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Homework Help: Mixed parallel & series RLC circuit

  1. Jun 9, 2012 #1
    1. The problem statement, all variables and given/known data
    pic: www(dot)freeimagehosting.net/hbnem

    Calculate impedance , current and power factor
    2. Relevant equations

    3. The attempt at a solution
    pic: www(dot)freeimagehosting.net/xmy2b

    First we solve parallel part. In parallel resistor and inductor are sharing voltage. Using phasor diagrams we found vector I_1 which is current in parallel part. Series circuit share current so I have attached phasor diagram for capacitor to I_1 (as you can see). Now i need to find vector V_S which is V_C + V_R. But i dont know how to find it.

    (sorry for the pics)
  2. jcsd
  3. Jun 9, 2012 #2
    Hi mrmlica. Not too sure what you're trying to do, but the equivalent impedance of a parallel circuit is just: [itex]\frac{1}{Z_p}=\frac{1}{Z_1}+\frac{1}{Z_2}+....[/itex] and for series is: [itex]Z_s=Z_1+Z_2+...[/itex]. Where Z is the complex impedance, Z_n is the n'th component in the given circuit, s=series & p=parallel. To find the current you use Ohm's law as you know the input voltage and the impedance. The power factor is the cosine of the phase angle between the current and the voltage. The tangent of the phase angle can be found from the argument of the complex impedance.
  4. Jun 9, 2012 #3
    I wasnt hoping for that good help. You didnt just solve me task, you learn me new diffrent way to look on AC current. Thank you alot.
    Last edited: Jun 10, 2012
  5. Jun 10, 2012 #4
    You're welcome. I'm glad I could help you with the problem in a different method to what you normally do. If you're finding any difficulty with my method just ask any questions you want to.
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