Magnetism and Electricity

Magnetism and electricity are two aspects of a single phenomenon, electromagnetism. A magnetic field surrounds any electric current, and a changing magnetic field can drive an electric current. This deep connection, worked out in the nineteenth century by physicists including Oersted, Ampere and Faraday, underlies the operation of motors, generators, transformers and most electrical machinery, and it was unified mathematically by Maxwell.

The link begins with the observation that an electric current produces a magnetic field. A straight wire carrying current is encircled by circular magnetic field lines, and winding the wire into a coil concentrates the field, producing an electromagnet whose strength depends on the current and the number of turns. Inserting an iron core greatly increases the field because the iron becomes magnetised. This effect lets electromagnets be switched on and off and is the basis of relays, solenoids and the rotating fields in electric motors, where the force between magnetic fields converts electrical energy into mechanical motion.

The reverse process, electromagnetic induction, is equally important. Faraday's law states that a changing magnetic flux through a circuit induces a voltage in it. Moving a magnet near a coil, or changing the current in a nearby coil, generates a voltage that can drive a current. Generators exploit this by rotating coils in a magnetic field to produce electricity, and transformers use it to transfer energy between coils linked by a shared magnetic core. Lenz's law adds that the induced current opposes the change that produced it, ensuring energy is conserved. Together these principles describe how electrical and magnetic energy are continually converted into one another.

Frequently asked questions

How does electricity create magnetism?

An electric current generates a magnetic field around it. Coiling the wire concentrates this field, and an iron core strengthens it, forming an electromagnet.

What is electromagnetic induction?

The generation of a voltage in a circuit by a changing magnetic field. Faraday's law relates the induced voltage to how fast the magnetic flux through the circuit changes.

How does a generator produce electricity?

It rotates coils within a magnetic field, so the magnetic flux through the coils changes continuously, inducing a voltage that drives current in the external circuit.