MCQOPTIONS
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MCQOPTIONS
This section includes 223 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
Which of the following does not change in a transformer? |
| A. | Current |
| B. | Voltage |
| C. | Frequency |
| D. | All of the above |
| Answer» D. All of the above | |
| 52. |
When a given transformer is run at its rated voltage but reduced frequency, its |
| A. | flux density remains unaffected |
| B. | iron losses are reduced |
| C. | core flux density is reduced |
| D. | core flux density is increased |
| Answer» E. | |
| 53. |
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 | |
| 54. |
Two transformers operating in parallel will share the load depending upon their |
| A. | leakage reactance |
| B. | per unit impedance |
| C. | efficiencies |
| D. | ratings |
| Answer» C. efficiencies | |
| 55. |
If R₂ is the resistance of secondary winding of the transformer and K is the transformation ratio then the equivalent secondary resistance referred to primary will be |
| A. | R₂/√K |
| B. | R₂/K² |
| C. | R₂²/K² |
| D. | R₂²/K |
| Answer» C. R₂²/K² | |
| 56. |
Buchholz's relay gives warning and protection against |
| A. | electrical fault inside the transformer itself |
| B. | electrical fault outside the transformer in outgoing feeder |
| C. | for both outside and inside faults |
| D. | none of the above |
| Answer» B. electrical fault outside the transformer in outgoing feeder | |
| 57. |
The transformer laminations are insulated from each other by |
| A. | mica strip |
| B. | thin coat of varnish |
| C. | paper |
| D. | any of the above |
| Answer» C. paper | |
| 58. |
In the transformer following winding has got more cross-sectional area |
| A. | Low voltage winding |
| B. | High voltage winding |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» B. High voltage winding | |
| 59. |
A transformer core is laminated to |
| A. | reduce hysteresis loss |
| B. | reduce eddy current losses |
| C. | reduce copper losses |
| D. | reduce all above losses |
| Answer» C. reduce copper losses | |
| 60. |
Greater the secondary leakage flux |
| A. | less will be the secondary induced e.m.f. |
| B. | less will be the primary induced e.m.f. |
| C. | less will be the primary terminal voltage |
| D. | none of the above |
| Answer» B. less will be the primary induced e.m.f. | |
| 61. |
The primary coil of a transformer is connected to a 60 V ac source. The secondary coil is connected to a 330 Ω load. The turns ratio is 3:1. What is the secondary voltage? |
| A. | 2 V |
| B. | 20 V |
| C. | 180 V |
| D. | 18 V |
| Answer» C. 180 V | |
| 62. |
If a transformer is continuously operated the maximum temperature rise will occur in |
| A. | core |
| B. | windings |
| C. | tank |
| D. | any of the above |
| Answer» C. tank | |
| 63. |
During short circuit test iron losses are negligible because |
| A. | the current on secondary side is negligible |
| B. | the voltage on secondary side does not vary |
| C. | the voltage applied on primary side is low |
| D. | full-load current is not supplied to the transformer |
| Answer» D. full-load current is not supplied to the transformer | |
| 64. |
While conducting short-circuit test on a transformer the following side is short circuited |
| A. | High voltage side |
| B. | Low voltage side |
| C. | Primary side |
| D. | Secondary side |
| Answer» C. Primary side | |
| 65. |
The starting torque of a squirrel-cage induction motor is |
| A. | low |
| B. | negligible |
| C. | same as full-load torque |
| D. | slightly more than full-load torque |
| Answer» B. negligible | |
| 66. |
The purpose of providing iron core in a step-up transformer is |
| A. | To provide coupling between primary and secondary |
| B. | To increase the magnitude of mutual flux |
| C. | To decrease the magnitude of magnetizing current |
| D. | To provide all above features |
| Answer» D. To provide all above features | |
| 67. |
No-load current in a transformer |
| A. | lags behind the voltage by about 75° |
| B. | leads the voltage by about 75° |
| C. | lags behind the voltage by about 15° |
| D. | leads the voltage by about 15° |
| Answer» B. leads the voltage by about 75° | |
| 68. |
In a transformer the tappings are generally provided on |
| A. | primary side |
| B. | secondary side |
| C. | low voltage side |
| D. | high voltage side |
| Answer» E. | |
| 69. |
A transformer has a 1:6 turns ratio and a secondary coil load resistance of 470 Ω. The load resistance as seen by the source is |
| A. | 1.3 Ω |
| B. | 7.8 Ω |
| C. | 78 Ω |
| D. | 13 Ω |
| Answer» E. | |
| 70. |
The use of higher flux density in the transformer design |
| A. | reduces weight per kVA |
| B. | reduces iron losses |
| C. | reduces copper losses |
| D. | increases part load efficiency |
| Answer» B. reduces iron losses | |
| 71. |
Which of the following is not a routine test on transformers? |
| A. | Core insulation voltage test |
| B. | Impedance test |
| C. | Radio interference test |
| D. | Polarity test |
| Answer» D. Polarity test | |
| 72. |
During open circuit test of a transformer |
| A. | primary is supplied rated voltage |
| B. | primary is supplied full-load current |
| C. | primary is supplied current at reduced voltage |
| D. | primary is supplied rated kVA |
| Answer» B. primary is supplied full-load current | |
| 73. |
An ideal transformer has infinite values of primary and secondary inductances. The statement is |
| A. | true |
| B. | false |
| Answer» C. | |
| 74. |
When the equivalent circuit diagram of doouble squirrelcage induction motor is constructed the two cages can be considered |
