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Step up transformer

  1. Sep 26, 2008 #1
    Hi, so I know that VI = P cos (theta), but during an experiment using a step up transformer,

    I got the primary voltage 7.42V, primary current 0.41A, and primary power 3.2W. How then should I calculate the angle theta. I can't use arcosine, 'cause that will give me undefined.

    Thanks a lot.
  2. jcsd
  3. Sep 26, 2008 #2
    Doesn't sound right. You have Power in Watts (3.2) higher than the VA figure (3.042)

    And P = VI x Cos phi
  4. Sep 27, 2008 #3


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    How are you measuring the power? And the voltage and current, for that matter?

    As Pumblechook said, P should be less than or equal to V*I=3.04 VA
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