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2 Loop RC circuit

  1. Feb 19, 2012 #1
    1. The problem statement, all variables and given/known data

    A circuit is constructed with four resistors, one capacitor, one battery and a switch as shown. The values for the resistors are: R1 = R2 = 37 Ω, R3 = 90 Ω and R4 = 105 Ω. The capacitance is C = 49 μF and the battery voltage is V = 12 V. The positive terminal of the battery is indicated with a + sign.

    What is Q(∞), the charge on the capacitor after the switch has been closed for a very long time?
    2. Relevant equations
    V = Q/C

    V= IR

    3. The attempt at a solution

    V = (R1 +R4)I + R3I3

    R3I3 + Q/C = R2IC

    I3 + IC = I

    I have 4 unknowns and 3 equations. :( I think I might be missing something fundamentally about capacitors though.

    Attached Files:

  2. jcsd
  3. Feb 19, 2012 #2


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    Staff: Mentor

    After a "long time", the capacitor will have attained its final charge and potential difference; the current Ic will be zero. In effect, the capacitor will no longer affect circuit operation and you can determine its final voltage by determining the voltage presented across its connection points by the resistor network around it, as though the capacitor itself was an open circuit.
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