Andre Ampere (1775-1836) was a French physicist who laid the foundations for the science of electrodynamics through his demonstration that electric currents produce magnetic fields, and through his subsequent investigation into the relationship between these two phenomena.
The
son of a well-to-do merchant, Ampere educated himself through diligent
reading in the family library. He survived the French Revolution to
become a science teacher, first in Lyons and then in Bourg. He later
took a post at the Ecole Polytechnique, and in 1808 became inspector
general of the university system in Paris. Beginning in 1824, he
also taught physics at the College de France and philosophy at the Faculte
des Lettres, pursuing diverse scientific interests in the midst of
personal tragedy. He was greatly affected by his father's execution
by guillotine during the Revolution and, after his first wife's early
death, had a catastrophic second marriage.
Ampere's most notable achievements were his independent determination (1814) of Avogadro's law and his work from 1820 to 1827 based on Oersted's discovery, announced in 1820, that a magnetic needle moves in the vicinity of an electric current. Ampere succeeded in explaining the latter phenomenon by assuming that an electric current is capable of exciting a magnetic field. He further demonstrated that the direction of the magnetic field is determined by the direction of the current. He developed a quantitative relationship for the strength of a magnetic field in relation to an electric current (Ampere's theorem) and propounded a theory as to how iron becomes magnetized. Ampere also devised a rule governing the mutual interaction of current-carrying wires (Ampere's law) and produced a definition of the unit of measurement of current flow, now known as the ampere.
The ampere is the unit for measuring electric current. As more accurate procedures have been devised, the definition of the quantity has been changed. The most modern definition is based on the ability of a specified current to deposit a precise amount of a substance on an electrode during electrolysis. Formerly, the definition involved the force that was produced between parallel wires carrying a current; still earlier, the ampere was defined as a flow of one coulomb per second, where the coulomb (a quantity of electrical charge) was taken as the basic unit.
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