Faraday's law of induction

Lore & Background

In 1820, Hans Christian Ørsted demonstrated that an electric current produces a magnetic field, prompting scientists to ask whether a magnetic field could generate an electric current. He later observed transient currents when moving a bar magnet into a coil and built a homopolar generator producing steady DC current by rotating a copper disk near a stationary magnet.

Reader's Guide

Faraday's law of induction is central to electromagnetism, providing the basis for transformers, inductors, electric motors, generators, and solenoids. Historically, the differing explanations for motional emf and transformer emf posed a conceptual problem, resolved in special relativity as frame-dependent: what appears as a magnetic force in one frame may appear as an induced electric field in another. The law has two formulations: the Maxwell–Faraday equation, which applies to fields without requiring a physical circuit, and the Faraday flux rule, which relates emf to the rate of change of magnetic flux through a closed loop. Lenz's law gives the direction of induced emf. Oliver Heaviside later referred to the differential equation form as Faraday's law, which is the version recognized today in Maxwell's equations.

Did You Know?

• Faraday's law of induction describes how a changing magnetic field can induce an electric current in a circuit.
• The law is used to refer to two distinct statements: the Maxwell–Faraday equation and the Faraday flux rule.