Editing Electromagnetism (section)

==Quantities and units==
{{see also|List of physical quantities|List of electromagnetism equations}}
Here is a list of common units related to electromagnetism:<ref>{{Cite web |title=Essentials of the SI: Base & derived units |url=https://physics.nist.gov/cuu/Units/units.html |access-date=2022-08-22 |website=physics.nist.gov |date=12 April 2010 |archive-date=2020-12-28 |archive-url=https://web.archive.org/web/20201228002022/https://physics.nist.gov/cuu/Units/units.html |url-status=live }}</ref>
{{Div col}}
* [[ampere]] (electric current, [[SI]] unit)
* [[coulomb]] (electric charge)
* [[farad]] (capacitance)
* [[henry (unit)|henry]] (inductance)
* [[ohm]] (resistance)
* [[siemens (unit)|siemens]] (conductance)
* [[tesla (unit)|tesla]] (magnetic flux density)
* [[volt]] (electric potential)
* [[watt]] (power)
* [[weber (unit)|weber]] (magnetic flux)
{{Div col end}}
In the electromagnetic [[CGS]] system, electric current is a fundamental quantity defined via [[Ampère's law]] and takes the [[Permeability (electromagnetism)|permeability]] as a dimensionless quantity (relative permeability) whose value in vacuum is [[one|unity]].<ref>{{Cite journal |date=April 1921 |title=Tables of Physical and Chemical Constants, and some Mathematical Functions |journal=Nature |language=en |volume=107 |issue=2687 |pages=264 |doi=10.1038/107264c0 |bibcode=1921Natur.107R.264. |issn=1476-4687|doi-access=free }}</ref> As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.

{{SI electromagnetism units}}

Formulas for physical laws of electromagnetism (such as [[Maxwell's equations]]) need to be adjusted depending on what system of units one uses. This is because there is no [[one-to-one correspondence]] between electromagnetic units in SI and those in CGS, as is the case for mechanical units. Furthermore, within CGS, there are several plausible choices of electromagnetic units, leading to different unit "sub-systems", including [[Gaussian units|Gaussian]], "ESU", "EMU", and [[Heaviside–Lorentz]]. Among these choices, Gaussian units are the most common today, and in fact the phrase "CGS units" is often used to refer specifically to [[Gaussian units|CGS-Gaussian units]].<ref>{{Cite web|title=Conversion of formulae and quantities between unit systems|url=http://nlpc.stanford.edu/nleht/Science/reference/conversion.pdf|access-date=29 January 2022|website=www.stanford.edu|archive-date=5 October 2022|archive-url=https://web.archive.org/web/20221005080303/https://nlpc.stanford.edu/nleht/Science/reference/conversion.pdf|url-status=dead}}</ref>