ordinary transformer ? |
| A. | Frequency |
| B. | Voltage |
| C. | Current |
| D. | Any of the above |
| Answer» B. Voltage | |
| 67. |
Two generators are running in parallel. One of the generators may run asmotor for which of the following reasons ? |
| A. | The direction of that generator is reversed |
| B. | The speed of that generator is increased |
| C. | The field of that generator is weakened |
| D. | That generator takes large share of loads |
| Answer» E. | |
| 68. |
For both lap and wave windings, there are as many commutator bars as thenumberof |
| A. | slots |
| B. | armature conductors |
| C. | winding elements |
| D. | poles |
| Answer» D. poles | |
| 69. |
Which of the following insulating materials can withstand the highest temperaturesafely ? |
| A. | Cellulose |
| B. | Asbestos |
| C. | Mica |
| D. | Glass fibre |
| Answer» D. Glass fibre | |
| 70. |
If residual magnetism is present in a D.C. generator, the induced e.m.f. at zero speedwill be |
| A. | zero |
| B. | small |
| C. | the same as rated voltage |
| D. | high |
| Answer» B. small | |
| 71. |
Gas is usually not liberated due to dissociation of transformer oil unless the oiltemperature exceeds |
| A. | 50°C |
| B. | 80°C |
| C. | 100°C |
| D. | 150°C |
| Answer» E. | |
| 72. |
The changes in volume of transformer cooling oil due to variation of atmospherictemperature during day and night is taken care of by which part of transformer |
| A. | Conservator |
| B. | Breather |
| C. | Bushings |
| D. | Buchholz relay |
| Answer» B. Breather | |
| 73. |
The essential condition for parallel operation of two D.C. generators is thatthey have ' |
| A. | same kW rating |
| B. | the same operation r.p.m. |
| C. | the same drooping voltage charac-teristics |
| D. | same percentage regulation |
| Answer» D. same percentage regulation | |
| 74. |
Which of the following load normally needs starting torque more than theratedtorque? |
| A. | Blowers |
| B. | Conveyors |
| C. | Air compressors |
| D. | Centrifugal pumps |
| Answer» C. Air compressors | |
| 75. |
The secondary of a current transformer is always short-circuited underoperatingconditions because it |
| A. | avoids core saturation and high voltage induction |
| B. | is safe to human beings |
| C. | protects the primary circuit |
| D. | none of the above |
| Answer» B. is safe to human beings | |
| 76. |
The mechanical power developed by a shunt motor will be maximum when theratio ofback e.m.f. to applied voltage is |
| A. | 4.0 |
| B. | 2.0 |
| C. | 1.0 |
| D. | 0.5 |
| Answer» E. | |
| 77. |
The terminal voltage of a D.C. shunt generator drops on load because ofall of the following reasons except |
| A. | armature reaction |
| B. | armature resistance drop |
| C. | field weakening due to armature reaction and armature |
| D. | commut ation |
| Answer» E. | |
| 78. |
In a D.C. generator in order to reduce sparking at brushes, the self-induced e.m.f. in the coil is neutralised by all of the following except |
| A. | interpoles |
| B. | dummy coils |
| C. | compensating winding |
| D. | shifting of axis of brushes |
| Answer» C. compensating winding | |
| 79. |
D.C. motor is to drive a load which has certain minimum value for most of thetime and some peak value for short duration. We will select the |
| A. | series motor |
| B. | shunt motor |
| C. | compound motor |
| D. | any of the above |
| Answer» B. shunt motor | |
| 80. |
The no load current in a transformer lags behind the appliedvoltage by an angle ofabout |
| A. | 180° |
| B. | 120" |
| C. | 90° |
| D. | 75° |
| Answer» E. | |
| 81. |
Which winding in a transformer has more number of turns ? |
| A. | Low voltage winding |
| B. | High voltage winding |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» C. Primary winding | |
| 82. |
Which of the following tests will be suitable for testing two similar D.C. series motors oflarge capacity ? |
| A. | Swinburne'stest |
| B. | Hopkinson'stest |
| C. | Field test |
| D. | Brake test |
| Answer» D. Brake test | |
| 83. |
If the supply frequency to the transformer is increased,"the iron loss will |
| A. | not change |
| B. | decrease |
