Electrical Machine Design MCQs

1. Which material is commonly used for the core of a transformer?
A. Copper
B. Aluminum
C. Steel
D. Brass
Answer: C

2. The efficiency of a transformer is highest when operated at:
A. Full load
B. Half load
C. No load
D. Overload
Answer: A

3. In a transformer, the leakage flux is maximum when the transformer is operating at:
A. Full load
B. No load
C. Half load
D. Overload
Answer: B

4. Which insulation class can withstand the highest temperature?
A. Class A
B. Class B
C. Class F
D. Class H
Answer: D

5. In an induction motor, slip is defined as:
A. (Synchronous speed – Actual speed) / Synchronous speed
B. (Actual speed – Synchronous speed) / Synchronous speed
C. Synchronous speed / Actual speed
D. None of the above
Answer: A

6. The main purpose of laminating the core in electrical machines is to:
A. Reduce eddy current losses
B. Increase flux density
C. Increase mechanical strength
D. Improve cooling
Answer: A

7. The power factor of a transformer is usually improved by:
A. Decreasing the core size
B. Increasing the core size
C. Decreasing the primary voltage
D. Installing capacitors
Answer: D

8. The speed of a DC shunt motor can be controlled by:
A. Varying the armature resistance
B. Varying the field resistance
C. Changing the supply voltage
D. All of the above
Answer: D

9. The braking torque of a DC motor is proportional to:
A. Armature current
B. Field current
C. Back emf
D. Armature resistance
Answer: A

10. Which law governs the magnetic circuit in electrical machines?
A. Ohm’s Law
B. Kirchhoff’s Law
C. Faraday’s Law
D. Ampere’s Law
Answer: D

11. The torque developed in a synchronous motor depends on:
A. Field excitation only
B. Armature current only
C. Both field excitation and armature current
D. None of the above
Answer: C

12. In a squirrel cage induction motor, rotor bars are usually made of:
A. Copper
B. Aluminum
C. Cast iron
D. Steel
Answer: B

13. The speed regulation of a DC motor is defined as the change in speed from:
A. No load to full load
B. Full load to no load
C. Full load to half load
D. Half load to full load
Answer: B

14. The specific magnetic loading in transformers is typically expressed in:
A. Ampere-turns per meter
B. Volt-amperes per square meter
C. Ampere-turns per square meter
D. Henrys per meter
Answer: C

15. The cogging effect in induction motors is primarily due to:
A. Uneven air gap
B. Rotor eccentricity
C. Harmonic torques
D. None of the above
Answer: A

16. The efficiency of a transformer is defined as:
A. Output power / Input power
B. Input power / Output power
C. Output power / Core losses
D. Input power / Copper losses
Answer: A

17. The slip ring in an induction motor is used to:
A. Improve efficiency
B. Control speed
C. Start the motor
D. Increase torque
Answer: B

18. The size of the conductors in electrical machines is determined by:
A. Voltage rating
B. Current rating
C. Power rating
D. All of the above
Answer: D

19. The inrush current in a transformer is highest when:
A. Energized at no load
B. Energized at full load
C. Energized at rated voltage
D. Energized at reduced voltage
Answer: A

20. The commutation process in DC machines is necessary to:
A. Generate voltage
B. Control speed
C. Avoid sparking at brushes
D. All of the above
Answer: C

21. The regulation of an alternator is defined as the change in voltage from:
A. No load to full load
B. Full load to no load
C. Full load to half load
D. Half load to full load
Answer: A

22. The armature reaction in DC machines affects primarily the:
A. Voltage regulation
B. Speed regulation
C. Commutation
D. Cooling
Answer: C

23. The losses in a transformer include:
A. Copper losses and iron losses
B. Eddy current losses and hysteresis losses
C. Mechanical losses and electrical losses
D. All of the above
Answer: D

24. The efficiency of a DC generator is maximum when operated at:
A. Rated load
B. Half load
C. No load
D. Overload
Answer: A

25. The method used to reduce the armature reaction in DC machines is:
A. Compensating winding
B. Interpo

26. Which of the following statements about transformers is true?
A. Transformers can only step up voltage.
B. Transformers can only step down voltage.
C. Transformers can step up or step down voltage.
D. Transformers are only used in AC systems.
Answer: C

