Hi Larry,
Yes I also have a copper tube and drop a magnetic down it and watch the
magnet drop much slower than if the tube was plastic. I also have a plastic
tube to show that it drops a lot faster.
The reason is Lenz's Law. Faraday's Induction law states that if a conductor
(the copper tube) is moved through a magnetic field, an electric current
will be inducted into the conductor (the copper tube). The electric current
flowing in the conductor (the copper tube) produces a magnetic field that
repels the magnetic. That is why the magnet drops slowly down the copper
tube.
Lenz's Law is also what makes it harder to turn a generator (work in) if a
load (work output) is placed on the generator output terminals (I.E.
electric light glob).
If anyone would like a practical exercise to show this, send me and email
off the list and I'll send you a PDF copy.
Also offered for educational value.
Roderick Wall.
-----Original Message-----
From: Larry McDavid
Sent: Thursday, January 06, 2011 12:34 PM
To: Sundial Reflector
Subject: More on Sundial Magnets
Try dropping a cylindrical or spherical rare earth magnet down a copper
tube. You'll be surprised at what happens, noting that copper is not
ferromagnetic and is not at all attracted by the magnet. I have a
physics demonstration apparatus I made using a 2-inch wide, 1/4-inch
thick pure copper bar. I can roll a steel ball bearing down the strip
without impediment; but a spherical rare earth magnet rolls down very
slowly. Since the nickel plated rare earth magnet looks exactly like the
ball bearing, some slight of hand makes this into an interesting
demonstration piece.
I offer this little essay just for its educational value!
--
Best wishes,
Larry McDavid W6FUB
NASS Registrar
Anaheim, CA (20 miles southeast of Los Angeles, near Disneyland)
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