Ampère's circuital law

In classical electromagnetism, Ampère's circuital law, often simply called Ampère's law, and sometimes Oersted's law, relates the circulation of a magnetic field around a closed loop to the electric current passing through that loop.

The law was inspired by Hans Christian Ørsted's 1820 discovery that an electric current generates a magnetic field. This finding prompted theoretical and experimental work by André-Marie Ampère and others, eventually leading to the formulation of the law in its modern form.

James Clerk Maxwell published the law in 1855. In 1865, he generalized the law to account for time-varying electric currents by introducing the displacement current term. The resulting equation, often called the Ampère–Maxwell law, is one of Maxwell's equations that form the foundation of classical electromagnetism.