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Help about millikan oil drops apparatus?

  1. Dec 25, 2013 #1
    1. The problem statement, all variables and given/known data

    in a millikan type apparatus, the horizontal plates are 2 cm apart. with the field switched off, an oil drop is observed to fall with a steady velocity of 2 x 10^-4 m/s. when the field is on, the upper plate being positive and the drop just remains stationary when the pd between two plates is 1150 v

    a/ calculate the radius of the oildrop
    b/ how many electrons charges does it carry

    2. Relevant equations
    a/ w=fd
    m g = 6 phi η r v

    b/ fe = w
    q Δv/d = m g

    3. The attempt at a solution

    a/ i don't understand how much is m, and η
    it is not mention in the question. what should i do? where should i put V?

    b/how much is m?
    Last edited: Dec 25, 2013
  2. jcsd
  3. Dec 25, 2013 #2


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    2017 Award

    Staff: Mentor

    η and the density of oil are something you have to look up (in the problem statement or somewhere else).
    m can be calculated as function of the radius of the oil drop and the density.

    "phi" is pi (##\pi##)?

    What do you mean here?
    v as velocity? Exactly where it is in the formula.
    V as volume? That is related to the mass.
    V as voltage? Exactly where it is in the formula.
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