27. The frequency of the induced emf in an alternator depends on:
A. Speed of rotation
B. Number of poles
C. Both speed of rotation and number of poles
D. None of the above
Answer: C

28. The primary function of the cooling system in electrical machines is to:
A. Reduce electrical losses
B. Increase efficiency
C. Maintain operating temperature within limits
D. Improve power factor
Answer: C

29. In an alternator, the armature reaction is responsible for:
A. Cross-magnetizing effect
B. Demagnetizing effect
C. Both cross-magnetizing and demagnetizing effects
D. None of the above
Answer: C

30. The insulation resistance of electrical machines is typically measured in:
A. Ohms
B. Volts
C. Amperes
D. Henrys
Answer: A

31. The power factor of a synchronous motor can be improved by:
A. Decreasing excitation
B. Increasing excitation
C. Decreasing load
D. Increasing load
Answer: B

32. The efficiency of an alternator is defined as:
A. Output power / Input power
B. Input power / Output power
C. Output power / Copper losses
D. Input power / Core losses
Answer: A

33. Which type of winding is commonly used in three-phase induction motors?
A. Lap winding
B. Wave winding
C. Concentric winding
D. Distributed winding
Answer: D

34. The voltage regulation of a transformer is influenced by:
A. Load power factor
B. Leakage reactance
C. Both load power factor and leakage reactance
D. None of the above
Answer: C

35. In a DC machine, the interpole is placed:
A. Between main poles
B. Along with main poles
C. On the armature
D. None of the above
Answer: A

36. Which material is commonly used for the brushes in DC machines?
A. Copper
B. Brass
C. Carbon
D. Aluminum
Answer: C

37. The temperature rise in electrical machines is primarily due to:
A. Copper losses
B. Iron losses
C. Both copper and iron losses
D. Mechanical losses
Answer: C

38. The efficiency of an induction motor is typically higher when operating at:
A. Full load
B. Half load
C. No load
D. Overload
Answer: A

39. The starting torque of a three-phase induction motor can be increased by:
A. Increasing rotor resistance
B. Decreasing rotor resistance
C. Increasing supply voltage
D. Decreasing supply voltage
Answer: C

40. The power rating of a transformer is determined primarily by its:
A. Voltage ratio
B. Current ratio
C. Power factor
D. KVA rating
Answer: D

41. In a DC motor, the back emf is directly proportional to:
A. Armature current
B. Speed of the motor
C. Field current
D. None of the above
Answer: B

42. The stray losses in electrical machines include:
A. Copper losses
B. Eddy current losses
C. Mechanical losses
D. None of the above
Answer: B

43. The leakage reactance in a transformer is due to:
A. Magnetic leakage
B. Electric leakage
C. Both magnetic and electric leakage
D. None of the above
Answer: A

44. The core of a transformer is laminated to:
A. Reduce eddy current losses
B. Increase hysteresis losses
C. Improve efficiency
D. Increase weight
Answer: A

45. The efficiency of a transformer is maximum when the ratio of copper loss to iron loss is:
A. Minimum
B. Maximum
C. Equal
D. Indeterminate
Answer: C

46. The function of the gasket in electrical machines is to:
A. Provide insulation
B. Enhance cooling
C. Prevent moisture ingress
D. Improve mechanical strength
Answer: C

47. The torque-speed characteristics of a DC series motor are suitable for applications requiring:
A. High starting torque
B. High efficiency
C. Constant speed
D. Low starting current
Answer: A

48. The term “Knee Point Voltage” is associated with:
A. Transformers
B. Induction motors
C. Synchronous motors
D. DC machines
Answer: A

49. The inductance of a coil in an electrical machine depends on:
A. Number of turns
B. Cross-sectional area
C. Permeability of the core material
D. All of the above
Answer: D

50. The voltage regulation of a synchronous generator is usually expressed as a percentage of the:
A. Full-load voltage
B. No-load voltage
C. Rated voltage
D. Terminal voltage
Answer: A

Electrical Machine Design MCQs

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