Michael Faraday discovered electromagnetic induction in 1831. The discovery showed that a changing magnetic field can produce an electric current, establishing a principle that later powered generators, transformers, and much of the modern electrical grid.
Faraday began his decisive experiments on 29 August 1831. In one famous setup, he wound two insulated coils around opposite sides of an iron ring. When current in one coil was switched on or off, a brief current appeared in the other coil. A steady current did not produce the same effect; change was the essential ingredient.
Faraday later demonstrated induction by moving a magnet through a wire loop, producing current in the loop. His experimental results became the foundation of Faraday’s law of induction, which relates induced voltage to the rate at which magnetic flux changes.
Joseph Henry made similar observations independently, but Faraday published first. The year 1831 is therefore the standard answer in biographies and science histories. It should not be confused with 1820, when Hans Christian Ørsted showed that an electric current creates a magnetic effect.