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Homework Help: Charge on droplets

  1. Apr 7, 2012 #1
    1. The problem statement, all variables and given/known data

    A spherical droplet of radius R and effective mass density ρ. carries a total charge q in a gravity field g. What electric field E iz, will suspend the charged droplet? Millikan found by this method that all droplets carried integer multiples ofnegative charge e= -1.6 x 10-coul.

    2. Relevant equations


    3. The attempt at a solution

    I would like to confirm if my attempt is okay or not. Please can you give explanation based on whatever method it is required to be solved in.

    q E = ρ g (4/3) ∏ R3

    E = ((ρ g)/q) (4/3) ∏ R3
  2. jcsd
  3. Apr 7, 2012 #2


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    Staff Emeritus
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    Gold Member

    It makes sense to me. You equated the gravitational force to the electric force (in magnitude). You computed the mass by multiplying the density by the volume. I don't see any problems.
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