Let us consider a point charge Q located in an isotropic homogeneous medium of dielectric constant e. The flux density at a distance r on a surface enclosing the charge is given by

...............................................(2.13)

If we consider an elementary area ds, the amount of flux passing through the elementary area is given by

.....................................(2.14)

But , is the elementary solid angle subtended by the area at the location of Q. Therefore we can write

For a closed surface enclosing the charge, we can write

which can seen to be same as what we have stated in the definition of Gauss's Law.