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Homework Help: Average power used by circuit?

  1. Mar 9, 2009 #1
    1. The problem statement, all variables and given/known data

    If the rms voltage across the generator is 149 V, calculate the average power P(at 402 Hz) being used by the circuit.

    R = 298 Ω, a capacitance C = 4.1 μF, inductance of L = 0.23 H

    https://tycho-s.physics.wisc.edu/cgi/courses/shell/common/showme.pl?courses/phys104/spring09/homework/07/rclseries/ex2s92p4.gif [Broken]


    2. Relevant equations

    V=IR
    Avg power=Vrms*Irms(cos phase angle)
    vrms=vmax/(sqrt 2)
    Irms=Imax/(sqrt 2)

    3. The attempt at a solution

    Vrms=IrmsR
    149/(sqrt 2)=Irms*298 I think that the 149 V given in the problem needs to be divided by 2 to get Vrms? is rms voltage across generator same as max voltage? i'm not exactly sure about that part...anyways I got:
    Irms=.35355
    Avg power= (.35355)(149/sqrt 2) cos (phase angle)
    i solved for XL (581) and XC (96.6), which were both correct. so I got the phase angle to be 58.4 degrees
    Avg power= (.35355)(149/sqrt 2) cos (58.4)

    I'm not getting the right answer, so maybe my approach was wrong? Any help is appreciated.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 9, 2009 #2
    nevermind, got it
     
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