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Phasor problem.

  1. Aug 18, 2007 #1
    Ok i have been given two trigonometric functions and asked to give them as phasors, and then calculate the average power supplied from this.

    v = 311 sin (200t+7[tex]\circ[/tex]) V

    i = 14 sin (200t - 16[tex]\circ[/tex]) A

    I'm used to the trigonometric functions being in the cosine form, what difference will this make?

    I believe it would be:
    v = 311 [tex]\angle7[/tex]
    and i=14[tex]\angle-16[/tex]

    If it was given in the cosine form. And from there it would be possible to work out the average power.

    Can anyone help me with this??

    Also i know i might need to give the magnitude in RMS form.

    EDIT: Is it 83 degrees instead? and 74 for i?
    Last edited: Aug 18, 2007
  2. jcsd
  3. Aug 19, 2007 #2
    Cosine leads sine by 90 degrees. If you wanted to use cosine to represent v and i, you would subtract 90 degrees rather than add 90.

    Vm = 311
    Im = 14

    To convert to phasor form multiply Vm and Im by .707

    Veff = 219.877
    Ieff = 9.898

    The angles remain the same.

    Pavg = Veff*Ieff*cos(theta), where theta is the phase angle between v and i.
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