RCL Series Circuit Question

Discussion in 'Homework Help' started by wildnixon, May 27, 2008.

  1. wildnixon

    Thread Starter Member

    May 1, 2008
    I am having trouble figuring out the phasor voltage and phasor current of an RCL series circuit. I am given the following values: v(t)=10sin(wt) (that w is a small Omega) and that the value of w is 1000 rad/sec. The inductance is 120mH, the capacitance= 1 micro Farad, and the resistance =100 ohms. I have calculated the frequency given the omega value, but I end up with a really small number : 6.3x10-3, and then I end up with a really small XL number and a really huge XC!! I know the math once I get the value of the frequency right, but I am just beating my head against the wall here!!
    Thanks for any help!
  2. mrmount

    Active Member

    Dec 5, 2007
    I am not sure how you came up with that value for w. w=2*Pi*f; f=w/2*pi. So you will be getting 159.23 Hz! The value you have found is 'T' or the time taken for one complete cycle of the sine wave.
  3. wildnixon

    Thread Starter Member

    May 1, 2008
    I will proceed to use the 159 Hz...I see now where I botched it...it's always something simple...
  4. silvrstring

    Active Member

    Mar 27, 2008

    omega = 2*pi*f. So f = omega/(2*pi) = 159.2Hz.
    X(L) = 2*pi*f*L, and will be at 90 degrees (or * j).
    X(c) = 1/(2*pi*f*C), and will be at -90 degrees (or * -j).
    Z = R + jX(l) - jX(c) = sqrt(R^2 + X^2) at angle tan^(-1) (X/R).
    10V is your peak Voltage.
    If you are keeping with peak voltage values, your pk V value is 10V at 0 degrees.
    I = V / Z.
    Subtract your denominator angle from your numerator angle to obtain your current angle (phase).
    example (10V at 0 degrees/500 ohms at 60 degrees = 20 mA at -60 degrees). Not the answer by the way!

    Hope this helps.
  5. zamansabbir


    May 27, 2008
    XL=w*L (w=small omega)

    R= 100 ohm
    Hence Z=R+J(XL-Xc) ohm
    in phasor form Z= sqrt(R^2+(XL-Xc)^2)< arc tangent of((XL-Xc)/R)
    then use V= I*Z;
    to get the current through every component and then use voltage divider rule or same ohms law to get the voltage phasor
    Hope u understand