The electric flux over a surface S is therefore given by the surface integral : where E is the electric field and dS is a differential area on the closed surface S with an outward facing surface normal defining its direction .
Using full vector notation , the electric flux through a small area is given by The electric flux over a surface S is therefore given by the surface integral : where E is the electric field and dA is a differential area on the surface with an outward facing surface normal defining its direction .