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Homework Help: Capacitors Network

  1. Sep 15, 2010 #1
    I have a circuit consisting of a battery and several capacitors, some quantities are known and some are not. The capacitors were completely uncharged before the battery was attached and we are considering the static situation. (Be sure to keep at least 3 sig. figs. in your answer for all parts of this problem.)

    Q1: 7.9e-6
    C1: 7.1e-6
    C2: 1.9e-6
    Energy stored on C2: W=5.6e-6 J
    C2 is parallel to C3

    I found:
    the potiential distance across C1 is 1.126 V

    I need to find:
    -Potenital distance across C2
    -Potential difference across C3
    -The charge of Q3 on C3

    Can you please help me? Thank you:)
  2. jcsd
  3. Sep 16, 2010 #2
    1) You know the relation
    W=1/2 * CV^2
    You can find V2 because you know C2 and W2

    2) Since C2 and C3 are parallel V2=V3 (Pot. diff. across C2 and C3 are same)

    3) I assumed C1 is in series with C2 || C3. Q1 is known. Since they are in series total charge in C2||C3 is Q1. (In series connected capacitors the amount of charge stored in each capacitor is same). You can find charge in C2 using relation
    From this Q3= Total charge in C2||C3 (ie., Q1) - Q2
  4. Sep 16, 2010 #3
    Ok, thank you:)
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