Electromagnetism

Here we can see the magnetic field lines around a bar magnet, running from the north pole, around the outside of the magnet, and into the south pole.

Running current through a wire creates a magnetic field around it. This is how electromagnets work: a coil of wire carrying current generates a magnetic field, just like a permanent magnet would.

Electromagnetic induction

Electromagnetic induction is the process of converting magnetic energy into electrical energy by moving a conductor through a changing magnetic field. One way you can change a magnetic field to create induction is by moving a magnet through wire coils.

Electromagnetic induction is the principle that makes inductors, transformers, and generators work, which we will cover next.

Inductors

An electrical device that converts electrical energy into a magnetic field, then releases that energy back into the circuit when needed. It is the electrical equivalent of a flywheel. Just as a flywheel resists changes in rotational speed, an inductor resists changes in current.

Inductors are typically made from a coil of wire, often wound around a metal core. Inductance is measured in Henries (H).

Transformers

Transformers are two inductors, like the ones we just covered, that transfer energy from one coil to another through electromagnetic induction. A transformer has a primary coil and a secondary coil, wrapped around a shared core. As AC flows through the primary coil, it creates a changing magnetic field. That changing field induces a current in the secondary coil, transferring energy between the two circuits without a direct electrical connection. Transformers only exist in AC, since a steady DC would not create the changing magnetic field induction requires.

A transformer that raises AC voltage is called a step-up transformer, while a transformer that lowers the voltage is called a step-down transformer. The change in voltage allows energy to be transmitted over long distances, which requires high voltage, but then lowers the voltage for home safety.

Motors

An electrical device that converts electric or electromagnetic energy into rotational mechanical energy.

A basic motor works by running current through a coil of wire that sits inside a magnetic field. The interaction between the current and the magnetic field produces a force that spins the coil, converting electrical energy into rotational motion.

Generators

A device that takes rotational energy and converts it into electrical energy through electromagnetic induction. As a coil of wire, or a magnet, rotates within a magnetic field, the changing field induces a current in the wire. This is the same principle covered above in electromagnetic induction, just driven by mechanical rotation instead of a moving magnet.

Motors and generators are essentially the same device used in opposite directions. A motor takes in electricity and produces rotation, while a generator takes in rotation and produces electricity. In fact, many motors can act as generators if you spin them by hand, and generators can act as motors if you run current through them.