1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Power dissipated in circuit

  1. Dec 19, 2003 #1
    An RLC series circuit constists of a resistor of 100 ohm, a capacitor of 10.0uF, and an inductor of 0.250 H. The circuit is connected to a power supply of 120 V and 60 Hz. What is the power dissipated in the circuit?

    I got 37 W (rounding 2 S.F's)
    the solutions manual has the answer as 73 W.
    Is 37 watts correct?
     
  2. jcsd
  3. Dec 19, 2003 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Edit: I had said your answer was wrong, but I was mistaken. I believe you are correct. ( )
     
    Last edited: Dec 19, 2003
  4. Dec 19, 2003 #3
    X_L= 94.25= 94 ohms
    X_C= 265.26= 265 ohms
    Z= 198.10 ohms=198 ohms
    I_rms= V_rms/Z = 120V/198ohms = .606 A

    -
    P= I_rms^2(R) = .606A^2 (100 ohms) = 36.7 W

    also tried this way:
    tan()=(X_L-X_C)/R = (94ohm-265ohm)/100ohm = -1.71
    phase angle =tan^-1(-1.71)= -59.7 degrees
    -
    P =V_rms^2/Z * cos ()=120V^2/198ohm (cos(-59.7))= 37 W

    another way tried:
    cos()=R/Z= 100ohm/198ohm= .505
    -
    P=I_rms*V_rms*cos()= .606A*120V*.505=37 W


    I supposed I could round 37 down some and multiply by 2 since it's an average
    and get the total number. Maybe question isn't asking for avg.
    or maybe use a different equation like

    -
    P = I_rms*V_rms= I_rms^2*R (equation was in the solution manual)
    = .606A*120V=73 W
    but I_rms^2*R = 37 W so that doesn't make sense (not equivalent)
     
  5. Dec 19, 2003 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Sorry fish, but you were right all along. (That's what I get for trying to do things in my head.) More importantly your methods are all correct. (I'll edit my earlier post.)

    That equation in the book is wrong; P = I_rms*V_rms*cosθ (they left out the phase factor).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Power dissipated in circuit
Loading...