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RL Circuit

  1. Mar 31, 2014 #1


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    Gold Member

    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    I am working on the second problem of an old midterm, and I cannot figure out how they got that answer for the voltage across that 9kΩ resistor. I said the current going through the resistor is the same as that going through the inductor, so I figured I would find the current as a function of time, then just multiply by the resistor value.

    I posted the solution as well

    Attached Files:

  2. jcsd
  3. Apr 1, 2014 #2


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    Gold Member

    When you present a symbolic expression as an answer, you have to be sure that all symbols are defined. Also you want each symbol to be a non changing value. IL is a dynamic value. While your answer of Vo=IL*R3 is correct. it not the simplest. Find IL as a function of the input current, L, R1, R2, and R3
  4. Apr 1, 2014 #3


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    Staff: Mentor

    When t=0 the exp(-t/T) term equals 1.

    So the expression you have for i becomes i(0) = i + ( i - i0 )

    This does not look right. You have a sign wrong, or something.
    Last edited: Apr 1, 2014
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