I am in trouble with this theorem. I did it from Griffith's electrodynamics but I am not getting the physics of it. So can someone explain it lucidly.
Ok, so that means that ANY system which obeys Maxwell’s equations will necessarily also obey Poynting’s theorem. It doesn’t matter if the charges are internal or external, if they move in response to the fields or in response to some other constraints, or whatever. As long as Maxwell’s equations are valid, so is Poynting’s theorem.Yes that's clear to me.