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Homework Help: Modern Physics

  1. Feb 27, 2009 #1
    1. The problem statement, all variables and given/known data
    Millikan: A tiny, charged, sphere of water, with a radius of 1.25 microns is suspended at rest, in a vacuum, between the parallel plates of a capacitor. If the plates are 1 cm. apart, and have a potential difference of 500 volts between them, find the number of individual electrons required on the charged drop (to keep it suspended). What would happen if a radioactive source of beta particles (electrons) were introduced? Why did Millikan not use water? BEFORE you do this problem, first calculate the number of water molecules in the 1.25 micron drop, and write down your GUESS aas to the number of electrons that you will find is needed.
    Why all the "ones"?

    2. Relevant equations

    1 cc=1 ml=1 gr for water, but the (mks) density for water is NOT one.

    Im not quite sure how to even get started on this one. Can someone help me out? toss a few bones at me such as equations i'll need? and perhaps some hints on the non mathematical aspect?
  2. jcsd
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