Getting Energy From Magnets

When people ask about the energy stored in a magnet, I suggest a thought experiment. Hold a strong horseshoe magnet above a piece of iron on the table. If they're close enough, the magnet will lift the iron off the table and stick to the magnet. By lifting the iron off the table against gravity, the magnet has literally done work on the piece of iron. Where did that energy come from? From the magnetic field in the magnet. But isn't the magnet still magnetized? Yes, but it can be shown that the field now contains less energy than before because of the iron stuck to the poles. This loss of energy is exactly equal to the work the magnet did in lifting the iron. Now pull the iron and magnet apart. You had to apply force, right? You did that over a distance, which means you did work on the iron/magnet system. Where did that work go? Back into the magnetic field of the magnet. So while it is possible to get energy out of a magnet, it's not free. You have to put it back or you can't get it again. It's much like letting a rock fall. Energy is released, but once the rock hits the ground that energy is gone. To get it back you have to lift the rock back to its starting point. There's no free lunch!
- Phil (age 57)
San Diego, CA

That's a nice clear explanation.

Mike W.

(published on 01/10/2014)

When a magnetic material is attracted by a permanent magnet , how daoes it get the kinetic energy and after attraction where does it go?
- kally (age 15)
nepal

Hi Kally,

One of our readers wrote in with a wonderful explanation of your question. Check out follow-up #7, and look around the thread and our site if you want further discussion.

Cheers,

David Schmid

(published on 11/07/2013)