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Homework Help: RLC Series Circuit

  1. Jun 30, 2008 #1
    Given that R = 1 kOhms, L=100mH and C = 1uF, calculate the frequency at which the current in the circuit lags the supply voltage by 45deg.

    Show how the impedance of the circuit is given by Z = sqr root R2 + (wL - 1/wC)2
    arctan [(wL - 1/wC) / R]

    I have not been given any information regarding supply voltages or frequencies.
    I can not see how i can calculate impedance with no frequencies.

    I am assuming for Q1 that tan theta = XL-XC/R, this can only be 1000/1000 = 1 = 45deg.
  2. jcsd
  3. Jul 4, 2008 #2


    User Avatar

    You already have that [tex]X_L - X_C = 1000[/tex]
    Write the impedances as functions of L and C (known) and the frequency (unknown).
    You have one equation with one unknown, so you can calculate it.
    Use the calculated frequency to obtain the impedance.
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