How Does Charge Distribution Affect Electric Field Calculation on a Disk?

[mcaro]

Homework Statement

A charge of -5.00 nC is spread uniformly over the surface of one face of a nonconducting disk of radius 1.15 cm. Find the magnitude of the electric field this disk produces at a point P on the axis of the disk a distance of 3.00 cm from its center.

Homework Equations

Surface area element for a disk [sigma]= Q / A

See attachments

The Attempt at a Solution

So I plugged the numbers in accordingly, had no luck.

I appreciate the help.

 

[mcaro]

I'm working on uploading a picture of my attempt.

 

[mcaro]

... uploaded

 

[ideasrule]

Surface area element for a disk [sigma]= Q / A

That equation only applies for infinitely large plates. This disk is not infinitely large.

Try using E=kq/r^2 to get the electric field due to the charge on one infinitely thin ring surrounding the center of the disk. Then, integrate over the disk.