Why Electric Flux \Phi is Defined

[yaik]

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

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

 

[ZapperZ]

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html#c3

It came from the dot product between E and dA, i.e. the projection of E along the differential area.

You may want to bookmark the entire Hyperphysics website.

Zz.

 

[tiny-tim]

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. ​

 

[yaik]

thx!