# Infinitesimal Electric field of slice of disk

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1. Oct 9, 2015

### j3dwards

1. The problem statement, all variables and given/known data
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.

2. Relevant equations
E=kQ/d2

3. The attempt at a solution
qEx=kdQ/r2

dQ=σdA=2πσr dr

dr=R-r

dEx=σ(R-r)/2rεo

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:

dEx=k2πσxr/(r2+x2)3/2

2. Oct 9, 2015

### rude man

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

3. Oct 10, 2015

### j3dwards

#### Attached Files:

• ###### electrodynamicsfig1.png
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4. Oct 10, 2015

### rude man

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