Editing Ampere (section)

=== Present definition ===
The [[2019 revision of the SI]] defined the ampere by taking the fixed numerical value of the [[elementary charge]] {{mvar|e}} to be {{physical constants|e|ref=no|unit=no}} when expressed in the unit C, which is equal to A⋅s, where the second is defined in terms of {{math|∆''ν''<sub>Cs</sub>}}, the unperturbed ground state hyperfine transition frequency of the [[caesium]]-133 atom.<ref>{{cite web |title=ampere (A) |url=https://www.npl.co.uk/si-units/ampere |website=www.npl.co.uk |access-date=21 May 2019}}</ref>

The SI unit of charge, the [[coulomb]], "is the quantity of electricity carried in 1 second by a current of 1 ampere".<ref>{{Citation | publisher = [[Bureau International des Poids et Mesures]] | year = 2006 | url = http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf | title = The International System of Units (SI) | edition = 8th | page = 144 | url-status = live | archive-url = https://web.archive.org/web/20131105051930/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf | archive-date = 5 November 2013 | df = dmy-all }}.</ref> Conversely, a current of one ampere is one coulomb of charge going past a given point per second:
:<math>\rm 1\ A=1\,\text{C/s}.</math>
In general, charge {{mvar|Q}} is determined by steady current {{mvar|I}} flowing for a time {{mvar|t}} as {{math|1=''Q'' = ''I'' ''t''}}.

Constant, instantaneous and average current are expressed in amperes (as in "the charging current is 1.2&nbsp;A") and the charge accumulated (or passed through a circuit) over a period of time is expressed in coulombs (as in "the [[battery (electricity)|battery]] charge is {{val|30000|u=C}}"). The relation of the ampere (C/s) to the coulomb is the same as that of the [[watt]] (J/s) to the [[joule]].