Re: Expanding Space

From: George Dishman (george_at_briar.demon.co.uk)
Date: 03/01/05 

Date: Tue, 1 Mar 2005 21:20:03 -0000

"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com> wrote in
message news:FE3Vd.82617$Yu.24620@fed1read01...
> Dear George Dishman:
>
> "George Dishman" <george@briar.demon.co.uk> wrote in message
> news:d02enq$ets$1@news.freedom2surf.net...
>>
>> "N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com> wrote in
>> message news:Ut_Ud.82583$Yu.28642@fed1read01...
>>> Dear Rudolf Drabek:
>>>
>>> "Rudolf Drabek" <rdrXs@aon.at> wrote in message
>>> news:422430c4$0$15788$91cee783@newsreader01.highway.telekom.at...
>>>>...
>>>> For me the carrier of the field is the copper and the spacer.
>>>
>>> Actually the signal in the coax is carried along the outer "layer" of
>>> the copper, and the inner layer of the shield. Barely constrained to the
>>> metal...
>>
>> David, what's your view of the Poynting vector ?
>
> I'm a mechanical engineer, so my comments will be uninteresting.

OK, I can't find a good diagram on the web but have a look at
these:

http://www.ati.surrey.ac.uk/preprint_docs/Jefferies2004Nov10155325.pdf

http://www.sp.phy.cam.ac.uk/teaching/em/transmit.pdf

The point is that although the curent flows along the wire,
the enrgy flows in the space around it.

> I just came across the discussion of where current ran, as a function of
> frequency. And I note that some very high frequency stuff has a
> metal-braided non-conductive fiber rope as the center conductor of "coax"
> cable.

"Skin effect" means that at high frequencies, the current
flows on the surface, not in the bulk of the material,
but that is different from the energy flow.

> Some interesting stuff involving crossed field antennas though. I suppose
> that is how "fractal" antennas (such as used in cell phones) work...
> URL:http://www.ee.surrey.ac.uk/Personal/D.Jefferies/poynting.html

That does ask some interesting questions about the
conventional interpretation but if you have ever
strapped a neon onto a feed wire, you'll know where
the energy flows ;-)

George

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