Electric force between two charges on z-axis

1. Oct 28, 2005

Reshma

Question:
Two charges -2q and +q are located on the z-axis at distance 'd' and '3d' respectively. The x-y plane is a grounded conductor. Find the force on the charge +q.
My work:
Let the force be F. Distance between the charges is '2d'.
$$F = \frac{1}{4\pi \epsilon_{0}}\left(\frac{(-2q)(q)}{{(2d)}^2}\right)$$
Can I apply the Coulomb's equation here the way I have done? Will the grounded x-y plane have any effect on the force?

2. Oct 28, 2005

Galileo

A better question is: does the charge below the grounded conductor have any effect on the force?

3. Oct 29, 2005

Reshma

Umm...the charges mentioned here are above the grounded plane. The grounded plane has a zero potential. Are you talking about image charges?

4. Oct 30, 2005

Reshma

Can someone help me proceed?

5. Oct 30, 2005

Physics Monkey

You know the grounded conductor will "draw up charge from infinity" so that it can maintain a constant potential over its surface. This charge will exert a force, right? How can you describe the field produced by a conducting sheet in the presence of point charges?

6. Nov 5, 2005

Reshma

Took me a while to read up on the theory. I am convinced this is an image problem. Well, the electric field is normal to the surface of the conducting sheet, right?
$$\vec E = \frac{\partial V}{\partial z}\hat z$$