What is a Magnetic Dipole moment?
First, let’s talk about a unipole, or monopole. And let’s talk about the electric force instead of the magnetic force (they follow the same rules, but as far as we know, there are no magnetic monopoles.) Suppose I have an electrically charged particle. Suppose you have another charged particle as a “test charge.” My particle is surrounded by a field, which exerts a force on your test charge according to the inverse-square formula: force equals 1/distance squared (multiplied by the amount of the test charge, times a constant). (Your particle is also surrounded by a field, but that’s not my focus here.) Now suppose I have two electrically charged particles, with equal but opposite charges, one inch apart. This is a dipole. These two charges will exert (in the limit where the distance to the test charge is very large) equal and opposite forces on your test charge, for a net force of zero. However, suppose that instead of having a test charge, you have a test dipole. My dipole will exert a
