Hand Battery Snack

From: DonRath@aol.com
Date: Mon Aug 21 2000 - 18:39:56 PDT

Dear Adela --

Sorry this response is so delayed -- I'll spare you the explanations/excuses,
and just offer my apology. I realize that the issue may no longer be timely,
but here are a few comments anyway.

It's been awhile since I actually set up the hand battery from scratch, so
like the person in the previous posting that Nina referenced in her initial
response to you, I also tried it in my kitchen. Since your question was
concerned with foil, I used a piece of aluminum foil (ordinary kitchen foil,
right out of the box) in place of one of the two kitchen pans. For the other
metal I used the copper bottom of a Revereware frying pan. I first used an
inexpensive ($17) digital multimeter. The lowest current range on the meter
was 200 microamps, and I got reading of about 20 microamps on this scale. I
then switched to the 20 volt scale and got a reading of about 0.8 volts. I
then also tried the same materials with an old analog meter (I got it in
1960!) and got similar readings on the 50 microamp and 5 volt scales. I tried
putting my hand on both the shiny and dull sides of the foil, but there
wasn't an appreciable difference that I could notice. When I dampened my
hands on a sponge, though, the readings were up to twice as large.

So the foil shouldn't have been the problem. I'm inclined to think the meter
the more likely culprit -- my analog meter was 20,000 ohms per volt, and
worked fine, but some of the very cheap analog meters have lower resistance,
meaning they need more current to operate them -- and the hand battery
doesn't provide much current. (Radio Shack sells one for about $15 that is
2000 ohms per volt, and whose lowest current scale is 150 milliamps -- this
won't work for the Hand Battery -- you need a current scale in the microamp
range.) Digital meters should work fine, so I'm hopeful that your trip to
Radio Shack to see if a digital meter would work was successful and solved
your problem.

One other thing to consider, if you're still having trouble, is the
electrical contacts. I've had situations where I was using alligator clip
leads in electric circuits, and the connection between the wire and the clip
was broken -- but not visible since it was hidden under a plastic insulated
sleeve covering the body of the clip. Also, be sure that that the metal
surfaces of the foil, pans, plates, etc. are clean -- a dirty, greasy, or
badly oxidized surface could block the flow of current.

Hope this helps. Again, my apologies for being so late. If it's not too much
trouble, let us know if you were finally succesful.


Don Rathjen
Exploratorium Teacher Institute

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