MCQOPTIONS
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MCQOPTIONS
This section includes 122 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 101. |
In an induction motor, the meaning of synchronous wattage means: |
| A. | Shaft output in watts |
| B. | Combined stator and rotor inputs in watts |
| C. | Stator input in watts |
| D. | Rotor input in watts |
| Answer» E. | |
| 102. |
Magnetising current of an induction motor is much larger than a two-winding transformer of the same rating. This is due to: |
| A. | Small leakage |
| B. | Rotating parts |
| C. | Air gap |
| D. | Laminations |
| Answer» D. Laminations | |
| 103. |
Assertion (A): The synchronous speed of an induction motor can be varied by varying the frequency of the applied voltage.Reason (R): With a smaller frequency of operation, there is a large value of slip and motor rotates non-linearly with the frequency ‘f ’ of the applied voltage. |
| A. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
| B. | Both (A) and (R) are true, but (R) is not the correct explanation of (A). |
| C. | (A) is true, but (R) is false. |
| D. | (A) is false, but (R) is true. |
| Answer» D. (A) is false, but (R) is true. | |
| 104. |
If there were no copper losses in the induction motor then ________ |
| A. | rotor does not run |
| B. | rotor runs at infinite speed |
| C. | rotor runs at normal speed |
| D. | rotor runs at synchronous speed |
| Answer» E. | |
| 105. |
Directions: It consists of two statements, one labelled as the ‘Statement (I)’ and the other as ‘Statement (II). Examine these two statements carefully and select the answer using the codes given below:Statement (I): The no load current drawn by the induction motor is usually more than that of a transformer.Statement (II): An induction motor can be considered as a generalized transformer. |
| A. | Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) |
| B. | Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I) |
| C. | Statement (I) is true but Statement (II) is false |
| D. | Statement (I) is false but Statement (II) is true |
| Answer» C. Statement (I) is true but Statement (II) is false | |
| 106. |
For a given three-phase induction motor, the slip at full load is: |
| A. | equal to slip at no-load |
| B. | less than slip at no-load |
| C. | greater than slip at no-load |
| D. | equal to zero |
| Answer» D. equal to zero | |
| 107. |
Maximum torque of a 3 - phase induction motor is |
| A. | Independent of rotor resistance |
| B. | Directly proportional to square of rotor resistance. |
| C. | Inversely proportional to rotor resistance. |
| D. | Proportional to rotor resistance. |
| Answer» B. Directly proportional to square of rotor resistance. | |
| 108. |
A 12-pole induction motor has a frequency of 60 Hz. Its synchronous speed would be: |
| A. | 600 rpm |
| B. | 480 rpm |
| C. | 660 rpm |
| D. | 500 rpm |
| Answer» B. 480 rpm | |
| 109. |
Calculate the frequency of rotor current if supply frequency is 50 Hz and slip is 5%. |
| A. | 2.5 Hz |
| B. | 25 Hz |
| C. | 50 Hz |
| D. | 10 Hz |
| Answer» B. 25 Hz | |
| 110. |
If all the stator coils of a motor are connected for the same magnetic polarity, there will be formed an equal number of ________. |
| A. | consequent poles with opposite polarity |
| B. | consequent poles with the same polarity |
| C. | rotor poles with opposite polarity |
| D. | rotor poles with the same polarity |
| Answer» B. consequent poles with the same polarity | |
| 111. |
For a three-phase induction motor \(\frac{{slip\;at\;No\;Load}}{{slip\;at\;Full\;Load}}\) =? |
| A. | always less than one |
| B. | always equal to one |
| C. | always less than zero |
| D. | always equal to zero |
| Answer» B. always equal to one | |
| 112. |
At the instant of starting, the per-unit slip of 3-phase induction motor is |
| A. | 0.05 |
| B. | 0.1 |
| C. | 1.0 |
| D. | 0.5 |
| Answer» D. 0.5 | |
| 113. |
For a particular kW rating of an induction motor, the kVAR rating of the shunt capacitor required is _______. |
| A. | More for high rated speed motor |
| B. | More for lower rated speed motor |
| C. | Independent of speed |
| D. | None of these |
| Answer» C. Independent of speed | |
| 114. |
Leakage flux in an induction motor is |
| A. | Flux that leaks through the machine |
| B. | Flux that links both stator and rotor windings |
| C. | Flux that links the stator winding or the rotor winding but not both |
| D. | None of these |
| Answer» B. Flux that links both stator and rotor windings | |
| 115. |
A 3-phase induction motor draws active power P and reactive power Q from grid. If it is operating as a generator, P and Q will respectively be |
| A. | Positive and negative |
| B. | Positive and positive |
| C. | Negative and negative |
| D. | Negative and positive |
| Answer» E. | |
| 116. |
A 3-phase induction motor while supplying a constant load has the fuse of one line suddenly blows off. The motor will continue to run with line current nearly increased to |
| A. | 3 times |
| B. | 6 times |
| C. | 5 times |
| D. | √3 times |
| Answer» E. | |
| 117. |
For a ________ induction motor, it is not possible to add any external resistance in series with the rotor circuit for starting purposes. |
| A. | Squirrel - cage |
| B. | Phase wound |
| C. | Slip - ring |
| D. | Wound |
| Answer» B. Phase wound | |
| 118. |
For a slip ring induction motor, if the supply voltage changes by 5 % it will produce approximately a change of ________ in rotor torque. |
| A. | 10% |
| B. | 21% |
| C. | 5% |
| D. | 15% |
| Answer» B. 21% | |
| 119. |
As compared to D.O.L. starter, star delta starter operates at: |
| A. | Full voltage |
| B. | 72% of full voltage |
| C. | 58% of full voltage |
| D. | 34% of full voltage |
| Answer» D. 34% of full voltage | |
| 120. |
For a three-phase machine, the three windings are displaced from each other by __________ electrical space degrees along the air-gap periphery. |
| A. | 180 |
| B. | 60 |
| C. | 90 |
| D. | 120 |
| Answer» E. | |
| 121. |
Find the number of poles required, if the frequency is 50 Hz and speed of the motor is 500 rpm. |
| A. | 24 poles |
| B. | 12 poles |
| C. | 5 poles |
| D. | 10 poles |
| Answer» C. 5 poles | |
| 122. |
Directions: The question consists of two statements, one labelled as ‘Statement (I)’ and the other labelled as ‘Statement (II)’. You are to examine these two statements carefully and select the answers to these items using the codes given below:Statement (I):In a three-phase induction motor, the maximum torque is directly proportional to standstill reactance.Statement (II):In a three-phase induction motor, the speed or the slip at which maximum torque occurs is determined by the rotor resistance. |
| A. | Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I). |
| B. | Both Statement (I) and Statement (II) are individually true, but Statement (II) is not the correct explanation of Statement (I). |
| C. | Statement (I) is true, but Statement (II) is false. |
| D. | Statement (I) is false, but Statement (II) is true. |
| Answer» E. | |