Dipole problem

1. Mar 4, 2007

Kolahal Bhattacharya

1. The problem statement, all variables and given/known data
Griffiths offers this problem: two point dipoles p1 and p2 are given.They are r distance away and they are perpendicular.We are asked to find torue of p1 (about p1's centre) due to p2 and vice versa.
Well, the situation is that I knoe it is =p cross E
even I know the formula for a point dipole pointing in the z direction:
E_dip=(1/(4*pi*epsilon))(p/r^3)[2cos(theta) (r^)+sin (theta) (theta^)
where (r^) and (theta^) are the unit vectors in a polar system coincident with the xyz system.
I can surely find the result for 1 part.Assuming p1 points in the z direction,it can be evaluated.What could be done in the second case?

2. Relevant equations

3. The attempt at a solution

2. Mar 4, 2007

Dick

Both torques are equally easy to compute. Just rotate your coordinate system. But you don't even have to. Their sum is the time rate of change of angular momentum, a conserved quantity. Think Newton's third law.

Last edited: Mar 4, 2007
3. Mar 4, 2007

Kolahal Bhattacharya

You are WRONG.If I rotate the axes,the relative difference of answers will not be visible.

4. Mar 5, 2007

Dick

Really? I have no idea what you mean to say, but I guess you know best.