{{Short description|Basic unit of electric charge in the CGS-emu system}} {{one source|date=September 2025}} {{Infobox unit | bgcolor = | name = abcoulomb | image = | caption = | standard = CGS electromagnetic units | quantity = | symbol = abC | symbol2 = aC | namedafter = Charles-Augustin de Coulomb | extralabel = Derivation | extradata = abA⋅s | units1 = CGS base units | inunits1 = g<sup>1/2</sup>⋅cm<sup>1/2</sup> | units2 = SI units | inunits2 = 10 C | units3 = CGS electrostatic units | inunits3 = {{val|2.997925|e=10|u=statC}} | units4 = Gaussian units | inunits4 = {{val|2.997925|e=10|u=Fr}} }} The '''abcoulomb''' ('''abC''' or '''aC''') or '''electromagnetic unit of charge''' ('''emu of charge''') is the derived physical unit of electric charge in the cgs-emu system of units. One abcoulomb is equal to ten coulombs.

The name "abcoulomb" was introduced by Kennelly in 1903 as a short form of ''(absolute) electromagnetic cgs unit of charge'' that was in use since the adoption of the cgs system in 1875.<ref>A.E. Kennelly (1903) [https://dokumen.tips/reader/f/magnetic-units-and-other-subjects-that-might-occupy-attention-at-the-next-international "Magnetic units and other subjects that might occupy attention at the next international electrical congress"] ''20th Annual Convention of the American Institute of Electrical Engineers, 1903''. Retrieved 10 December 2020.{{dead link|date=September 2025}}</ref> The abcoulomb was coherent with the cgs-emu system, in contrast to the coulomb, the practical unit of charge that had been adopted too in 1875.

CGS-emu (or "electromagnetic cgs") units are one of several systems of electromagnetic units within the centimetre gram second system of units; others include CGS-esu, Gaussian units, and Heaviside–Lorentz units. In these other systems, the abcoulomb is not used; CGS-esu and Gaussian units use the statcoulomb instead, while the Heaviside–Lorentz unit of charge has no specific name.

In the electromagnetic cgs system, electric current is a fundamental quantity defined via Ampère's law and takes the permeability as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.

The definition of the abcoulomb follows from that of the abampere: given two parallel currents of one abampere separated by one centimetre, the force per distance of wire is 2 dyn/cm. The abcoulomb is the charge flowing in 1 second given a current of 1 abampere.

==References== {{reflist}}

{{CGS units}} {{Authority control}}

Category:Units of electrical charge Category:Centimetre–gram–second system of units

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