Editing Electric generator (section)

===Faraday disk generator===
[[File:Faraday disk generator.jpg|thumb|right|The [[Faraday disk]] was the first electric generator. The horseshoe-shaped magnet ''(A)'' created a magnetic field through the disk ''(D)''. When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact ''m'', through the external circuit, and back into the center of the disk through the axle.]]
{{Main|Homopolar generator}}

The operating principle of electromagnetic generators was discovered in the years of 1831–1832 by [[Michael Faraday]]. The principle, later called [[Faraday's law of induction]], is that an [[electromotive force]] is generated in an electrical conductor which encircles a varying [[magnetic flux]].

Faraday also built the first electromagnetic generator, called the [[Faraday disk]]; a type of [[homopolar generator]], using a [[copper]] disc rotating between the poles of a horseshoe [[magnet]]. It produced a small [[direct current|DC voltage]].

This design was inefficient, due to self-cancelling counterflows of [[electric current|current]] in regions of the disk that were not under the influence of the magnetic field. While current was induced directly underneath the magnet, the current would circulate backwards in regions that were outside the influence of the magnetic field. This counterflow limited the power output to the pickup wires and induced waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction.

Another disadvantage was that the output [[voltage]] was very low, due to the single current path through the magnetic flux. Experimenters found that using multiple turns of wire in a coil could produce higher, more useful voltages. Since the output voltage is proportional to the number of turns, generators could be easily designed to produce any desired voltage by varying the number of turns. Wire windings became a basic feature of all subsequent generator designs.