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Help with circuit

  1. Jun 1, 2013 #1
    1. The problem statement, all variables and given/known data

    q3.png

    2. Relevant equations
    XL = wL
    XC = 1/wC


    3. The attempt at a solution
    XL = 4pi


    Thanks in advance.
     
  2. jcsd
  3. Jun 1, 2013 #2

    NascentOxygen

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    Staff: Mentor

    The first step is to determine the resultant impedance of the two parallel branches. There should be an imaginary operator, j, included in your impedance term for the L and C elements.
     
  4. Jun 1, 2013 #3
    and then what's the next step?
     
  5. Jun 2, 2013 #4

    NascentOxygen

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    Staff: Mentor

    Step 2 is to equate the impedance to be a pure resistance, because at resonance a circuit appears purely resistive to any applied voltage.
     
  6. Jun 2, 2013 #5
    doesn't this mean XL=XC, i already found XL and XC is the same and then solve for c?
     
  7. Jun 2, 2013 #6

    NascentOxygen

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    Staff: Mentor

    It does, where XL and Xc are the only impedances present. But there is an R here, and that makes things more interesting.

    That gives a rough approximation, and will usually get you near the right answer, but can be wrong by up to about 15%.
     
  8. Jun 2, 2013 #7
    I think you need to find impedance in the form: Z= f(R) + j*f(R, XL, XC).
    Then solve f(R, XL, XC) = 0 for C with R, XL and W given.
     
  9. Jun 3, 2013 #8
    I don't know what you mean, can you please make it clearer?

    Thanks
     
  10. Jun 3, 2013 #9
    Can you get the impedance of two parallel branches?
    Using ZL = jXL and ZC = -jXC
    The first branch: Z1= ZC = -jXC
    The second branch: Z2 = R + jXL
    Then total impedance:
    1/Z = 1/Z1 + 1/Z2
    You need to solve for Z and then force imaginary part of Z equals zero. You will find C.
     
  11. Jun 3, 2013 #10
    I couldn't do it, can someone please do it and attach a picture or a screenshot of the working out.

    Thanks
     
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