A soft iron ball is fixed a distance d above the pole of a rectangular dipole magnet which is permanently magnetized. What is the force the iron ball feels due to the magnetic field?
The dimensions of the dipole magnet are a x a x b, where a < b
[tex]m = pl[/tex]
p = magnetic dipole strength (how is this even calculated?)
l = displacement vector between poles
The Attempt at a Solution
I know the following:
[tex]F = qv x B[/tex]
But I don't think I can use that because there's no velocity as the iron ball is fixed.
The ball has to feel some kind of force, though that formula suggests it isn't possible. It seems to me that if I hung a ball from a string, the tension in the string would increase if a magnet was placed below the iron ball. Is there some concept I'm not understanding, here?