Electrical Machines (Part-15)

What is the primary function of the rotor in an electric motor?

A To rotate and produce mechanical output
B To generate electrical power
C To create a magnetic field
D To regulate voltage

What type of electrical machine is used to charge batteries?

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

What is the relationship between slip and speed in an induction motor?

A Slip increases as speed increases
B Slip decreases as speed increases
C Slip remains constant regardless of speed
D Slip is independent of speed

What type of electrical machine is used in domestic water pumps?

A Universal motor
B Single-phase induction motor
C DC motor
D Stepper motor

What type of loss is directly proportional to the square of the current?

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

What type of motor is commonly used in electric vehicles?

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

What is the primary purpose of field windings in electrical machines?

A To carry current
B To produce the magnetic field
C To step up voltage
D To reduce losses

What is the purpose of an autotransformer in electrical machines?

A To step up or step down voltage with a single winding
B To isolate circuits
C To improve power factor
D To step up current

What is the main purpose of cooling oil in a transformer?

A To provide insulation and cool the transformer
B To step up voltage
C To increase power factor
D To increase current

What type of rotor is used in a squirrel cage induction motor?

A A rotor with bars short-circuited by end rings
B A rotor with salient poles
C A rotor with permanent magnets
D A rotor with windings connected to slip rings

What is the main function of the core in a transformer?

A To provide a low-reluctance path for magnetic flux
B To insulate the windings
C To step up or step down voltage
D To reduce eddy current losses

What is the function of the centrifugal switch in a single-phase motor?

A To disconnect the starting winding after the motor reaches a certain speed
B To increase torque
C To improve power factor
D To reduce resistance

What is the purpose of a yoke in a DC machine?

A To provide mechanical support and act as a protective cover
B To carry current
C To step up voltage
D To increase speed

What is the primary purpose of excitation in a synchronous machine?

A To provide the magnetic field for operation
B To reduce copper losses
C To regulate speed
D To step up voltage

What type of rotor is used in synchronous machines for high-speed applications?

A Squirrel cage rotor
B Cylindrical rotor
C Salient pole rotor
D Hollow rotor

What is the main cause of mechanical losses in electrical machines?

A Eddy current losses
B Friction in bearings and windage
C Copper losses
D Core losses

What is the role of the stator in a three-phase induction motor?

A To produce a rotating magnetic field
B To generate mechanical output
C To carry current to the rotor
D To reduce losses

What happens to the torque in an induction motor as the load increases?

A Torque increases
B Torque decreases
C Torque remains constant
D Torque becomes zero

What type of motor is most commonly used in electric clocks?

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

What is the main advantage of a squirrel cage rotor?

A Simple, rugged, and reliable
B High starting torque
C Easily controlled speed
D Low maintenance cost