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Homework Help: Calculating the charge of an electron from Millikan's Oil drop experiment

  1. Nov 7, 2012 #1
    1. The problem statement, all variables and given/known data
    I did the lab and have to analyze the data to determine the quantized charge of an electron.
    I have used the data to determine the 'total' charge on the observed drops using the following equation.

    2. Relevant equations

    q = 3 ∏ r (E) η (Vup+Vdown)

    Where r is the known radius of the drop, E is the known electric field, η is the known efffective air viscosity and Vup and Vdown are terminal velocities of the particle going up and down (determined from data), respectively.

    3. The attempt at a solution

    I have determined the charge on each of the drops observed. But I don't know how to further analyze the data to find what the charge is per electron.

    I presume it is the greatest common factor or highest common denominator but calculating that doesn't bring me any closer to the charge of an electron.
    Any suggestions?

    All of my q values are on the order of 10^-17, so I'm probably missing a factor of 100 somewhere but I don't know where. Everything in mm is converted to m in my calculations prior to solving. This is the main problem.
    Last edited: Nov 7, 2012
  2. jcsd
  3. Nov 7, 2012 #2

    Simon Bridge

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  4. Nov 8, 2012 #3
    best way i found to find the charge of an electron is to plot a your drop charge vs the drop number, and you should be able to see a step difference of ~ 1.6x10^-19 C

    If you have done an adequate amount of drops you should have multiple sitting on each line.

    Hopefully your drops all 10 or less electrons or it will be fairly hard to determine the charge
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