====== Gaussian units ======
[[Gauss]] constructed a [[CGS]] system of units by considering the value of the permittivity of free space

$$ \epsilon_0 = \frac{1}{4\pi} $$

which makes [[Coulomb]]'s law very simple by making $4\pi\epsilon_0=1$ giving rise to the electric field

$$ E = \frac{q}{r^2} $$

that is a charge $q$ creates an electric field of magnitude $E$ at a distance $r$.

Because speed of light [[c]] is just $(\epsilon_0\mu_0)^{-1/2}$, in Gaussian units we can find the permeability of free space as

$$ \mu_0 = \frac{4\pi}{c^2}. $$