# 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 6.241509074×10^{18} 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 | |
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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 10^{19} elementary charges moving every 1.602176634 seconds or 6.241509074×10^{18} 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.