# Physics:Abcoulomb

__: Basic unit of electric charge in the CGS-emu system__

**Short description**abcoulomb | |
---|---|

Unit system | CGS electromagnetic units |

Symbol | abC or aC |

Named after | Charles-Augustin de Coulomb |

Derivation | abA⋅s |

Conversions | |

1 abC in ... | ... is equal to ... |

CGS base units | g^{1/2}⋅cm^{1/2} |

SI units | 10 C |

CGS electrostatic units | 2.997925×10^{10} statC |

Gaussian units | 2.997925×10^{10} 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.^{[1]} 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.

## References

- ↑ A.E. Kennelly (1903) "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*accessed 10 December 2020

Original source: https://en.wikipedia.org/wiki/Abcoulomb.
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