Input (grade 12): where Î 0 and Î 1\/4 0 are two universal constants, called the permittivity of free space and permeability of free space, respectively.
Output (grade 11): In free space, the permeability Î 1\/4 is the permeability of free space, Î 1\/4 0, which is exactly 4 Ï Ã - 10-7 W\/A Â m, by definition. Also, the permittivity is the permittivity of free space Î 0.