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Homework Help: Addition of Potentials

  1. Nov 10, 2007 #1
    1. The problem statement, all variables and given/known data
    27 drops of salt water with same radius, are each charged to a potential of V volts. They are made to coalesce into a single drop. How is the potential of a new drop compared to the potential of the original drops.

    2. Relevant equations
    V ( potential ) = k* q/r

    3. The attempt at a solution
    I know that the total potential of collection of point charges is ( assuming we can take the drops as point charges ): Vtotal = k Σ q/r; so Vtotal should be 27V. Now if we add another drop and we measure the potential at the same distance as we have measure it from the original drops, the new drop will have potetntial V.
    So from the ratio Vtotal/V can be seen that the original drops have a potential 27times bigger then a single new drop. Is this even nearly correct? Thanks
  2. jcsd
  3. Nov 10, 2007 #2


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    Science Advisor
    Homework Helper

    I THINK they mean how does the potential of a single drop in isolation measured at the surface of a single drop compare with the potential of the combined drops, again measured at the surface of the combined drop. I'm guessing that because the '27' is convenient number for this problem. The question isn't very clearly worded.
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