AC Circuit Problem

Discussion in 'Homework Help' started by mhanssler, Jul 7, 2011.

  1. mhanssler

    Thread Starter New Member

    Jul 7, 2011
    4
    0
    I cannot seem to wrap my head around this problem...

    If the voltage across and the current through the series combination of a resistance and an unknown energy-storage (presumably an inductor) element are:

    v=200cos(10^2t + 60°)
    i=5.547cos(10^2t + 93.96°)

    then find the resistance as well as the unknown element

    Any help would be much appreciated.
     
  2. tubelite

    New Member

    Jul 20, 2010
    6
    0
    a hint: you could use phasors/polar coordinates to solve this problem.
     
  3. mhanssler

    Thread Starter New Member

    Jul 7, 2011
    4
    0
    Yeah. I am just learning about them now. I have been stuck on this problem for awhile....

    So, I have two unknowns (R and L)

    I know that Z=R+jwL
    I know that V/I=Z

    I just cannot seem to come up with two equations that will allow me to solve this...

    any stronger hints that you can help with??
     
  4. mhanssler

    Thread Starter New Member

    Jul 7, 2011
    4
    0
    also, I know:

    This is a simple voltage divider circuit....
    hence

    Vr= R/(r+jwL)Vs where Vs is 200arg(60deg)

    If I found Vr I could use that to find R by dividing by the current i. This is true because the circuit is in series...

    But again... I need values for R and L so I am thinking this is the wrong way to go...
     
  5. blah2222

    Well-Known Member

    May 3, 2010
    554
    33
    You were on the right track with Z = V/I. If you perform the phasor division you can obtain Z, then convert that into rectangular complex to find the values that you are looking for.

    Phasor: Z = Zmag<(argZ)

    Rectangular: Z = R + jwL
     
  6. lazukan

    New Member

    Mar 29, 2011
    5
    0
    Convert it to the phasor and Use R= V/ I and make some algebra in complex numbers , its pretty easy

    Regards

    Lazukan
     
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