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Ampère, André Marie

current flowing electric currents

[ãpair] (1775–1836) French physicist and mathematician: pioneer of electrodynamics.

Ampère was a very gifted child, combining a passion for reading with a photographic memory and linguistic and mathematical ability. He was largely self-taught. His life was disrupted by the French Revolution when, in 1793, his father, a Justice of the Peace, was guillotined along with 1500 fellow citizens in Lyon. For a year Ampère seems to have suffered a state of shock; he was aged 18. Ten years later, his adored young wife died following the birth of his son. His second marriage, undertaken on the advice of friends, was a disaster. His professional life ran more smoothly.

In 1802 Ampère was appointed to the first of a series of professorships, and in 1808 was appointed inspector-general of the university system by Napoleon, a post he retained until his death.
Ampère was a versatile scientist, interested in physics, philosophy, psychology and chemistry, and made discoveries in this last field that would have been important had he not been unfortunate in being pre-empted by others on several occasions. In 1820 he was stimulated by discovery, that an electric current generates a magnetic field, to carry out pioneering work on electric current and electrodynamics. Within months he had made a number of important discoveries: he showed that two parallel wires carrying currents flowing in the same direction attracted one another while when the currents ran in opposite directions they were repelled; he invented the coiled wire solenoid; and he realized that the degree of deflection of Oersted’s compass needle by a current could be used as a measure of the strength of the current, the basis of the galvanometer. Perhaps his most outstanding contribution, however, came in 1827, when he provided a mathematical formulation of electromagnetism, notably Ampère’s Law, which relates the magnetic force between two wires to the product of the currents flowing in them and the inverse square of the distance between them. It may be generalized to describe the magnetic force generated at any point in space by a current flowing along a conductor. The SI unit of electric current, the ampere (sometimes abbreviated to amp) is named in his honour. The ampere is defined as that steady current which, when it is flowing in each of two infinitely long, straight, parallel conductors that have negligible areas of cross-section and are 1 metre apart in a vacuum, causes each conductor to exert a force of 2×10 –7 N on each metre of the other.

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