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Homework Help: Problem related to Milikan's Oil Drop Experiment

  1. Dec 3, 2004 #1
    How would I figure out the answer to this question (what formulas)?

    Here are the formulas I've been using for this homework assignment:
    PEe = -qEd
    V = W/q
    V = -Ed
    C = q/V

    An oil drop having a charge of 8 x 10^-19 C is suspended between two charged parallel plates. The plates are seperated by a distance of 8 mm, and there is a potential difference of 1200 V between the plates. What is the weight of the suspended oil drop?
  2. jcsd
  3. Dec 3, 2004 #2
    By the way... this assigment is being collected & graded.
  4. Dec 3, 2004 #3
    wait a minute... I think I have it. I just need the weight of one electron (in kg). Anyone know that?
  5. Dec 3, 2004 #4
    OOps... I meant mass in kg or weight in Newtons.
  6. Dec 3, 2004 #5
    The oil drop experiment doesn't measure the mass of an electron. It measures the charge of an electron.

    The idea is that if you can measure how big the oil droplet is, you can figure out its weight. If it's floating, then the charge is balancing the weight.

    The charge might be any number of electrons though: 1, 2, 3, etc.

    So you have to look for the drops that float, but only just - the ones that float easily with a low voltage on the plates have two or more spare electrons on them.
  7. Dec 3, 2004 #6
    Ask yourself what forces are acting on this droplet? Since the droplet isn't moving, what can you say about these forces? Draw a diagram if need be.
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