[meteorite-list] A bit OT: magnets and conductors

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Mon Sep 11 14:15:19 2006
Message-ID: <A8044CCD89B24B458AE36254DCA2BD0701DFBA88_at_0005-its-exmp01.us.saic.com>

Hi Kevin,

> Hey, meteorite collectors, go and get your rare earth magnets
> (mine is 3/4 inch dia, 1 inch long) and a small bit of flat
> Aluminium. Hold the magnets N or S end (doesn't matter which)
> about 2 or 3 mm above the Aluminium and move the magnet quickly
> from one end to the other, DaDaaaaaaa, the Aluminium follows
> the magnet. I tried this with gold and the same thing happens.

> Wowee was I surprised, all my life I thought Aluminium, Copper,
> Gold were not affected by a magnet. It is apparently called
> Lenz's law and involves magnetic coupling to usually non-
> magnetic material.

What you're seeing is an excellent demonstration of the relationship
between electricity and magnetism. Non-magnetic materials that
are nevertheless good conductors of electricity (gold, silver,
copper, platinum, aluminum, etc.) are affected by changing
magnetic fields because those fields will cause currents to
flow in the conductors. And whenever you have current flowing
in a conductor, that current itself produces a magnetic field.

In Kevin's example, the current-created magnetic field opposes
the field of the rare earth magnet. An experiment that shows
this effect even more dramatically is to drop a small disk-shaped
neodymium magnet through a hollow copper pipe held vertically.
(Use a copper pipe that has an inner diameter just a tiny bit
larger than the magnetic disk's diameter.) You will be shocked
how slowly the magnet freefalls through the pipe!

--Rob
Received on Mon 11 Sep 2006 02:14:55 PM PDT