Magnetic Pendulums

Date: Sun Mar 19 2000 - 09:51:22 PST

You need to wrap two coils of wire for the magnetic pendulums snack (each
coil with at LEAST 50 turns -- more turns should enhance the effect
somewhat). Each coil should have a hole in the middle that is about an inch
in diameter. If the hole is too big, there will be too much space between the
coil and the magnet, and the magnetic field won't be strong enough to do the
job. If the hole is too small, the coil will hit the magnet as it swings.
Ideally what you want is the smallest hole that will allow the coil to swing
freely over the end of the magnet. So you need to find something to wrap the
wire around that is about an inch in diameter -- a one inch wooden dowel, or
a D cell battery would be examples. A cardboard toilet paper tube is almost
two inches, so it's probably a little too big -- but you might overcome that
by wrapping more turns. When you're through wrapping, just remove the object
that you you used as the core, and you'll have the coil you need. You may
want to use some tape to keep the coil from coming apart.

You need to leave about three feet of wire unwrapped on each end of the coil,
so that you can position the coils on the wooden frame and connect them, as
shown in the drawing with the snack.

The lead with alligator clips is used only if you want to short the coils
out, as noted in the last paragraph in the To Do and Notice section and
explained in the last paragraph of the What's Going On section.

I hoe this helps.

Don Rathjen
Exploratorium Teacher Institute

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