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Homework Help: Computing Rth

  1. Mar 17, 2014 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    3. The attempt at a solution

    I'm trying to calculate Rth so I can compute τ. The problem is that after the switched is flipped for t>0, here is what is left: rxZkCds.png

    So you would expect Rth to be 3 ohms but it is actually 2 ohms.

    Solution for reference: KSpKitJ.png
  2. jcsd
  3. Mar 17, 2014 #2


    User Avatar

    Staff: Mentor

    The circuit you have drawn is for the left side of the circuit after the switch is closed. That part is irrelevant. The part with the time constant is the right side of the circuit, which has just the 2 Ohm resistor and the inductor. After the switch is closed, the two sides of the circuit are independent of each other, because of the short circuit between them.
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