sci.physics.electromag

"Bill Miller" wrote in message
news:xYyzj.709755$kj1.250245@bgtnsc04-news.ops.worldnet.att.net...
>
>

Please don't hack the attributes of who said what when snipping.

>>>>> 2. What "basic observation" can you cite that proves that, for
>>>>> instance, an E field CAUSES an H field?
>>>>
>>>> The fact that electro-magnets work.
>>
>>
>>> An electromagnet works because electrons are in motion; not because
>>> any causal relationship exists between an electric field and a
>>> magnetic field.
>>>
>>> Such relationship cannot be causal because E fields and H fields
>>> exist simultaneously. The basic concept of causality is that A must
>>> precede B in order for A to cause B.

>> Don't you think the E field from the electrons in motion help to make
>> the B field of the electro-magnet?
>
> There is no *measured* evidence that demonstrates any such
> relationship. There have been numerous attempts and they have all had
> null results. For a nice summary, see D.F. Bartlett, "Conduction and
> the magnetic field in a circular capacitor." Am. J. physics 58,
> 1168-1172 (1990)

I will look that up.

>>Do you think the magnetic field of the electrons in motion are enough
>>to make the total mag field of the electro-magnet?
>
> As near as I have been able to determine, the only way that a magnetic
> field can exist is through the motion of charges. This appears to be
> the case in permanent magnets also, but I have not seen rigorous
> theory -- as well as empirical evidence -- to support this contention.

I don't think it is due to motion of charges in the case of permanent
magnets but due to electron spin being aligned. In that case, it IS the
magnet moments of the electrons all adding up. No electrons are
physically moving from A to B in the magnet; however a bound current
does exist. Griffiths explains this well in "Intro. to
Electrodynamics". Now quantum theory would have you believe that
quantum spin is not due to motion but I suspect otherwise. IOW, there
is a kind of "local" motion wrt each electron. But I don't think you
can attribute the B field of a permanent magnet to actual charge density
motion.

Now, in the case of electromagnetic radiation fields, I do agree that E
and H exist simultaneously and don't cause each other. It is a long
story as to why. ;-)

Best,

Fred Diether
Co-moderator sci.physics.foundations