## Focus on Lenz’s Law

by Ted Beyer

Ahhh, Eddy Current Tubes – you would never think that a hunk of copper pipe and a magnet could make anyone grin from ear to ear. I just love these things.

So simple in appearance, and yet so magical to see and use. Whenever I happen to have a set at home, I soon lose control of them to my wife who is just as fascinated by them as I am.

Although they can be used in fairly high end physics demonstrations, they are stunning enough that everyone who has a chance to see them is simply amazed.

Just realized – you may not have not seen one, have you? Here’s a video for you:

Kinda cool, huh? So, since I have (hopefully) gotten you to say “wow,” I’ll just bet you are wondering “why” — here’s some science:

## Eddy Current Tubes with Video

by: Ron Perkins

An eddy current is a current set up in a conductor in response to a changing magnetic field.  Lenz’s law predicts that the current moves in such a way as to create a magnetic field opposing the change; to do this in a conductor, electrons swirl in a plane perpendicular to the changing magnetic field.  Because the magnetic fields of the eddy currents oppose the magnetic field of the falling magnet; there is attraction between the two fields. Energy is converted into heat.

This principle is used in damping the oscillation of the lever arm of many mechanical balances. At the end of the arm a piece of flat aluminum is positioned to move through the magnetic field of a permanent magnet. The faster the arm oscillates, the greater the eddy currents and the greater the attraction to the permanent magnet. However, when the arm comes to rest, the attraction is negligible. Read the rest of this entry »