Electromagnetic induction

In 1821, Faraday had shown that electricity could produce motion—the electric motor. Ten years later, he discovered the reverse: motion could produce electricity. On August 29, 1831, in the basement of the Royal Institution, Faraday wrapped two coils of wire around opposite sides of an iron ring and connected one to a battery. The moment he completed the circuit, a galvanometer attached to the second coil twitched. When he disconnected the battery, it twitched again. A changing magnetic field had induced an electric current. This discovery would make the modern world possible.

The adjacent possible for electromagnetic induction required the electric motor to exist first. Having established that current flowing near a magnet produces force, the question of whether the reverse was true became natural to ask. Faraday spent years pursuing this question, recording failed experiments in his notebooks, before finally achieving success with the iron ring configuration that concentrated and channeled the magnetic field.

Faraday's critical insight was that static conditions produced nothing—only change mattered. A steady magnetic field near a wire generated no current. But move that magnet, or change the current creating the magnetic field, and electricity appeared. The rate of change determined the amount of current induced. This principle, later formalized as Faraday's law, became one of the foundational equations of electromagnetism.

Within months of his iron ring experiment, Faraday built the first electric generator: the Faraday disc. A copper plate spinning between the poles of a horseshoe magnet produced continuous current. The device was inefficient and impractical, but it proved that mechanical motion could be converted to electrical power indefinitely. Where batteries exhausted their chemicals, a generator could run as long as something turned it.

Joseph Henry in America discovered the same phenomenon independently, but published after Faraday. The convergent discovery reinforced that induction was an inevitable consequence of the electromagnetic principles already understood—once someone asked the right question, the answer followed.

Electromagnetic induction became the foundation of electrical power generation. Every power plant, from coal-fired steam turbines to nuclear reactors to wind farms, converts mechanical rotation into electricity through induction. Transformers use induction to step voltage up or down for efficient transmission. Induction motors run factories and appliances. The principle Faraday demonstrated with two coils and an iron ring now generates and distributes essentially all the electricity humanity uses.