# Nonconducting surface uniform charge hole

1. Oct 14, 2010

### Liquidxlax

1. The problem statement, all variables and given/known data
Didn't know what to put for thread title, my notes and textbook were a little to ambiguous

A large, flat, nonconducting surface carries a uniform charge density σ. Into the middle of this sheet has been cut a small, circular hole of radius R. Ignoring fringing fields from the edges, calculate the electric field at a point, P that is a distance z from the center of the hole along its axis. hint: consider the electric field from a sheet of charge and the electric field from a disk of charge

edit** nevermind i was being dumb, i got it

Last edited: Oct 15, 2010
2. Oct 16, 2010

### rl.bhat

You can consider the large, flat, nonconducting surface carries a uniform charge density +σ

and the hole as a disc carrying a uniform charge density -σ.

The electric field due to the surface is

$$E_1 = \frac{+\sigma}{2\epsilon_{0}}$$

The electric field due to the disc is

$$E_2 = \frac{-\sigma}{2\epsilon_{0}}(1 - \frac{z}{\sqrt{z^2 + r^2}})$$

Now find the net field at P.

3. Oct 16, 2010

### Liquidxlax

that is exactly how i did it. thanks, i finished it yesterday, but i'm not sure how to delete threads