Cambridge Encyclopedia » Cambridge Encyclopedia Vol. 23

electromagnetism - SI electricity units

magnetic faraday current produced

Phenomena involving both electric and magnetic fields, and the study of such phenomena. The first indication of a link between electricity and magnetism was shown by Hans Christian Ørsted, who demonstrated that an electrical current caused the deflection of a compass needle (1819). This established that magnetic effects are produced by a moving electrical charge. Ørsted's observation was interpreted by Michael Faraday in terms of lines of magnetic influence circulating around the wire. Ampère deduced an expression for the magnetic force between two current-carrying wires to give the original form of what is now called Ampère's law (1827). Faraday demonstrated that switching off a current in a circuit produced a momentary current in a nearby circuit, and that moving a magnet close to a circuit also produced momentary currents (1831). This established that electrical charge can be made to flow by changing magnetic fields, the basis of electromagnetic induction (expressed as Faraday's law). Similar work was performed by Joseph Henry (1829). The first generator was built by Faraday in 1831.

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