MCQOPTIONS
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MCQOPTIONS
This section includes 82 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering Questions knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Which type of bearing is provided in small induction motors to support the rotor shaft ? |
| A. | Ball bearings |
| B. | Cast iron bearings |
| C. | Bush bearings |
| D. | None of the above |
| Answer» B. Cast iron bearings | |
| 2. |
Which of the following methods is easily applicable to control the speed of the squirrel-cage induction motor _____________? |
| A. | By changing the number of stator poles |
| B. | Rotor rheostat control |
| C. | By operating two motors in cascade |
| D. | By injecting e.m.f. in the rotor circuit |
| Answer» B. Rotor rheostat control | |
| 3. |
Which is of the following data is required to draw the circle diagram for an induction motor ? |
| A. | Block rotor test only |
| B. | No load test only |
| C. | Block rotor test and no-load test |
| D. | Block rotor test, no-load test and stator resistance test |
| Answer» E. | |
| 4. |
When the equivalent circuit diagram of doouble squirrel-cage 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 | |
| 5. |
When /?2 is the rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running conditions will be_____________? |
| A. | sR2X2 = 1 |
| B. | sR2 = X2 |
| C. | R2 = sX2 |
| D. | R2 = s2X2 |
| Answer» D. R2 = s2X2 | |
| 6. |
What will happen if the relative speed between the rotating flux of stator and rotor of the induction motor is zero ? |
| A. | The slip of the motor will be 5% |
| B. | The rotor will not run |
| C. | The rotor will run at very high speed |
| D. | The torque produced will be very large |
| Answer» C. The rotor will run at very high speed | |
| 7. |
The vafcie of transformation ratio of an induction motor can be found by__________? |
| A. | open-circuit test only |
| B. | short-circuit test only |
| C. | stator resistance test |
| D. | none of the above |
| Answer» C. stator resistance test | |
| 8. |
The torque of a rotor in an induction motor under running condition is maximum__________? |
| A. | at the unit value of slip |
| B. | at the zero value of slip |
| C. | at the value of the slip which makes rotor reactance per phase equal to the resistance per phase |
| D. | at the value of the slip which makes the rotor reactance half of the rotor |
| Answer» D. at the value of the slip which makes the rotor reactance half of the rotor | |
| 9. |
The torque of an induction motor is___________? |
| A. | directly proportional to slip |
| B. | inversely proportional to slip |
| C. | proportional to the square of the slip |
| D. | none of the above |
| Answer» B. inversely proportional to slip | |
| 10. |
The torque developed in the cage induction motor with autostarter is___________? |
| A. | k/torque with direct switching |
| B. | K x torque with direct switching |
| C. | K2 x torque with direct switching |
| D. | k2/torque with direct switching |
| Answer» D. k2/torque with direct switching | |
| 11. |
The torque developed by a 3-phase induction motor least depends on__________? |
| A. | rotor current |
| B. | rotor power factor |
| C. | rotor e.m.f. |
| D. | shaft diameter |
| Answer» E. | |
| 12. |
The term ‘cogging’ is associated with___________? |
| A. | three phase transformers |
| B. | compound generators |
| C. | D.C. series motors |
| D. | induction motors |
| Answer» E. | |
| 13. |
The stating torque of the slip ring induction motor can be increased by adding__________? |
| A. | external inductance to the rotor |
| B. | external resistance to the rotor |
| C. | external capacitance to the rotor |
| D. | both resistance and inductance to rotor |
| Answer» C. external capacitance to the rotor | |
| 14. |
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 | |
| 15. |
The starting torque of a three phase induction motor can be increased by__________? |
| A. | increasing slip |
| B. | increasing current |
| C. | both A. and (b) |
| D. | none of the above |
| Answer» D. none of the above | |
| 16. |
The starting torque of a 3-phase squirrel cage induction motor is____________? |
| A. | twice the full load torque |
