André-Marie Ampère

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The physicist who turned Ørsted's observation into electrodynamics, and who first drew the distinction between current and voltage.

Ørsted's experiment was reproduced at the Paris Academy in September 1820; Ampère presented his first reflections on it a week later and spent the following six years turning it into mathematics. The speed matters less than the difference in kind: Ørsted observed that a current deflects a needle, and Ampère produced a theory that predicted by how much. Separating current from voltage is the distinction every practical electrical measurement rests on, and the unit of the first carries his name.

Also known as: ampere, ampère, ampere's law, electrodynamics

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