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Displacement current density

  1. Jan 27, 2010 #1
    Hi, just to check which equation for Jd (the displacement current density) is correct:

    1) Jd = ε0εr(dE/dt), or
    2) Jd = ε0(εr-1)(dE/dt)

    1) came from the fact that Jd = ε(dE/dt) and ε=ε0εr
    2) came from differentiating P = ε0(εr-1)E (since Jd=dP/dt).

    It's only a minor thing but in a question I'm doing, it gives a different answer to 1 s.f. so you can't really just say that εr = εr-1.

  2. jcsd
  3. Jan 27, 2010 #2


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    The first equation is correct. The displacement current has two sources.
    One is dE/dt, and one is dP/dt, which add to each other. Your second equation is only for the dP/dt part.
  4. Jan 27, 2010 #3
    Ah ok, thanks a lot =)
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