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A homopolar motor is a direct current electric motor with two magnetic poles, the conductors of which always cut unidirectional lines of magnetic flux by rotating a conductor around a fixed axis so that the conductor is at right angles to a static magnetic field. The resulting EMF (Electromotive Force) being continuous in one direction, the homopolar motor needs no commutator but still requires slip rings. The name ''homopolar'' indicates that the electrical polarity of the conductor and the magnetic field poles do not change (i.e., that it does not require commutation). ==History== The homopolar motor was the first electrical motor to be built. Its operation was demonstrated by Michael Faraday in 1821 at the Royal Institution in London.〔Michael Faraday, "New Electro-Magnetic Apparatus," ''Quarterly Journal of Science, Literature and the Arts'' 12, 186-187 (1821). (Scanned pages )〕〔Michael Faraday, "Description of an Electro-magnetic Apparatus for the Exhibition of Rotatory Motion," ''Quarterly Journal of Science, Literature and the Arts'' 12, 283-285 (1821). (Scanned pages ) (Original illustration (''plate'') of the homopolar motor, referred to on p. 283 of Faraday's second article ). (Index of Quarterly Journal for Faraday, Michael )〕 In 1821, soon after the Danish physicist and chemist Hans Christian Ørsted discovered the phenomenon of electromagnetism, Humphry Davy and British scientist William Hyde Wollaston tried, but failed, to design an electric motor.〔("Archives Biographies: Michael Faraday", The Institution of Engineering and Technology. )〕 Faraday, having discussed the problem with the two men, went on to build two devices to produce what he called "electromagnetic rotation". One of these, now known as the ''homopolar motor'', caused a continuous circular motion that was engendered by the circular magnetic force around a wire that extended into a pool of mercury wherein was placed a magnet. The wire would then rotate around the magnet if supplied with current from a chemical battery. These experiments and inventions formed the foundation of modern electromagnetic technology. In his excitement, Faraday published results without acknowledging his work with either Wollaston or Davy. The resulting controversy within the Royal Society strained his mentor relationship with Davy and may well have contributed to Faraday’s assignment to other activities, which consequently prevented his involvement in electromagnetic research, for several years.〔Hamilton's ''A Life of Discovery: Michael Faraday, Giant of the Scientific Revolution'' (2004) pp. 165–71, 183, 187–90.〕〔Cantor's ''Michael Faraday, Sandemanian and Scientist'' (1991) pp. 231–3.〕 B. G. Lamme described in 1912 a homopolar machine rated 2,000 kW, 260 V, 7,700 A and 1,200 rpm with 16 slip rings operating at a peripheral velocity of 67 m/s. A unipolar generator rated 1,125 kW, 7.5 V 150,000 A, 514 rpm built in 1934 was installed in a U.S. steel mill for pipe welding purposes.〔Lynn, p. 842〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Homopolar motor」の詳細全文を読む スポンサード リンク
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