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.
| 101. |
Which of the following loss in a transformer is zero even at full load ? |
| A. | Core loss |
| B. | Friction loss |
| C. | Eddy current loss |
| D. | Hysteresis loss |
| Answer» C. Eddy current loss | |
| 102. |
A transformer cannot raise or lower the voltage of a D.C. supply because |
| A. | There is no need to change the D.C. voltage |
| B. | A D.C. circuit has more losses |
| C. | Faraday's laws of electromagnetic induction are not valid since the rate of change of flux is zero |
| D. | None of the above |
| Answer» D. None of the above | |
| 103. |
The size of a transformer core will depend on |
| A. | frequency |
| B. | area of the core |
| C. | flux density of the core material |
| D. | (A) and (B) both |
| Answer» E. | |
| 104. |
The full-load copper loss of a transformer is 1600 W. At half-load, the copper loss will be |
| A. | 6400 W |
| B. | 1600 W |
| C. | 800 W |
| D. | 400 W |
| Answer» E. | |
| 105. |
In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of |
| A. | less than 15 A |
| B. | more than 15 A |
| C. | 15 A |
| D. | none of the above |
| Answer» B. more than 15 A | |
| 106. |
No-load current of a transformer has |
| A. | has high magnitude and low power factor |
| B. | has high magnitude and high power factor |
| C. | has small magnitude and high power factor |
| D. | has small magnitude and low power factor |
| Answer» E. | |
| 107. |
The permissible flux density in case of cold rolled grain oriented steel is around |
| A. | 1.7 Wb/m² |
| B. | 2.7 Wb/m² |
| C. | 3.7 Wb/m² |
| D. | 4.7 Wb/m² |
| Answer» B. 2.7 Wb/m² | |
| 108. |
The path of the magnetic flux in transformer should have |
| A. | high reluctance |
| B. | low reactance |
| C. | high resistance |
| D. | low resistance |
| Answer» C. high resistance | |
| 109. |
The path of a magnetic flux in a transformer should have |
| A. | high resistance |
| B. | high reluctance |
| C. | low resistance |
| D. | low reluctance |
| Answer» E. | |
| 110. |
Which winding of the transformer has less cross-sectional area? |
| A. | Primary winding |
| B. | Secondary winding |
| C. | Low voltage winding |
| D. | High voltage winding |
| Answer» E. | |
| 111. |
Which of the following is not a part of transformer installation? |
| A. | Conservator |
| B. | Breather |
| C. | Buchholz relay |
| D. | Exciter |
| Answer» E. | |
| 112. |
The secondary of a current transformer is always short-circuited under operating conditions 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 | |
| 113. |
A transformer can have zero voltage regulation at |
| A. | leading power factor |
| B. | lagging power factor |
| C. | unity power factor |
| D. | zero power factor |
| Answer» B. lagging power factor | |
| 114. |
The voltage transformation ratio of a transformer is equal to the ratio of |
| A. | primary turns to secondary turns |
| B. | secondary current to primary current |
| C. | secondary induced e.m.f. to primary induced e.m.f. |
| D. | secondary terminal voltage to primary applied voltage |
| Answer» D. secondary terminal voltage to primary applied voltage | |
| 115. |
In a transformer the energy is conveyed from primary to secondary |
| A. | through cooling coil |
| B. | through air |
| C. | by the flux |
| D. | none of the above |
| Answer» D. none of the above | |
| 116. |
An open-circuit test on a transformer is conducted primarily to measure |
| A. | insulation resistance |
| B. | copper loss |
| C. | core loss |
| D. | total loss |
| Answer» D. total loss | |
| 117. |
A common method of cooling a power transformer is |
| A. | natural air cooling |
| B. | air blast cooling |
| C. | oil cooling |
| D. | any of the above |
| Answer» D. any of the above | |
| 118. |
The complete circle diagram of induetion motor can be drawn with the help of data found from |
| A. | noload test |
| B. | blocked rotor test |
| C. | stator resistance test |
| D. | all of the above |
| Answer» E. | |
| 119. |
Natural air cooling is generally restricted for transformers up to |
| A. | 1.5 MVA |
| B. | 5 MVA |
| C. | 15 MVA |
| D. | 50 MVA |
| Answer» B. 5 MVA | |
| 120. |
Which of the following properties is not necessarily desirable for the material for transformer core? |
| A. | Low hysteresis loss |
| B. | High permeability |
| C. | High thermal conductivity |
| D. | Adequate mechanical strength |
| Answer» D. Adequate mechanical strength | |
| 121. |
Which of the following property is not necessarily desirable in the material for transformer core? |
| A. | Mechanical strength |
| B. | Low hysteresis loss |
| C. | High thermal conductivity |
| D. | High permeability |
| Answer» D. High permeability | |
| 122. |
Efficiency of a power transformer is of the order of |
| A. | 100 per cent |
| B. | 98 per cent |
| C. | 50 per cent |
| D. | 25 per cent |
| Answer» C. 50 per cent | |
| 123. |
Iron loss of a transformer can be measured by |
| A. | low power factor wattmeter |
| B. | unity power factor wattmeter |
| C. | frequency meter |
| D. | any type of wattmeter |
| Answer» B. unity power factor wattmeter | |
| 124. |
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 | |
| 125. |
In a power or distribution transformer about 10 per cent end turns are heavily insulated |
| A. | to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns |
| B. | to absorb the line surge voltage and save the winding of transformer from damage |
| C. | to reflect the line surge and save the winding of a transformer from damage |
| D. | none of the above |
| Answer» B. to absorb the line surge voltage and save the winding of transformer from damage | |
| 126. |
The efficiency of a transformer, under heavy loads, is comparatively low because |
