Advanced Electrical Machines MCQs

1. Which of the following machines operates on the principle of electromagnetic induction? A) DC Generator B) Synchronous Motor C) Induction Motor D) Transformer Answer: D) Transformer 2. The armature current in a DC motor is maximum when: A) The motor is running at no load B) The motor is running at full load C) The motor is starting D) The motor is decelerating Answer: B) The motor is running at full load 3. Slip in an induction motor is defined as: A) Difference between synchronous speed and rotor speed B) Difference between rotor speed and stator speed C) Ratio of rotor speed to synchronous speed D) Ratio of synchronous speed to rotor speed Answer: A) Difference between synchronous speed and rotor speed 4. In a synchronous machine, hunting refers to: A) Oscillations in speed when load changes B) Over-excitation of the field winding C) Vibrations due to unbalanced rotor D) Overheating of the stator winding Answer: A) Oscillations in speed when load changes 5. The starting torque of a single-phase induction motor is: A) High B) Low C) Moderate D) Zero Answer: B) Low 6. The main advantage of a switched reluctance motor is: A) High efficiency at all loads B) High starting torque C) Low cost and simple construction D) High speed operation Answer: C) Low cost and simple construction 7. The back emf in a DC motor: A) Increases with increase in speed B) Decreases with increase in speed C) Is independent of speed D) Depends on armature current Answer: A) Increases with increase in speed 8. The speed of a three-phase induction motor can be controlled by: A) Changing the supply voltage B) Changing the number of stator poles C) Changing the rotor resistance D) All of the above Answer: D) All of the above 9. The power factor of an induction motor under no-load conditions is typically: A) Leading B) Lagging C) Unity D) Zero Answer: A) Leading 10. The term ‘cogging’ in a permanent magnet synchronous motor refers to: A) Starting torque B) Rotor position errors C) Uncontrolled movements D) Reluctance torque Answer: B) Rotor position errors 11. Which type of rotor is used in a squirrel cage induction motor? A) Salient pole rotor B) Wound rotor C) Smooth cylindrical rotor D) None of the above Answer: C) Smooth cylindrical rotor 12. The efficiency of a transformer is maximum when: A) The transformer is lightly loaded B) The transformer is fully loaded C) The transformer is operating at half load D) The transformer is at no load Answer: B) The transformer is fully loaded 13. In a synchronous generator, the armature reaction affects: A) Voltage regulation B) Power factor C) Speed regulation D) Excitation voltage Answer: A) Voltage regulation 14. The inrush current in a transformer is higher than normal operating current because of: A) Core losses B) Hysteresis losses C) Eddy current losses D) Magnetizing current Answer: D) Magnetizing current 15. Which motor has the highest power factor at full load? A) DC shunt motor B) Induction motor C) Synchronous motor D) Switched reluctance motor Answer: C) Synchronous motor 16. The speed-torque characteristic of a DC series motor is: A) High starting torque, variable speed B) High starting torque, constant speed C) Low starting torque, variable speed D) Low starting torque, constant speed Answer: A) High starting torque, variable speed 17. The slip rings in an induction motor are used for: A) Starting torque B) Speed control C) Supplying power to the rotor windings D) Providing a path for stator flux Answer: C) Supplying power to the rotor windings 18. The efficiency of a transformer is approximately: A) 100% B) 99% C) 98% D) 97% Answer: C) 98% 19. The armature reaction in a DC motor affects: A) Speed regulation B) Torque C) Efficiency D) Voltage regulation Answer: D) Voltage regulation 20. The starting torque of a synchronous motor is: A) Zero B) High C) Low D) Moderate Answer: A) Zero 21. A universal motor operates on: A) DC supply only B) AC supply only C) Both AC and DC supply D) None of the above Answer: C) Both AC and DC supply 22. The direction of rotation of a split-phase induction motor can be reversed by: A) Interchanging the supply terminals B) Changing the supply frequency C) Changing the rotor resistance D) None of the above Answer: A) Interchanging the supply terminals 23. The function of a commutator in a DC machine is to: A) Control the armature current B) Reverse the direction of current in the armature C) Control the field winding current D) Provide mechanical support to the armature Answer: B) Reverse the direction of current in the armature 24. The power factor of a synchronous motor can be adjusted by varying the: A) Armature resistance B) Field excitation C) Rotor resistance D) Supply voltage Answer: B) Field excitation 25. The starting current of a squirrel cage induction motor is typically: A) Equal to