Re: curie point (fwd)

Date: Fri Feb 18 2000 - 15:28:03 PST

I hadn't actually done the Curie Point snack for several years, so I set it
up and tried it before writing you. I didn't have a large lantern battery, so
I tried it with four D cells in series (using a strand of wire from braided
picture hanging wire and an ordinary ceramic donut-shaped magnet). It didn't
work -- just as you said, the wire wouldn't get hot. I actually measured the
current, and was getting about 2.5 amps. Then I put a couple of C cells in
series with what I already had, and got up to 3.5 amps, but that didn't do it

At this point, I broke down and got a 6 volt lantern battery as specified in
the materials list and shown in the picture with the snack. That gave me
around 7 amps, which made the wire glow red and released the magnet in less
than five seconds! I did it a few more times, and noticed that the current
went down to about 4 amps or less when the wire was glowing, which is
logical, since the hot wire has greater resistance than the cold wire.

Finally, I tried two stacks of four D cells, with the two stacks wired in
parallel, still giving 6 volts, but in theory giving more current capacity.
But I could only get a little over 4 amps maximum, which didn't heat the wire
enough. Maybe you can play around with even more D cells, but I'm not

So the bottom line is that the snack works with the large lantern battery.
The bad news is that the large lantern battery can now very expensive -- a
Duracell was almost $20 at one hardware store! Maybe you can shop around to
find the cheapest one available. Also there is a smaller size 6-volt lantern
battery that's cheaper -- maybe that might work, but I don't know.

Hope this helps. Let us know how things turn out!

Don Rathjen
Exploratorium Teacher Institute

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