Solving Two Point Dipoles - Find Torque of p1 & p2

AI Thread Summary
The discussion revolves around calculating the torque experienced by two perpendicular point dipoles, p1 and p2, separated by a distance r. The formula for the electric field due to a dipole is provided, and the torque is expressed as the cross product of the dipole moment and the electric field. Participants debate the implications of rotating the coordinate system on the calculation of torque, with one asserting that it does not affect the relative difference in results. The conversation highlights the importance of understanding angular momentum conservation in this context. Ultimately, the participants seek clarity on the correct approach to evaluate the torque for both dipoles.
Kolahal Bhattacharya
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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

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

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