Speed of waves
 

"Brian Howie" napisal w wiadomosci
...
In message , Szczepan Bialek
writes
"This finding had practical applications for telegraph communications. For
example, Heaviside actually solved one of the biggest problems affecting
long distance telegraph and telephone communication in 1887 -distortion.
It
was known that different frequencies travel with different speeds on a
long
cable. For example, the low bass frequencies in a voice signal travel
faster
than the high treble frequencies. When the cable is long enough, the
frequencies smear, and both voice and telegraph signals become garbled
noise. Heaviside used his equations to show that if inductances (i.e., a
small coil of wire) were added along the length of the cable, the
distortion
could be reduced." From:
http://www.ieeeghn.org/wiki/index.php/Oliver_Heaviside

" It was known that different frequencies travel with different speeds on
a
long cable".

Is the same in air and space?

Yes in air , and no in space.

Yes close to the Earth. But what is close to the Sun?
S*

Speed of waves
 

Wimpie wrote:
On 25 mar, 16:46, wrote:
Szczepan Bialek wrote:
I am simple asking if radio people have trouble with the fact that the speed
of waves are frequeny dependent.

No, they are not because the speed of electromagnetic waves is NOT frequeny
dependent, the speed is media dependent, you babbling, ignorant, trolling,
moron.

--
Jim Pennino

Remove .spam.sux to reply.

Hello Jim,

Given a certain medium, both phase and group velocity can be frequency
dependent (example: ionosphere).

The speed of light is media dependent.

The media may or may not have characteristics that are frequency dependent.

Cart - Horse.


--
Jim Pennino

Remove .spam.sux to reply.

Speed of waves
 

Brian Howie wrote:

" It was known that different frequencies travel with different speeds
on a
long cable".

Is the same in air and space?

Yes in air , and no in space.

B

Depends what you mean by "space".. perfect vacuum, sure..

But what's between the planets in the Solar System isn't a perfect
vacuum, and so, it shows dispersion due to the presence of small amounts
of ionization.

Granted, it's generally a better vacuum than you are likely to achieve
on Earth by mechanical means.

Speed of waves
 

"Jim Lux" napisal w wiadomosci
...
Brian Howie wrote:

" It was known that different frequencies travel with different speeds
on a
long cable".

Is the same in air and space?

Yes in air , and no in space.

B

Depends what you mean by "space".. perfect vacuum, sure..

But what's between the planets in the Solar System isn't a perfect vacuum,
and so, it shows dispersion due to the presence of small amounts of
ionization.

Granted, it's generally a better vacuum than you are likely to achieve on
Earth by mechanical means.

Speed of waves in a dispersive medium is temperature dependent.
In the Solar System the temperatures are decreasing with the distance from
the Sun.

You have send us: http://ipnpr.jpl.nasa.gov/progress_report/42-65/65I.PDF

It seems to me that the no answer for Maxwell's question:
"Incidentally, Maxwell once suggested that Roemer's method could be used to
test for the isotropy of light speed, i.e., to test whether the speed of
light is the same in all directions. Roemer's method can be regarded as a
means of measuring the speed of light in the direction from Jupiter to the
Earth. Jupiter has an orbital period of about 12 years, so if we use
Roemer's method to evaluate the speed of light several times over a 12 year
period, we will be evaluating the speed in all possible directions (in the
plane of the ecliptic). "

Do you know the answer?
S*

Speed of waves
 

Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Brian Howie wrote:

" It was known that different frequencies travel with different speeds
on a
long cable".

Is the same in air and space?
Yes in air , and no in space.

B
Depends what you mean by "space".. perfect vacuum, sure..

But what's between the planets in the Solar System isn't a perfect vacuum,
and so, it shows dispersion due to the presence of small amounts of
ionization.

Granted, it's generally a better vacuum than you are likely to achieve on
Earth by mechanical means.

Speed of waves in a dispersive medium is temperature dependent.

Maybe.. depends on the medium, I should think, and the mechanism of the
dispersion. Some dispersion might be due to ionization (which may or
may not be temperature dependent).

In the Solar System the temperatures are decreasing with the distance from
the Sun.


Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles.
When the number density gets down in the "few atoms per cubic meter" and
the mean free path gets to be meters or km, I think you need to start
thinking in different ways.

One common confusion is an assumption of a particular velocity
distribution in charged particles and then using the 11000K = 1 eV relation.

Speed of waves
 

"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:

Speed of waves in a dispersive medium is temperature dependent.

Maybe.. depends on the medium, I should think, and the mechanism of the
dispersion. Some dispersion might be due to ionization (which may or may
not be temperature dependent).

It is known that the speed of light in air is temperature dependent ( mirage
and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.

In the Solar System the temperatures are decreasing with the distance
from the Sun.


Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles. When
the number density gets down in the "few atoms per cubic meter" and the
mean free path gets to be meters or km, I think you need to start thinking
in different ways.

