Monday, 3 December 2012
Friday, 30 November 2012
Michael Faraday
Michael Faraday
Michael Faraday, FRS (22 September 1791 – 25 August 1867) was an English scientistwho contributed to the fields of electromagnetism and electrochemistry. His main discoveries include those of electromagnetic induction, diamagnetism and electrolysis.
Although Faraday received little formal education he was one of the most influential scientists in history,[1] and historians of science[2] refer to him as having been the bestexperimentalist in the history of science.[3] It was by his research on the magnetic fieldaround a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetismcould affect rays of light and that there was an underlying relationship between the two phenomena.[4][5] He similarly discovered the principle of electromagnetic induction,diamagnetism, and the laws of electrolysis. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts that electricity became practical for use in technology.
As a chemist, Faraday discovered benzene, investigated the clathrate hydrate of chlorine, invented an early form of the Bunsen burner and the system of oxidation numbers, and popularised terminology such as anode, cathode, electrode, and ion. Faraday ultimately became the first and foremost Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a lifetime position.
Faraday was an excellent experimentalist who conveyed his ideas in clear and simple language; his mathematical abilities, however, did not extend as far as trigonometry or any but the simplest algebra. James Clerk Maxwell took the work of Faraday and others, and summarized it in a set of equations that is accepted as the basis of all modern theories of electromagnetic phenomena. On Faraday's uses of the lines of force, Maxwell wrote that they show Faraday "to have been in reality a mathematician of a very high order – one from whom the mathematicians of the future may derive valuable and fertile methods."[6] The SIunit of capacitance, the farad, is named in his honour.
Albert Einstein kept a picture of Faraday on his study wall, alongside pictures of Isaac Newton and James Clerk Maxwell.[7] Physicist Ernest Rutherford stated; "When we consider the magnitude and extent of his discoveries and their influence on the progress of science and of industry, there is no honour too great to pay to the memory of Faraday, one of the greatest scientific discoverers of all time".
Early life
Faraday was born in Newington Butts,[9] which is now part of the London Borough of Southwark, but which was then a suburban part ofSurrey.[10] His family was not well off; his father, James, was a member of the Glassite sect of Christianity. James Faraday moved his wife and two children to London during the winter of 1790 from Outhgill in Westmorland, where he had been an apprentice to the village blacksmith.[11] Michael was born the autumn of that year. The young Michael Faraday, who was the third of four children, having only the most basic school education, had to educate himself.[12] At fourteen he became the apprentice to George Riebau, a local bookbinder and bookseller in Blandford Street.[13] During his seven-year apprenticeship he read many books, including Isaac Watts' The Improvement of the Mind, and he enthusiastically implemented the principles and suggestions contained therein. At this time he also developed an interest in science, especially in electricity. Faraday was particularly inspired by the book Conversations on Chemistry byJane Marcet.[14]
In 1812, at the age of twenty, and at the end of his apprenticeship, Faraday attended lectures by the eminent English chemist Humphry Davy of the Royal Institution and Royal Society, and John Tatum, founder of the City Philosophical Society. Many of the tickets for these lectures were given to Faraday by William Dance, who was one of the founders of theRoyal Philharmonic Society. Faraday subsequently sent Davy a three-hundred-page book based on notes that he had taken during these lectures. Davy's reply was immediate, kind, and favourable. When Davy damaged his eyesight in an accident with nitrogen trichloride, he decided to employ Faraday as a secretary. When one of the Royal Institution's assistants, John Payne, was sacked, Sir Humphry Davy was asked to find a replacement, and appointed Faraday as Chemical Assistant at the Royal Institution on 1 March 1813.[4]
In the class-based English society of the time, Faraday was not considered a gentleman. When Davy set out on a long tour of the continent in 1813–15, his valet did not wish to go. Instead, Faraday went as Davy's scientific assistant, and was asked to act as Davy's valet until a replacement could be found in Paris. Faraday was forced to fill the role of valet as well as assistant throughout the trip. Davy's wife, Jane Apreece, refused to treat Faraday as an equal (making him travel outside the coach, eat with the servants, etc.), and made Faraday so miserable that he contemplated returning to England alone and giving up science altogether. The trip did, however, give him access to the scientific elite of Europe and exposed him to a host of stimulating ideas.[4]
Faraday married Sarah Barnard (1800–1879) on 12 June 1821.[15] They met through their families at the Sandemanian church, and he confessed his faith to the Sandemanian congregation the month after they were married. They had no children.[9]
Faraday was a devout Christian; his Sandemanian denomination was an offshoot of the Church of Scotland. Well after his marriage, he served as deacon and for two terms as an elder in the meeting house of his youth. His church was located at Paul's Alley in theBarbican. This meeting house was relocated in 1862 to Barnsbury Grove, Islington; this North London location was where Faraday served the final two years of his second term as elder prior to his resignation from that post.[16][17] Biographers have noted that "a strong sense of the unity of God and nature pervaded Faraday's life and work."[18]
Electricity and magnetism
Faraday is best known for his work regarding electricity and magnetism. His first recorded experiment was the construction of a voltaic pile with seven halfpence pieces, stacked together with seven disks of sheet zinc, and six pieces of paper moistened with salt water. With this pile he decomposed sulphate of magnesia (first letter to Abbott, 12 July 1812).
