impedance of circuit?

Discussion in 'Homework Help' started by kerny, Jun 10, 2011.

  1. kerny

    Thread Starter New Member

    Apr 16, 2011
    6
    0
    Hi
    i have the following circuit and im not sure how to find the total impedance of it.

    http://i.imgur.com/r9Cn0.jpg

    The two sources are AC and I have the power equation

    P = (V1 * V2)*sin theta / X

    so i want to find the impedance of the circuit to get the power. i dont know if i can use superposition or not since this is impedance.

    any help is appreciated.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    The current in the resistor (which determines the power) is not influenced by the inductance. The effective impedance between the AC voltage (?) sources is determined solely by the series addition of R & C [R+1/jωC]. You may use superposition to determine the current in R and hence the power dissipated.
     
  3. blah2222

    Well-Known Member

    May 3, 2010
    553
    33
    The impedance depends on frequency, so another question to ask is: Are the power supplies operating at the same frequency?
     
  4. kerny

    Thread Starter New Member

    Apr 16, 2011
    6
    0
    Thanks for replying.

    I think your method will help find the power that is dissipated in the resistor, but i want to find the power flow between the two voltage sources.

    For example, let's imagine that all 3 of the components were reactances, wouldn't there still be a power flow between V1 and V2? This youtube video is more of what im looking for (around the 42:44 mark), and might give a better idea of why i want to find the reactance.

    http://www.youtube.com/watch?v=IxAykEoeWFA


    Could you also explain why the inductor has no influence on the current? By superposition, I can see that when you short out the voltage source on the right, that no current will flow through the inductor, but when the other voltage source (left side) is shorted, there will be some current flow through that inductor.

    TIA

    Edit: yes, the two voltage sources are operating at the same frequency
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    For real power flow to occur there must be a means of dissipating power. Certainly there will be reactive power flow between the sources.

    The inductor will draw reactive power from the source in parallel with it, but no real power is drawn by the inductor.
     
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