There are many ways to express Gauss’s law, and although notation differs among textbooks, the integral form is generally written like this: I S ~ E ^ nda ¼ q enc e 0 Gauss’s law for electric fields (integral form). The left side of this equation is no more than a mathematical description of the electric flux – the number of electric field lines – passing through a closed surface S, whereas the right side is the total amount of charge contained within that surface divided by a constant called the permittivity of free space