Question

what do you mean by permittivity of a medium and why does it have a value though there is no charge in space?

Answer 1

it has a constant values while othe s have a different value

Answer 2

Permittivity of a medium is a measure of the resistance (opposition) it offers to the spreading of electric field due to an electrostatic charge.  It is the inverse of the total electric flux through a closed surface, arising due to a unit electric charge.

       epsilon =  q / (fi)  =  q / (E  * S)
               S= 4πR² for a sperical surface at distance R from the point charge q.

       Flux = q/ epsilon

     permittivity is defined through  Coulombs law for electric  force or electric field. Its units are Farad/meter