Finding an electric field on a disk using surface charge density

[gretchin]

Homework Statement

A disk of radius 2.30 cm has a surface charge density of 5.22 μC/m2 on its upper face. What is the magnitude of the electric field produced by the disk at a point on its central axis at distance z = 11.2 cm from the disk?

Homework Equations

Formula for an electric field

The Attempt at a Solution

(int)dEz= sigma/2ep0 (1-z/sqrt(z^2+r^2)

 

[pabloenigma]

Break up the disk into elementary rings and integrate.