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This section includes 21 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. |
In squirrel cage induction motors, the rotor slots are usually given slight skew in order to |
A. | reduce windage losses |
B. | reduce eddy currents |
C. | reduce accumulation of dirt and dust |
D. | reduce magnetic hum |
Answer» E. | |
2. |
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 | |
3. |
A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor e.m.f. will be |
A. | 200 Hz |
B. | 50 Hz |
C. | 2 Hz |
D. | 0.2 Hz |
Answer» D. 0.2 Hz | |
4. |
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 | |
5. |
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 | |
6. |
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 | |
7. |
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 | |
8. |
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. | |
9. |
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. | |
10. |
Stepless speed control of induction motor is possible by which of the following methods ? |
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 | |
11. |
A change of 4% of supply voltage to an induction motor will produce a change of appromimately |
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. | |
12. |
A pump induction motor is switched on to a supply 30% lower than its rated voltage. The pump runs. What will eventually happen ? It will |
A. | stall after sometime |
B. | stall immediately |
C. | continue to run at lower speed without damage |
D. | get heated and subsequently get damaged |
Answer» E. | |
13. |
A 3-phase induction motor stator delta connected, is carrying full load and one of its fuses blows out. Then the motor |
A. | will continue running burning its one phase |
B. | will continue running burning its two phases |
C. | will stop and carry heavy current causing permanent damage to its winding |
D. | will continue running without any harm to the winding |
Answer» B. will continue running burning its two phases | |
14. |
If an induction motor with certain ratio of rotor to stator slots, runs at 1/7 of the normal speed, the phenomenon will be termed as |
A. | humming |
B. | hunting |
C. | crawling |
D. | cogging |
Answer» D. cogging | |
15. |
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 | |
16. |
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 | |
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. |
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 | |
19. |
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 | |
20. |
A 500 kW, 3-phase, 440 volts, 50 Hz, A.C. induction motor has a speed of 960 r.p.m. on full load. The machine has 6 poles. The slip of the machine will be |
A. | 0.01 |
B. | 0.02 |
C. | 0.03 |
D. | 0.04 |
Answer» E. | |
21. |
5 H.P., 50-Hz, 3-phase, 440 V, induction motors are available for the following r.p.m. Which motor will be the costliest ? |
A. | 730 r.p.m. |
B. | 960 r.p.m. |
C. | 1440 r.p.m. |
D. | 2880 r.p.m. |
Answer» B. 960 r.p.m. | |