# Purcell's Electricity and Magnetism - question

1. Feb 23, 2008

### apw235

1. The problem statement, all variables and given/known data
Purcell 3.3: In the field of a point charge over a plane, if you follow a field line that starts at the point charge in a horizontal direction, that is, parallel to the plane, where does it meet the surface of the conductor?

2. Relevant equations
The problem 'hint' is "You'll need Gauss' law and a simple integration."

3. The attempt at a solution
The electric field on the surface of the conductor at a radius R=$$\sqrt{r^{2}+h^{2}}$$ (h is the height of the pt charge, r is the x component of the radius on the plane), the Electric field due to the point charge is:
E=$$\frac{-2Qh}{(r^{2}+h^{2})^{3/2}}$$. This is given in the book.
I have no idea where to start..

2. Feb 23, 2008

anybody?