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Rc circuit- please help

  1. Nov 16, 2009 #1
    1. The problem statement, all variables and given/known data

    A capacitor is placed parallel across a resistive load in a circuit. C= 0.829*10-6 F and R = 229 ohms. What fraction of the current goes through the capacitor when the frequency is 100 sec-1?

    2. Relevant equations
    I(resistor) = V/R
    I(capacitor) = C * (dV/dt) = ω*C*V (?)

    3. The attempt at a solution
    Ic / (Ir + Ic) = [ω*C*V] / [(V/R) + (ω*C*V)] reduces to [ω*C*R] / [1 + ω*C*R]
    The answer I got was 0.106569. I don't know if the work is wrong or if the format of my answer wrong, like is that the "fraction" or do I have to do something else to it? Thanks.
  2. jcsd
  3. Nov 17, 2009 #2


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    Homework Helper

    The problem here is that I_tot does not equal Ir+Ic. The instantaneous current at any point in time does obey I_tot=Ir+Ic, but not the effective current in an AC circuit. You have to calculate the total effective current in a different way (what way?)
  4. Nov 17, 2009 #3
    The only thing I can find is for an RC circuit in series. is it the same for parallel?
  5. Nov 17, 2009 #4
    do you mean I_tot (sqrt 2)? can someone please help me it's almost due :/
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