full-load current B) Less than full-load current C) Greater than full-load current D) Zero Answer: C) Greater than full-load current 26. The direction of rotation of a three-phase induction motor can be reversed by: A) Interchanging any two supply lines B) Changing the supply frequency C) Changing the rotor resistance D) None of the above Answer: A) Interchanging any two supply lines 27. The armature winding in a DC machine is: A) Concentrated B) Distributed C) Both concentrated and distributed D) None of the above Answer: B) Distributed 28. The speed of a DC shunt motor can be controlled by: A) Changing the supply voltage B) Changing the field current C) Changing the armature resistance D) All of the above Answer: D) All of the above 29. Which of the following losses occur in a transformer? A) Eddy current losses B) Hysteresis losses C) Copper losses D) All of the above Answer: D) All of the above 30. The efficiency of a DC generator is maximum when: A) The generator is lightly loaded B) The generator is fully loaded C) The generator is operating at half load D) The generator is at no load Answer: B) The generator is fully loaded 31. The emf induced in the armature of a DC generator depends on: A) Armature speed B) Field current C) Both armature speed and field current D) None of the above Answer: C) Both armature speed and field current 32. Which motor does not require a starting mechanism? A) Synchronous motor B) Induction motor C) DC series motor D) Universal motor Answer: A) Synchronous motor 33. The speed of a synchronous motor is: A) Constant B) Variable C) Zero D) Indeterminate Answer: A) Constant 34. The no-load current in a transformer is mainly due to: A) Core losses B) Eddy current losses C) Magnetizing current D) Copper losses Answer: C) Magnetizing current 35. Which motor has the highest starting torque? A) Induction motor B) DC shunt motor C) Synchronous motor D) Switched reluctance motor Answer: D) Switched reluctance motor 36. The torque in an induction motor is maximum when: A) Slip is zero B) Slip is one C) Slip is 0.5 D) Slip is indeterminate Answer: A) Slip is zero 37. The power factor of a capacitor-run induction motor is: A) Leading B) Lagging C) Unity D) Zero Answer: A) Leading 38. In a wound rotor induction motor, external resistances are used to: A) Control speed B) Control torque C) Control power factor D) All of the above Answer: D) All of the above 39. The function of laminations in the core of a transformer is to reduce: A) Eddy currents B) Hysteresis losses C) Copper losses D) All of the above Answer: A) Eddy currents 40. The armature reaction in a synchronous machine affects: A) Voltage regulation B) Power factor C) Speed regulation D) Efficiency Answer: A) Voltage regulation 41. The speed of a DC series motor decreases with increasing: A) Armature resistance B) Field current C) Load torque D) Supply voltage Answer: C) Load torque 42. A transformer with a primary winding connected to a sinusoidal AC supply will induce: A) An AC voltage in the secondary winding B) A DC voltage in the secondary winding C) No voltage in the secondary winding D) None of the above Answer: A) An AC voltage in the secondary winding 43. The slip rings in a wound rotor induction motor are used to connect: A) The rotor windings to the stator windings B) The rotor windings to the external resistances C) The rotor windings to the DC supply D) None of the above Answer: B) The rotor windings to the external resistances 44. The eddy current loss in a transformer core depends on: A) The frequency of the supply B) The thickness of the laminations C) The material of the core D) All of the above Answer: D) All of the above 45. The power factor of a synchronous generator is typically: A) Leading B) Lagging C) Unity D) Zero Answer: A) Leading 46. The starting torque of a shaded-pole induction motor is: A) High B) Low C) Moderate D) Zero Answer: B) Low 47. The torque developed in an induction motor is proportional to: A) Slip B) Speed C) Supply voltage D) Both slip and speed Answer: D) Both slip and speed 48. The regulation of an alternator is defined as: A) The difference between no-load and full-load terminal voltage B) The difference between synchronous speed and actual speed C) The difference between excitation voltage and terminal voltage D) None of the above Answer: A) The difference between no-load and full-load terminal voltage 49. The power factor of an induction motor decreases with: A) Increasing load B) Decreasing load C) Increasing supply voltage D) Increasing rotor resistance Answer: B) Decreasing load 50. The torque-speed characteristic of a universal motor is similar to that of a: A) DC series motor B) Synchronous motor C) Induction motor D) None of the above Answer: A) DC series motor

Advanced Electrical Machines MCQs

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