Electric Generator

The electric generator is Faraday's discovery that a *changing* magnetic field drives current through a wire — mechanical motion converted directly into electricity, and the exact reverse of the electric motor. On 29 August 1831 Michael Faraday wound two separate coils on opposite sides of an iron ring and found that switching current on or off in the first coil produced a brief pulse in the second: the current came only from the *change*, not from the steady field. Two months later, on 28 October 1831, he spun a copper disc between the poles of a horseshoe magnet with contacts at its rim and axle, and for the first time drew a steady, continuous current from nothing but rotation — the first generator.

Batteries make electricity by consuming metal and acid, so their current is expensive and finite; a generator makes it from anything that turns — falling water, expanding steam, wind, muscle. Faraday's disc converted a laboratory trickle into a principle that could be scaled without limit, because the source of energy was now motion rather than chemistry. Electricity as a bulk commodity — cheap enough to light cities and drive factories — begins here.

See recipe. Faraday's own disc was a copper wheel cranked by hand between the poles of a large permanent magnet, with one brush pressing on the rim and another on the axle to tap the induced current; the flow was feeble but unbroken, and his galvanometer read it clearly. He set out the full law behind it — that the induced force depends on the rate at which magnetic lines are cut — before the Royal Society in November 1831, in the first of his *Experimental Researches in Electricity*.

The disc was tiny, but the law behind it scaled without ceiling: within fifty years, coil-and-magnet dynamos driven by steam engines and water wheels were feeding power stations, and the grid, the electric light, the tram, and industrial machinery followed. Because a generator run backward is a motor, the same discovery gave civilization both the means to make electricity and the means to spend it as motion. Every power plant on Earth — hydro, coal, nuclear, wind — is still a magnet and a coil in relative motion, doing exactly what Faraday's disc did.