Editing Elementary charge (section)

== As a unit ==
{{see also|2019 revision of the SI}}
{{Infobox unit
| bgcolour      = 
| name          = Elementary charge
| image         = 
| caption       = 
| standard      = [[Atomic units]]
| quantity      = [[electric charge]]
| symbol        = ''e''
| namedafter    = 
| units1        = [[coulomb]]s
| inunits1      = {{physconst|e|unit=no}}
| units2        = <math>\sqrt{\varepsilon_0\hbar c}</math>{{br}}([[natural units]])
| inunits2      = 0.30282212088
| units3        = [[statC]]
| inunits3      = ≘&nbsp;{{val|4.80320425|(10)|e=-10}}
}}

In some [[natural unit]] systems, such as the system of [[atomic units]], ''e'' functions as the [[units of measurement|unit]] of [[electric charge]]. The use of elementary charge as a unit was promoted by [[George Johnstone Stoney]] in 1874 for the first system of natural units, called [[Stoney units]].<ref>
{{cite journal
 |author=G. J. Stoney
 |year=1894
 |title=Of the "Electron," or Atom of Electricity
 |url=http://www.chemteam.info/Chem-History/Stoney-1894.html
 |journal=[[Philosophical Magazine]]
 |series=5 |volume=38 |pages=418–420
 |doi=10.1080/14786449408620653
}}</ref> Later, he proposed the name ''electron'' for this unit. At the time, the particle we now call the [[electron]] was not yet discovered and the difference between the particle ''electron'' and the unit of charge ''electron'' was still blurred. Later, the name ''electron'' was assigned to the particle and the unit of charge ''e'' lost its name. However, the unit of energy [[electronvolt]] (eV) is a remnant of the fact that the elementary charge was once called ''electron''.

In other natural unit systems, the unit of charge is defined as <math>\sqrt{\varepsilon_0\hbar c},</math> with the result that 
<math display=block>e = \sqrt{4\pi\alpha}\sqrt{\varepsilon_0 \hbar c} \approx 0.30282212088 \sqrt{\varepsilon_0 \hbar c},</math>
where {{mvar|α}} is the [[fine-structure constant]], {{mvar|c}} is the [[speed of light]], {{math|''ε''<sub>0</sub>}} is the [[electric constant]], and {{mvar|ħ}} is the [[reduced Planck constant]].