|Unit system||CGS electromagnetic units|
|Symbol||abC or aC|
|Named after||Charles-Augustin de Coulomb|
|CGS base units||g1/2?cm1/2|
|SI units||10 C|
|CGS electrostatic units|
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. 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 Lorentz-Heaviside units. In these other systems, the abcoulomb is not used; CGS-esu and Gaussian units use the statcoulomb instead, while the Lorentz-Heaviside 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.