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Homework Help: Phase angle RC circuit

  1. Aug 20, 2010 #1
    1. The problem statement, all variables and given/known data
    Pls see the attachment.

    2. Relevant equations

    3. The attempt at a solution
    Obviously I have B and C correct but for a the only thing I can find is tan(phi)=XL-Xc/R
    This seems to be for a series RLC circuit though and I only have RC.
    also I know that the current lags the p.d by 900 in an RC circuit but I cant see how I can use this????
    any help appreciated.

    Attached Files:

    • PF.jpg
      File size:
      25.5 KB
  2. jcsd
  3. Aug 20, 2010 #2


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    Phase angle can found by using

    cosφ = R/sqrt(R^2 + XC^2)
    Last edited: Aug 20, 2010
  4. Aug 20, 2010 #3
    I dont know capacitive inductance though?????
  5. Aug 20, 2010 #4


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    Sorry. It should be XC. = 1/ωC
  6. Aug 20, 2010 #5
    Thanks that worked, although the answer was negative 89 degrees???
  7. Aug 20, 2010 #6


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    You can use the equation tan(phi)=(XL-Xc)/R for a series RCL circuit, even for XL=0 as it is the case now.

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