| A. | copper loss becomes high in proportion to the output |
| B. | iron loss is increased considerably |
| C. | voltage drop both in primary and secondary becomes large |
| D. | secondary output is much less as compared to primary input |
| Answer» B. iron loss is increased considerably | |
| 127. |
Harmonics in transformer result in |
| A. | increased core losses |
| B. | increased I2R losses |
| C. | magnetic interference with communication circuits |
| D. | all of the above |
| Answer» E. | |
| 128. |
Reduction in core losses and increase in permeability are obtained with transformer employing |
| 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 | |
| 129. |
The maximum load that a power transformer can carry is limited by its |
| A. | temperature rise |
| B. | dielectric strength of oil |
| C. | voltage ratio |
| D. | copper loss |
| Answer» D. copper loss | |
| 130. |
Natural oil cooling is used for transformers up to a rating of |
| A. | 3000 kVA |
| B. | 1000 kVA |
| C. | 500 kVA |
| D. | 250 kVA |
| Answer» B. 1000 kVA | |
| 131. |
Material used for construction of transformer core is usually |
| A. | wood |
| B. | copper |
| C. | aluminium |
| D. | silicon steel |
| Answer» E. | |
| 132. |
Transformer breaths in when |
| A. | load on it increases |
| B. | load on it decreases |
| C. | load remains constant |
| D. | none of the above |
| Answer» C. load remains constant | |
| 133. |
What will happen if the transformers working in parallel are not connected with regard to polarity? |
| A. | The power factor of the two transformers will be different from the power factor of common load |
| B. | Incorrect polarity will result in dead short circuit |
| C. | The transformers will not share load in proportion to their kVA ratings |
| D. | none of the above |
| Answer» C. The transformers will not share load in proportion to their kVA ratings | |
| 134. |
Which of the following parts of a transformer is visible from outside? |
| A. | Bushings |
| B. | Core |
| C. | Primary winding |
| D. | Secondary winding |
| Answer» B. Core | |
| 135. |
A no-load test is performed on a transformer to determine |
| A. | core loss |
| B. | copper loss |
| C. | efficiency |
| D. | magnetising current |
| E. | magnetising current and loss |
| Answer» F. | |
| 136. |
The noise produced by a transformer is termed as |
| A. | zoom |
| B. | hum |
| C. | ringing |
| D. | buzz |
| Answer» C. ringing | |
| 137. |
The leakage flux in a transformer depends upon |
| A. | load current |
| B. | load current and voltage |
| C. | load current, voltage and frequency |
| D. | load current, voltage, frequency and power factor |
| Answer» B. load current and voltage | |
| 138. |
Which of the following is the most likely source of harmonics in a transformer? |
| A. | poor insulation |
| B. | Overload |
| C. | loose connections |
| D. | Core saturation |
| Answer» E. | |
| 139. |
When secondary of a current transformer is open-circuited its iron core will be |
| A. | hot because of heavy iron losses taking place in it due to high flux density |
| B. | hot because primary will carry heavy current |
| C. | cool as there is no secondary current |
| D. | none of above will happen |
| Answer» B. hot because primary will carry heavy current | |
| 140. |
The main reason for generation of harmonics in a transformer could be |
| A. | fluctuating load |
| B. | poor insulation |
| C. | mechanical vibrations |
| D. | saturation of core |
| Answer» E. | |
| 141. |
In case of 3-phase induction motors, plugging means |
| A. | pulling the motor directly on line without a starter |
| B. | locking of rotor due to harmonics |
| C. | starting the motor on load which is more than the rated load |
| D. | interchanging two supply phases for quick stopping |
| Answer» E. | |
| 142. |
Which of the following insulating materials can withstand the highest temperature safely? |
| A. | Cellulose |
| B. | Asbestos |
| C. | Mica |
| D. | Glass fibre |
| Answer» D. Glass fibre | |
| 143. |
The magnetising current of a transformer is usually small because it has |
| A. | small air gap |
| B. | large leakage flux |
| C. | laminated silicon steel core |
| D. | fewer rotating parts |
| Answer» B. large leakage flux | |
| 144. |
Power transformers are generally designed to have maximum efficiency around |
| A. | no-load |
| B. | half-load |
| C. | near full-load |
| D. | 10% overload |
| Answer» D. 10% overload | |
| 145. |
Distribution transformers are generally designed for maximum efficiency around |
| A. | 90% load |
| B. | Zero load |
| C. | 25% load |
| D. | 50% load |
| Answer» E. | |
| 146. |
In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be |
| A. | Ns |
| B. | s.N. |
| C. | (l-s)Ns |
| D. | (Ns-l)s |
| Answer» D. (Ns-l)s | |
| 147. |
A shell-type transformer has |
| A. | high eddy current losses |
| B. | reduced magnetic leakage |
| C. | negligibly hysteresis losses |
| D. | none of the above |
| Answer» C. negligibly hysteresis losses | |
| 148. |
Spacers are provided between adjacent coils |
| A. | to provide free passage to the cooling oil |
| B. | to insulate the coils from each other |
| C. | both (A) and (B) |
| D. | none of the above |
| Answer» B. to insulate the coils from each other | |
| 149. |
The efficiency of a transformer will be maximum when |
| A. | copper losses = hysteresis losses |
| B. | hysteresis losses = eddy current losses |
| C. | eddy current losses = copper losses |
| D. | copper losses = iron losses |
| Answer» E. | |
| 150. |
Insertion of resistance in the rotcir of an induction motor to develop a given torque |
| A. | decreases the rotor current |
| B. | increases the rotor current |
| C. | rotor current becomes zero |
| D. | rotor current rernains same |
| Answer» E. | |