The Millikan L'Eggs Experiment
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Coleman, Roy Morgan Park High School
To use discrete masses to simulate the Millikan experiment (the
discrete charge on the electron).
one balance per group and EITHER
a large number of L'Eggs eggs (from panty-hose) individually numbered
and filled with ball bearings or clay such that the filler is
divided into 'unit masses' i.e. for a ball bearing filler, use
multiples of 7 bearings (or some multiple larger than the weight of
the 'shell'). It is nice to have several regular intervals and
then skip one (put in two additional unit masses)
10 numbered plastic Easter eggs filled with clay or bearings (as with
the L'Eggs eggs) for each group
Present the problem of how to find the mass of a unit 'yoke' where
there is a shell and at least one 'yoke' in each egg. If the students
cannot come up with the idea to mass them on a balance, suggest it.
After they have massed their eggs, some may see a pattern but suggest
that they draw a histogram of their data (mass vs. number of eggs with
that mass (NOT egg number)). It should be obvious from the graph that
the masses fall into several groups. From the average mass of each
group, students should be able to see that the groups fall at regular
intervals and that these intervals correspond to each additional unit
mass (one more 'yoke').
A discussion should be held to talk about the number of digits of
accuracy needed in the measurements since the shells and unit masses
will each vary by some small amount. It is possible for the students
to become so involved with making accurate measurements that they miss
the pattern or waste too much time on the weighing.
After the experiment is done, a comparison should be made between this
experiment and Millikan's oil drop experiment where he found the unit
charge of the electron by looking for regular intervals (or discrete
units of charge).