Coulomb’s Law

If two charged particles have the charges $q_1$ and $q_2$ and of a distance $r$ apart, then they exert an Electric Force:

${\vec{F}}_{\text{1 on 2}}=-{\vec{F}}_{\text{2 on 1}}=\frac{k{q}_1{q}_2}{r^2}\widehat{r_{q_1{q}_2}}$ where

• $k$ is the Coulomb’s Constant
• $\hat{r}$ is the unit vector pointing in direction from $q_1$ to $q_2$

Intuitively, the direction of the force:

• Two charges of equal sign repel each other
• Two charges of opposite sign attract each other

Limitations

• Charged bodies must be very small compared to $r$ (infinitesimally small)
• Force must be inversely proportional to $r^2$

Related

• Principle of Superposition