What is Electric Motor ?

which provides power to an external circuit.

The armature can be on either the rotor or the stator, depending on the design, with the field coil or magnet on the other part.

Before the connection between magnetism and electricity was discovered, electrostatic generators were invented. They operated on electrostatic principles, by using

moving electrically charged belts, plates, and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms:

electrostatic induction or the triboelectric effect. Such generators generated very high voltage and low current. Because of their inefficiency and the difficulty of

insulating machines that produced very high voltages, electrostatic generators had low power ratings, and were never used for generation of commercially significant

quantities of electric power. Their only practical applications were to power early X-ray tubes, and later in some atomic particle accelerators.

Faraday disk generator

Main article: 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, is that an electromotive force is generated in an electrical conductor which encircles a

varying magnetic flux.

He 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 DC voltage.

This design was inefficient, due to self-cancelling counterflows of 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.

Jedlik and the self-excitation phenomenon

Independently of Faraday, the Hungarian Ányos Jedlik started experimenting in 1827 with the electromagnetic rotating devices which he called electromagnetic self-