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Poynting vector and DC current

  1. Nov 1, 2016 #1
    We all know that poynting vector could be used to calculate energy transferred in AC system, but I want to know if that theorem could also be applied to DC current? How to prove this? And how to prove energy transferred in AC system could be calculated via poynting vector?
  2. jcsd
  3. Nov 1, 2016 #2


    Staff: Mentor

  4. Nov 1, 2016 #3


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    Science Advisor

    Why should DC be any different to AC?

    When electricity was invented and the first contacts closed, a transient step occurred that had a continuous Fourier spectrum, covering periods of a nanosecond out to many centuries.

    When you turn a DC LED light on at dusk, then off when you go to bed, that is just a delta function on the scale of the year. If you do it every night of the year, it becomes a year long pulse train, which has an AC component with a real DC component.

    DC is really just very low frequency AC.
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