I know that if any insulator or dielectric is placed between the electric charges then coulomb force decreases by factor known as dielectric constant.So, what will the effect when any conductor is placed?
When a conductor is placed there would kind of same phenomenon. The electrons will develop on the side of positive plate. But here unlike dielectric there will be complete accumulation of charges on the surface. Hence there will be complete cancellation of Electric field inside the conductor. Hence the force will decrease more.
the force between two charges will be zero if a conductor is placed between the two charges because the relative permitivity of conductors is infinite..