| A. | in series |
| B. | in parallel |
| C. | in series-parallel |
| D. | in parallel with stator |
| Answer» C. in series-parallel | |
| 75. |
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. | |
| 76. |
For the parallel operation of single phase transformers it is necessary that they should have |
| A. | same efficiency |
| B. | same polarity |
| C. | same kVA rating |
| D. | same number of turns on the secondary side. |
| Answer» C. same kVA rating | |
| 77. |
Sumpner's test is conducted on transformers to determine |
| A. | temperature |
| B. | stray losses |
| C. | all-day efficiency |
| D. | none of the above |
| Answer» B. stray losses | |
| 78. |
The power transformer is a constant |
| A. | voltage device |
| B. | current device |
| C. | power device |
| D. | main flux device |
| Answer» E. | |
| 79. |
The noise resulting from vibrations of laminations set by magnetic forces, is termed as |
| A. | Magnetostriction |
| B. | Boo |
| C. | Hum |
| D. | Zoom |
| Answer» D. Zoom | |
| 80. |
The efficiencies of transformers compared with that of electric motors of the same power are |
| A. | about the same |
| B. | much smaller |
| C. | much higher |
| D. | somewhat smaller |
| Answer» D. somewhat smaller | |
| 81. |
Losses which occur in rotating electric machines and do not occur in trans formers are |
| A. | friction and windage losses |
| B. | magnetic losses |
| C. | hysteresis and eddy current losses |
| D. | copper losses |
| Answer» B. magnetic losses | |
| 82. |
A transformer oil must be free from |
| A. | sludge |
| B. | odour |
| C. | gases |
| D. | moisture |
| Answer» E. | |
| 83. |
The dielectric strength of transformer oil is expected to be |
| A. | lkV |
| B. | 33 kV |
| C. | 100 kV |
| D. | 330 kV |
| Answer» C. 100 kV | |
| 84. |
No-load on a transformer is carried out to determine |
| A. | copper loss |
| B. | magnetising current |
| C. | magnetising current and loss |
| D. | efficiency of the transformer |
| Answer» D. efficiency of the transformer | |
| 85. |
In a transformer routine efficiency depends upon |
| A. | supply frequency |
| B. | load current |
| C. | power factor of load |
| D. | both (B) and (C) |
| Answer» E. | |
| 86. |
Which type of winding is used in 3phase shell-type transformer? |
| A. | Circular type |
| B. | Sandwich type |
| C. | Cylindrical type |
| D. | Rectangular type |
| Answer» C. Cylindrical type | |
| 87. |
Which motor is preferred for use in mines where explosive gases exist? |
| A. | Air motor |
| B. | Induction motor |
| C. | Shunt motor |
| D. | Synchronous motor |
| Answer» B. Induction motor | |
| 88. |
Negative voltage regulation is indicative that the load is |
| A. | capacitive only |
| B. | inductive only |
| C. | inductive or resistive |
| D. | none of the above |
| Answer» B. inductive only | |
| 89. |
Primary winding of a transformer |
| A. | is always a low voltage winding |
| B. | is always a high voltage winding |
| C. | could either be a low voltage or high voltage winding |
| D. | none of the above |
| Answer» D. none of the above | |
| 90. |
Which of the following is the main advantage of an auto-transformer over a two winding transformer? |
| A. | Hysteresis losses are reduced |
| B. | Saving in winding material |
| C. | Copper losses are negligible |
| D. | Eddy losses are totally eliminated |
| Answer» C. Copper losses are negligible | |
| 91. |
Open circuit test on transformers is conducted to determine |
| A. | hysteresis losses |
| B. | copper losses |
| C. | core losses |
| D. | eddy current losses |
| Answer» D. eddy current losses | |
| 92. |
Noise level test in a transformer is a |
| A. | special test |
| B. | routine test |
| C. | type test |
| D. | none of the above |
| Answer» D. none of the above | |
| 93. |
An ideal transformer is one which has |
| A. | no losses and magnetic leakage |
| B. | interleaved primary and secondary windings |
| C. | a common core for its primary and secondary windings |
| D. | core of stainless steel and winding of pure copper metal |
| Answer» B. interleaved primary and secondary windings | |
| 94. |
The hum in a transformer is mainly attributed to |
| A. | load changes |
| B. | oil in the transformer |
| C. | magnetostriction |
| D. | mechanical vibrations |
| Answer» D. mechanical vibrations | |
| 95. |
Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is |
| A. | approximately equal to one |
| B. | less than one |
| C. | great than one |
| D. | none of the above |
| Answer» B. less than one | |
| 96. |
The power factor of an induction motor under no-load conditions will be closer to |
| A. | 0.2 lagging |
| B. | 0.2 leading |
| C. | 0.5 leading |
| D. | unity |
| Answer» B. 0.2 leading | |
| 97. |
Which of the following acts as a protection against high voltage surges due to lightning and switching? |
| A. | Horn gaps |
| B. | Thermal overload relays |
| C. | Breather |
| D. | Conservator |
| Answer» B. Thermal overload relays | |
| 98. |
In a certain transformer, the input power to the primary is 120 W. If 8.5 W are lost to the winding resistance, what is the output power to the load, neglecting any other issues? |
| A. | 0 W |
| B. | 14.1 W |
| C. | 111.5 W |
| D. | 1,020 W |
| Answer» D. 1,020 W | |
| 99. |
Short circuit test on transformers is conducted to determine |
| A. | hysteresis losses |
| B. | copper losses |
| C. | core losses |
| D. | eddy current losses |
| Answer» C. core losses | |
| 100. |
Part of the transformer which is most subject to damage from overheating is |
| A. | iron core |
| B. | copper winding |
| C. | winding insulation |
| D. | frame or case |
| Answer» D. frame or case | |