Curie Point

Date: Sun May 07 2000 - 16:13:37 PDT

Thanks for sending your account of your efforts. I received both the one you
sent to me directly, and also a copy of the reply sent to you from snacktalk,
which also contained your same original. We appreciate having your comments,
and they will be useful to us for both helping anyone in the future with this
particular activity, and for keeping us alert to the types of
misunderstandings that can occur as we write new items. I don't have much to
add here, since we covered things fairly completely on the phone, but I'm
sending you the text of the older e-mail on Curie Point that I read to you
over the phone, for whatever it's worth at this point. Thinking about it
all again, my guess is that the key factor is using the larger 6 volt lantern
battery, as shown in the photo. That seems to be about the only thing that
you and I ultimately did differently.

Our specification of "picture hanging wire," and our photo showing the 6 volt
lantern battery are consistent with our intent to clearly specify materials,
but I offer my apologies about the use of the word "iron," and not specifying
the "large" 6 volt lantern battery in writing. We certainly didn't foresee
the problems these would cause you. As best I can remember (but it's almost
10 years ago now!), I don't think we ever even thought about the smaller
lantern battery, and the use of "iron" probably just seemed a reasonable way
to differentiate from copper or aluminum or some other wire which would not
be attracted by a magnet.

I did want to respond to your note/question about whether anyone ever tries
the experiments before we post them. I can absolutely say YES! Taking Curie
Point as an example, we definitely did it, and it worked. If we are to take
blame, it will have to be for failing to communicate our experience clearly
and unambiguously.

We certainly didn't intend that you have all the problems you had, or spend
the time and money you spent. But since it happened and it can't be undone,
it's perhaps worth noting, for whatever comfort you can derive from it at
this point, that the experience that you and your son had was in truth
probably a lot closer to an authentic science experience than if things had
gone perfectly. Theres an old saying that goes something like this: "If it
wiggles it's biology, if it smells it's chemistry, and if it doesn't work
it's physics." Lots of physics students, physics teachers, and physicists (in
truth all individuals associated with the scientific enterprise) have
experienced the sort of frustration you obviously felt -- but hopefully this
may lead to some learning and insight that ultimately proves interesting and

Lastly, thanks for the compliment on the What's Going On explanations!


Don Rathjen
Exploratorium Teacher Institute


Printed below is the text of the earlier Curie Point e-mail to another person
that I read to you over the phone:

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!


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