What is "statcoulomb"

n. The cgs unit of electrical charge, equal to 33.35640 picocoulombs.

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 =dyn cm= cm g s.

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 ↔ statC ≈ ⇒ 1 statC ↔ ~.
• For electric flux (Φ): 1 C ↔ 4π× statC ≈ ⇒ 1 statC ↔ ~.

The symbol "↔" is used instead of "=" because the two sides are not necessarily interchangeable, as discussed below. The number is 10 times the value of the speed of light expressed in meters/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:

1 C/m ↔ 4π××10 statC/cm ≈ ⇒ 1 statC/cm ↔ ~

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.