Radio waves vs light waves

Katherine,

Physicists call it "radiation pressure" and it's
measureable in a lab.


you can drive spaceships with it, though. There's a great scifi story
by Arthur C. Clarke about a solar yacht race using radiation pressure
from the sun on big "sails".

--
Thomas Borchert (EDDH)

Scrawled on a toilet stall at Caltech sometime in the early '80s:
"Heisenberg sat here yesterday."
Then, in different handwriting immediately below:
"Pauli was here at the same time."


I was there. It goes:

"Heisenberg might have been here."
"Pauli was here too, but not at the same time."

It refers to the Heisenberg uncertanty principle (one can measure the position
or momentum of a particle, but not both at the same time (*)), and the Pauli
exclusion principle (no two electrons (**) can be in the same state at the same
time)

(*) You can measure them both, but the more accurately you measure one, the
less accurate the other is. It's not too farfetched to say that the concept of
a particle having a precise position and momentum at the same time is
meaningless.

(**) Not just electrons, but an entire class of particles (called Fermions)
behave this way. Common fermions are electrons, protons, and neutrons.
Compare with Bosons, which like to be in the same state. Photons are bosons,
which is why a laser works... all the light waves can line up in step. An
electron laser would be impossible (or would lead to a huge physics advance)

All this is related to aviation in that thinking about it makes one high. g

Jose


--
(for Email, make the obvious changes in my address)

On Thu, 19 Feb 2004 13:17:36 +0100, Thomas Borchert
wrote:

Katherine,

Physicists call it "radiation pressure" and it's
measureable in a lab.


you can drive spaceships with it, though. There's a great scifi story
by Arthur C. Clarke about a solar yacht race using radiation pressure
from the sun on big "sails".

I've always wondered about the following:

Ok - so we all agree that a light puts out a small amount of force.
Newton tells us that an equal an opposite amount of force would be
directed in the opposite direction. F=ma.

So why can't we use high-intensity lights powered by a nuclear reactor
as a source of space propulsion? Is the F so small and the 'm' so
large that the 'a' would be miniscule? There's no wind resistance to
overcome in space, so you don't have to fight against that. I imagine
gravity would still be a factor though.

-Nathan

"Jay Honeck" wrote in message news:%

....Radio waves are the same as light
waves, except they're not in the visible spectrum, right?

.....I wondered aloud if the lens in my
eye was at that moment focusing powerful radio waves onto my retina.

[fade theme].......You're traveling through another dimension....a dimension not only of sight and sound but of mind....

"C J Campbell" wrote in message
Particles of light that do not make it through the window and which are
not
reflected by the surface are absorbed into the structure.

So, over the course of time your house gets lighter?

"Teacherjh" wrote in message

....Compare with Bosons, which like to be in the same state.

Not true. There used to be great herds of bosons, and they would roam
across several states in the great plains. They're gone now.

:-)

Jay

The wavelength of a VOR transmission is about 8ft long. The wavelength
of a visbile light is about 0.5 micrometer. You can fit thousands of
wavelengths inside the pupil of your eye, but you cannot fit even a
small fraction of a radio wave. For a lens to behave like a lens, its
size must be much larger than a wavelength. If it is smaller, only a
tiny fraction of a wavelength will get through. It's like trying to
squeeze a large object through a small hole. Insteading of focusing,
it simply scatters (diffracts).

If you are concerned about a VOR, consider that commercial radio and
TV stations transmit at much higher power levels. Think about that
next time you stare at a TV tower :-)




"Jay Honeck" wrote in message news:%uRYb.353608$na.522124@attbi_s04...
Okay, here's a weird one for the group: Radio waves are the same as light
waves, except they're not in the visible spectrum, right?

Here's why it matters: As we were departing from Muscatine, IA today (a
beautiful day to fly in the Midwest, BTW -- clear and warm) after a great
lunch, my gaze fell on their on-field VOR transmitter. Focusing closely on
the "Hershey's Kiss"-shaped structure (with my new glasses -- wow, what a
difference a new prescription makes!), I wondered aloud if the lens in my
eye was at that moment focusing powerful radio waves onto my retina.

Mary, a scientist with a strong physics background, was not sure if radio
waves behaved the same as light waves.

I've never heard of anyone frying their retinas by looking at a radio
transmitter, but this begs the question: Can the lens in your eye focus
radio waves?

If not, why not?

Ya did really good...
Just one point... to effectively refract i.e., focus radio waves the
antenna can be as small as one half wavelength in dimension...
If I had a chalk board on here where I could scribble and wave my hands it
would become clear - taint clear unless I talk with my hands - It's the
time/phase delay due to C that allows a half wavelength structure to
effectively refract,
i.e. the arrows all add up to the shortest path - see R. Feinman, et. al.

Larger is better, however... Look at the dish at Arecibo for example..
http://www.rainforestsafari.com/observe.html
It is an efficient focuser of very weak, short wave length, radio waves
because it is many wavelengths across, gathering numerous wave fronts in
phase, and focusing them on the sampling probe...

Similarily, a camera lens that works efficiently at lower light levels will
be larger in diameter for a given focal length than one that doesn't work as
efficiently... i.e., an f:2.8 lens versus an f:1.4 lens..

denny
"Katherine" wrote
To noticably refract radio waves, I think you'd need something with a
thickness at least on the order of the wavelength of the waves. VHF
radio has wavelengths on the order of several meters.

Hope i did all that math right,

--Kath

No, the cornea is too small in terms of wavelength to effectively refract,
focus radio waves... Plus there is the issue of the low refractive index
of the lens at radio frequencies, even were it were large enough...

That's not to say that radio waves cannot cause heating damage to the
tissues of the cornea and the retina, even if unfocused, as they pass
through your body...
The millimeter wavelengths - including your microwave oven - can certainly
heat damage body tissues, ask any hotdog...
But a discussion of that has to include the wavelengths involved, the
intensity of the radio field at that point in space, the temporal length of
exposure, etc... Too big a topic for this type of forum, but radar
technicians have accidently had eye damage from looking into a working
antenna...

Interestingly, or maybe not ham radio operators have to fill out an
engineering form that quantifies the level of exposure to radiation of
people near to their antennas and file it with the government... If you
have more than a passing interest in that item let me know and I'll refer
you to the relevant literature...

cheers ... denny

"Jay Honeck" wrote I wondered aloud if the lens
in my
eye was at that moment focusing powerful radio waves onto my retina.

There used to be great herds of bosons, and they would roam
across several states in the great plains. They're gone now.


Nope. They are in Washington DC. All in the same state. The state of
confusion.

Jose

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(for Email, make the obvious changes in my address)