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Homework Help: [rcl circuits] is this a contradiction?

  1. Sep 20, 2014 #1
    Problem: upload_2014-9-20_13-52-45.png

    But here is what happens when I apply nodal analysis to the same node at t>0:

    Is this a contradiction? Is the voltage of the resistor at t=0+ equal to 16V or 0V?
  2. jcsd
  3. Sep 20, 2014 #2
    I think I figured it out. At ##t=0^-##, the capacitors are replaced with open circuits and the inductors are replaced with wires but this does not apply at ##t=0^+##.
  4. Sep 20, 2014 #3
    When t<0, an inductor acts as a short circuit and a capacitor acts as an open circuit. At the instant t=0+, the circuit goes through a transient phase. Once t>>0, the circuit becomes steady state and once again the inductor acts as a short and the capacitor as an open.
  5. Sep 21, 2014 #4
    Thank you for this. Argh, I wish my textbook explained this to me. Why does the inductor and capacitor act as closed/open circuits in the steady state but not in the transient phase?
  6. Sep 21, 2014 #5
    Basically an inductor goes from some high voltage to 0, which would cause all the current to flow through it (which is a short) when time goes to infinity. I'm not sure if you've seen the graphs of these, but that should help you, so I'd say look it up.
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