Coulomb's law states that the force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them.The constant of proportionality in a vacuum is k where k = 1/4πε0 = 9.0 × 109 Nm2C-2.ε0 is the permittivity of free space and equals 8.85 × 10-12 Fm-1