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How to find i(t) when t>0

  1. Dec 15, 2016 #1
    1. The problem statement, all variables and given/known data
    I am given that vs(t)=25u(t)-10 and the following circuit
    upload_2016-12-15_21-20-37.png

    2. Relevant equations


    3. The attempt at a solution
    I would set the 12H and 8H as short circuits and then try to use KVL to find the current, but this doesn't work. I know that the answer is: 90-150e^-5t mA
     
  2. jcsd
  3. Dec 15, 2016 #2

    jedishrfu

    Staff: Mentor

    What level of study? What other rules have you been given?

    Did your book have a step by step solved example?
     
  4. Dec 15, 2016 #3
    2nd year university level, I wasn't given any rules for this question. My book has some solved examples, but they are different from this one. I just don't know where to start on solving this problem
     
  5. Dec 15, 2016 #4

    jedishrfu

    Staff: Mentor

  6. Dec 15, 2016 #5

    gneill

    User Avatar

    Staff: Mentor

    Before doing anything I'd suggest simplifying the circuit first, making a Thevenin equivalent out of the resistor network. That would leave you with a single loop containing a (scaled) source function, one resistor, and one inductor.

    Then consider the implications of the source function having a non-zero component that predates time t = 0. Hint: it might be helpful to find the steady state conditions for t < 0 and t >>0. How will the transition between those states look (what form will it take graphically)?
     
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