sci.physics.electromag

"FrediFizzx" wrote in message
news:63be46F26nj5eU1@mid.individual.net...
> "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.

OK
>
>>>>>> 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.

From the above, you can see why I said that there is no rigorous theory
supported by empirical evidence. Until someone comes up with some real-life
experiments, this issue is very much up in the air IMNTBHO.

>
> 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. ;-)

When you get your Jefimenko book, he shows just exactly why.

BTW, the E H equations he derives were also derived independently -- using
an entirely different process -- by Panofsky several years previously. See
Wikipedia's listing for Jefimenko's equations and Kirk McDonald's paper
commenting on the similarities. Kirk's paper may be found on his website.

Happy reading!

Bill

> Best,
>
> Fred Diether
> Co-moderator sci.physics.foundations