Infinitesimal Electric field of slice of disk

[j3dwards]

Homework Statement

A disk of radius R carries a uniform surface charge density σ.

(a) Using the results for the uniformly charged ring given in the lectures, or otherwise, compute the infinitesimal electric field dE due to the circular slice the disk of charge dQ shown in the figure. Express the result in terms of σ, r and R.

Homework Equations

E=kQ/d²

The Attempt at a Solution

qE_x=kdQ/r²

dQ=σdA=2πσr dr

dr=R-r

dE_x=σ(R-r)/2rε_o

I'm not sure whether to put the distance d as x or just use the origin so just use r?

But when I used x as the distance, i couldn't put the answer in terms of σ, r and R. My workings for the use of x as the distance were:

dE_x=k2πσxr/_(r²+x²)3/2

 

[rude man]

" ... shown in the figure. ..."??

 

[j3dwards]

" ... shown in the figure. ..."??

 

[rude man]

"Using the results for the uniformly charged ring given in the lectures, ... "
Are you doing this? What did they give you?