# Homework Help: Force on a dipole

1. Nov 17, 2008

### Maxwhale

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

A dipole of moment p is lined up with the z-axis at the origin of coordinates. A second dipole of moment p is at the point (a,0,a) and is pointed towards the origin. What is the force on the second dipole?

2. Relevant equations

p = $$\int r' \rho (r) d \tau '$$

3. The attempt at a solution

I tried this:

F = v (p. E)

2. Nov 17, 2008

### gabbagabbahey

The first step is to identify what causes the force on the second dipole....so what would that be in this case?

3. Nov 17, 2008

### Maxwhale

Electric field

4. Nov 17, 2008

### gabbagabbahey

Yes, but what electric field in particular? The electric field due to the second dipole? The electric field due to the first dipole? The electric field due to both dipoles? The electric field due to some strange charge distribution on the far side of the moon?

5. Nov 17, 2008

### Maxwhale

haha, of course not from the charge distribution on the far side of the moon.

The second dipole experiences the force due to the first dipole

6. Nov 17, 2008

### gabbagabbahey

Good, so what is the electric field of the first dipole?