The Millikan L'Eggs Experiment

Coleman, Roy Morgan Park High School

Objective: To use discrete masses to simulate the Millikan experiment (the discrete charge on the electron). Apparatus: 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) OR 10 numbered plastic Easter eggs filled with clay or bearings (as with the L'Eggs eggs) for each group Strategy: 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').

Discussion: 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).
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