The Millikan L'Eggs Experiment

Coleman, Roy                         Morgan Park High School
                                     881-5050
                           

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).