Also , the permittivity is the permittivity of free space Î 0 . So , in free space , the equation is : These are formally identical to the general formulation in terms of E and B ( given above ) , except that the permittivity of free space was replaced with the permittivity of the material , the permeability of free space was replaced with the permeability of the material , and only free charges and currents are included ( instead of all charges and currents ) .