A Question for My Readers: Lenz’s Law, Magnetism, and Copper

August 29th, 2014 by Roy W. Spencer, Ph. D.

This has nothing to do with climate…that I know of.

I have a question for any readers who know about how magnets and conductors work, like in an electric motor.

There are some cool videos showing how you can drop a powerful magnet through a copper tube, and it falls very slowly. Here’s my favorite, which involves a huge magnet and an even more impressive piece of copper (see especially 0:40 to 0:44):

According to Lenz’s Law, the electrical current generated in the copper by the falling magnet generates an opposing magnetic field which slows the fall of the magnet.

I’ve ordered a small version of the disk magnet, 1.5″ by 1″, which is supposed to hold 146 lbs (!). Rather than getting 2″ diameter copper tube to drop it through, I plan on wrapping copper wire (say #12 or #14) around a piece of PVC pipe.

My question is this: How can I wrap the wire to maximize the slow-fall effect? Or is a solid copper tube going to provide the maximum effect? Does the amount of copper (thickness of the tube wall, number of copper windings) have an impact?

I suppose I can answer this with some experimentation, but I’d like to know a little more about the variables (which I assume are all transferable from electric motor design) ahead of time.


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