Editing Electric charge (section)

== Unit ==

The [[International System of Units|SI]] unit of [[quantity]] of electric charge is the [[coulomb]] (symbol: C). The coulomb is defined as the quantity of charge that passes through the [[cross section (geometry)|cross section]] of an [[electrical conductor]] carrying one [[ampere]] for one [[second]].<ref name=CIPM1946>{{cite web |url=https://www.bipm.org/en/committees/ci/cipm/41-1946/resolution-2 |publisher=BIPM |title=CIPM, 1946: Resolution 2}}</ref> This unit was proposed in 1946 and ratified in 1948.<ref name=CIPM1946/> The lowercase symbol ''q'' is often used to denote a quantity of electric charge. The quantity of electric charge can be directly measured with an [[electrometer]], or indirectly measured with a [[galvanometer|ballistic galvanometer]].

The [[elementary charge]] is defined as a fundamental constant in the SI.<ref name=9thSIp127>{{SIbrochure9th}}, p. 127</ref> The value for elementary charge, when expressed in SI units, is exactly {{physconst|e|after=.}}

After discovering the [[charge quantization|quantized]] character of charge, in 1891, [[George Johnstone Stoney|George Stoney]] proposed the unit 'electron' for this fundamental unit of electrical charge. [[J. J. Thomson]] subsequently discovered the particle that we now call the electron in 1897. The unit is today referred to as {{em|elementary charge}}, {{em|fundamental unit of charge}}, or simply denoted ''e'', with the charge of an electron being −''e''. The charge of an isolated system should be a multiple of the elementary charge ''e'', even if at [[macroscopic scale|large scales]] charge seems to behave as a continuous quantity. In some contexts it is meaningful to speak of fractions of an elementary charge; for example, in the [[fractional quantum Hall effect]].

The unit [[Faraday constant|faraday]] is sometimes used in electrochemistry. One faraday is the magnitude of the charge of one mole of elementary charges,<ref>{{cite book |last1=Gambhir |first1=RS |last2=Banerjee |first2=D |last3=Durgapal |first3=MC |title=Foundations of Physics, Vol. 2 | date=1993 |publisher=Wiley Eastern Limited |location=New Delhi |page=51 |url=https://books.google.com/books?id=r-Qpy0KQayIC&pg=PA51 |access-date=10 October 2018|isbn=9788122405231 }}</ref> i.e. {{physconst|F|unit=C|after=.|ref=no}}