On Oct 31, 12:08 pm, Jim Kelley wrote:
Owen Duffy wrote:
Jim Kelley wrote in
:

Owen Duffy wrote:

Jim Kelley wrote in news:fg8c3e$kbc$1
:

I don't think it matters where it is, or how much space is involved.
For a single source to create an interferernce pattern, there must be
a reflector somewhere. An antenna tuner for example. Interference
is the result of the overlap of waves.

Jim, could a diffractor or refractor provide the physical device that
might lead to interference?

Owen

I am almost certain that you already know the answer to that
question, so I'm left to wonder why you are asking it.

No, I am not certain, and in the interest of learning from you I am
questioning the generality of whether a reflector is the only means of
creating interference from a single source.

Owen

Fair enough, Owen. The easiest way I can think of to demonstate
interference of light is with a laser and a pair of narrow, closely
spaced slits. A diffration grating is essentially an array of
slit-like reflectors that generates a more complex type of
interference pattern. You could use one of the internal surfaces of a
prism (refractor) as a reflector. Partially reflective beam splitters
or mirrors are often used in interfereometers. And there are of
course methods by which to create sonic interference. The simplest
way is to wire a pair of stereo speakers out of phase and observe the
frequency dependent phase cancellation effect by listening to music at
different positions and speaker separations.

There are any number of possible ways to generate interference
phenomena, all of which utilize real physical objects to redirect
radiation. It is the real physical objects used to create the
interference pattern that redirect energy.

73, ac6xg

You can also use pure refraction--for example through multiple prisms
whose output face is not parallel with the input face, to bend the
light around as many total degrees as you wish (barring attenuation in
the prism). You can also bend the light away, and then back, to get a
displacement. But I suppose in all these, the effect depends on waves
coming from what appear to be different points in space.

Of course, it does not require coherent sources to see the effects of
interference. Interference is an instantaneous effect, and you can
take the average over a single cycle to see the power. So even with
sources on slightly different frequencies, it's easy to see the
pattern. However, with different frequencies, the pattern is ever-
changing, repeating when the sources are all back to the starting
phase.

As H.A.S. says, "waves of average nausea" or maybe it's becoming
intense nausea. Are we sea-sick yet? Or just sick and tired of it.

Cheers,
Tom

K7ITM wrote:
Of course, it does not require coherent sources to see the effects of
interference.

True, but it does require coherent waves to accomplish
the permanent wave cancellation described at:

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."

This is what happens to the reflected waves at a Z0-match
in a transmission line.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
K7ITM wrote:
Of course, it does not require coherent sources to see the effects of
interference.

True, but it does require coherent waves to accomplish
the permanent wave cancellation described at:

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html


"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."

This is what happens to the reflected waves at a Z0-match
in a transmission line.

Cecil,

The FSU website you like to reference is a perfect example of the
problem Jim is describing.

As shown, the FSU demonstration is physically impossible. There is no
way for two plane waves to be trucking along independently and then
suddenly decide to interfere.

There is basically nothing wrong with the demo as far as it goes; it
nicely shows the effects of combined phase and amplitude on the
resulting wave. However, the demo is not rigorous science or
mathematics. It is not suitable as an authoritative reference.

73,
Gene
W4SZ

Gene Fuller wrote:
As shown, the FSU demonstration is physically impossible. There is no
way for two plane waves to be trucking along independently and then
suddenly decide to interfere.

They do NOT "truck along and then suddenly decide to
interfere". Such nonsense is just a strawman presented
for the purpose of obfuscating the technical facts.

The two independent waves are generated at a physical
impedance discontinuity, the Z0-match point, and are
immediately canceled at that point. The energy in the
canceled waves is redistributed in the only other
direction possible in a one-dimensional transmission
line.

Exactly the same thing happens when the external
reflection is canceled by the internal reflection
at a non-reflective 1/4WL thin-film coating on
glass. Quoting the Melles Groit web page:

"In the absence of absorption or scatter, the principle
of conservation of energy indicates all 'lost' reflected
intensity will appear as enhanced intensity in the
transmitted beam."

i.e. the energy re-reflected at the Z0-match joins the
forward wave toward the load. The conservation of energy
principle will not allow any other result. Dr. Best's
phantom waves continuing to flow toward the source with
zero energy is just a wet dream.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
As shown, the FSU demonstration is physically impossible. There is no
way for two plane waves to be trucking along independently and then
suddenly decide to interfere.

They do NOT "truck along and then suddenly decide to
interfere". Such nonsense is just a strawman presented
for the purpose of obfuscating the technical facts.

The two independent waves are generated at a physical
impedance discontinuity, the Z0-match point, and are
immediately canceled at that point. The energy in the
canceled waves is redistributed in the only other
direction possible in a one-dimensional transmission
line.

Exactly the same thing happens when the external
reflection is canceled by the internal reflection
at a non-reflective 1/4WL thin-film coating on
glass. Quoting the Melles Groit web page:

"In the absence of absorption or scatter, the principle
of conservation of energy indicates all 'lost' reflected
intensity will appear as enhanced intensity in the
transmitted beam."

i.e. the energy re-reflected at the Z0-match joins the
forward wave toward the load. The conservation of energy
principle will not allow any other result. Dr. Best's
phantom waves continuing to flow toward the source with
zero energy is just a wet dream.

Nice. So you don't really want to refer to the FSU page at all. Why
bring it up? The topic was about free space interference and had nothing
to do with match points.

Same ol' Cecil; try to sneak in some irrelevancy and then get agitated
when you are called on it.

73,
Gene
W4SZ

Gene Fuller wrote:
Nice. So you don't really want to refer to the FSU page at all. Why
bring it up? The topic was about free space interference and had nothing
to do with match points.

As much as you like to deny it, Gene, EM waves *are*
EM waves, no matter where they are.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

They [waves] do NOT "truck along and then suddenly decide to
interfere".

Nor do they interfere and then suddenly decide to truck along in a
different direction.

73, ac6xg

Jim Kelley wrote:

Cecil Moore wrote:
They [waves] do NOT "truck along and then suddenly decide to
interfere".

Nor do they interfere and then suddenly decide to truck along in a
different direction.

I hope we can agree that EM waves do not have
the ability to decide to do anything - that they
must obey the laws of physics, some of which humans
may have not yet discovered.
--
73, Cecil http://www.w5dxp.com

Jim Kelley wrote:
Nor do they interfere and then suddenly decide to truck along in a
different direction.

But during wave cancellation, as described by the Melles-Groit
and FSU web pages, the conservation of energy principle leaves
them no choice but that their energy be redistributed in a
different direction toward which constructive interference
can occur.

www.mellesgriot.com/products/optics/oc_2_1.htm

"Clearly, if the wavelength of the incident light and the thickness
of the film are such that a phase difference exists between reflections
of p, then reflected wavefronts interfere destructively, and overall
reflected intensity is a minimum. If the two reflections are of equal
amplitude, then this amplitude (and hence intensity) minimum will be
zero." (Referring to 1/4 wavelength thin films.)

"In the absence of absorption or scatter, the principle of conservation
of energy indicates all 'lost' reflected intensity will appear as
enhanced intensity in the transmitted beam."

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Jim Kelley wrote:

Nor do they interfere and then suddenly decide to truck along in a
different direction.


But during wave cancellation, as described by the Melles-Groit
and FSU web pages, the conservation of energy principle leaves
them no choice but that their energy be redistributed in a
different direction toward which constructive interference
can occur.

How energy redistribution is described on those web sites in not a
matter of contention.

73, ac6xg