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I Induced potential - when do you have to consider EM waves?

  1. Dec 7, 2016 #1
    There's a long conductor carrying a 60 hz AC current. There's a second conductor parallel to the first current carrying conductor, and a hundred meters away from it.

    I want to know what the electric potential induced by the changing B field is in the second conductor.

    Theoretically I could use the biot-savart law to calculate B and then Faraday's law to calculate the induced electric potential from the changing B. However the alternating current also produces EM waves whose B field would induce an electric potential separate from that calculated by the biot-savart law as described above.

    Is it justifiable to ignore the electric potential induced by the EM waves? Why/why not? Or am I just confused?
  2. jcsd
  3. Dec 7, 2016 #2


    Staff: Mentor

    The usual rule of thumb is that you can use a "quasi static" approximation whenever the length scales are small compared to the wavelength of the EM waves. At 60 Hz the wavelengths are so much larger than 100 m that the quasi static approximation should be fine.

    See this textbook, especially ch 8
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