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Math Help - electric circuits problem

  1. #1
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    electric circuits problem

    this problem im not so sure of, they give me the values for I(0) = 0 Eo = 120 volts R = 600 ohms and L = 4 Henry's , when does the current reach 90% of its limiting value? i attached a copy of where i started or where im stuck, any suggestions? thanks in advance. diffy q problem 2.pdf
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  2. #2
    MHF Contributor Calculus26's Avatar
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    4dI/dt + 600 I = 120
    There is no further info on E so E= constant= 120

    dI/dt + 150 I = 30

    You need a coefficient of 1 in front of dI/dt or the integrating factor
    won't work

    In factor is e^(150t)

    I*e^(150t) = integral(30e^(150t))= 1/50 e^(150t) + C

    I = .02 + C e^(-150t)

    I(0) = 0 C = -.02

    I = .02 -.02 e^(-150t)

    The limiting value is .02 now you can finish
    Last edited by Calculus26; February 4th 2010 at 01:21 PM.
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