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Homework Help: Capacitance Circuit - Voltage and Charge

  1. Sep 22, 2009 #1
    1. The Question
    a. What is the equivalent capacitance of the combination shown in the figure ?
    b. If a 100V battery is connected across the combination, what is the charge on each capacitor?
    c. What is the voltage across each?

    2. Equations
    C=Q/V, adding capacitance rules

    3. Solution attempt
    For part a, I added C2 and C3 to get .03, then added the two in series (1/.02)+(1/.03) and took the inverse to get a combination capacitance of .012 microF

    I am stuck on parts b and c, though. For B, we know Q=V/C and for C2 it would be Q=(100V)(0.01microfarads) which gives a charge of 1 microcoulomb.

    for C3 it would be Q=(100V)(.02microfarads)=2 microcoulombs.
    And for C1 it would be Q=(100V)(.02microF)= 2 microcoulombs.

    However this answer is not working.

    For part C, I tried plugging the charge and C in to the same equation to get the V back out, but again this has not worked. I'm not sure if my units are off, or if I am missing something conceptually.[/b]

    Any help would be appreciated!
  2. jcsd
  3. Sep 22, 2009 #2
    Nevermind, I just figured it out - I was trying to use the individual capacitance of C2 and C3 when I should have been using the combined since they are in parallel. :)
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