Displacement current density

  • Thread starter ryanwilk
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  • #1
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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.

Thanks.
 

Answers and Replies

  • #2
Meir Achuz
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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.
 
  • #3
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Ah ok, thanks a lot =)
 

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