# Electric flux

Why the electric flux $$\Phi$$ is defined as EAcos$$\theta$$?

I don't understand the part about cos$$\theta$$.....

tiny-tim
Homework Helper
Welcome to PF!

Hi yaik! Welcome to PF!

Imagine you want to know the flux of bugs flying horizontally along a road.

If you count the number that go splat on your windscreen, then you'll collect less (in a given time) if the windscreen is tilted: the number will be greatest at 90º, and zero at 0º: it'll be proportional to cosθ.

Mathematically, flux of a field E through a surface with area A is E.(Añ), where ñ is the unit vector normal (perpendicular) to the surface.

thx!!!