Re: Energy

[David Bowman <David_Bowman@GEORGETOWNCOLLEGE.EDU>]

Regarding Joel's question:

> Does the above discussion mean that I can consider (in the context
> of classical E&M theory) generalized current (the sum of so called
> "conduction current" and "displacement current") as an entity that
> "flows"?

No, it does not mean this.  The sum of the 'conduction current' and
the 'displacement current' does *not* satisfy a local conservation
law and, therefore, does not flow.  It is true that this sum is
divergence free and thus obeys an integral form of Kirchoff's
current law, but this is insufficient.  There is no such
"generalized charge" whose density and flux obey a continuity
equation(i.e. local conservation law).  It is the *actual* charge
density and flux that obeys such a differential continuity law.
Being locally conserved is not the same as being divergence-free
(i.e. transverse).  Being transverse (in space) for a field
quantity merely means that it can be written as a curl (in the
case of the above sum of 'currents' the curl is of the B field)
and that the lines of flux have no sources.  All such field lines
either circulate and connect back on themselves or escape to
'infinity' where the total lines escaping outward in some
directions balance those coming in from 'infinity' in other
directions.

David Bowman
David_Bowman@georgetowncollege.edu