Measuring the size of a molecule

  1. Hi,

    1. The problem statement, all variables and given/known data
    I am trying to determine the size of a molecule..by doing the oil drop experiment where we drop a tiny droplet of oil on water covered with a thin layer of powder...and then make calculations based on the diameter of the circle... the droplet forms in oil.

    3. The attempt at a solution
    However, the oil droplet for me is not making a circle..rather is spreading out irregularly. How can I fix this.

    Everything i have used is according to this site:
    Code (Text):

    http://www.practicalphysics.org/go/Experiment_633.html
     
    but i have used talcum powder instead of lycopodeum powder
     
    Last edited: May 17, 2011
  2. jcsd
  3. Delphi51

    Delphi51 3,410
    Homework Helper

    I never saw a circular oil patch when my students did this experiment.
    An irregular size is not much of a problem because the whole experiment is more of an estimate than a measurement. Just estimate the area of the oil patch. You can make a very good estimate if you make a grid of square cm on a transparency and hold it over the patch. A nice touch is to estimate the minimum and maximum possible area. Use a number midway between these as your "best" value, but also work out the size of a molecule using the low and the high. Then you will have not only a "best" answer but a known accuracy range.
     
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