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Homework Help: Derived the expression for voltage

  1. Mar 3, 2006 #1
    The current in a 15 millihenry inductor is known to be:
    i = 4 amperes, for t < 0 and
    i = A1 * e -2000*t + A2 * e -8000*t amperes, for t > 0

    The voltage across the inductor (assuming the passive sign convention) is 58 volts at t = 0(+) seconds.

    I need to find the constants a1 and a2. I have already derived the expression for voltage @ t=0: 58=-30(a1+4*a2).

    Unfortunately, I am now lost. I cannot figure out an equation with 2 unknowns. Any help would be greatly appreciated.

    I don't believe the fact that i = 4 amperes, for t < 0 is significant for this part of the problem.
    Last edited: Mar 3, 2006
  2. jcsd
  3. Mar 3, 2006 #2
    never mind, I was overthinking the problem.
  4. Mar 3, 2006 #3


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    Occupational hazard of smart people. :biggrin:
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