Electric Machines: Motors, Generators and Alternators

Electric machines convert energy between mechanical and electrical forms using the interaction of magnetic fields and currents. A motor turns electrical energy into rotation, while a generator does the reverse, producing electricity from mechanical motion. The same machine can often work either way, because both modes rely on the same physics: a current in a magnetic field experiences a force, and a conductor moving through a field has a voltage induced across it. An alternator is a generator that produces alternating current, as found in vehicles and power stations.

Machines are grouped by the type of supply and construction. Direct-current motors use a commutator to switch current in the rotor windings, giving smooth torque and easy speed control. Alternating-current machines include induction motors, where a rotating field in the stator drags the rotor around, and synchronous machines whose rotor turns in exact step with the supply frequency. Specialised designs such as stepper motors move in discrete steps for positioning, and switched-reluctance motors exploit the tendency of a rotor to align with the strongest magnetic path.

Because the action depends on rotating magnetic fields and on forces that are not directly visible, animations are an effective teaching aid. A simulation can show the stator field sweeping around, the rotor following it, and the way commutation or pole switching keeps the torque acting in one direction. Watching field lines, current directions and the resulting attraction or repulsion makes the connection between the windings and the shaft motion far clearer than a static diagram.

Frequently asked questions

What is the difference between a motor and a generator?

A motor converts electrical energy into mechanical rotation, while a generator converts mechanical motion into electricity. Many machines can perform either role.

What is an alternator?

An alternator is a generator that produces alternating current. Vehicle alternators and power-station generators both work this way before any rectification.

How does an induction motor turn?

Its stator creates a rotating magnetic field that induces currents in the rotor. The interaction of these currents with the field drags the rotor around behind the field.