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Homework Help: Simple question: Find charge given mass, electric potential difference and radius

  1. May 12, 2012 #1
    1. The problem statement, all variables and given/known dataFind the charge
    find the charge:
    mass : 3.6*10^-12 kg
    electric potential difference: 250.4 V
    parallel plates are 0.41 cm apart

    PLEASE DO NOT link me a wikipedia page.. or give me a one sentance explanation of something unrelated to this question
    Just need to know how to find charge in this case
    Thanks for the help in advance!

    2. Relevant equations
    I thought it was:
    so q= (Vr)/k
    But what would the mass be there for?

    3. The attempt at a solution
    q= (Vr)/k
    q= (250.4*0.0041m)/(9.0*10^9)

    i dont know whether this is the right way of finding it
  2. jcsd
  3. May 12, 2012 #2


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    Staff: Mentor

    wow22, I think you have abbreviated the details too much, and what you provided is not meaningful. Parallel plates I understand, voltage across the plates I understand. But mass....? What body is this whose mass is part of the question? And what is it is that has a radius?
  4. May 12, 2012 #3
    It's the mass of an oil drop and im looking for the charge of it. That's basically all the info given to me, and the question isn't really given to me in a word question, it just says to find the charge of the drop with info in chart provided.
  5. May 12, 2012 #4


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    Staff: Mentor

    Why didn't you explain the setup in your first post? Without context your question is indecipherable.

    What is the electric field strength between the plates?
    What forces are acting on the charged droplet?
  6. May 12, 2012 #5
    not sure ..
    considering it didn't say i'm going to assume that it's stationary.
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