# Potential at a point

1. Sep 22, 2011

### vrinda mukund

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

The work done in bringing a charge +q from infinity in free space to a postion at a distance D in front of a semi-infinite grounded metal surface?

3. The attempt at a solution
Actually i know the method to solve it, but didn't understand its logic.
F=[-1/(4pi*e0)](q*-q)/(2d*d)
When we integrate this F as integral of F.dr between the limits x= d and x= infinity we get the result.
my question is what is this semi infinte grounded metal? how does this (2d*d) appear in the denominator? des this q and -q appears because of induction charging ?

2. Sep 23, 2011

### omoplata

Isn't this the http://en.wikipedia.org/wiki/Method_of_image_charges" [Broken]?

Dont' know what's meant by a "semi-infinite" grounded metal though.

Maybe it's metal taking up half of all available space, and having a plane surface, like http://upload.wikimedia.org/wikipedia/commons/4/4c/Method_of_mirror_images.png" [Broken]. In that case, yeah the -q would be the induced charge. But it looks to me like it would be ((2x)*(2x)) instead of (2d*d) in the denominator, where x is the variable distance of the charge +q from the surface as it moves.

Last edited by a moderator: May 5, 2017