Permitivity, Relative Permitivity, Dielectric constant

Permittivity is a measure of the property of the medium surrounding electric charge which determine the forces between the charges.Its value is known as Absolute permittivity of that Medium e

More is Permittivity of medium, Less is coulombs Force. 

For water, permittivity is 80 times then that of vacuum, hence force between two charges in water will be 1/80 time force in vacuum (or air.)

Relative Permittivity(er) : It is a dimension-less characteristic constant, which express absolute 

permittivity of a medium w.r.t. permittivity of vacuum or air. It is also called  Dielectric constant (K) K= er = em/e0