hi, I'm having trouble understanding what the difference is between the B and H fields. What my understanding is, if you have a magnetic dipole on its own, its going to have some B field around it. Then say you bring some material into the field, and the field within the boundaries of the material will be modified right? it'll increase or decrease or something? And this field is called the H field, am I right? So why then do we have the expression [tex] B=\mu_0 H [/tex] or [tex] B=\mu_0 (H + M) [/tex] where M is the sample's magnetization? Shouldn't the permeability, which has units, really just be some unitless number? Why does H have units of magnetization, ie. the magnetic dipole moment per unit volume? Thanks. PS. if this is in the wrong section, please say so and I'll put it elsewhere.