Dear Colleen --
The spark from the film can Leyden jar in the Charge and Carry snack (or from
a charged ballon) is indeed associated with a high voltage. The average
resistance of the human body (under normal conditions, not wet) is about
500,000 ohms. Assuming 10, 000 volts as you mentioned, Ohm's Law -- I = V/R
-- would give a current of 0.02 amp. As far as I know (not from actual
experience!), about 0.005 amps may become painful, about 0.015 may cause loss
of muscle control, and about 0.07 amps may kill. So 0.02 amps is significant.
The reason you don't get hurt is that there is not enough charge present to
produce this current or to sustain it for a long enough time to do damage if
it is produced momentarily. If, however, you built a LARGE Leyden jar, which
could store more charge before sparking (still at the same voltage), then it
can indeed kill you (and devices like this, or charged capacitors in
electronic devices, which are similar, have killed people).
The dielectric strength of air is 3 million volts per meter, or 30,000 volts
per centimeter. This means that it takes 30,000 volts to make a spark jump 1
centimeter through air. If you got a 0.5 cm spark from a balloon, this would
be about 15,000 volts, so the balloon voltage and current would be somewhat
comparable to the 10,000 volts we used above, and again the size and duration
of the current would be limited by the amount of charge present.
Hope this helps.
Exploratorium Teacher Institute
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