Work Done on Charge +q at Distance D from Semi-Infinite Grounded Metal

[vrinda mukund]

Homework Statement

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?

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 infinite grounded metal? how does this (2d*d) appear in the denominator? des this q and -q appears because of induction charging ?

 

[omoplata]

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

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" . 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.