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Elementary Charge / Oil Drop clarification

  1. May 22, 2007 #1
    In an early set of experiments, Milikan observed that the following measure charges, among others, appeared at different times on a single oil drop. What value of elementary charge can be deduced from these data?

    1) 6.563 x 10^-19 C
    2) 8.204 x 10^-19 C
    3) 11.50 x 10^-19 C
    4) 13.13 x 10^-19 C
    5) 16.48 x 10^-19 C
    6) 18.08 x 10^-19 C
    7) 19.71 x 10^-19 C
    8) 22.89 x 10^-19 C
    9) 26.13 x 10^-19 C

    So what i was thinking is, that you would go #2 - #1 = elementary charge which in this case would come out to 1.641 x 10^-19 C.

    And if you go #3 - #2, it would give you a mutiple of this elemtary charge. Which in this case would be 3.296 x 10^-19 C. Which is roughly a multiple of the elementary charge i got earlier because if you divide this by 2, you get 1.648 x 10^-19.

    So do i keep doing that? then since each elementary charge I get is slightly off, then I just add up and take average?
  2. jcsd
  3. May 22, 2007 #2

    Chi Meson

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    Your reasoning is OK, but you can't assume that the difference between #2 and #1 is automatically the elementary charge. Furthermore there is nr rule that says you can only compare 3 with 2 and 4 with 3, etc.

    Have you considered plotting the measurements on a graph? (well, more like on a numberline as there is no "y-axis" here).
  4. May 22, 2007 #3
    Ok. So how would i go about creating a chart and how would i find the elementary charge with this data?
  5. May 22, 2007 #4

    Chi Meson

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    Set up an "x axis" for charge such that you can plot with 4 sig figs, and put a dot on the axis for each charge you've got.

    Then notice the spaces between the dots.
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