| C. | increase |
| D. | any of the above |
| Answer» D. any of the above | |
| 84. |
Losses which occur in rotating electric machines and do not occur in transformers are |
| A. | friction and windage losses |
| B. | magnetic losses |
| C. | hysteresis and eddy current losses |
| D. | copper losses |
| Answer» B. magnetic losses | |
| 85. |
A shunt generator running at 1000 r.p.m. has generated e.m.f. as 200 V. If thespeed increases to 1200 r.p.m., the generated e.m.f. will be nearly |
| A. | 150 V |
| B. | 175 V |
| C. | 240 V |
| D. | 290V |
| Answer» D. 290V | |
| 86. |
Ifthe percentage impedances of the two transformers working in parallel aredifferent, then |
| A. | transformers will be overheated |
| B. | power factors of both the trans-formers will be same |
| C. | parallel operation will be not possible |
| D. | parallel operation will still be possible, but the power factors at which the two tr |
| Answer» B. power factors of both the trans-formers will be same | |
| 87. |
Following D.C. generator will be in a position to build up without anyresidual magnetism in the poles |
| A. | series generator |
| B. | shunt generator |
| C. | compound generator |
| D. | self-excited generator |
| Answer» E. | |
| 88. |
Which of the following components of a D.C, generator plays vital role forproviding direct current of a D.C. generator ? |
| A. | Dummy coils |
| B. | Commutator |
| C. | Eye bolt |
| D. | Equilizer rings |
| Answer» C. Eye bolt | |
| 89. |
Which of the following method of speed control of D.C. machine will offer minimumefficiency ? |
| A. | Voltage control method |
| B. | Field control method |
| C. | Armature control method |
| D. | All above methods |
| Answer» D. All above methods | |
| 90. |
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» C. 6.77% | |
| 91. |
Series field of DC generators consists of ___number of turns and ____ conductors respectively |
| A. | Large and thick |
| B. | Large and thin |
| C. | 7.45 kN |
| D. | Less and thin |
| Answer» C. 7.45 kN | |
| 92. |
For a dc machine shunt resistance and armature resistance values are |
| A. | High and high |
| B. | High and low |
| C. | By tipping it over |
| D. | Low and high |
| Answer» D. Low and high | |
| 93. |
DC machine windings are |
| A. | Full pitched |
| B. | Short pitched |
| C. | 1 : 4 |
| D. | None of the above |
| Answer» D. None of the above | |
| 94. |
A synchronous generator is feeding a zero power factor (lagging) load at rated current. The armature reaction is |
| A. | magnetizing |
| B. | demagnetizing |
| C. | Annual usage value |
| D. | ineffective |
| Answer» D. ineffective | |
| 95. |
In DC generators brushes are used for |
| A. | Collecting of current with minimum sparking |
| B. | Collecting of voltage |
| C. | A\[\to \]3, B\[\to \]2, C\[\to \]1 |
| D. | Convert ac armature current in to dc |
| Answer» C. A\[\to \]3, B\[\to \]2, C\[\to \]1 | |
| 96. |
Thin laminations are used in a machine in order to reduce |
| A. | Eddy current losses |
| B. | Hysteresis losses |
| C. | Cost of material wasted |
| D. | Copper losses |
| Answer» D. Copper losses | |
| 97. |
The spit phase induction motor has |
| A. | Low starting current and high starting torque |
| B. | Moderate starting current and moderate starting torque |
| C. | Increase 1.414 times |
| D. | Moderate starting current and low starting torque |
| Answer» B. Moderate starting current and moderate starting torque | |
| 98. |
Which test is also called as back to back test? |
| A. | Retardation test |
| B. | Sumpner's test |
| C. | Direct cost |
| D. | Voltage drop test |
| Answer» D. Voltage drop test | |
| 99. |
m normal dc machines operating at full-load conditions, the most powerful electromagnet is |
| A. | field winding |
| B. | armature winding |
| C. | 30 |
| D. | inter pole and compensating windings together |
| Answer» D. inter pole and compensating windings together | |
| 100. |
For an induction motor, operating at a slip s, the ratio of gross power output to air gap power is equal to |
| A. | \[{{(1-s)}^{2}}\] |
| B. | \[(1-s)\] |
| C. | 4 |
| D. | \[(1-\sqrt{s})\] |
| Answer» E. | |