Electrical Machines (Part-6)

What does the efficiency of an electrical machine depend on?

A Power losses
B Torque
C Voltage
D Speed

What is the effect of increasing load on the speed of a DC motor?

A Speed fluctuates
B Speed increases
C Speed remains constant
D Speed decreases

In which type of motor is torque directly proportional to the square of the current?

A Stepper motor
B DC motor
C Induction motor
D Synchronous motor

What type of loss occurs due to the resistance of the windings in an electrical machine?

A Copper loss
B Mechanical loss
C Eddy current loss
D Core loss

How does the torque in a synchronous motor behave under varying load?

A Fluctuates unpredictably
B Remains constant
C Increases linearly
D Decreases linearly

What is the purpose of using a cooling system in electrical machines?

A To reduce vibration
B To maintain insulation
C To increase efficiency
D To prevent overheating

What is the primary cause of core losses in electrical machines?

A Friction
B Hysteresis
C Eddy currents
D Copper resistance

How does the speed of a synchronous motor relate to the supply frequency?

A Inversely proportional
B Directly proportional
C Independent of frequency
D Constant at all frequencies

What is the role of the stator in an induction motor?

A Control speed
B Reverse current
C Produce magnetic field
D Generate mechanical power

What does “slip” in an induction motor refer to?

A Difference in speed
B Voltage drop
C Frequency variation
D Difference between rotor and stator speed

What is the function of the armature in a DC motor?

A Produce magnetic field
B Control speed
C Convert electrical power to mechanical power
D Generate torque

In a synchronous motor, what happens if the load increases beyond a certain point?

A The motor stalls
B The motor accelerates
C The motor maintains constant speed
D The motor slows down

What is the typical starting method for a squirrel-cage induction motor?

A Slip-ring starting
B Direct-on-line starting
C Star-delta starting
D Autotransformer starting

What happens to the torque in a motor if the armature resistance increases?

A Torque remains unchanged
B Torque increases
C Torque decreases
D Torque fluctuates

What is the main disadvantage of a DC motor compared to an induction motor?

A Requires frequent maintenance
B More torque
C Higher cost
D Higher efficiency