What is the relationship between Rotor Speed and the speed of the Rotating Magnetic Field in an Asynchronous Motor?

In an asynchronous motor, also known as an induction motor, the rotor operates at a speed that is always less than the speed of the rotating magnetic field produced by the stator. This difference in speed creates the necessary conditions for inducing current in the rotor, which in turn allows the motor to produce torque.

The rotating magnetic field moves at a synchronous speed, which depends on the supply frequency and the number of poles in the motor. The rotor, however, cannot reach this synchronous speed due to the way induction motors operate. Instead, a slip develops between the rotor speed and the speed of the magnetic field. This slip is essential because it is the factor that enables the flow of current in the rotor windings, providing the torque needed for the rotor to turn.

If the rotor were to reach the same speed as the magnetic field, there would be no relative motion between them, and thus, no induced current or torque would be generated. Therefore, the relationship is one where the rotor speed is always less than that of the magnetic field, confirming that the correct answer reflects this fundamental operational principle of asynchronous motors.