Electrical Machines MCQs
1. What is the function of commutator in a DC machine?
A) To regulate speed
B) To convert AC to DC
C) To control voltage
D) To reverse the direction of current
Answer: B) To convert AC to DC
2. In a synchronous machine, hunting can be minimized by:
A) Decreasing the excitation
B) Increasing the excitation
C) Decreasing the load
D) Increasing the load
Answer: A) Decreasing the excitation
3. The slip rings in an induction motor are used to:
A) Convert AC to DC
B) Transfer power to the rotor
C) Regulate the speed
D) Provide a path for current to flow
Answer: B) Transfer power to the rotor
4. In a DC machine, armature reaction results in:
A) Reduced flux in the air gap
B) Increased speed
C) Decreased generated voltage
D) Improved commutation
Answer: A) Reduced flux in the air gap
5. The slip of an induction motor is defined as:
A) (Ns – N) / Ns
B) (N – Ns) / N
C) (Ns – N) / N
D) (N – Ns) / Ns
Answer: B) (N – Ns) / N
6. The voltage induced in the rotor of an induction motor is:
A) AC
B) DC
C) Sine wave
D) Square wave
Answer: A) AC
7. In a transformer, the function of the core is to:
A) Provide mechanical strength
B) Maintain insulation
C) Increase the voltage
D) Provide a path for magnetic flux
Answer: D) Provide a path for magnetic flux
8. A single-phase induction motor is inherently:
A) Self-starting
B) Reversible
C) High-speed
D) Efficient
Answer: A) Self-starting
9. The starting torque of a shaded-pole motor is:
A) High
B) Low
C) Zero
D) Variable
Answer: B) Low
10. A universal motor can run on:
A) DC supply only
B) AC supply only
C) Both DC and AC supply
D) Solar power
Answer: C) Both DC and AC supply
11. A reluctance motor operates based on:
A) Induction principle
B) Synchronous principle
C) Reluctance torque
D) Permanent magnetism
Answer: C) Reluctance torque
12. In a synchronous motor, pulling into synchronism means:
A) Starting from standstill
B) Locking into a fixed speed
C) Achieving maximum torque
D) Operating in reverse direction
Answer: A) Starting from standstill
13. A stepper motor is typically used for:
A) High-speed applications
B) Continuous rotation
C) Precise positioning
D) Heavy-duty operations
Answer: C) Precise positioning
14. The direction of rotation of a DC motor can be reversed by:
A) Changing the supply voltage
B) Interchanging field and armature connections
C) Changing the load
D) Adjusting the speed controller
Answer: B) Interchanging field and armature connections
15. Slip power in an induction motor is converted into:
A) Mechanical power
B) Electrical power
C) Heat
D) Light
Answer: C) Heat
16. The speed of a DC shunt motor can be controlled by varying:
A) Armature resistance
B) Field resistance
C) Both armature and field resistances
D) Supply voltage
Answer: D) Supply voltage
17. The efficiency of an electric motor is given by:
A) Output power / Input power
B) Input power / Output power
C) Output voltage / Input voltage
D) Input current / Output current
Answer: A) Output power / Input power
18. A capacitor-start induction-run motor is suitable for applications requiring:
A) High starting torque
B) Variable speed control
C) Continuous duty
D) High efficiency
Answer: A) High starting torque
19. The power factor of an induction motor is improved by:
A) Increasing the load
B) Decreasing the load
C) Connecting a capacitor
D) Using a larger rotor
Answer: C) Connecting a capacitor
20. Which motor is preferred for elevators and cranes due to its high starting torque?
A) Synchronous motor
B) DC series motor
C) Induction motor
D) Universal motor
Answer: B) DC series motor
21. The rotor of a squirrel-cage induction motor is made of:
A) Copper bars
B) Aluminum bars
C) Laminated silicon steel
D) Cast iron
Answer: B) Aluminum bars
22. The slip speed in an induction motor is highest when:
A) Starting
B) Running at synchronous speed
C) Running at full load
D) Running at no load
Answer: A) Starting
23. The power developed by a DC motor is proportional to:
A) Armature resistance
B) Armature current
C) Field current
D) Supply voltage
Answer: B) Armature current
24. A single-phase induction motor has which type of starting mechanism?
A) Split-phase
B) Capacitor-start
C) Shaded-pole
D) Universal
Answer: A) Split-phase
25. Which motor has the highest starting torque?
A) DC shunt motor
B) Synchronous motor
C) Induction motor
D) Universal motor
Answer: D) Universal motor
