SEE, I DONT THINK ITS ONLY VALID IN VACUUM. ITS JUST THT WE HAVE DERIVED IT IN VACUUM. NOW WHEN I WENT THROUGH THE PROCEDURE AND UR CONDITION OF ANY MEDIUM OTHER THAN VACUUM , I GOT TO THE CONCLUSION THT WE MAY APPLY IT FOR ANY OTHER MEDIUM MAKING A SLIGHT MODIFICATION IN GAUSS LAW. AS FAR AS I GOT IT, WE MAY USE THE EQUATION

 

where  is relative permittivity of the medium. WELL I GOT IT USING MY METHOD OF DERIVATION AND WOULD REALLY LIKE OTHERS TO VERIFY AND LET ME KNOW WHETHER IT IS RIGHT OR NOT. AS FAR AS I THINK IT SHOULD BE LIKE THIS.

RATE IF SATISFIED.