Experiments on electricity and magnetism

Electricity and magnetism are closely linked aspects of a single physical phenomenon, electromagnetism, and experiments reveal the connections between them. Magnetism describes the forces exerted by magnets and by moving electric charges. A bar magnet has two poles, north and south, and the rule that like poles repel while unlike poles attract can be shown with two magnets or with a compass needle that aligns itself with a magnetic field. Iron filings sprinkled around a magnet trace out the pattern of its field lines.

A key discovery, demonstrated in the early nineteenth century, is that an electric current produces a magnetic field. Passing current through a wire deflects a nearby compass needle, and winding the wire into a coil around an iron core makes an electromagnet whose strength depends on the current and the number of turns. This effect underlies electric motors, in which magnetic forces on a current-carrying coil produce rotation, and it can be shown with simple homemade apparatus.

The reverse effect, electromagnetic induction, is equally important: moving a magnet near a coil of wire, or changing the magnetic field through it, generates an electric voltage in the coil. Faraday's experiments establishing this principle are commonly reproduced in classrooms and form the basis of electric generators and transformers. Demonstrations of induction, electromagnets and magnetic fields together show how the two phenomena are unified, and how the same ideas scale from a simple compass to the machines that generate and distribute electrical power.

Frequently asked questions

How are electricity and magnetism connected?

An electric current creates a magnetic field, and a changing magnetic field creates a voltage in a conductor; together these effects make up electromagnetism.

What is an electromagnet?

It is a coil of wire, often wound around an iron core, that becomes magnetic when current flows through it and loses its magnetism when the current stops.

What is electromagnetic induction?

It is the generation of a voltage in a coil when the magnetic field through it changes, the principle behind electric generators and transformers.