Induction and Synchronous Machines MCQs (Part-7)

What is the key factor that determines the synchronous speed of a motor?

A The size of the motor
B The supply voltage
C The frequency of the power supply and the number of poles
D The type of rotor used

In an induction motor, what is the significance of the slip?

A It indicates the motor’s efficiency
B It shows the difference between the stator and rotor speed
C It determines the motor’s operating temperature
D It controls the motor’s torque

What is the primary difference between a squirrel-cage rotor and a wound rotor in an induction motor?

A Squirrel-cage rotors require external resistors, while wound rotors do not.
B Squirrel-cage rotors are simpler and more durable.
C Wound rotors have a fixed resistance, while squirrel-cage rotors have variable resistance.
D Squirrel-cage rotors are used only for high-power applications.

What is the primary purpose of using a wound rotor in an induction motor?

A To provide higher efficiency
B To control the speed and torque characteristics
C To reduce the starting current
D To improve the power factor

What happens to the torque of an induction motor as the slip increases?

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

What is the effect of under-excitation in a synchronous motor?

A It leads to a leading power factor
B It leads to a lagging power factor
C It increases the motor’s speed
D It decreases the motor’s efficiency

In an induction motor, what is the relationship between the slip and the motor’s torque?

A Torque is inversely proportional to slip
B Torque is directly proportional to slip
C Torque remains constant throughout the speed range
D Torque is maximum when slip is zero

What is the typical use of squirrel-cage rotors in industrial applications?

A High starting torque applications
B Constant-speed applications
C High-efficiency applications
D Low-power applications

What is the effect of increasing the number of poles in a synchronous motor?

A The synchronous speed increases
B The synchronous speed decreases
C The torque produced by the motor increases
D The motor becomes more efficient

What is the role of slip rings in a wound-rotor induction motor?

A To allow external resistances to be added to the rotor circuit
B To maintain constant motor speed
C To cool the rotor
D To transfer electrical power to the stator

What is the primary advantage of using an induction motor over a synchronous motor in industrial applications?

A Higher efficiency
B Easier to start
C Constant speed
D Lower operating cost

What is the primary disadvantage of using a synchronous motor?

A It is difficult to start without external equipment
B It has low efficiency at light loads
C It requires a high starting current
D It operates at variable speeds

What is the primary advantage of using a squirrel-cage rotor over a wound rotor?

A It requires no external electrical connections
B It provides better speed control
C It allows for higher starting torque
D It is more efficient at low speeds

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

A To create a rotating magnetic field
B To interact with the stator’s magnetic field to produce mechanical power
C To provide excitation current
D To regulate the motor’s speed

What is the typical use of squirrel-cage rotors in industrial applications?

A Constant-speed applications
B Variable-speed applications
C High-efficiency applications
D Low-power applications

What happens to the efficiency of an induction motor when it operates under no-load conditions?

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

What is the typical application of a wound rotor induction motor?

A Applications requiring precise control of speed and torque
B General-purpose motor applications
C Low-power applications
D Applications requiring high starting torque

What is the effect of increasing the number of poles in an induction motor?

A It increases the motor’s speed
B It decreases the motor’s speed
C It increases the motor’s torque
D It decreases the motor’s efficiency

What is the effect of slip in an induction motor when operating under full-load conditions?

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

What is the purpose of using laminated cores in induction motors?

A To reduce eddy current losses
B To reduce mechanical friction
C To increase the motor’s power factor
D To improve the motor’s efficiency