Solving Two Point Dipoles - Find Torque of p1 & p2

[Kolahal Bhattacharya]

Homework Statement

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?

Homework Equations

The Attempt at a Solution

 

[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.

 

[Kolahal Bhattacharya]

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

 

[Dick]

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

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