MCQOPTIONS
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MCQOPTIONS
This section includes 240 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Starting winding of a single phase motor of a refrigerator is disconnected from thecircuit by means of a |
| A. | magnetic relay |
| B. | thermal relay |
| C. | centrifugal switch |
| D. | none of the above |
| Answer» B. thermal relay | |
| 2. |
If a particular application needs high speed and high starting torque, then which of thefollowing motor will be preferred ? |
| A. | Universal motor |
| B. | Shaded pole type motor |
| C. | Capacitor start motor |
| D. | Capacitor start and run motor |
| Answer» B. Shaded pole type motor | |
| 3. |
In a capacitor start and run motors the function of the running capacitor in series withthe auxiliary winding is to |
| A. | improve power factor |
| B. | increase overload capacity |
| C. | reduce fluctuations in torque |
| D. | to improve torque |
| Answer» B. increase overload capacity | |
| 4. |
In split-phase motor iauxiliary winding is of |
| A. | thick wire placed at the bottom of the slots |
| B. | thick wire placed at the top of the slots |
| C. | thin wire placed at the top of the slots |
| D. | thin wire placed at the bottom of the slots |
| Answer» D. thin wire placed at the bottom of the slots | |
| 5. |
Two-value capacitor motor finds increased application as compressor motor in smallhome air-conditioners because |
| A. | it is comparatively cheaper |
| B. | it has almost non-destructible capacitor |
| C. | it has low starting as well as running currents at relatively high power factor |
| D. | it is quiet in operation |
| Answer» D. it is quiet in operation | |
| 6. |
A capacitor-start single phase induction motor is switched on to supply with itscapacitor replaced by an inductor of equivalent reactance value. It will |
| A. | start and then stop |
| B. | start and run slowly |
| C. | start and run at rated speed |
| D. | not start at all |
| Answer» E. | |
| 7. |
Centrifugal switch disconnects the auxiliary winding of the motor at about ____percent of synchronous speed |
| A. | 30 to 40 |
| B. | 70 to 80 |
| C. | 80 to 90 |
| D. | 100 |
| Answer» C. 80 to 90 | |
| 8. |
As hysteresis motors are free from mechanical and magnetic vibrations thereforethese are considered as suitable for |
| A. | fans |
| B. | blowers |
| C. | sound equipment |
| D. | mixer grinders |
| Answer» D. mixer grinders | |
| 9. |
Hysteresis motor is particularly useful for high-quality record players and tape- recorders because |
| A. | it revolves synchronously |
| B. | it is not subject to any magnetic or mechanical vibrations |
| C. | it can be easily manufactured in extremely small sizes of upto 1 W output |
| D. | it develops hysteresis torque which is extremely steady both in amplitude and phase |
| Answer» E. | |
| 10. |
Which of the following single-phase induction motors is generally used in timephonographs ? |
| A. | Resistance start |
| B. | Capacitor start capacitor run |
| C. | Shaded pole |
| D. | Universal |
| Answer» D. Universal | |
| 11. |
To reverse the direction of rotation of acapacitor start motor while it is running weshould |
| A. | disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding |
| B. | disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding |
| C. | reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply |
| D. | reverse the direction of connections of the auxiliary winding and im-mediately connect it to supply |
| Answer» B. disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding | |
| 12. |
In a capacitor start motor, the phase displacement between starting and runningwinding can be nearly |
| A. | 10° |
| B. | 30° |
| C. | 60° |
| D. | 90° |
| Answer» E. | |
| 13. |
Which of the following statements regarding repulsion-start induction motor isincorrect ? |
| A. | It requires more maintenance of commutator and other mechanical devices |
| B. | It makes quite a bit of noise on starting |
| C. | In fractional horse power motors, it has replaced the capacitor motors |
| D. | It is not easily reversed |
| Answer» D. It is not easily reversed | |
| 14. |
Which of the following single-phase motors is suitable for timing and controlpurposes ? |
| A. | Reluctance motor |
| B. | Series motor |
| C. | Repulsion motor |
| D. | Universal motor |
| Answer» B. Series motor | |
| 15. |
The running winding of a single phase motor on testing with meggar is found to beground. Most probable location of the ground will be |
| A. | at the end connections |
| B. | at the end terminals |
| C. | anywhere on the winding inside a slot |
| D. | at the slot edge where coil enters or comes out of the slot |
| Answer» E. | |
| 16. |
The direction of rotation of universal motor can be reversed the by reversing the flowof current through |
| A. | armature winding |
| B. | field winding |
| C. | either armature winding or field winding |
| D. | none of the above |
| Answer» D. none of the above | |
| 17. |
If the centrifugal switch of a two-value capacitor motor using two capacitors fails toopen then |
| A. | motor will not come upto speed |
| B. | motor will not carry the load |
| C. | current drawn by the motor will be excessively high |
| D. | electrolytic capacitor will, in all probability, suffer break down |
| Answer» E. | |
| 18. |
The repulsion-start induction-run motor is used because of |
| A. | good power factor |
| B. | high efficiency |
| C. | minimum cost |
| D. | high starting torque |
| Answer» E. | |
| 19. |
In case of a reluctance motor, when the load is increased so that it cannot maintainsynchronous speed the motor will |
| A. | become unstable |
| B. | draw excessive armature current and may burn out |
| C. | fall out of synchronism and come to stand still |
| D. | run as induction motor |
| Answer» E. | |
| 20. |
Direction of rotation of a split phase motor can be reversed by reversing theconnection of |
| A. | running winding only |
| B. | starting winding only |
| C. | either (a) or (b) |
| D. | both (a) and (b) |
| Answer» D. both (a) and (b) | |
| 21. |
Which of the following statements regarding single-phase induction motoris correct? |
