Coulomb's Law

Coulomb’s Law

Coulomb’s Law gives the equaton for electrostatic forces acting on two particles. For two particles, where particle 1 has charge $q_1$, particle 2 has charge $q_2$, separated by distance $r$, the electostatic force is given as

\[\vec{F} = k \frac{q_1 q_2}{r^2} \hat{r}\]

where $\hat{r}$ is a unit vector that points along the radial axis extending through the two particles and $k$ is the electrostatic constant $\frac{1}{4 \pi \epsilon_0}$, where $\epsilon_0$ is the permittivitiy constant, and is $\epsilon_0 = 8.85 \times 10^{-12} ~ C^2 / N \cdot m^2$.

The magnitude of the electrostatic force in Coulomb’s law becomes

\[F = \frac{1}{4 \pi \epsilon_0} \frac{|q_1| |q_2|}{r^2}\]

A coulumb is defined as the charge that flows from 1 ampere of current in one second:

\[1 C = (1 A)(1 s)\]