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Homework Help: Frequency where reactence is zero

  1. Jul 16, 2008 #1
    1. The problem statement, all variables and given/known data
    At what frequency (in Hz) are the reactances of a 58 mH inductor and a 84 µF capacitor equal?


    2. Relevant equations
    Xl=1/2(Pi)fL
    Xc=2(Pi)fC



    3. The attempt at a solution[/b
    F needs to be the same for both, so i got f by itself in both equations, then had them equal each other, giving me Xl2(Pi)L=1/2(Pi)XcC, but im stuck from there
     
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  3. Jul 16, 2008 #2

    Hootenanny

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    I think you have misunderstood the question. The question wants to know for what frequencies are the reactances the same. In other words, find f such that Xc = Xl.
     
  4. Jul 16, 2008 #3
    so if Xl=Xc, then 1/2(Pi)fl=2(Pi)fC? i tried that then got 1=(2pi fL)*(2pi fC). is that on the right track?
     
  5. Jul 16, 2008 #4

    nicksauce

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    Yes, now just solve for f.

    On a related note, wikipedia tells me
    Xc = 1 / (2pi*f*C)
    Xl = 2*pi*f*L
    Which seems to be the opposite of what you have written, although it should still give the same answer.
     
  6. Jul 16, 2008 #5

    Hootenanny

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    Looks good thus far :approve:.
     
  7. Jul 16, 2008 #6
    got it!!! thanks a lot
     
  8. Jul 16, 2008 #7

    Hootenanny

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    A pleasure :smile:.
     
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