What is relation between Dielectric Constant and Force Between two Charges.

If two charges $q_1$ and $q_2$ are separated by distance $r$ in vacuum then electrostatic force between them will be given by the Coulomb law as below:

$$F_v=\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2}{r^2}...(1)$$ Now if these charges are placed in a medium of absolute permittivity $ϵ$ , then electrostatic force between these charges will be $$F_m=\frac{1}{4\pi ϵ}\frac{q_1{q}_2}{r^2}...(2)$$ We know that $$ϵ={ϵ}_0{ϵ}_r=K{ϵ}_0$$ where $K$ is dielectric constant or Relative permittivity or specific inductive capacity. or $$K=\frac{ϵ}{{ϵ}_0}$$ Now, eqn. (2) becomes, $$F_m=\frac{1}{4\pi K{ϵ}_0}\frac{q_1{q}_2}{r^2}...(3)$$ Dividing eqn. (1) by eqn. (3), $$\frac{F_v}{F_m}=\frac{\left(\frac{1}{4\pi {ϵ}_0}\frac{q_1{q}_2}{r^2}\right)}{\left(\frac{1}{4\pi K{ϵ}_0}\frac{q_1{q}_2}{r^2}\right)}=K$$ Hence, dielectric constant (or relative permittivity) of a medium is defined as the ratio of the electrostatic force between two point charges when placed a certain distance apart in vacuum to the electrostatic force between the same charges when placed same distance apart in a medium.

This means a dielectric reduces the force between two charges.