Amperemeter hg.jpg
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.
Unit information
Unit system SI base unit
Unit of Electric current
Symbol A 
Named after André-Marie Ampère

The ampere ( SI unit symbol: A, dimension symbol: I), [1] often shortened to "amp", [2] is a unit of electric current. In the International System of Units (SI) [3] [4] the ampere is one of the seven [5] SI base units. It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electrodynamics.

SI defines the ampere in terms of other base units by measuring the electromagnetic force between electrical conductors carrying electric current. The earlier CGS measurement system had two different definitions of current, one essentially the same as the SI's and the other using electric charge as the base unit, 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. [6] In SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second.

In the future, the SI definition may shift back to charge as the base unit, with the coulomb defined in terms of the elementary charge on electrons and protons (one coulomb equals the charge of roughly 6.242×1018 protons).


Illustration of the definition of the ampere unit

SI defines ampere as follows:

The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length. [7] [3] [8]

Ampère's force law [9] [10] states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere.

The SI unit of charge, the coulomb, "is the quantity of electricity carried in 1 second by a current of 1 ampere". [11] Conversely, a current of one ampere is one coulomb of charge going past a given point per second:

In general, charge Q is determined by steady current I flowing for a time t as Q = It.

Constant, instantaneous and average current are expressed in amperes (as in "the charging current is 1.2 A") and the charge accumulated, or passed through a circuit over a period of time is expressed in coulombs (as in "the battery charge is 30000 C"). The relation of the ampere (C/s) to the coulomb is the same as that of the watt (J/s) to the joule.

Other Languages
العربية: أمبير
asturianu: Amperiu
azərbaycanca: Amper
беларуская (тарашкевіца)‎: Ампэр
български: Ампер
Boarisch: Ampere
བོད་ཡིག: ཨམ་ཕེར།
bosanski: Amper
brezhoneg: Amper
català: Ampere
Чӑвашла: Ампер
čeština: Ampér
Cymraeg: Amper
dansk: Ampere
Deutsch: Ampere
eesti: Amper
español: Amperio
Esperanto: Ampero
euskara: Anpere
فارسی: آمپر
français: Ampère
Frysk: Ampêre
furlan: Ampere
Gaeilge: Aimpéar
galego: Ampere
한국어: 암페어
हिन्दी: एम्पियर
hrvatski: Amper
Bahasa Indonesia: Ampere
íslenska: Amper
italiano: Ampere
עברית: אמפר
ಕನ್ನಡ: ಎಂಪಿಯರ್
ქართული: ამპერი
Kiswahili: Ampea
Kurdî: Amper
latviešu: Ampērs
Lëtzebuergesch: Ampère (Eenheet)
lietuvių: Amperas
Limburgs: Ampère
la .lojban.: xampo
magyar: Amper
македонски: Ампер
മലയാളം: ആം‌പിയർ
मराठी: ॲम्पिअर
Bahasa Melayu: Ampere
монгол: Ампер
မြန်မာဘာသာ: အမ်ပီယာ
Nederlands: Ampère (eenheid)
日本語: アンペア
Nordfriisk: Ampere
norsk bokmål: Ampere
norsk nynorsk: Ampere
oʻzbekcha/ўзбекча: Amper
پنجابی: ایمپیر
Patois: Ampier
ភាសាខ្មែរ: អំពែរ
Piemontèis: Ampère
Plattdüütsch: Ampere
polski: Amper
português: Ampere
română: Amper
русский: Ампер
Scots: Ampere
shqip: Amperi
Simple English: Ampere
slovenčina: Ampér
slovenščina: Amper
Soomaaliga: Ambeer
српски / srpski: Ампер
srpskohrvatski / српскохрватски: Amper
suomi: Ampeeri
svenska: Ampere
Tagalog: Amperyo
தமிழ்: ஆம்பியர்
తెలుగు: ఆంపియర్
Türkçe: Amper
тыва дыл: Ампер
українська: Ампер
اردو: ایمپئیر
Tiếng Việt: Ampe
Winaray: Amperahe
粵語: 安培
Zazaki: Amper
中文: 安培