User:David J Weiss/Notebook/people/weiss/Millikan

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Summary of the Oil Drop Lab

SJK Incomplete Feedback Notice
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My feedback is incomplete on this page for two reasons. First, the value of the feedback to the students is low, given that the course is over. Second, I'm running out of time to finish grading!
SJK 18:45, 16 December 2009 (EST)
18:45, 16 December 2009 (EST)
So did you enjoy staring at the droplets or not? Looks to me like you got the charge calculations...and probably with some more data John's method would have deduced the charge for you.

The main goal of this lab was to determine through experimentation the value of the charge of an electron. We did this by measuring how fast an electron falls under the influence of gravity and how it rises in the presence of an electric field. This can be done by observing a shit-ton of oil-drops in a chamber with an attached grid of measurable distances.

So I found the charges of seven different oil drops each containing a different number of electrons. I took the values I got from calculating the charges on the individual oil drops and with some help (thanks Dr. Koch) I found out that the reasons the charges were so much larger than value of e was that there were multiple charges on the oil drops so to find out how many electrons were in each oil drop I just divided the charges on the oil drops by the expected value of e which I obtained from the manual for the instrumentation. The values obtained are as follows:

  • The first drop had a charge of 3.38(19)*10^-9 e.s.u. and it had 7 electrons

and an error of 40%

  • The second drop had a charge of 1.545(05)*10^-9 e.s.u. and 3 electrons

and an error of .1%

  • The third drop had a charge of 2.27(003)*10^-9 e.s.u. and 5 electrons and an error of .59%
  • The forth drop had a charge of 8.34(06)*10^-9 e.s.u. and 17 electrons and an error of 11.62%
  • The fifth drop had a charge of 3.59(01)*10^-9 e.s.u. and 7 electrons and an error of 2.31%
  • The sixth drop had a charge of 4.33(07)*10^-9 e.s.u. and 9 electrons and an error of 1.29%
  • The seventh drop had a charge of 4.41(07)*10^-9 e.s.u. and 9 electrons and an error of 1.37%
  • The excepted value for the electron is 4.803*10^-10 e.s.u. from the Pasco Manual

So from my data you can see some of the measurements were good and some not so good. This could be from fatigue due to a strain on the eye caused by looking in the eye peace to watch those damned drops falling or possibly due to a error when measuring the time that it took for each drop to rise or fall and that could throw off the data quite a bit. So what I learned is that staring in that dam eye peace sucks and that through multiple trials you can get some data that is good and some that sucks. With enough data you can get closer and closer to the value that you want to find through your experiment. As evidenced from my experiment my error ranged from less than 1% all the way to 40% which is a somewhat large range so I would have to look at all the data i collect in the future to figure out where I made mistakes and how to correct them in the future when I preform an experiment again so that my data would have less a range for error.

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