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Capacitance Question

  1. Oct 27, 2007 #1
    Hey gang,
    I am doing a Mastering physics question, and it's got me stumped. ><

    Q: You need a capacitance of 50.0 microF, but you don't happen to have a 50.0 microfarads capacitor. You do have a 80.0 microF capacitor.

    What additional capacitor is needed to get a capacitance of 50 microF?

    I was thinking it has something to do w/ C = Q / deltaV. But that would mean that I would need to have some sort of knowledge of Q. I then tried

    Ceq = (1/C1 +1/C2)^-1
    and solved for 1/C1 to get 49.9875 microF. But that doesn't seem logical (+ I got it wrong ><)

    Any suggestions / help? Greatly appreciated!
  2. jcsd
  3. Oct 27, 2007 #2


    User Avatar
    Gold Member

    Well you obviously solved for the unknown incorrectly. Why not try to solve the simpler equation (assuming series capacitors):

    [tex]C_{eq} = \frac{C1 \cdot C2}{C1+C2}[/tex]
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