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This article is missing information about the use of statcoulomb as a unit of electric flux. (September 2019)
|Unit system||esu-cgs, Gaussian|
|Unit of||electrical charge|
|Symbol||statC or Fr, esu|
|1 statC in ...||... is equal to ...|
|SI||10 × (ccgs)−1 C≈3.33564×10−10 C, where ccgs = 2.99792458×1010 cm/s is the speed of light expressed in cgs unit.|
|CGS base units||1 statC = cm3/2⋅g1/2⋅s−1|
The statcoulomb (statC) or franklin (Fr) or electrostatic unit of charge (esu) is the physical unit for electrical charge used in the esu-cgs (centimetre–gram–second system of units) and Gaussian units. It is a derived unit given by
- 1 statC = dyn1/2 cm = cm3/2 g1/2 s−1.
It can be converted using
- 1 newton = 105 dyne
- 1 cm = 10−2 m
- 1 C = 2997924580 statC ≈ 3.00×109 statC
- 1 statC ≈ 3.33564×10−10 C.
The number 2997924580 is 10 times the value of the speed of light expressed in meters/second or, in other words, the speed of light in decimeters per second.
Definition and relation to cgs base units
The statcoulomb is defined as follows: if two stationary objects each carry a charge of 1 statC and are 1 cm apart, they will electrically repel each other with a force of 1 dyne. This repulsion is governed by Coulomb's law, which in the Gaussian-cgs system states:
where F is the force, q1 and q2 are the two charges, and r is the distance between the charges.
In SI units, the parallel statement for the force between two charges is:
where ε0 is the electric constant. The effect of the Gaussian-cgs definition is to fold the "1/4πε0" factor into the definition of the statcoulomb by setting it equal to unity in terms of length, mass, and time; which results in the Gaussian unit of electric charge possessing the cgs dimensions of L3/2 M1/2 T−1.