# Electric Field inside a nonconducting sheet

## Homework Statement

A huge (essentially infinite) horizontal nonconducting sheet 10.0 cm thick has charge uniformly spread over both faces. The upper face carries +95.0 nC/m2 while the lower face carries -25.0 nC/ m2. What is the magnitude of the electric field at a point within the sheet 2.00 cm below the upper face? (\varepsilon_0 = 8.85 × 10-12 C2/N · m2)

## Homework Equations

electric flux = ∫E*da = q(enc)/ε_0

## The Attempt at a Solution

I figured this problem should be relatively easy, but the fact that the charge densities are different on each side is throwing me off...

First, I thought to find the E field at some particular point, I ought to use a Gaussian surface, and my thought was to use a cylinder, sticking in as far as .02m below the upper face. Doing so, gives me E=σA/ε_0*A, and the A's cancel, of course.

What I'm really confused about is how to take into account the fact that it's only .02m into the sheet. And for that matter, because the charge density is different on each side, I'm not sure how to go about finding the charge density at that particular point of .02m inside the sheet.

If anyone could help clear some of this up, I'd really appreciate it.

Thanks!

Simon Bridge
Homework Helper
Principle of superposition.
You can do it OK as a single sheet of charge right?