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Michael Faraday - Реферат


Michael Faraday
Michael Faraday (September 22, 1791 - August 25, 1867) was a British scientist (a physicist and chemist) who contributed significantly to the fields of electromagnetism and electrochemistry. He also invented the earliest form of the device that was to become the Bunsen burner, which is used almost universally in science laboratories as a convenient source of heat.
Michael Faraday was one of the great scientists in history. Some historians of science refer to him as the greatest experimentalist in the history of science. It was largely due to his efforts that electricity became viable for use in technology. The SI unit of capacitance, the farad (symbol F) is named after him.
Early career
Michael Faraday was born in Newington Butts, near present-day Elephant and Castle, London. His family was poor (his father, James Faraday, was a blacksmith) and he had to educate himself. At fourteen he became apprenticed to bookbinder and seller George Riebau and, during his seven year apprenticeship, read many books, developing an interest in science and specifically electricity.
At the age of twenty Faraday attended lectures by the eminent scientist Sir Humphry Davy, president of the Royal Society, and John Tatum, founder of the City Philosophical Society. After Faraday sent Davy a sample of notes taken during the lectures, Davy said he would keep Faraday in mind but should stick to his current job of book-binding. After Davy damaged his eyesight in an accident with nitrogen trichloride, also known as trichloramine, he employed Faraday as a secretary. When John Payne of the Royal Society was fired, Davy recommended Faraday for the job of laboratory assistant. Faraday eagerly left his bookbinding job as his new employer, Henry de la Roche, was hot-tempered.
In a class-based society, Faraday was not considered a gentleman; it has been said that Davy's wife, Jane Apreece, refused to treat him as an equal and, when on a continental tour, made Faraday sit with the servants. However, it was not long before Faraday surpassed Davy.
He also was the first to link electricity to magnetism and then link magnetism back to electricity - i.e. he induced an electric current using magnets - thus inventing the dynamo, predecessor to today's electric generator.
Scientific career
His greatest work was with electricity. In 1821, soon after the Danish chemist, Hans Christian ?rsted discovered the phenomenon of electromagnetism, Davy and William Hyde Wollaston tried but failed to design an electric motor. Faraday, having discussed the problem with the two men, went on to build two devices to produce what he called electromagnetic rotation: a continuous circular motion from the circular magnetic force around a wire. A wire extending into a pool of mercury with a magnet placed inside would rotate around the magnet if charged with electricity by a chemical battery. This device is known as a homopolar motor. These experiments and inventions form the foundation of modern electromagnetic technology. Unwisely, Faraday published his results without acknowledging his debt to Wollaston and Davy, and the resulting controversy caused Faraday to withdraw from electromagnetic research for several years.
Ten years later, in 1831, he began his great series of experiments in which he discovered electromagnetic induction, though the discovery may have been anticipated by the work of Francesco Zantedeschi. He found that if he moved a magnet through a loop of wire, an electric current flowed in the wire. Thecurrent also flowed if the loop was moved over a stationary magnet.
His demonstrations established that a changing magnetic field produces an electric field. This relation was mathematically modelled by Faraday's law, which subsequently became one of the four Maxwell equations. These in turn evolved into the generalization known as field theory.
Faraday then used the principle to construct the electric dynamo, the ancestor of modern power generators.
Faraday proposed that electromagnetic forces extended into the empty space around the conductor, but did not complete his work involving that proposal. Faraday's concept of lines of flux emanating from charged bodies and magnets provided a way to visualize electric and magnetic fields. That mental model was crucial to the successful development of electromechanical devices which dominated engineering and industry for the remainder of the 19th century.
Faraday also dabbled in chemistry, discovering chemical substances such as benzene, inventing the system of oxidation numbers, and liquefying gases such as chlorine. He also discovered the laws of electrolysis and popularized terminology such as anode, cathode, electrode, and ion.
In 1845 he discovered what is now called the Faraday effect and the phenomenon that he named diamagnetism. The plane of polarization of linearly polarized light propagated through a material medium can be rotated by the application of an external magnetic field aligned in the propagation direction. He wrote in his notebook, "I have at last succeeded in illuminating a magnetic curve or line of force and in magnetising a ray of light". This established that magnetic force and light were related.
In his work on static electricity, Faraday demonstrated that the charge only resided on the exterior of a charged conductor, and exterior charge had no influence on anything enclosed within a conductor. This is because the exterior charges redistribute such that the interior fields due to them cancel. This shielding effect is used in what is now known as a Faraday cage.
Miscellaneous
He gave a successful series of lectures on the chemistry and physics of flames at the Royal Institution, entitled The Chemical History of a Candle; this was the origin of the Christmas lectures for young people that are still given there every year and bear his name.
Faraday was known for designing ingenious experiments, but lacked a good mathematics education. (However, his affiliation with James Clerk Maxwell helped in this regard, as Maxwell was able to translate Faraday's experiments into mathematical language.) He was regarded as handsome and modest, declining a knighthood and presidency of the Royal Society (Davy's old position).
Michael Faraday on a British ?20 banknote.
His picture has been printed on British ?20 banknotes.
His sponsor and mentor was John 'Mad Jack' Fuller, who created the Fullerian Professorship of Chemistry at the Royal Institution. Faraday was the first, and most famous, holder of this position to which he was appointed for life.
Faraday was also devoutly religious and a member of the small Sandemanian denomination, an offshoot of the Church of Scotland. He served two terms as an elder in the group's church.
Faraday married Sarah Barnard in 1821 but they had no children. They met through attending the Sandemanian church.
He died at his house at Hampton Court on August 25, 1867.
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