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Homework Help: Phasor representaion math

  1. Jan 21, 2010 #1
    http://i47.tinypic.com/2mg2iyf.jpg
    i ant to find the current in phasor representation.
    i made found the Z total 210+j232.5
    the current sourse is 2170
    [tex]I=\frac{2170}{310+j232.5}=1454.56-j1610.4[/tex]

    but the calculation igives another result
    why?
     
    Last edited: Jan 21, 2010
  2. jcsd
  3. Jan 21, 2010 #2

    cepheid

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    The first problem that comes to mind is that the 210 ohms (real part) should actually be 310 ohms.

    Also, do you know how to express a complex number in such a way that the imaginary part appears only in the numerator (i.e. there is no j on the bottom)?
     
  4. Jan 21, 2010 #3
    sorry on paper i wrote 310
    and i did multiply the numerator and denominator by the "opposite"
    of the compex number that is on the denominator

    and i got a totaly different result

    who is correct?
     
  5. Jan 21, 2010 #4

    cepheid

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    The solution in the jpg image you posted is correct. You have to multiply the expression in your first post (numerator and denominator) by the complex conjugate of the impedance and then simplify.
     
  6. Jan 21, 2010 #5
    [tex]
    I=\frac{2170(310-j232.5)}{387.5}=1176-j1302
    [/tex]

    i did that as you see
    why i still get the wrong result ?
     
  7. Jan 21, 2010 #6

    vela

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    It looks like you took the square root of the bottom. You should have zz*=|z|2 there, not |z|.
     
  8. Jan 21, 2010 #7
    thanks:)
     
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