| B. | 1.5 times the full load torque |
| C. | equal to full load torque |
| Answer» C. equal to full load torque | |
| 17. |
The speed of a squirrel-cage induction motor can be controlled by all of the following except_____________? |
| A. | changing supply frequency |
| B. | changing number of poles |
| C. | changing winding resistance |
| D. | reducing supply voltage |
| Answer» D. reducing supply voltage | |
| 18. |
The speed characteristics of an induction motor closely resemble the speedload characteristics of which of the following machines? |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | universal motor |
| D. | none of the above |
| Answer» C. universal motor | |
| 19. |
The shape of the torque/slip curve of induction motor is__________? |
| A. | parabola |
| B. | hyperbola |
| C. | rectangular parabola |
| D. | straigth line |
| Answer» D. straigth line | |
| 20. |
The shaft of an induction motor is made of_____________? |
| A. | high speed steel |
| B. | stainless steel |
| C. | carbon steel |
| D. | cast iron |
| Answer» D. cast iron | |
| 21. |
The rotor of an induction motor runs at__________? |
| A. | synchronous speed |
| B. | below synchronous speed |
| C. | above synchronous speed |
| D. | any of the above |
| Answer» C. above synchronous speed | |
| 22. |
The purpose of using short-circuit gear is___________? |
| A. | to short circuit the rotor at slip rings |
| B. | to short circuit the starting resistances in the starter |
| C. | to short circuit the stator phase of motor to form star |
| D. | none of the above |
| Answer» B. to short circuit the starting resistances in the starter | |
| 23. |
The power scale of circle diagram of an induction motor can be found from__________? |
| A. | stator resistance test |
| B. | no-load test only |
| C. | short-circuit test only |
| D. | none of the above |
| Answer» D. none of the above | |
| 24. |
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 | |
| 25. |
The number of slip rings on a squirrel cage induction motor is usually____________? |
| A. | two |
| B. | three |
| C. | four |
| D. | none |
| Answer» E. | |
| 26. |
The maximum torque in an induction motor depends on___________? |
| A. | frequency |
| B. | rotor inductive reactance |
| C. | square of supply voltage |
| D. | all of the above |
| Answer» E. | |
| 27. |
The low power factor of induction motor is due to___________? |
| A. | rotor leakage reactance |
| B. | stator reactance |
| C. | the reactive lagging magnetizing current necessary to generate the magnetic flux |
| D. | all of the above |
| Answer» E. | |
| 28. |
The injected e.m.f. in the rotor of induction motor must have__________? |
| A. | zero frequency |
| B. | the same frequency as the slip frequency |
| C. | the same phase as the rotor e.m.f. |
| D. | high value for the satisfactory speed control |
| Answer» C. the same phase as the rotor e.m.f. | |
| 29. |
The good power factor of an induction motor can be achieved if the average flux density in the air gap is___________? |
| A. | absent |
| B. | small |
| C. | large |
| D. | infinity |
| Answer» C. large | |
| 30. |
The frame of an induction motor is usually made of____________? |
| A. | silicon steel |
| B. | cast iron |
| C. | aluminium |
| D. | bronze |
| Answer» C. aluminium | |
| 31. |
The efficiency of an induction motor can be expected to be nearly____________? |
| A. | 60 to 90% |
| B. | 80 to 90% |
| C. | 95 to 98% |
| D. | 99% |
| Answer» C. 95 to 98% | |
| 32. |
The crawling in the induction motor is caused by____________? |
| A. | low voltage supply |
| B. | high loads |
| C. | harmonics develped in the motor |
| D. | improper design of the machine |
| E. | none of the above |
| Answer» D. improper design of the machine | |
| 33. |
The ‘crawling” in an induction motor is caused by___________? |
| A. | high loads |
| B. | low voltage supply |
| C. | improper design of machine |
| D. | harmonics developed in the motor |
| Answer» E. | |
| 34. |
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. | |
| 35. |
The ‘cogging’ of an induction motor can be avoided by____________? |
| A. | proper ventilation |
| B. | using DOL starter |
| C. | auto-transformer starter |
