Electricity and Magnetism

Electricity and magnetism are two closely related aspects of a single fundamental force, electromagnetism. Electric charge is the source of electric fields, which exert forces on other charges, while moving charges and magnetic materials produce magnetic fields. Although they were once studied separately, experiments in the nineteenth century revealed that the two phenomena are deeply intertwined, leading to a unified theory of the electromagnetic field.

An electric field describes the force a stationary charge would experience at any point in space, and Gauss’s law relates the field to the charge that produces it. A core principle is the conservation of electric charge, which states that charge is neither created nor destroyed. When charges move, they generate magnetic fields, described by the Biot–Savart law and Ampère’s law. A charged particle moving through electric and magnetic fields feels a combined push described by the Lorentz force law, and a related effect, the Hall effect, appears when a current flows through a conductor placed in a magnetic field.

The link between the two fields becomes especially clear in electromagnetic induction, in which a changing magnetic field generates an electric field and can drive a current. Lenz’s law gives the direction of the induced current, opposing the change that produced it. The Ampère–Maxwell law completes the picture by showing that changing electric fields also create magnetic fields. Together these laws predict electromagnetic waves, the basis of light and radio, and they explain how permanent magnets and electric currents interact.

Frequently asked questions

How are electricity and magnetism related?

They are aspects of one electromagnetic force: moving charges create magnetic fields, and changing magnetic fields create electric fields.

What is the Lorentz force?

It is the combined force on a charged particle from electric and magnetic fields, depending on the charge, its velocity and the field strengths.

What is electromagnetic induction?

It is the generation of an electric field, and possibly a current, by a changing magnetic field, with Lenz’s law giving the direction of the effect.