The amount by which the force between the charge (in presence of medium) is relatively less than that in a vacuum, is called the dielectric constant of that medium or relative permittivity (\\\\(\\epsilon_r\\\\))\\\\(\\epsilon_r=\\dfrac{\ ext{Force between charges in air or vaccum}}{\ ext{Force between charges in medium}}\\\\)\\\\(\ herefore\\,\\,\\varepsilon_r=\\dfrac{\\varepsilon}{\\varepsilon_0}\\\\)