An AC motor is a device that converts alternating current (AC) electrical energy into mechanical energy, and its operation relies on fundamental electromagnetic principles. To understand how it works, let’s break down its key components and the sequence of events that enable motion.

First, let’s identify the main parts. Most AC motors, especially the common induction motor, consist of two primary components: the stator and the rotor. The stator is the stationary outer part of the motor, containing a set of electromagnets (called stator windings) arranged in a circular pattern around the central axis. These windings are connected to an AC power source. The rotor, on the other hand, is the rotating inner part, typically a cylindrical core made of laminated metal sheets with conductive bars (often copper or aluminum) embedded in its surface, forming a “squirrel cage” structure in many induction motors. These bars are shorted at both ends by rings, allowing electric current to flow through them.

The magic of an AC motor begins with the rotating magnetic field generated by the stator. When alternating current flows through the stator windings, each winding becomes an electromagnet whose polarity reverses as the current alternates (since AC changes direction periodically). Crucially, the stator windings are spaced at specific angles (usually 120 degrees apart in three-phase motors) and connected to phases of the AC supply that are out of sync with each other. This phase difference causes the magnetic field produced by the stator to rotate smoothly around the axis at a speed known as the synchronous speed, which depends on the frequency of the AC power and the number of poles in the stator windings. For example, a 60 Hz power supply with a 4-pole stator creates a synchronous speed of 1800 revolutions per minute (RPM).

Next, electromagnetic induction comes into play, driving the rotor to spin. As the rotating magnetic field from the stator cuts across the conductive bars of the rotor, it induces an electric current in the rotor bars (thanks to Faraday’s law of induction). This induced current, in turn, creates its own magnetic field around the rotor (Ampère’s law). The interaction between the stator’s rotating magnetic field and the rotor’s magnetic field generates a torque—a twisting force—that causes the rotor to follow the rotating field.

In induction motors, the rotor never quite reaches the synchronous speed of the stator’s magnetic field. This difference, known as slip, is necessary to maintain the induction of current in the rotor. If the rotor matched the synchronous speed, there would be no relative motion between the rotor and the magnetic field, so no current would be induced, and no torque would be produced. Instead, the rotor spins at a slightly lower speed (typically 2–5% less than synchronous speed in standard motors), ensuring a continuous induction of current and torque.

In summary, an AC motor operates through the coordinated action of a rotating magnetic field (generated by the stator’s AC-powered windings) and electromagnetic induction (which induces current in the rotor, creating a magnetic field that interacts with the stator’s field to produce torque). This elegant process efficiently converts electrical energy into mechanical motion, making AC motors indispensable in countless applications, from household appliances to industrial machinery.