Homework Help: Force between 2 magnetic dipoles

1. Apr 23, 2009

eyenkay

Ok, so I have two magnetic dipoles, both lie on the x-axis, pointing in the positive x direction, say at x = 0 and x = a. I am to find the force of attraction between the two dipoles using the equation F=grad(m*B), as well as by the equation F=2(pi)IRBcos(theta), where R is the radius of a loop carrying current I. (I think, but not sure, that theta is the angle between the magnetic field vector and the plane of the loop)
My question is: should I express each dipole as a loop of current, or maybe just one.. or when using the first formula is ok to just leave the dipoles as is (Im not sure how you say that, I guess you would say the 'ideal representation', when he dipoles just appear as arrows in the diagram). If I do this, it only takes about 2 steps, and I get (-3(mewnot)m)/2(pi)r^4 in the x direction. (Sorry, I couldnt get the LaTex to work for some reason this time) When I go to do it using the loop representation, however, it gets ugly when trying to find the field. Which is the correct approach?

Last edited: Apr 23, 2009