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Homework Help: First Order RC Analysis

  1. Jul 3, 2013 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    vc(t) = vc(∞) + [vc(0+) - vc(∞)]*e-t/τ (Voltage in a driven RC circuit)

    τ = RC (time constant for an RC circuit)

    3. The attempt at a solution

    I'm pretty shaky with these sorts of problems and am quite unconfident of my work here. Step functions tend to confuse me and I'm not quite certain I interpreted this one right- I understand it to mean Vin(t) = V0 when t ≤ τ. Also, my time constant appears to be inconsistent with the one given in the problem, but I'm not sure if it's supposed to be the same thing.

    Would appreciate some clarification.
  2. jcsd
  3. Jul 3, 2013 #2
    Your calculations are correct. What problems do you have?
  4. Jul 3, 2013 #3
    Okay, great. I just haven't performed many of these problems and wasn't sure. But one question persists: why does my time constant differ from the given one? Is 6RC the time constant before t=0?
  5. Jul 3, 2013 #4
    Yes, we have [itex]\tau=6RC[/itex] for [itex]t<0[/itex]. But the circuit changes at [itex]t=0[/itex] so [itex]\tau[/itex] also changes.
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