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Faraday, Michael

electricity electrolysis discovered quantity

(1791–1867) British chemist and physicist: discovered benzene and the laws of electrolysis; invented an electric motor, dynamo and transformer; creator of classical field theory.

Faraday had an intuitive grasp of the way physical nature may work, combined with a genius for experiment and great energy had the view that physical science has two couples of equal magnitude; and Faraday and an interesting equation.

Faraday’s talents ripened late (he was at his best in his 40s; many scientists have their major ideas behind them at 30), but he began his education late. His father was an ailing blacksmith and the boy became a bookseller’s errand boy at 13. He learned bookbinding, read some of the books and was captivated by an article on electricity in an encyclopedia he had to rebind and by Conversations on Chemistry . These books were to shape his life, and he soon joined a club of young men who met weekly to learn elementary science. He was given tickets to attend last course of lectures at the Royal Institution and he wrote elegant notes of these and bound them. These notes he sent to Davy, and applied for a job with him. Davy firmly recommended him to stay with bookbinding, but he had injured an eye (making NCl3 ) and took Faraday as a temporary helper. After a few weeks he gave him a permanent job as assistant; Faraday was later to become his co-worker, then his successor at the Royal Institution and in time his superior as a scientist. Faraday learned quickly and he was lucky, because Davy decided to make a grand European tour, taking Faraday with him as helper and valet. The young man was to meet most of the leading scientists during a one-and-a-half year tour, made despite the Anglo-French war by special permission; it was a strange education, but it gave him an awareness of most of the physical and chemical science of the time and he became a skilful chemical analyst. The main omission was mathematics, a shortcoming which he never repaired. His first solo research, made when he was 29, was the synthesis of the first known chlorocarbons (C2 Cl6 and C2 Cl4 ) and until 1830 he was mainly a chemist. In 1825 he discovered benzene, which was later to be so important in both theoretical and technical chemistry. He worked on alloy steels and he liquefied chlorine and a range of other gases by pressure and cooling. He was established at the Royal Institution, became an excellent lecturer and never left until retirement; he could have become rich from consultant work, but he belonged to a fervent religious group and he declined both wealth and public honours.

From about 1830 he increasingly studied electricity. An early venture was the study of electrolysis, and in 1832 and 1833 he reported the fundamental laws of electrolysis: (1) the mass of a substance produced by a cathode or anode reaction in electrolysis is directly proportional to the quantity of electricity passed through the cell, and (2) the masses of different substances produced by the same quantity of electricity are proportional to the equivalent masses of the substances (by equivalent mass is meant the relative atomic mass divided by the valence). Faraday had an excellent set of new words devised for him by for work in this area: electrolysis, electrolyte, electrode, anode, cathode, ion. It follows from the laws of electrolysis that an important quantity of electricity is that which will liberate one mole of singly charged ions. This amount, the Faraday constant, F , is defined by F = N A e where N A is the Avogadro constant and e is the charge on an electron. F can be measured accurately (eg by electrolysis of a silver solution) and has the value 9.648 × 10 4 C mol –1 . Also named for Faraday is the unit of capacitance, the farad (F). It is the capacitance of a capacitor (condenser) having a charge of one coulomb © when the potential difference across the plates is one volt. This is a large unit and the more practical unit is the microfarad, equal to 10 –6 F.

Faraday’s work on electricity in the 1830s largely developed the subject had shown that a current could produce a magnetic field; Faraday argued that a magnetic field should produce a current. He found this to be so, provided that ‘a conductor cut the lines of magnetic force’. He had discovered electromagnetic induction (independently discovered by ) and to do it he used his idea of lines and fields of force producing a strain in materials, an idea which was to be highly productive. With it he was able to devise primitive motors, a transformer and a dynamo; he cast off the old idea of electricity as a fluid (or two fluids) and moved to solve some basic problems. For example, he showed that current from an electrostatic machine, a voltaic cell and a dynamo is the same, and devised methods to measure its quantity. He examined capacitors and the properties of dielectrics, and he discovered diamagnetism. In the early 1840s he was unwell for 5 years with ‘ill health connected with my head’. It may have been mercury poisoning.

Back at work in 1845, he worked on his idea that the forces of electricity, magnetism, light and gravity are connected and was able to show that polarized light is affected by a magnetic field. He failed to get a similar result with an electric field ( succeeded in 1875) and the general theme of the ‘unity of natural forces’ has been pursued to the present day. In 1846 was due to speak at the Royal Institution, but at the last moment panicked and Faraday had to improvise a lecture. He included his ‘Thoughts on Ray Vibrations’, which Maxwell claimed were the basis of the electromagnetic theory of light that Maxwell, with new data and more mathematical skill, devised 18 years later.

Faraday had a very strange mind, but it well fitted the needs of physics at the time. His personality offers curious contrasts; he had much personal charm, but no social life after 1830. He had great influence on later physicists, but no students, and worked with his own hands helped only by a long-suffering ex-soldier, Sergeant Anderson. He had highly abstract ideas in science, but he was a most effective popularizer; his Christmas lectures for young people, begun in 1826, are still continued and are now televised. In quality and in quantity, he remains the supreme experimentalist in physics.


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