
Originally Posted by
Woozie
H and B are closely related quantities but technically aren't the exact same thing. Normally we use B = uH (where u is the permeability of free space), though in some cases (certain magnetic materials) it looks a little different (H = B/u - M. This is the more general formula, and B = uH is really just a special case. But it's this special case that allows us to use B and H interchangeably since they are directly proportional to each other. It's just a matter of changing the units you use or attaching a constant to your equations).