In alternating current (AC) motors, the alternating current passing through the stator windings generates a rotating magnetic field. This field induces a current in the rotor through electromagnetic induction, causing the rotor to start rotating at a speed close to that of the magnetic field. This principle forms the operating mechanism of asynchronous motors. In synchronous motors, the rotor rotates at the same speed as the stator's rotating magnetic field, allowing precise speed control through synchronization.

In direct current (DC) motors, the operating principle is slightly different. DC motors utilize the Lorentz force generated when an electric current passes through a conductor within a magnetic field. This force moves the conductor, causing the rotor to rotate. In brushed DC motors, the current is directed via a commutator and brushes, while brushless DC motors use electronic control circuits to achieve more efficient and quieter operation.

The formation of the magnetic field and its effect on the rotor are critical for motor operation. The stronger the magnetic field, the greater the force on the rotor and the higher the produced torque. Additionally, motor efficiency is affected by factors such as winding resistance, magnetic core losses, friction, and air gap.

Cooling systems also play a significant role in maintaining healthy motor operation. Heat generated during operation can reduce efficiency or damage insulation materials. Therefore, motors are protected using methods such as fan cooling, liquid cooling, or natural airflow.

In summary, the working principle of an electric motor is based on converting electrical energy into mechanical motion via magnetic fields. This conversion process may vary depending on the motor type, structure, and application, but the fundamental principle is generating rotational motion through torque produced by electromagnetic forces.