1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Millikan oil drop experiment charge determination

  1. Oct 13, 2016 #1
    Howdy y'all!

    If you could help with the following question, my physics class and I would be extremely grateful.

    A charged oil droplet is suspended motionless between two parallel plates (d=0.01m) that are held at a potential difference V. Periodically, the charge on the droplet changes as in the original oil drop experiment. Each time the charge changes, V is adjusted so that the droplet remains motionless. Here is a table of recorded values of the voltage:

    i. 350 V

    ii. 408.3 V

    iii. 490 V

    iv. 612.5 V

    From the data above, determine the charge on the dorplet for case (i) above. What assumptions do you need to make? (Hint: the ratio of voltages = ?)

    Thanks a ton, we've been stumped.

    I'm gonna be honest here, me and 2 friends have been working on this for about 4 hours, and we don't really have any substantial work to show. Any help would be great. Thanks.
  2. jcsd
  3. Oct 13, 2016 #2

    Charles Link

    User Avatar
    Homework Helper

    I can give you a hint, but I haven't solved it myself yet: ## 350* \, Q_1=408.3* \, Q_2=490* \, Q_3=612.5* \, Q_4 ##. ## Q_4<Q_3<Q_2<Q_1 ##. Find some ## Q_o ## so that ## Q_4=n_4 \, Q_o ##, ## Q_3=n_3 \, Q_o ##, etc., ## n_4, n_3,... ## integers (hopefully small ones). Sorry, I edited a couple of times because I read it incorrectly.
    Last edited: Oct 13, 2016
  4. Oct 13, 2016 #3

    Okay, this makes sense. However, where can we go from here? Is there anyway to solve for the integers?
  5. Oct 13, 2016 #4

    Charles Link

    User Avatar
    Homework Helper

    I have it, but I'm not allowed to give the solution. I can give you a hint though. The smallest number, ## Q_4 ## is greater than 3. Another hint is the numbers are exact enough, that I think the data is probably simply constructed by the professor as a good learning exercise. One additional hint=let ## Q_4=n_4 ## (Ignore the ## Q_o ## part mentioned previously.) Please let us know if you figured out the answer.
    Last edited: Oct 13, 2016
  6. Oct 13, 2016 #5
    Okay, so we talked it out a little bit. So does this mean that the answer is 7e=1.12x10^-18 coulumbs?
  7. Oct 13, 2016 #6

    Charles Link

    User Avatar
    Homework Helper

    Yes. One additional question for you=what did you get for the other 3 integers? And were the calculations almost exact?
  8. Oct 13, 2016 #7
    We got all the integers as 7,6,5, and 4. Thank you so much! We just screamed in excitement and relief.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Millikan oil drop experiment charge determination