Just as an electrical current induces a magnetic field (see October 27: Electromagnets), so does a changing magnetic field cause current to flow in a conductor. Scientists call this property electromagnetic induction. It allows us to convert mechanical energy, the energy of motion, into electricity. The impact that this simple physical property has had on the modern world is incalculable.

A changing magnetic field passing through a conductor causes a current to flow in the conductor. This current in turn induces a magnetic field. The induced magnetic field points in the opposite direction of the changing magnetic field, opposing the changing field. (This is called Lenz's Law.) The external field must be changing! The induced field opposes the change in the external field, not the field itself. If the field is not changing, there is nothing to oppose and there is no current.

One way to create a changing magnetic field is to move the field's source, the magnet, giving it some velocity. If the field changes direction, as above, the resulting current will be alternating current, or AC for short. This is the type of current that we use in our houses.

An electric motor utilizes the property of electromagnetic induction to convert electricity into mechanical energy to make things move. The conductor itself, a coiled wire, will move to oppose the magnetic field. Just when it gets into position the current is reversed, and the coil spins round and round like a dog chasing its tail, full of mechanical energy.

A generator is simply the same process in reverse, converting mechanical energy into electricity. Almost all of the electrical energy we use in our daily lives is supplied by electric generators. The above photo displays an early General Electric alternating current generator.

You may be surprised to know that you already have an electric motor in your own car. Your ignition system uses a small electric motor to get your car started. In very early cars, this had to be done manually. A removable crank fit into the engine, and the driver would have to turn it to get the car started, acting as a human generator.

Electric and Gas/Electric cars are one of the most promising applications for electric motors in the near the future. Someday gas stations may be replaced by solar stations. Depicted above is the Honda Insight, and right the GM EV1 charging under a solar station.

The Grand Coulee Dam, located on the Columbia river in central Washington, holds the largest hydroelectric generator in the world (825 Megawatts). The mechanical energy of water flowing through its flood gates turns turbines connected to generators, which produce electricity.