| A. | It requires only one winding |
| B. | It can rotate in one direction only |
| C. | It is self-starting |
| D. | It is not self-starting |
| Answer» E. | |
| 22. |
If the centrifugal switch does not open at 70 to 80 percent of synchronous speed ofmotor, it would result in |
| A. | damage to the starting winding |
| B. | damage to the centrifugal switch |
| C. | overloading of running winding |
| D. | none of the above |
| Answer» B. damage to the centrifugal switch | |
| 23. |
Burning out of windings is due to |
| A. | short circuited capacitor |
| B. | capacitor value hiving changed |
| C. | open circuiting of capacitor |
| D. | none of the above |
| Answer» B. capacitor value hiving changed | |
| 24. |
A centrifugal switch is used to dis- connect 'starting winding when motor has |
| A. | run for about 1 minute |
| B. | run for about 5 minutes |
| C. | picked up about 50 to 70 per cent of rated speed |
| D. | picked up about 10 to 25 per cent of rated speed |
| Answer» D. picked up about 10 to 25 per cent of rated speed | |
| 25. |
Which of the following motors is preferred for tape-recorders ? |
| A. | Shaded pole motor |
| B. | Hysteresis motor |
| C. | Two value capacitor motor |
| D. | Universal motor |
| Answer» C. Two value capacitor motor | |
| 26. |
When a D.C. series motor is connected to A.C. supply, the power factor will be lowbecause of |
| A. | high inductance of field and armature circuits |
| B. | induced current in rotor due to variations of flux |
| C. | fine copper wire winding |
| D. | none of the above |
| Answer» B. induced current in rotor due to variations of flux | |
| 27. |
After the starting winding of a single phase induction motor is disconnected fromsupply, it continues to run only on |
| A. | running winding |
| B. | rotor winding |
| C. | field winding |
| D. | compensating winding |
| Answer» B. rotor winding | |
| 28. |
The rotor slots, in an induction motor, are usually not quite parallel to the shaftbecause it |
| A. | improves the efficiency |
| B. | helps the rotor teeth to remain under the stator teeth |
| C. | helps in reducing the tendency of the rotor teeth to remain under the stator teeth |
| D. | improves the power factor |
| Answer» D. improves the power factor | |
| 29. |
When /?2 is tne rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condi-tions will be |
| A. | sR2X2 = 1 |
| B. | sR2 = X2 |
| C. | R2 = sX2 i |
| D. | R2 = s2X2 |
| Answer» D. R2 = s2X2 | |
| 30. |
Size of a high speed motor as compared to low speed motorfor the same H.P. will be |
| A. | bigger |
| B. | smaller |
| C. | same |
| D. | any of the above |
| Answer» C. same | |
| 31. |
The good power factor of an induction motor can be achieved if the average fluxdensity in the air gap is |
| A. | absent |
| B. | small |
| C. | large |
| D. | infinity |
| Answer» C. large | |
| 32. |
The speed of a squirrel-cage induction motor can be controlled by all of the followingexcept |
| A. | changing supply frequency |
| B. | changing number of poles |
| C. | changing winding resistance |
| D. | reducing supply voltage |
| Answer» D. reducing supply voltage | |
| 33. |
When the equivalent circuit diagram of doouble squirrel-cage induction motor isconstructed 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 | |
| 34. |
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 | |
| 35. |
Which motor is preferred for use in mines where explosive gases exist ? |
| A. | Air motor |
| B. | Induction motor |
| C. | D.C. shunt motor |
| D. | Synchronous motor |
| Answer» B. Induction motor | |
| 36. |
The auto-starters (using three auto transformers) can be used to start cage inductionmotor 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 | |
| 37. |
In three-phase induction motors sometimes copper bars are placed deep in the rotorto |
| A. | improve starting torque |
| B. | reduce copper losses |
| C. | improve efficiency |
| D. | improve power factor |
| Answer» B. reduce copper losses | |
| 38. |
Stepless speed control of induction motor is possible by which of the followingmethods ? |
| A. | e.m.f. injection in rotor eueuit |
| B. | Changing the number of poles |
| C. | Cascade operation |
| D. | None of the above |
| Answer» C. Cascade operation | |
| 39. |
Which of the following component is usually fabricated out of silicon steel ? |
| A. | Bearings |
| B. | Shaft |
| C. | Statorcore |
| D. | None of the above |
| Answer» D. None of the above | |
| 40. |
Which is of the following data is required to draw the circle diagram for an inductionmotor ? |
| 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. | |
| 41. |
What will happen if the relative speed between the rotating flux of stator and rotor ofthe 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 | |
| 42. |
A change of 4% of supply voltage to an induction motor will produce a change ofappromimately |
| A. | 4% in the rotor torque |
| B. | 8% in the rotor torque |
| C. | 12% in the rotor torque |
| D. | 16% in the rotor torque |
| Answer» E. | |
| 43. |
Which of the following methods is easily applicable to control the speed of thesquirrel-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 | |
| 44. |
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 | |
| 45. |
The speed characteristics of an induction motor closely resemble the speedloadcharacteristics 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 | |
| 46. |
If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of thenormal speed, the phenomenon will be termed as |
| A. | humming |
| B. | hunting |
| C. | crawling |
| D. | cogging |
| Answer» D. cogging | |
| 47. |
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. | |
| 48. |
For which motor the speed can be controlled from rotor side ? |
| A. | Squirrel-cage induction motor |
| B. | Slip-ring induction motor |
| C. | Both (a) and (b) |
| D. | None of the above |
| Answer» C. Both (a) and (b) | |
| 49. |
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 | |
| 50. |
For driving high inertia loods best type of induction motor suggested is |
| A. | slip ring type |
| B. | squirrel cage type |
| C. | any of the above |
| D. | none of the above |
| Answer» B. squirrel cage type | |