Define electric flux.

(N/A) Electric flux is a measure of the total number of electric field lines passing through a given surface area. Mathematically,for a surface $S$ in an electric field $\vec{E}$,the electric flux $\Phi_E$ is defined as the surface integral of the electric field over that surface: $\Phi_E = \int_S \vec{E} \cdot d\vec{A}$. If the electric field is uniform and the surface is flat with area $A$,the flux is given by $\Phi_E = EA \cos \theta$,where $\theta$ is the angle between the electric field vector $\vec{E}$ and the area vector $d\vec{A}$ (which is normal to the surface).