# Homework Help: Electrostatics - force on point charges by electric field

1. Oct 29, 2008

### risk2112

1. The problem statement, all variables and given/known data
A square, with each corner as a point charge, A, B, C, and D. They all have the same charge of 5.0 x 10 ^(-6) C. Length of each side of the square is 0.1 m. 2 negative charges diagonal from eachother, and the other two are positive, diagonal from eachother.
Question asks net force on each point charges and electric field and electric potential at centre of the square.
A, B, C, D = 5.0 x 10^(-6) C
2 negative charges diagonal
2 positive charges diagonal
Square of four corners A, B, C, D.

2. Relevant equations
F_e = kq1q2/r^2
F_e = qE
idk equation for electric potential

3. The attempt at a solution
For each net force, are they all the same except with opposite directions? Like say 5 N NW, 5 SW, 5 SE, 5 NE. If so, then I can figure out that part.
I really have no idea for the electric potential or electric field, but im guessing one of the two is going to have either an electric potential of 0 or electric field of 0. I don't know how to solve for either of them though.

2. Oct 30, 2008

### risk2112

Re: Electrostatics

I calculated the force, being 9.1 x 10^(something, forgot) N, but I dont know how to use F_e for the middle, with a charge in the middle as q...in order to get E (electric field) for middle. Also, is the E for electric field what makes V (electric potential) = radius x electric field?