Coloumb's Law

$F=k\frac{qQ}{r^2}\hat{r}$

• $k$ is the Coloumb constant
• ${\epsilon }_0$ is the permittivity of free space
• $r=\vec{r}-{\vec{r}}^{\prime }$ where $\vec{r}$ is the is vector pointing from the origin to the test charge and ${\vec{r}}^{\prime }$ is the vector pointing from the origin to the source charge. The overall vector is thus pointing from the source charge to the test charge