Sure, here are 25 unique and accurate MCQs about three-phase induction motors:
1. The rotating magnetic field in a three-phase induction motor is produced by:
A. The stator windings
B. The rotor windings
C. The air gap
D. the centrifugal force
Answer: (A)
2. The speed of the rotating magnetic field in a three-phase induction motor is:
A. the same as the synchronous speed
B. the same as the rotor speed
C. slightly less than the synchronous speed
D. slightly greater than the synchronous speed
Answer: (C)
3. The slip in a three-phase induction motor is:
A. The difference between the synchronous speed and the rotor speed
B. The ratio of the synchronous speed and the rotor speed
C. the ratio of the rotor speed and the synchronous speed
D. the product of the synchronous speed and the rotor speed
Answer: (A)
4. The starting torque of a three-phase induction motor is:
A. high
B. low
C. zero
D. infinite
Answer: (B)
5. The rotor of a three-phase induction motor can be of the following types:
A. squirrel cage
B. wound rotor
C. Both squirrel cage and wound rotor
D. none of the above
Answer: (C)
6. The squirrel cage rotor of a three-phase induction motor has:
A. distributed windings
B. concentrated windings
C. both distributed and concentrated windings
D. no windings
Answer: (A)
7. The wound rotor of a three-phase induction motor has:
A. distributed windings
B. concentrated windings
C. both distributed and concentrated windings
D. no windings
Answer: (B)
8. The starting current of a three-phase induction motor is:
A. high
B. low
C. zero
D. infinite
Answer: (A)
9. The starting current of a three-phase induction motor can be reduced by:
A. connecting a star-delta starter
B. Connecting a resistor-capacitor starter
C. both connecting a star-delta starter and a resistor-capacitor starter
D. neither connecting a star-delta starter nor a resistor-capacitor starter
Answer: (C)
10. The speed of a three-phase induction motor can be controlled by:
A. varying the supply frequency
B. varying the supply voltage
C. both varying the supply frequency and the supply voltage
D. neither varying the supply frequency nor the supply voltage
Answer: (C)
11. The power factor of a three-phase induction motor is:
A. unity
B. lagging
C. leading
D. can be leading or lagging, depending on the load
Answer: (C)
12. The efficiency of a three-phase induction motor is:
A. high
B. low
C. moderate
D. can be high or low, depending on the load
Answer: (D)
13. The three-phase induction motor is used in the following applications:
A. fans
B. pumps
C. compressors
D. all of the above
Answer: (D)
14. The three-phase induction motor is more efficient than a single-phase induction motor.
A. True
B. False
Answer: (True)
15. The three-phase induction motor has a higher starting torque than a single-phase induction motor.
A. True
B. False
Answer: (False)
16. The three-phase induction motor is more expensive than a single-phase induction motor.
A. True
B. False
Answer: (True)
17. The three-phase induction motor is more common than a single-phase induction motor.
A. True
B. False
Answer: (True)
18. The three-phase induction motor is used in high-power applications, while the single-phase induction motor is used in low-power applications.
A. True
B. False
Answer: (False)
19. The synchronous speed of a three-phase induction motor is given by the formula:
A. f / p
B. p / f
C. 2πf / L
D. 2πL / f
Answer: (A)
20. The slip of a three-phase induction motor is given by the formula:
A. s = (f – p) / f
B. s = (p – f) / f
C. s = f / (p – f)
D. s = f / (p + f)
Answer: (A)
21. The rotor resistance of a three-phase induction motor is given by the formula:
A. R = 2πfL
B. R = L / (2πf)
C. R = 2πf / L
D. R = L / 2πf
Answer: (B)
22. The rotor reactance of a three-phase induction motor is given by the formula:
A. X = 2πfL
B. X = L / (2πf)
C. X = 2πf / L
D. X = L / 2πf
Answer: (A)
23. The torque developed by a three-phase induction motor is given by the formula:
A. T = Ks
B. T = K / s
C. T = Ks²
D. T = K / s²
Answer: (A)
24. The power factor of a three-phase induction motor is improved by:
A. connecting a capacitor in parallel with the motor
B. connecting a resistor in parallel with the motor
C. both connecting a capacitor and a resistor in parallel with the motor
D. neither connecting a capacitor nor a resistor in parallel with the motor
Answer: (A)
25. The efficiency of a three-phase induction motor can be improved by:
A. increasing the supply voltage
B. decreasing the supply voltage
C. both increasing and decreasing the supply voltage
D. neither increasing nor decreasing the supply voltage
Answer: (B)