Statcoulomb
CGS unit of electric charge / From Wikipedia, the free encyclopedia
The franklin (Fr), statcoulomb (statC), or electrostatic unit of charge (esu) is the physical unit for electrical charge used in the centimetre–gram–second electrostatic units variant (CGS-ESU) and Gaussian systems of units. It is a derived unit given by
statcoulomb | |
---|---|
Unit system | Gaussian, CGS-ESU |
Unit of | electrical charge |
Symbol | Fr, statC, esu |
Derivation | dyn1/2⋅cm |
Conversions | |
1 Fr in ... | ... is equal to ... |
CGS base units | 1 cm3/2⋅g1/2⋅s−1 |
SI (charge) | ≘ ~3.33564×10−10 C |
SI (flux) | ≘ ~2.65×10−11 C |
That is, it is defined so that the CGS-ESU quantity that corresponds to the Coulomb constant is a dimensionless quantity equal to 1.
It can be converted using
The SI system of units uses the coulomb (C) instead. The conversion between C and statC is different in different contexts. The most common contexts are[lower-alpha 1]:
- For electric charge:1 C ≘ ~2997924580 statC ≈ 3.00×109 statC⇒ 1 statC ≘ ~3.33564×10−10 C.
- For electric flux (ΦD): 1 C ≘ ~4π × 2997924580 statC ≈ 3.77×1010 statC⇒ 1 statC ≘ ~2.65×10−11 C.
The symbol "≘" ('corresponds to') is used instead of "=" because the two sides are not interchangeable, as discussed below. The number 2997924580 is 10 times the numeric value of the speed of light expressed in metres/second, and the conversions are exact except where indicated. The second context implies that the SI and CGS units for an electric displacement field (D) are related by:
due to the relation between the metre and the centimetre. The coulomb is an extremely large charge rarely encountered in electrostatics, while the statcoulomb is closer to everyday charges.