# Homework Help: Potential difference across a square

1. Jul 25, 2010

### shawli

potential difference across a "square"

1. The problem statement, all variables and given/known data

Two charges are placed at the corners of a square. One charge, +4.0 μ C, is fixed to one corner and another, −6.0 μ C, is fixed to the opposite corner. What charge would need to be placed at the intersection of the diagonals of the square in order to make the potential difference zero at each of the two unoccupied corners?

2. Relevant equations

V= (k*q)/ r

3. The attempt at a solution

I tried to make an equation adding V1+V2+V3=0, but I end up having two unknowns ("d" for distance and "q" for the unknown charge at the intersection). Can someone help me set up the equation please?

2. Jul 26, 2010

### Onamor

Re: potential difference across a "square"

show your working. I think you can just do this in one equation, the problem is symmetric.

The equation you suggested is correct, and you know one side immediately, right?

3. Jul 26, 2010

### sagardip

Re: potential difference across a "square"

Hey , the problem is symmetric as suggested by Onamor and you know that the length of half a diagonal is 1/(2)^(0.5) times the side of the square. So in your equation all the d's will be cancelled and u will be left with q as the only variable