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Millikan Oil Drop Experiment Question

  1. May 17, 2009 #1
    1. The problem statement, all variables and given/known data
    An oil drop with a mass of 7.20*10^-16kg moves upward at a constant speed of 2.50 m/s between two horizontal, parallel plates. If the electric field strength between these plates is 2.20*10^4 V/m, what is the magnitude of the charge on the oil drop?


    2. Relevant equations
    F = ma
    Fg = mg
    Fe = qE
    E = V/d


    3. The attempt at a solution
    F = ma
    F = m(0)
    Fnet = 0

    Fnet = Fe - Fg
    Fg = Fe
    q = mg/E

    q = 3.2*10^-19C

    My problem is conceptual. I don't really understand how the particle can have a constant velocity and a net Force of zero upon it.

    How did the particle accelerate from stationary to it's current velocity?
     
  2. jcsd
  3. May 17, 2009 #2

    LowlyPion

    User Avatar
    Homework Helper

    The history of the particle isn't all that important. The mention of constant velocity is to reinforce the idea that it is not accelerating, and hence no net force.
     
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