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 dyne1 cm = 10−2 m
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:
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 "↔" is used instead of "=" because the two sides are not necessarily interchangeable, as discussed below. The number 2997924580 is 10 times the value of the speed of light expressed in meters/second, and the conversions are exactexcept where indicated. The second context implies that the SI and cgs units for an electric displacement field (D) are related by:
1 C/m2 ↔ 4π × 2997924580×10−4 statC/cm2 ≈ 3.77×106 statC/cm2⇒ 1 statC/cm2 ↔ ~2.65×10−7 C/m2
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.
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