Electric Flux
The total number of lines of force passing through the unit area of a surface held perpendicularly is called Electric Flux.Think of air blowing in through a window.
How much air comes through the window depends upon the speed of the air, the direction of the air, and the area of the window. We might call this air that comes through the window the air flux.
We will define the electric flux θ for an electric field that is perpendicular to an area as :-
θ = E A
Flux is a measure of the number of field lines passing through an area. If we define area as a vector, with its direction perpendicular to the surface, the electric flux is given by:
θE = E . Acos(θ)
where θ is the angle between the electric field and the area vector .