Cecil Moore wrote:

Tim Wescott wrote:

All this is covered in a good college E&M course.


Uhhhh Tim, those were rhetorical questions aimed at people
who believe that the energy in EM waves can slosh around
at sub-light speeds. Where the heck did that idea come
from anyway?

If you're responding to something you should post things as a followup,
even if it's a continuing argument -- saves us new folks to the list
some confusion.

Besides, energy in EM waves can and does travel (or "slosh around", if
there's reflections) at sub-light speeds, specifically in coax,
waveguides and just about any bulk material (including air) that has an
index of refraction higher than 1.

--
-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On Fri, 17 Jun 2005 22:37:05 +0000 (UTC), "Reg Edwards"
wrote:
Richard, now you're plagiarising Charles Dickens.

Ah Reg,

"'t'is a far, far better thing that I do, than I have ever done"

Straight from Ronald Colman, Old Son. (who the dickens is Charles?)

73's
Richard Clark, KB7QHC

A few months ago, I came upon a book that really looks like it might fill
the bill: _Engineering Electromagnetics_ by Nathan Ida. The text is clear
but doesn't skimp on math or theory. At the end of each section, there are
numerous examples showing how the concept is applied in the solution of
real problems -- something sorely missing in most other texts and, for
that matter, in a lot of college courses. For example, after the
"Inductance and Inductance" section in the "Magnetic Materials and
Properties" chapter are the following fully worked and explained examples:

Application: Self-inductance of a toroidal coil
Application: Self-inductance of a long solenoid - Inductance per unit
length
Application: Inductance per unit length of coaxial cables
Application: Mutual inductance between a wire and a toroidal core -
core memory
Mutual inductance between straight wire and loop
Self- and mutual inductances in multiple coils

It's sort of like a Shaum's Outlines and textbook combined, but in a way
that you can see the transition from the theory to practice. It's also a
good reference to use later on.

And the answers to all the problems (but no details about how they were
solved) are at the back of the book.

I was lucky and found a used one at Powell's while browsing in their
technical bookstore, but even new it's a bargain.

Roy Lewallen, W7EL

Looks interesting. I just ordered it for $79 Canadian from www.amazon.ca

Thanks,

Frank

Frank wrote:
Looks interesting. I just ordered it for $79 Canadian from www.amazon.ca

Let us know if it says anything about "sloshing" EM wave energy
including reflected light waves in free space.
--
73, Cecil http://www.qsl.net/w5dxp


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Did Maxwell ever mention the scientific concept of "sloshing"?

No. The electron had not yet been discovered.

=======================================

Electrons sloshing about in conductors, in the same general direction,
always attempt to avoid each other.

This unsociable characteristic results in a pressure which drives them
to flow near to the surface of conductors in which they are sloshing.

Hence skin and proximity effects.

There is an opposite effect. When electrons slosh about in opposite
general directions they form a great liking for each other.

The result is a mechanical attractive force between a pair of parallel
conductors carrying current in opposite directions. Also another
proximity effect.

It's all so simple. Can't imagine why you have sloshing problems. But
no doubt Cecil will introduce reflections, standing waves on meters
which don't measure them, and SHF scattering parameters. ;o)
----
Reg, G4FGQ

Reg Edwards wrote:
But
no doubt Cecil will introduce reflections, standing waves on meters
which don't measure them, and SHF scattering parameters. ;o)

How about I just introduce photons? EM waves are photonic energy
whether they are traveling in free space or in a transmission
line. How do the photons slosh around? The electrons that slosh
around are the carriers of the EM wave and are not the EM wave.

Who has published a scientific paper on photon sloshing?
--
73, Cecil http://www.qsl.net/w5dxp

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Reg Edwards wrote:
But
no doubt Cecil will introduce reflections, standing waves on meters
which don't measure them, and SHF scattering parameters. ;o)

How about I just introduce photons? EM waves are photonic energy
whether they are traveling in free space or in a transmission
line. How do the photons slosh around? The electrons that slosh
around are the carriers of the EM wave and are not the EM wave.

Who has published a scientific paper on photon sloshing?
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil, W5DXP wrote:
"If so, where does the inductance and capacitance in free space come
from to generate that 377 ohms of characteristic impedance?"

First, impedance is a voltage to current ratio as in Ohm`s law. It can
be complex if reactance and resistance are involved, but it`s still a
voltage to current ratio. Antennas radiate power which has the units of
watts, and from the expanding radiation wavefront in free space, this
amounts to watts per square meter.

A wire one meter long placed for maximum excitation when swept by the
passing wave will have a voltage induced across it equal to the wave`s
signal strength in volts per meter.

There are no volts or amps in the wave, only the ability to generate
volts and amps in conductors.

The 377 phms of characteristic impedance is the ratio of the electric
field strength to the magnetic field strength in the wave. Its purpose
is to get the units right. The ratio of energy in the electric and
magnetic components of the wave is really one to one. It is really the
same energy swapped back and forth between the electric field and
magnetic field which physically are at a right angle and both are at
right angles to the direction of travel.

Kraus has done the math for us on page 170 of the 3rd edition of
"Antennas". His answer is 376.7 ohms, a pure resistance. This is the far
field in free space.

Best regards, Richard Harrison, KB5WZI

Richard Clark wrote:
On Fri, 17 Jun 2005 15:48:08 -0500, Cecil Moore
wrote:

We can demonstrate standing waves using a laser beam normal to a perfect mirror.

"We?"

Let's see, a hypothetical argument, involving
a hypothetical "We," performing
a hypothetical analysis that contains 0 places of precision, yielding
a hypothetical answer that will be
hypothetically true and
hypothetically false
hypothetically


What if there were no hypothetical arguments? ;^)

- Mike KB3EIA -

Richard Harrison wrote:
Cecil, W5DXP wrote:
"If so, where does the inductance and capacitance in free space come
from to generate that 377 ohms of characteristic impedance?"

First, impedance is a voltage to current ratio as in Ohm`s law.

Thanks, Richard. The question was somewhat rhetorical and was aimed at
the people who believe that EM wave energy "sloshes" around in a
transmission line between the inductance and capacitance in the
transmission line and that there is really no forward EM wave energy or
momentum traveling at the speed of light and no reflected EM wave
energy or momentum traveling at the speed of light.

So I provided a mental example of a laser beam with reflections
demonstrating standing waves in free space. Except for the wavelength,
all field conditions are similiar to an RF transmission line with
standing waves. So how does the light energy "slosh" around without the
inductance and capacitance in free space?
--
73, Cecil http://www.qsl.net/w5dxp