E-field above square

1. Oct 8, 2007

nicksauce

1. The problem statement, all variables and given/known data
Find the electric field a height z above a square of side length $$a$$ with uniform surface charge $$\sigma$$

2. Relevant equations

3. The attempt at a solution
$$E=\frac{z\sigma}{4\pi\epsilon_0}\int^{a/2}_{-a/2}\int^{a/2}_{-a/2}\frac{dx dy}{(x^2+y^2+z^2)^{3/2}}$$
(in the z direction). However, unless I maple'd wrong, this gives the wrong answer. Can you anyone see a problem with the way the integral is set up?

2. Oct 8, 2007

learningphysics

Looks right to me.