In 1821, soon after the Danish physicist and chemist Hans Christian Ørsted discovered the phenomenon of electromagnetism, Davy and British scientist William Hyde Wollaston tried, but failed, to design an electric motor.[5] 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.[28][29]
From his initial discovery in 1821, Faraday continued his laboratory work, exploring electromagnetic properties of materials and developing requisite experience. In 1824, Faraday briefly set up a circuit to study whether a magnetic field could regulate the flow of a current in an adjacent wire, but he found no such relationship.[30] This experiment followed similar work conducted with light and magnets three years earlier that yielded identical results.[31][32] During the next seven years, Faraday spent much of his time perfecting his recipe for optical quality (heavy) glass, borosilicate of lead,[33] which he used in his future studies connecting light with magnetism.[34] In his spare time, Faraday continued publishing his experimental work on optics and electromagnetism; he conducted correspondence with scientists whom he had met on his journeys across Europe with Davy, and who were also working on electromagnetism.[35] Two years after the death of Davy, in 1831, he began his great series of experiments in which he discoveredelectromagnetic induction. Joseph Henry likely discovered self-induction a few months earlier and both may have been anticipated by the work of Francesco Zantedeschi in Italy in 1829 and 1830.[36]
Faraday's breakthrough came when he wrapped two insulated coils of wire around an iron ring, and found that, upon passing a current through one coil, a momentary current was induced in the other coil.[5] This phenomenon is now known asmutual induction.[37] The iron ring-coil apparatus is still on display at the Royal Institution. In subsequent experiments, he found that, if he moved a magnet through a loop of wire, an electric current flowed in that wire. The current 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 modelled mathematically by James Clerk Maxwell as Faraday's law, which subsequently became one of the four Maxwell equations, and which have in turn evolved into the generalization known today as field theory. Faraday would later use the principles he had discovered to construct the electric dynamo, the ancestor of modern power generators.
In 1839, he completed a series of experiments aimed at investigating the fundamental nature of electricity; Faraday used "static", batteries, and "animal electricity" to produce the phenomena of electrostatic attraction, electrolysis, magnetism, etc. He concluded that, contrary to the scientific opinion of the time, the divisions between the various "kinds" of electricity were illusory. Faraday instead proposed that only a single "electricity" exists, and the changing values of quantity and intensity (current and voltage) would produce different groups of phenomena.[5]
Near the end of his career, Faraday proposed that electromagnetic forces extended into the empty space around the conductor. This idea was rejected by his fellow scientists, and Faraday did not live to see the eventual acceptance of his proposition by the scientific community. Faraday's concept of lines of flux emanating from charged bodies and magnets provided a way to visualize electric and magnetic fields; that conceptual model was crucial for the successful development of the electromechanical devices that dominated engineering and industry for the remainder of the 19th century.
Diamagnetism
In 1845, Faraday discovered that many materials exhibit a weak repulsion from a magnetic field: a phenomenon he termed diamagnetism.[39]
Faraday also discovered that the plane of polarization of linearly polarized light can be rotated by the application of an external magnetic field aligned in the direction which the light is moving. This is now termed the Faraday effect. 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".
Later on in his life, in 1862, Faraday used a spectroscope to search for a different alteration of light, the change of spectral lines by an applied magnetic field. The equipment available to him was, however, insufficient for a definite determination of spectral change. Pieter Zeeman later used an improved apparatus to study the same phenomenon, publishing his results in 1897 and receiving the 1902 Nobel Prize in Physics for his success. In both his 1897 paper[40] and his Nobel acceptance speech,[41] Zeeman made reference to Faraday's work.
Faraday cage
In his work on static electricity, Faraday's ice pail experiment demonstrated that the charge resided only 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.
Royal Institution and public service
Faraday was the first Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a position to which he was appointed for life. His sponsor and mentor was John 'Mad Jack' Fuller, who created the position at the Royal Institution. Faraday was elected a member of the Royal Society in 1824,[9] appointed director of the laboratory in 1825; and in 1833 he was appointed Fullerian Professor of Chemistry in the institution for life, without the obligation to deliver lectures.
Beyond his scientific research into areas such as chemistry, electricity, and magnetism at the Royal Institution, Faraday undertook numerous, and often time-consuming, service projects for private enterprise and the British government. This work included investigations of explosions in coal mines, being an expert witness in court, and the preparation of high-quality optical glass. In 1846, together with Charles Lyell, he produced a lengthy and detailed report on a serious explosion in the colliery at Haswell County Durham, which killed 95 miners. Their report was a meticulous forensic investigation and indicated that coal dust contributed to the severity of the explosion. The report should have warned coal owners of the hazard of coal dust explosions, but the risk was ignored for over 60 years until the Senghenydd Colliery Disaster of 1913.
As a respected scientist in a nation with strong maritime interests, Faraday spent extensive amounts of time on projects such as the construction and operation of light houses and protecting the bottoms of ships from corrosion. His workshop still stands at Trinity Buoy Wharf above the Chain and Buoy Store, next to London's only lighthouse and a school that is named after him.
Faraday was also active in what would now be called environmental science, or engineering. He investigated industrial pollution atSwansea and was consulted on air pollution at the Royal Mint. In July 1855, Faraday wrote a letter to The Times on the subject of the foul condition of the River Thames, which resulted in an oft-reprinted cartoon in Punch. (See also The Great Stink.)
Faraday assisted with the planning and judging of exhibits for the Great Exhibition of 1851 in London. He also advised the National Gallery on the cleaning and protection of its art collection, and served on the National Gallery Site Commission in 1857.
Education was another of Faraday's areas of service; he lectured on the topic in 1854 at the Royal Institution, and in 1862 he appeared before a Public Schools Commission to give his views on education in Great Britain. Faraday also weighed in negatively on the public's fascination with table-turning, mesmerism, and seances, and in so doing chastised both the public and the nation's educational system.[42]
Faraday 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 one of the earliest Christmas lectures for young people, which are still given each year. Between 1827 and 1860, Faraday gave the Christmas lectures a record nineteen times.
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