Charges on Balloon
Name: Jim D.
In The Energy Story
Chapter 2: What is Electricity?
there are the statements:
"Try this experiment.
Rub a balloon on a wool sweater or on your hair. Then hold it up to a
wall. The balloon will stay there by itself.
Now rub two balloons, hold them by strings at the end and put them next to
each other. They'll move apart.
Rubbing the balloons gives them static electricity. When you rub the
balloon it picks up extra electrons from the sweater or your hair and
becomes slightly negatively charged."
How many electrons are on the balloon after rubbing it on your hair?
I cannot say exactly, but I would roughly estimate the charge to be about 1
nanoCoulomb. This is not much of a charge, but it does work out to be about
ten billion electrons. I cannot say for certain because things such as
temperature, humidity, how hard you press, how fast you rub, and how the
wool is sewn can all affect the number of electrons.
Dr. Ken Mellendorf
Illinois Central College
The "short answer" is NOT VERY MANY. To compare the strength of the
gravitational force to the electrical force, it is instructive to compare
the ratio of the force of gravitational attraction / force of electrical
repulsion of two electrons, since so far as we know, the charge on the
electron is the "fundamental" unit of electrical charge. This ratio is
useful because both forces are proportional to: 1/ R^2 so in the ratio, the
effect of distance,R, cancels (where the distances are not too too large or
too too small).
That ratio is 0.24x10^-42. This fantastically small number is not an
accident of the units of measure, but is a "pure" number. I have no idea
what its significance is --
neither does Richard Feynman -- see "Lectures on Physics" Vol. I, chapter 7.
That chapter is humbling if you ever get sloppy and think that we
"understand" the nature of the fundamental forces operating in nature.
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Update: June 2012