Why Does Gauss's Law Use Cylinder Circumference Instead of Area?

[CollegeStudent]

Homework Statement

So I was looking at this site reading up again on Gauss's Law and was a tad confused

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecyl.html

1st thing on the page...

Homework Equations

The Attempt at a Solution

It states that the electric flux will just be the Electric field times the area of the cylinder...

However in the calculation, the circumference of the cylinder is used...why is that?

 

[Doc Al]

However in the calculation, the circumference of the cylinder is used...why is that?

The circumference times the length L gives the surface area.

 

[CollegeStudent]

Oh okay! I was taking into account the full area but since the Electric field lines will never cross through the 2 ends of the cylinder the area needed will just be the circumference times the length..

Thank you Doc Al!