Magnetization Energy

Wait, bear with me here... How is it possible to get energy by dissipating magnet's? A magnet has a energy density of 100 J/cm^3. It's domains are mostly aligned. By causing those domain's to lose their alignment (demagnetization) there is energy gained in the form of heat = 100J? I'm confused. Because there are multiple energy terms in magnetization. The energy density in the field should = the magnetization? This is based of my understanding from what you said earlier.
- Holvets (age 24)
Seattle

The energy density in the field is not the same as the magnetization. One way to see that is that energy density is a scalar number but the magnetization is a vector, pointing some direction. The energy density is proportional to the square of the magnetic field, in empty space. If you have two little domains they can lower the energy by lining their fields up in the same direction along the line from one domain to the other. Another way to lower the energy is to line up opposite directions at right angles to the line between the domains. For a little needle, the lowest energy state can be just a single domain lined up along the needle direction. For wider samples, energy can be lowered by breaking into stripe-like domains next to each other, pointing opposite ways, or into more complicated patterns. That leaves very little net magnetization.

Mike W.

(published on 12/03/2013)

Odd question, statement I know. Chances are that you have had it before. Energy can't be lost, only converted. Manufacturing a magnet requires energy.... so in theory, that energy could be recovered. Right? However I have been told that magnetism is a force. So the question is.... When creating a magnet, why are we unable to recover the energy. Alternatively how does energy as we know it become a force, like gravity, instead of a usable energy?
- lee (age 29)
south Africa

I think your question about recovering the energy is pretty much cobvered in follow-up #4 above.

Force and energy aren't the same thing, but they are related. When the energy of two things depends on their relative position, there's a force toward the lower energy positions. That force can be used to recover usable energy. In this case, it would be far less than the enrgy required to make the magnets.

Mike W.

posted without checking while Lee H heads for Puerto Vlllarta, and the temperature plumets toward -25·C here. Not that I'm envious or anything.

(published on 01/04/2014)