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Homework Help: Complex Power, calc load impedance

  1. Nov 30, 2012 #1
    1. The problem statement, all variables and given/known data

    A load absorbs 58959W at a lagging power factor of pf = 0.73. If the current flowing through the load is ix = 0.001A-rms , determine the impedance of the load.

    2. Relevant equations

    Ohms law
    Impedance/Voltage/Power Triangles

    3. The attempt at a solution
    If the load absorbs 58959W, I'm assuming that is apparent power (S)

    If 58959W is S then by Pavg = S*pf = Irms2R

    R = 58959*.73/.0012 = 43.04 GΩ (must be wrong...)

    I would then take R/pf = Z... but the number gets more ridiculous. How am I going about this wrong?
  2. jcsd
  3. Nov 30, 2012 #2


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    Staff: Mentor

    Apparent power is usually specified in VA rather than W. Real power is given in W, reactive power in VAR.
  4. Nov 30, 2012 #3
    then 58959 = Pavg

    and Pavg = irms2 * R

    so 58959/.0012 = R = 5.9 * 1010

    Z = R/pf = 5.9 * 1010 / 0.73
  5. Nov 30, 2012 #4


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    Staff: Mentor

    Okay, but usually an impedance is specified by its real and reactive components (it's actually a complex number), or in magnitude and angle form.
  6. Nov 30, 2012 #5
    ah that's what was wrong with my input.. lol. Thanks gneill
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