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Homework Help: Finding i(t) (Source Free RL Circuit)

  1. Jul 10, 2008 #1
    1. http://img529.imageshack.us/img529/6205/87421877rv5.jpg [Broken][/URL]

    3. First I found i(0)

    the equation for a source free RL circuit is

    i(t) = i(0)e^(-t)/T

    T = L/Req

    Since the inductor will be shorted when t<0, i(0) must be 5mA.

    Now to find Req I added series and parallel appropriately to find

    Req = 3/4k Ohms

    so my equation is

    i(t)= (5x10^-3)e^(-t)/T
    where T = (1x10^-3)/(3/4x10^3)

    can someone please check that, Thanks!
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Jul 10, 2008 #2


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    By that arrow pointing to t=0, do you mean that the switch is closed for a very long time for t<0 and is opened at t=0?
  4. Jul 11, 2008 #3
    ya for a very long time (t<0) the switch is "horizontal" then at t=0 it is moved to the lower point.
  5. Jul 11, 2008 #4


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    Yeah I got the same answer.
  6. Jul 11, 2008 #5
    ok great, thanks!!!!
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