Potential difference between 2 points

[ledwardz]

Homework Statement

2 points x and y, are along orthogonal directions from a 60uc charge. For x and y determine the potential difference between them. ( its in a vacuum also )
x= 10cm, y = 15cm

Homework Equations

okay, i know the equation is q/4*pi * EoEr *(1/ry - 1/rx)

what i don't understand is the end bit. the distance between them is not (1/ry - 1/rx)
can anyone explain to me how this works?

when i work out the electric fields at each point then multiply this by the distance to give me the potential difference (voltage) at each point too subtract one from the other i get the wrong answer. wtf is going on?

cheers for any help, Lee.

 

[ledwardz]

ahh pooooo never mind I've done it stupid mistake ... my bad