Electrostatic Potencial Problem

[loba333]

Homework Statement

Here is the problem :
http://i1200.photobucket.com/albums/bb327/loba333/untitled.jpg
ill write it out again aswell
A particle with charge +9 μC is placed at the origin, and another particle of charge –2 μC is at x = L. At what two points is the net electrostatic potential equal to zero?

Homework Equations

V=KQ/r

The Attempt at a Solution

I could understand if they were the same sign charges then there would be an area of 0 field strength.
Could someone please explain to me what's going on and how to solve it.

Cheers

 

[gneill]

The charges have opposite polarity, what more could you want?

 

[loba333]

The charges have opposite polarity, what more could you want?

sorry i ment same sign charges

 

[ehild]

Both charges have their own electric fields, and their potentials add up. One is negative, the other is positive, and their magnitudes are the same at certain points. Choose the point at x. What is the distance of the selected point from the negative charge when x<L and what is it when x>L? What are the potentials?

ehild