May be, but at first I must know if the mirage works in vacuum.

One common confusion is an assumption of a particular velocity
distribution in charged particles and then using the 11000K = 1 eV
relation.

Yes. But the simple measurement of the mirage or E. Schmidt's effect in
vacuum will clarify everything.
"I am sure that such experiments were done". Could you help?
S*

Speed of waves
 

Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:
Speed of waves in a dispersive medium is temperature dependent.
Maybe.. depends on the medium, I should think, and the mechanism of the
dispersion. Some dispersion might be due to ionization (which may or may
not be temperature dependent).

It is known that the speed of light in air is temperature dependent ( mirage
and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.
In the Solar System the temperatures are decreasing with the distance
from the Sun.

Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles. When
the number density gets down in the "few atoms per cubic meter" and the
mean free path gets to be meters or km, I think you need to start thinking
in different ways.

May be, but at first I must know if the mirage works in vacuum.
One common confusion is an assumption of a particular velocity
distribution in charged particles and then using the 11000K = 1 eV
relation.

Yes. But the simple measurement of the mirage or E. Schmidt's effect in
vacuum will clarify everything.
"I am sure that such experiments were done". Could you help?
S*



How about Ordinary and Extraordinary rays in the dispersive medium of
the ionosphere. Is the ionosphere "vacuum" enough for you? The space
station orbits in the middle of it, and most folks think that qualifies
as vacuum (1e-6 Torr, or so). Electron density runs pretty high: about
1E10-1E12/m3

At the top, the pressure runs about 1E-5 Pascal (7.5E-8 torr) & mean
free path is on the order of tens of km.


There's lots and lots and lots of data about dispersion of EM
propagation in the ionosphere.

Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)

Speed of waves
 

On 3/30/2011 11:50 AM, Jim Lux wrote:
Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:
Speed of waves in a dispersive medium is temperature dependent.
Maybe.. depends on the medium, I should think, and the mechanism of
the dispersion. Some dispersion might be due to ionization (which may
or may not be temperature dependent).

It is known that the speed of light in air is temperature dependent (
mirage and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.
In the Solar System the temperatures are decreasing with the
distance from the Sun.

Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles.
When the number density gets down in the "few atoms per cubic meter"
and the mean free path gets to be meters or km, I think you need to
start thinking in different ways.


(snip)


Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)

Isaac Asimov touched on this in his book on physics. He said the
temperature up there is high because of the high molecule velocity, but
that *heat* is another matter. So, you can have a high "temperature"
even if the "heat" is practically nil.

That makes you correct. One must carefully state what is meant by
temperature and what is meant by heat.

Speed of waves
 

On 3/30/2011 1:04 PM, John - KD5YI wrote:
On 3/30/2011 11:50 AM, Jim Lux wrote:
Szczepan Bialek wrote:
"Jim Lux" napisal w wiadomosci
...
Szczepan Bialek wrote:
Speed of waves in a dispersive medium is temperature dependent.
Maybe.. depends on the medium, I should think, and the mechanism of
the dispersion. Some dispersion might be due to ionization (which may
or may not be temperature dependent).

It is known that the speed of light in air is temperature dependent (
mirage and E. Schmidt's method in Fluid dynamics).
in vacuum also. But I culd find the results.
In the Solar System the temperatures are decreasing with the
distance from the Sun.

Temperature in a vacuum and with ionized particles is tricky to define.
It has to do with mean free path and the velocity of the particles.
When the number density gets down in the "few atoms per cubic meter"
and the mean free path gets to be meters or km, I think you need to
start thinking in different ways.


(snip)


Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)

Isaac Asimov touched on this in his book on physics. He said the
temperature up there is high because of the high molecule velocity, but
that *heat* is another matter.

because of extremely low molecular density at that altitude.

So, you can have a high "temperature"
even if the "heat" is practically nil.



That makes you correct. One must carefully state what is meant by
temperature and what is meant by heat.

Speed of waves
 

John - KD5YI wrote:


Again, I'm not sure "temperature" is the relevant measure for something
like that. You can define temperature for a very low pressure gas like
this, but it's not in the same sort of sense as one would apply to a
bulk tangible medium (like air at the Earth's surface or water)

Isaac Asimov touched on this in his book on physics. He said the
temperature up there is high because of the high molecule velocity, but
that *heat* is another matter. So, you can have a high "temperature"
even if the "heat" is practically nil.


I suppose, too, that the whole things still works in terms of, say,
propagation velocity of sound, because that is driven by velocity of
molecules/atoms (and is related to square root of Temperature).

So, sound propagates very quickly in the ionosphere (it's got a fairly
high temperature), but because there's not a whole lot of atoms around,
the attenuation will be quite high (essentially infinite, I suspect)

And that's totally different than propagating something by EM waves.



That makes you correct. One must carefully state what is meant by
temperature and what is meant by heat.