Purcell's Electricity and Magnetism - question

[apw235]

Homework Statement

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?

Homework Equations

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

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..

 

[apw235]

anybody?