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AC circuit doubts

  1. Jun 19, 2010 #1
    Now this is not a homework question, just a practise question and my answer doesn't match.

    An AC source of 200 V rms supplies active power of 600 W and reactive power of 800 VAR. The rms current drawn from the source is ? (the answer is 3.75 while mine is 5)

    I did was squared and added the powers to get V^2*I^2, plugged in the value of V and got I as 5... Any help?
     
  2. jcsd
  3. Jun 19, 2010 #2

    vk6kro

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    Science Advisor

    I like your answer.

    Try it with 24 ohms resistive and 32 ohms reactive in series.
    I squared R:
    5 * 5 * 24 = 600 watts
    I squared X
    5 * 5 * 32 = 800 VAR

    resultant of r + x:
    SQ rt of (24 * 24 + 32 * 32) = 40 ohms
    200 V / 40 ohms = 5 amps
     
    Last edited: Jun 20, 2010
  4. Jun 20, 2010 #3
    p=sqrt(3)*V*I*p.f
     
  5. Jun 20, 2010 #4
    from where did that sqrt(3) factor come into? I have seen this factor before, but as far as I remember that was in 3 phase systems... And I am not dealing with such problem yet I think...
     
  6. Jun 20, 2010 #5
    sorry, my mistake, you're right dump the sqrt(3).
     
  7. Jun 20, 2010 #6
    hmm okiess... thanks all
     
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