# Homework Help: Stress Between Two Charges

1. Oct 28, 2012

### quantumfoam

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

Hi guys! If I have two positive charges really close to each other, what would be the electric stress between the positive charges? Now I don't need a numerical answer, but I would like to know if my attempt is correct.

2. Relevant equations σ=ε(EiEj-(1/2)δij(E^2))

3. The attempt at a solution I figured that I should add the electric fields between the two positive charges and then use that as E in the equation above to calculate the stress between them.

2. Oct 28, 2012

### Staff: Mentor

Stress? Force per area?
I would expect that you have two parallel plates with some constant charge density (?).
You can calculate the electric field of one plate and calculate the corresponding force on the electric charges in the other plate.

3. Oct 28, 2012

### quantumfoam

And then I could divide that by the surface area in which the electric field form one plate and charge from the other plate are interacting with each other?

4. Oct 28, 2012

### quantumfoam

And we could use the plates if you want

5. Oct 28, 2012

### quantumfoam

And yes they have constant charge density.

6. Oct 28, 2012

### Staff: Mentor

Which is equivalent to the surface of the plates, right.

7. Oct 28, 2012

### quantumfoam

Yes What if the two charges were spherical with the same radius? This would still apply right?

8. Oct 28, 2012

### Staff: Mentor

Charge distribution on those surfaces would not be uniform (at least for conductors) and you would get all sorts of messy integrals in the evaluation - but the basic concept is the same.