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Dipole problem

  1. Mar 4, 2007 #1
    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. jcsd
  3. Mar 4, 2007 #2


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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: Mar 4, 2007
  4. Mar 4, 2007 #3
    You are WRONG.If I rotate the axes,the relative difference of answers will not be visible.
  5. Mar 5, 2007 #4


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