# Question on 2d charge arrays

1. Jan 31, 2012

### stonecoldgen

1. The problem statement, all variables and given/known data
Derive and simplify an expression for the electrical potential energy of the charge configuration. It's an equilateral triangle with charges +q, -q and +q.

2. Relevant equations
Ep=Kq2/r

3. The attempt at a solution
I know how to do this with squares (it's basically exploding the symmetry). For example in a square there are charges #s1,2,3 and 4. I do the equation with 1 respect to 2,3 and 4. Then with 2 respect to 3 and 4. Finally, 3 respect to 4. I see which terms cancel out, then it's all algebra.

I did this in this triangle, getting -kq2/r as the final expression, which for some reason doesn't convince me (perhaps because it's too simple? lol).

I don't know if in the square you are ''unconsciently'' multiplying by the sin90, therefore I should multiply by sin60 here. If so, is it just multiplying sin60 by each term?

I do know that electrical potential energy is a vector quantity and not a scalar quantity like voltage, right?

Thanks.

2. Jan 31, 2012

### stonecoldgen

so would the expression be -kq2/r *sin60?

3. Feb 1, 2012

### ehild

The potential energy is a scalar quantity. Show your work in detail, please.

ehild

Last edited: Feb 1, 2012
4. Feb 1, 2012

### ehild

It is correct if you mean the side of the triangle by "r".

ehild