# Homework Help: Electric Fields using EPE

1. Feb 15, 2010

### nhartung

1. Three posative charges +Q lie on the corners of a square which is rotated 45 degrees with respect to the x-axis. Calculate the electric field at the origin, in terms of the variables Q and a.

I think this question is much easier than I think it is but I'm stuck on it. There is a picture along with this problem but it isn't very complex so i'll describe it here. As stated in the problem the square is rotated 45 degrees with respect to the x axis. Then the 3 charges +Q are located at 3 corners located at: (-a, 0), (a, 0) and (0, -a). I'm assuming this is an Electric Potential Energy problem because it comes in that section of the homework (however, this may not be the case).

So far i've got out of my notes that V = -Edcos(ø). Solving for E gives: E = -(V/dcos(ø))

I've also noticed that the charges at (-a, 0) and (a, 0) will cancel each other out leaving only (0, -a) affecting the force on the origin. I know that I could also substitute EPE/q for V, but I don't think this is the route to go.

2. Feb 16, 2010

### nhartung

Noone has any input? =(