Consider a Gaussian surface enclosing 30 electrons inside it. What would be the value of electric flux through the surface and the electric field at a distance of 0.6 meters from the center to its surface? Recall the expression for Gauss's law: by multiplying the known values of the charge of an electron with the total electrons present inside it, the total charge can be obtained. By substituting the known quantities—the total charge and the permittivity of free space—into the Gauss's law expression, the electric flux can be calculated. To find the electric field on the surface, remember that flux is the product of the electric field times the area of the surface. Rearranging the expression and writing the area in terms of the radius, the electric field can be calculated. Suppose there are additional charges in and around the Gaussian surface; then, the total flux through the surface can be obtained by summing up only those charges that are enclosed inside the surface divided by the permittivity of free space.