Actually, AC motor is everywhere in our life. For example, it is widely applied in the lampblack machine, washing machine, vacuum cleaner, electric fan, ventilator, hairdryer and etc. How does it work? Take single-phase AC motor, one type of the AC motors, for instance. Single-phase AC motor has two windings, the starting winding and the running winding. The starting winding is connected in series on a large capacitor. When the running winding and the starting winding go through the single-phase alternating current, it reached the maximum value because the capacitor makes the current in the starting winding has an angle of 90 degrees ahead of the running winding in time. Then the same two pulse magnetic fields are formed in the time and space so that a revolving magnetic field is generated in the air gap between the stator and the rotor. In the effect of revolving magnetic field, induction current is produced in a rotor. In the meantime, with the electromagnetic torque produced by the interaction between revolving magnetic field and current, the motor rotates.