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Homework Help: RLC Parallel Circuit

  1. Mar 30, 2014 #1


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

    See image

    2. Relevant equations


    3. The attempt at a solution

    How do I calculate the current for a circuit of this type? I am unable to find any examples in our text. Can I use the following formulas to solve for the current flowing through each component:

    I(r) = V/R
    I(L) = V/X(L)
    I(C) = V/X(C)

    Would it be possible to find the energy stored in each component at t = .4 s?

    Or would it be okay to use the energy equations for the L and C, accordingly.
    In this case, .5(100^2)10*10^-6 = 50mJ

    Attached Files:

    Last edited: Mar 30, 2014
  2. jcsd
  3. Mar 30, 2014 #2

    Simon Bridge

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    You are given the current.

    You can use kirkoffs laws.
    You also have some notes about finding equivalent impedences and/or reactances and so on.
    You are expected to use that information to solve problems you have not seen before.
  4. Mar 30, 2014 #3


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    huh? I'm not sure what you mean by your last two sentences...

    I need to find the current going into the inductor, I wasn't sure if I was supposed to use the I(L) in order to find tat.
  5. Mar 30, 2014 #4

    Simon Bridge

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    The problem statement you provided in the attachment does not tell you to find the current ... you are given the current for the inductor at t=0.
    To find the current at another time, you will need to use this value.

    ... let me clarify:

    When you said:
    - this means that this is a problem you have not seen before. You are expected to be able to use knowledge you learn in your coursework to solve problems you have not seen before.

    You asked about how to find currents and stored energy for a circuit like that.
    To do that, you have to use your understanding of AC equivalent circuits, reactances, and impedences.
    You should have some notes in your coursework, and in the textbook, about these things already.

    I want to get you off trying to find an existing equation and on to using your understanding of physics.
    Chances are you don't have an equation to cover exactly this circuit - so you'll have to derive one.
  6. Mar 30, 2014 #5


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    I will give it a try and take a look at it. My mind turns into spaghetti after looking at this stuff too long! My apologies for the confusion.
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