"blackhead" <larryharson@[EMAIL PROTECTED]
> wrote in message
news:dcf5289b-d496-4929-a447-a0b312a8e916@[EMAIL PROTECTED]
> There seems to be quite a few people in this newsgroup who, when they
> can, keep bringing up the subject of E and B not causing one another,
> contrary to what is outlined in most text books.
THIS is the problem! Maxwell's equations are not (and cannot be) causal
since they represent entities that occur simultaneously. The basic idea
behind causality is very simple: A cause MUST PRECEDE an effect.
As you stated above, most textbooks teach that E causes H and vice versa.
THAT -- as I mentioned in another thread -- has caused any number of
researchers, engineers and business people to spend large amounts of time
and MONEY. The waste occurred in trying to build devices to *use* the
non-existent ability of an E field to generate an H field!
>That Jefimenko was
> the first to see this,
Actually, it looks like Panofsky was the first to express E and H in terms
of retardation and charges. I don't know if Jefimenko developed his
equations without knowing of Panofsky's work (he does not reference
Panofsky
anywhere) but it appears that they both arrived at the same basic
equations
via different procedures.
>via his equations which express E and B in
> terms of their sources at retarded time t'. E and B are functions of
> the charge density Rho(r', t'), d/dt Rho(r', t'), current density
> J(r', t'), d/dt J((r', t'), and R
>
> where R = r - r', retarded time t' = t - R/c, r is the field point at
> time t, r' is the position of the source at time t':
>
> http://en.wikipedia.org/wiki/Jefimenko's_equations
>
> On the other hand, the Lienard-Wiechert equations were derived over
> 100 years ago and, in my view, go further by exploiting the fact that
> most EM problems consist of charge moving continuously through space.
> The equations thus end up vastly simplified giving E and B just in
> terms of the position of the charge and observation point; velocity
> and acceleration of the moving charge:
>
> E_ = e[ (n_ - B_)( 1 - B^2) / k^3R^2 + n_ x (( n_ - B_) x a_) /
> c^2K^3R
>
> B_ = [_n] X E_
>
> Where:
> e = charge on moving source
> c = speed of light
> _ is a vector
> R_ is the position vector from where the charge was to the field point
> n_ = R_/R,
> _B = u_/ c
> K = 1 - B_ dot n_
>
> I don't see any advantages to using Jefimenko's over those of Lienard-
> Wiechert and would be interested in your views.
>
> Cheers.
In my opinion, the primary advantage to Jefimenko's approach lies not in
the
simplicity (or lack thereof) of the equations. It lies instead in the
logical -- and rigorous -- manner that he uses the basic idea of
causality.
Bill
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