Magnetic Circuits

Suppose we have an objectmade of magnetizable material and we build a coil around it to magnetize it with a certain amount of ampere-turns. Would it get more magnetized if we create an iron magnetic circuit connecting the 2 poles of the cylinder? Note that in both cases the coil is built only around the magnet with the same ampere-turns.
- Federico (age 30)
TN, Italy

Yes, the iron "circuit" reduces the free-energy needed to magnetize your material. Think of it this way. Imagine the iron as being very hot and not magnetic. Turn on your coil to magnetize your material. Now let the iron cool down. It will magnetize, lowering the free energy. The more the material magnetizes, the more field there is driving the iron to magnetize and thus the more it lowers the free energy. So adding the iron gives a term in the free energy that gets more negative for more magnetization of the material. That shifts the equilibrium value toward greater magnetization.

Mike W.

(published on 01/19/2016)