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Discharging a capacitor through resistor and uncharged cap

  1. Jun 2, 2016 #1
    1. The problem statement, all variables and given/known data

    Given v0 c1c2 r1 need to find the current on r1 picture
    New Document(16)-page-002.jpg
    switch 1 is closed for long time and on t=0 opened and switch 2 is closed
    2. Relevant equations

    3. The attempt at a solution
    in the attached file New Document(16)-page-001.jpg
    i was trying to use kvl assuming that q0(charge on cap before opening switch 1) is v0 adn the sum of q1 and q2 (the charge after switch 2 is closed) is equal to q0
    how to find cons c and I(t)?
  2. jcsd
  3. Jun 2, 2016 #2


    User Avatar

    Staff: Mentor

    Usually one uses known boundary conditions (initial, steady state) to solve for the unknown constants, plugging the known conditions into the general solution of the differential equation.

    For this problem it might be easier to just look at the initial and final conditions and "connect" them with the known behavior of an RC circuit. That is, if you can determine the initial current that flows the instant after the switch S2 is closed and the final current at steady state, you know that the current must follow an exponential decay between those states. You've already determined the time constant, so the rest will be straight forward.
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