| D. | having number of rotor slots more or less than the number of stator slots (not equal) |
| Answer» E. | |
| 36. |
The circle diagram for an induction motor cannot be used to determine____________? |
| A. | efficiency |
| B. | power factor |
| C. | frequency |
| D. | output |
| Answer» B. power factor | |
| 37. |
The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type__________? |
| A. | star connected only |
| B. | delta connected only |
| C. | A. and B. both |
| D. | none of the above |
| Answer» D. none of the above | |
| 38. |
Rotor rheostat control method of speed control is used for____________? |
| A. | squirrel-cage induction motors only |
| B. | slip ring induction motors only |
| C. | both A. and (b) |
| D. | none of the above |
| Answer» C. both A. and (b) | |
| 39. |
Reduced voltage starter can be used with_____________? |
| A. | slip ring motor only but not with squirrel cage induction motor |
| B. | squirrel cage induction motor only but not with slip ring motor |
| C. | squirrel cage as well as slip ring induction motor |
| D. | none of the above |
| Answer» D. none of the above | |
| 40. |
Lubricant used for ball bearing is usually___________? |
| A. | graphite |
| B. | grease |
| C. | mineral oil |
| D. | molasses |
| Answer» C. mineral oil | |
| 41. |
Low voltage at motor terminals is due to____________? |
| A. | inadequate motor wiring |
| B. | poorely regulated power supply |
| C. | any one of the above |
| D. | none of the above |
| Answer» D. none of the above | |
| 42. |
Less maintenance troubles are experienced in case of___________? |
| A. | slip ring induction motor |
| B. | squirrel cage induction motor |
| C. | both A. and (b) |
| D. | none of the above |
| Answer» C. both A. and (b) | |
| 43. |
It is advisable to avoid line-starting of induction motor and use starter because__________? |
| A. | motor takes five to seven times its full load current |
| B. | it will pick-up very high speed and may go out of step |
| C. | it will run in reverse direction |
| D. | starting torque is very high |
| Answer» B. it will pick-up very high speed and may go out of step | |
| 44. |
It is advisable to avoid line starting of induction motor and use starter because____________? |
| A. | it will run in reverse direction |
| B. | it will pick up very high speed and may go out of step |
| C. | motor takes five to seven times its full load current |
| D. | starting torque is very high |
| Answer» D. starting torque is very high | |
| 45. |
Insertion of resistance in the stator of an induction motor___________? |
| A. | increases the load torque |
| B. | decreases the starting torque |
| C. | increases the starting torque |
| D. | none of the above |
| Answer» C. increases the starting torque | |
| 46. |
Insertion of reactance in the rotor circuit_______? |
| A. | reduces starting torque as well as maximum torque |
| B. | increases starting torque as well as maximum torque |
| C. | increases starting torque but maxi-mum torque remains unchanged |
| D. | increases starting torque but maxi-mum torque decreases |
| Answer» B. increases starting torque as well as maximum torque | |
| 47. |
Insertion of resistance in the rotor 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. | |
| 48. |
In three-phase induction motors sometimes copper bars are placed deep in the rotor to___________? |
| A. | improve starting torque |
| B. | reduce copper losses |
| C. | improve efficiency |
| D. | improve power factor |
| Answer» B. reduce copper losses | |
| 49. |
In three-phase squirrel-cage induction motors____________? |
| A. | rotor conductor ends are short-circuited through slip rings |
| B. | rotor conductors are short-circuited through end rings |
| C. | rotor conductors are kept open |
| D. | rotor conductors are connected to insulation |
| Answer» C. rotor conductors are kept open | |
| 50. |
In the squirrel-cage induction motor the rotor slots are usually given slight skew__________? |
| A. | to reduce the magnetic hum and locking tendency of the rotor |
| B. | to increase the tensile strength of the rotor bars |
| C. | to ensure easy fabrication |
| D. | none of the above |
| Answer» B. to increase the tensile strength of the rotor bars | |