I had a question about the Millikan Oil drop experiment. I did the experiment for my physics class where we had to determine the voltage that would make the droplet stationary. We did this ten times, so I have ten different voltages. The mass, gravity, and distance remains the same it is only the voltage that is changing. The part I am struggling with is, I must determine my own fundamental charge from this experiment and compare it to the accepted value of 1.6x10^-19. How do I determine my own fundamental charge when I am given 10 different voltages? I believe that I am supposed to use the q=mgd/V equation but I am not fully sure. My mass is: 1.57x10^-15 C My distance: 0.1 m Gravity: 9.81 m/s^2 My voltages: 400, 457, 384, 369, 400, 355, 369, 436, 384, and 369.

  • $\begingroup$ Have you tried calculating q for each of your values of V? $\endgroup$ Commented Dec 12, 2020 at 23:11
  • $\begingroup$ Yes, I calculated all of the q values for V. $\endgroup$
    – Lulu
    Commented Dec 12, 2020 at 23:18
  • $\begingroup$ Were those q values mostly near $1.6\times10^{-19}$ C, $2 \times 1.6\times10^{-19} $ C, ... ? Or perhaps were they near $some value$, $2 \times some value$, ...? $\endgroup$
    – mmesser314
    Commented Dec 12, 2020 at 23:57
  • $\begingroup$ They were not. They were actually around values like, 3.37x10^-18 C all the way to 4.17x10^-18 C. I calculated the differences between all the charges and then I got values around 1.6x10^-19 C to 4.9x10^-19 C. $\endgroup$
    – Lulu
    Commented Dec 13, 2020 at 0:03
  • $\begingroup$ The smallest non-zero difference between your calculations should be due to only 1 electron. $\endgroup$ Commented Dec 13, 2020 at 0:33

1 Answer 1


It appears that your measurements may have been very imprecise. However, given your data, the best approach is to find a value for e such that the RMS differences between the charges $q_i$ you found and the nearest values of $n_i e$ to the $q_i$ is minimized. That is, minimize the square root of the sum of the squares of $(n_i e -q_i)^2$ by fiddling with the value of $e$. Choose $n_i$ for each $q_i$ so that $n_i e$ is as close as possible to $q_i$. Easy to do in a spreadsheet.


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