Faraday's magnet and coil experiment, c 1831.
© Science Museum / Science & Society Picture Library
Reconstruction. A wire can be subjected to a changing magnetic field by moving a nearby permanent magnet. In an experiment by Michael Faraday (1791-1867), a rod-shaped permanent magnet was thrust in and out of a coil of wire. The magnet was surrounded by invisible 'lines of magnetic force', an idea proposed by Faraday. If the magnet is still there is no change in the magnetic field, and no current flows; if the magnet moves, its lines of force cros the wire and so induce a current, which can be detected by a galvanometer (shown).