What is the correct equation for displacement current density?

[ryanwilk]

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.

 

[Meir Achuz]

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.

 

[ryanwilk]

Ah ok, thanks a lot =)