What is the role of the stator in an electrical machine?
A Supply power
B Produce magnetic field
C Generate torque
D Control speed
The stator is responsible for creating the rotating magnetic field in an electrical machine, especially in motors. This field induces current in the rotor, which interacts with it to generate torque and produce mechanical power.
What is the primary function of the rotor in an induction motor?
A To regulate voltage
B To control speed
C To generate a magnetic field
D To produce mechanical output
In an induction motor, the rotor is the rotating part that interacts with the magnetic field produced by the stator. The induced current in the rotor creates a magnetic field, generating the mechanical torque that drives the load.
In a synchronous machine, where are the field windings typically located?
A Armature
B Shaft
C Rotor
D Stator
In a synchronous machine, the field windings are located on the rotor. These windings generate the magnetic field necessary for the motor’s operation. The rotor’s magnetic field locks with the stator’s field to achieve synchronous speed.
What happens if the rotor in a synchronous motor is not synchronized with the stator?
A Motor stalls
B Motor increases efficiency
C Motor accelerates
D Motor speeds up
If the rotor in a synchronous motor is not synchronized with the stator’s magnetic field, the motor will stall. The rotor must rotate at synchronous speed to maintain synchronization and produce continuous torque.
How does the stator winding in a synchronous motor affect the motor’s performance?
A Supplies current
B Controls speed
C Generates torque
D Creates magnetic field
The stator winding in a synchronous motor creates a rotating magnetic field when supplied with alternating current. This field interacts with the rotor’s magnetic field, enabling the motor to maintain synchronous speed and produce torque.
What is the effect of increasing the number of poles in an electrical machine?
A Increases torque
B Decreases speed
C No effect
D Increases speed
Increasing the number of poles in an electrical machine decreases the synchronous speed. The synchronous speed is inversely proportional to the number of poles and the supply frequency, so more poles result in a slower motor speed.
What happens to the torque in an induction motor if the slip is high?
A Torque remains constant
B Torque decreases
C Torque fluctuates
D Torque increases
In an induction motor, torque increases with higher slip. Slip is necessary for torque production; as the slip increases (with higher load), the relative motion between the stator’s magnetic field and the rotor increases, which leads to more torque.
How does the rotor of an induction motor receive current?
A From stator’s magnetic field
B Through commutator
C From external power supply
D Through field windings
The rotor of an induction motor receives current through electromagnetic induction from the rotating magnetic field created by the stator. This induced current in the rotor creates its own magnetic field, which interacts with the stator’s field to produce torque.
In a DC machine, what role do the field windings play?
A Reverse current direction
B Control speed
C Generate the magnetic field
D Generate power
In a DC machine, the field windings are responsible for generating the magnetic field. This magnetic field interacts with the current flowing through the armature windings, generating the mechanical torque that drives the motor or generator.
What is the function of the armature in a DC motor?
A Supply current
B Reverse current direction
C Create magnetic field
D Generate mechanical power
The armature in a DC motor converts electrical energy into mechanical energy. The current flowing through the armature windings interacts with the magnetic field produced by the field windings, generating the torque required to rotate the motor shaft.
What effect does high resistance in the rotor of an induction motor have?
A Increases torque
B Decreases efficiency
C Increases speed
D Increases efficiency
High resistance in the rotor of an induction motor results in higher I²R losses, which lead to reduced efficiency. The increased heat dissipation from resistance reduces the motor’s overall performance and increases energy consumption.
In a synchronous motor, what determines the speed at which the motor operates?
A Load
B Voltage
C Rotor resistance
D Number of poles and supply frequency
The speed of a synchronous motor is determined by the number of poles in the rotor and the frequency of the supply current. The formula for synchronous speed is: Speed = 120 × Frequency / Number of Poles.
How is the torque‐speed characteristic of an induction motor affected by the load?
A Torque increases with load
B Speed increases with load
C Speed remains constant
D Torque decreases with load
In an induction motor, the torque increases with the load due to increased current and slip. As the load increases, the rotor slows down slightly, which increases the slip and, in turn, the torque produced by the motor.
What is the primary purpose of the field winding in a DC generator?
A To generate electricity
B To create magnetic field
C To reverse current
D To regulate speed
The field winding in a DC generator is responsible for creating the magnetic field necessary for the generation of electricity. As the armature rotates within this magnetic field, an electromotive force (EMF) is induced in the armature windings, generating power.
What type of motor is often used in applications requiring precise position control?
A DC motor
B Synchronous motor
C Stepper motor
D Induction motor
Stepper motors are ideal for applications requiring precise position control, such as in robotics, 3D printers, and CNC machines. They move in discrete steps, offering highly accurate control of speed and position without the need for feedback systems.