Statcoulomb
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Statcoulomb
statcoulomb
Unit systemesu-cgs, Gaussian
Unit ofelectrical charge
SymbolstatC or Fr, esu
Conversions
SI10 × (ccgs)-1 ?, where is the speed of light expressed in cgs unit.
emu-cgs(ccgs)-1
CGS base units1 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

The SI unit of charge is the coulomb (C). The conversion between C and statC is:

• 1 C = ?
• 1 statC ? .

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 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:

${\displaystyle F={\frac {q_{1}q_{2}}{r^{2}}}}$

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:

${\displaystyle F={\frac {q_{1}q_{2}}{4\pi \varepsilon _{0}r^{2}}}}$

where ?0 is the electric constant. The effect of the Gaussian-cgs definition is to fold the "1/40" 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 L3/2M1/2T-1.