Ampere

The ampere (/ˈæmpɛər/, US: /ˈæmpɪər/;[1][2][3] symbol: A),[4] often shortened to amp,[5] is the unit of electric current in the International System of Units (SI). One ampere is equal to 1 coulomb or 6.241509074×10¹⁸ electrons worth of charge moving past a point in a second.[6][7][8] It is named after French mathematician and physicist André-Marie Ampère (1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted.

ampere
Demonstration model of a moving iron ammeter. As the current through the coil increases, the plunger is drawn further into the coil and the pointer deflects to the right.
General information
Unit system	SI
Unit of	electric current
Symbol	A
Named after	André-Marie Ampère

As of the 2019 redefinition of the SI base units, the ampere is defined by fixing the elementary charge e to be exactly 1.602176634×10⁻¹⁹ C (coulomb),[6][9] which means an ampere is an electrical current equivalent to 10¹⁹ elementary charges moving every 1.602176634 seconds or 6.241509074×10¹⁸ elementary charges moving in a second. Prior to the redefinition the ampere was defined as the current that would need to be passed through 2 parallel wires 1 metre apart to produce a magnetic force of 2×10⁻⁷ newtons per metre.

The earlier CGS system had two definitions of current, one essentially the same as the SI's and the other using Coulomb's law as a fundamental relationship, with the unit of charge defined by measuring the force between two charged metal plates. The ampere was then defined as one coulomb of charge per second.[10] In SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second.