# What is the Unit of Electric Charge?

The SI unit of electric charge is Coulomb (C) and the CGS unit of electric charge is esu (electrostatic unit). The CGS unit of charge is also known as Statcoulomb. Here we will know more about coulomb and statcoulomb.

In SI unit system:

When two points charges q1 and q2 are placed in a vacuum at a distance of r from each other, then the effective force that is working between them is

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

$Or\; F=9\times 10^{9}\frac{q_{1}q_{2}}{r^{2}}$

$(\because\;\frac{1}{4\pi \varepsilon _{o}} =9\times 10^{9})$

If q= q= 1 C and r = 1 m, then F =  9 × 109 N. From this, we can give the following definition of electric charge

1 Coulomb: 1 Coulomb is the amount of electric charge that when placed at a distance of 1 m from another charge of the same magnitude in a vacuum experiences an electrical force of repulsion of magnitude 9 × 109 N.

In CGS unit system:

When two points charges q1 and q2 are placed in a vacuum at a distance of r from each other, then the effective force that is working between them is

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

$Or\;F=\frac{q_{1}q_{2}}{r^{2}}\;(For \;vacuum\;K=1)$

If q= q= 1 statcoulomb  and r = 1 cm, then F =  1 dyne. From this, we can give the following definition of electric charge

1 Statcoulomb: 1 statcoulomb is the amount of electric charge that when placed at a distance of 1 cm from another charge of the same magnitude in a vacuum experiences an electrical force of repulsion of magnitude 1 dyne.

Relation between 1 Coulomb and 1 Statcoulomb: 1 Coulomb (C) = 3 × 109 esu (electrostatic unit). or 1 Coulomb (C) = 3 × 10Statcoulomb.