- #1

anban

- 20

- 0

## Homework Statement

Hi,

I have a problem that describes a uniformly charged disk and the electric field a distance z from the center.

I have found an equation that describes the E field at any point z already. Now I have to find out how the E field decreases as z increases-- as 1/r^2, I assume, but I am not sure.

## Homework Equations

E = 2[itex]\pi[/itex]kσz(1-[itex]\frac{z}{\sqrt{z^{2}+R^{2}}}[/itex]) where R is the radius of the disk and z is the distance away from the disk.

## The Attempt at a Solution

I know I have to do a binomial expansion of (R/z). I think I am having mathematical issues rather than physical issues.

Before the expansion, I need to get some term (R/z). Does taking out a z^{2) from the denominator leave a z^{4} out front? Or a z^{3} out front? If I can figure this out then I know the rest.