If the charges are situated in a medium of permittivity ε, then the magnitude of the force between them will be, If the charges are situated in a medium of permittivity ε, then the magnitude of the force between them will be,
Fm = 1/4∏€ X q1q2/r2 -------------------------------------(2)
Dividing equations 1 and 2 we get F/Fm = € / €0 = € r. This ratio is called as relative permittivity or dielectric constant. This is equal to 1 in air. Hence the force between two charges depends on the medium in which they are situated.