26. The torque developed in a DC motor is maximum when:
A) Armature and field currents are maximum
B) Armature current is maximum
C) Field current is maximum
D) Armature and field currents are minimum
Answer: A) Armature and field currents are maximum
27. The back emf in a DC motor depends on:
A) Armature resistance
B) Armature current
C) Speed of the motor
D) Field current
Answer: C) Speed of the motor
28. A hysteresis motor operates based on:
A) Eddy currents
B) Hysteresis losses
C) Electromagnetic induction
D) Permanent magnetism
Answer: B) Hysteresis losses
29. The armature windings of a DC machine are usually made of:
A) Copper
B) Aluminum
C) Silver
D) Tungsten
Answer: A) Copper
30. Which motor is not self-starting?
A) Squirrel-cage induction motor
B) Shaded-pole motor
C) Permanent magnet DC motor
D) Universal motor
Answer: B) Shaded-pole motor
31. The slip in an induction motor is necessary for:
A) Improving efficiency
B) Increasing power factor
C) Producing torque
D) Controlling speed
Answer: C) Producing torque
32. The speed of a three-phase induction motor is:
A) Synchronous speed
B) Less than synchronous speed
C) More than synchronous speed
D) Variable
Answer: B) Less than synchronous speed
33. The starting torque of a synchronous motor is:
A) Zero
B) Very low
C) High
D) Variable
Answer: C) High
34. The efficiency of a transformer is maximum when:
A) Load is maximum
B) Load is minimum
C) Load power factor is leading
D) Load power factor is lagging
Answer: A) Load is maximum
35. The rotor of a wound-rotor induction motor is connected to external resistance for:
A) Speed control
B) Voltage regulation
C) Starting purposes
D) Efficiency improvement
Answer: C) Starting purposes
36. The slip ring of a DC machine is made of:
A) Brass
B) Copper
C) Carbon
D) Aluminum
Answer: B) Copper
37. The commutation process in a DC machine is necessary to:
A) Control speed
B) Control torque
C) Avoid sparking at brushes
D) Change the direction of rotation
Answer: C) Avoid sparking at brushes
38. The transformer core is laminated to:
A) Increase cost
B) Reduce eddy current losses
C) Increase voltage
D) Reduce mechanical strength
Answer: B) Reduce eddy current losses
39. The speed of a DC series motor decreases with an increase in:
A) Load
B) Field resistance
C) Armature resistance
D) Supply voltage
Answer: A) Load
40. A single-phase induction motor operates on:
A) Single-phase AC supply
B) Three-phase AC supply
C) DC supply
D) Variable frequency supply
Answer: A) Single-phase AC supply
41. The torque developed in an induction motor is maximum when:
A) Slip is minimum
B) Slip is maximum
C) Rotor resistance is high
D) Rotor resistance is low
Answer: A) Slip is minimum
42. In a three-phase induction motor, the direction of rotation can be reversed by:
A) Interchanging any two supply lines
B) Changing the supply voltage
C) Changing the rotor winding connections
D) Adjusting the speed controller
Answer: A) Interchanging any two supply lines
43. A capacitor-start capacitor-run motor has:
A) High starting torque and low efficiency
B) High starting torque and high efficiency
C) Low starting torque and high efficiency
D) Low starting torque and low efficiency
Answer: B) High starting torque and high efficiency
44. The speed regulation of a DC shunt motor is:
A) Poor
B) Fair
C) Good
D) Excellent
Answer: C) Good
45. The starting torque of a synchronous motor is __________ compared to an induction motor.
A) Higher
B) Lower
C) Same
D) Variable
Answer: A) Higher
46. A split-phase motor is mainly used in applications requiring:
A) High starting torque
B) Variable speed control
C) Low starting current
D) High efficiency
Answer: C) Low starting current
47. The back emf in a DC motor increases with:
A) Decrease in speed
B) Increase in speed
C) Decrease in armature current
D) Increase in armature current
Answer: B) Increase in speed
48. Which type of motor has the highest starting current?
A) DC series motor
B) DC shunt motor
C) Synchronous motor
D) Induction motor
Answer: A) DC series motor
49. In a DC motor, the armature reaction causes:
A) Reduced speed
B) Increased speed
C) Distortion of the main field flux
D) Better commutation
Answer: C) Distortion of the main field flux
50. A hysteresis motor is preferred for applications requiring:
A) High starting torque
B) Low starting current
C) Precise speed control
D) Continuous operation
Answer: C) Precise speed contro