## Conceptual Physics (12th Edition)

Coulomb's Law is an inverse-square law, meaning the force is inversely proportional to the square of the distance. $$F = k \frac{q_{1} \; q_{2}}{d^{2}}$$ If the two charges are brought closer together, reducing their separation distance by a factor of 2, the force increases by a factor of 4. If the two charges are brought closer together, reducing their separation distance by a factor of 3, the force increases by a factor of 9.