- #1

Shell_E

- 3

- 1

He first assumed an image charge q inside Sphere with radius a, so the potential for real change and image charge is

The by set potential equal to 0 at x=a, he solved q' and y'

Then he can get potential, thus get E field, also can get force on real charge q.

Then he figured out surface charge density by:

Then he mentioned that the force on unit area da is just :

So this is the part I don't get, I understand that

**σ***da = dq is the charge on area da, but what is the rest part? I don't really get why dF = dq * (

**σ**/2

**ε**), is that indicate the E field at da is (

**σ**/2

**ε**)? if so, how do we get this?

Thank you!