Darren New <dne### [at] sanrrcom> wrote:
> At least, that's the naive layman understanding I use to sound like I know 
> what I'm talking about in newsgroups. ;-)

  Of course it gets more complicated when you consider that some materials
let visible light through (such as glass) while other materials don't, even
though their density might be the same.

-- 
                                                          - Warp

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On Sat, 01 Aug 2009 14:29:00 +0100, Orchid XP v8 <voi### [at] devnull> wrote:

>Listening to some music, I observe that most of the drumbeat sounds 
>appear to be in the region below 200 Hz.
>
>Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
>wavelength of about 170 cm.
>
>Question: Since the doorway to be bedroom is less than 170 cm wide, does 
>that mean those waves can't leave the room? Or does the fact that it's 
>more than 170 cm tall negate that?

Sound waves are compressional (is that a word?) and rely on a medium to travel
in. 
So tell your mother that she can't possibly be hearing them. ;)
-- 

Regards
     Stephen

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On 2-8-2009 11:22, Stephen wrote:
> On Sat, 01 Aug 2009 14:29:00 +0100, Orchid XP v8 <voi### [at] devnull> wrote:
> 
>> Listening to some music, I observe that most of the drumbeat sounds 
>> appear to be in the region below 200 Hz.
>>
>> Wolfram Alpha tells me [EVENTUALLY!] that a 200 Hz sound has a 
>> wavelength of about 170 cm.
>>
>> Question: Since the doorway to be bedroom is less than 170 cm wide, does 
>> that mean those waves can't leave the room? Or does the fact that it's 
>> more than 170 cm tall negate that?
> 
> Sound waves are compressional (is that a word?) and rely on a medium to travel
> in. 
> So tell your mother that she can't possibly be hearing them. ;)

Because Andy's mum is not a medium?

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On Sun, 02 Aug 2009 15:40:29 +0200, andrel <a_l### [at] hotmailcom> wrote:

>On 2-8-2009 11:22, Stephen wrote:
>> 
>> Sound waves are compressional (is that a word?) and rely on a medium to travel
>> in. 
>> So tell your mother that she can't possibly be hearing them. ;)
>
>Because Andy's mum is not a medium?

If she were then Andrew could give her a drink then punch her. Which would be
striking a happy medium. :P
-- 

Regards
     Stephen

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On 08/01/09 13:54, Darren New wrote:
> I think the way it works is this:
>
> X-rays actually are small enough to go between the atoms (altho they'll
> still interact with the electrons, which is why metal still stops them,
> having a "sea" of electrons on the surface).

	Here I'd rather view them as photons, to whom I do not want to attach a 
size. Perhaps the wavelength can be used to "fake" a size of the photon, 
though.

	Keep in mind that everything I say is a bit of guessing and not 
actually studied (well, not all of it at least).

> Visible light hits (most) atoms and gets absorbed, reflected, etc.

	Essentially, an electron in an atom will usually absorb a photon only 
if the photon has an energy such that there is an available energy level 
for the electron to go to. For insulators, that means it will (usually) 
have to cross the band gap. For metals, there is no (initial) band gap 
and so electrons of low frequency are readily absorbed. Perhaps that's 
why metals can easily get in the way of radio waves?

	However, I think there are higher bandgaps in metals, and so photons of 
a certain energy range will pass through.

	(Insulators also have higher bandgaps).

	There's no "true" reflection. Quoting Wikipedia:

"Light waves incident on a material induce small oscillations of 
polarisation in the individual atoms, causing each atom to radiate a 
weak secondary wave (in all directions like a dipole antenna). All of 
these waves add up to specular reflection..."

	For stuff like refraction, essentially, the material will get polarized 
by the fields of the photons trying to pass through it. This will result 
in internal electric fields that interact with that of the photon, and 
result in a reduced speed, change in direction, etc. Essentially, the 
relative permittivity that we used in physics courses is simply a model 
of the effect of polarization on the external waves.

	I find it disturbing that Wikipedia's article on refraction has no 
actual physical explanation, but I suspect I'm close. 	

> Radio waves are physically bigger than the atoms (and the whole house,
> for that matter) so they basically are ghosting along like a car through
> air.

	For me, I'd prefer to view it more in terms of photons interacting 
electrically with the solid (and/or taking into account the band 
structure) rather than size. Although as I said, perhaps one could 
produce an "effective" size which matches both what you say and the 
actual theory - although there may be materials that fail the "size" 
theory.

	When I studied solid state physics, we didn't cover interactions with 
light. And I never thought to see if there was a pattern between lattice 
constants (the spacing between atoms in the crystal), and their band 
energies. I actually expect that the relationship between the band 
energies/gaps and lattice constant is poor/nonexistent - which may 
weaken your approach of using size for intermediate frequencies.


-- 
Kotter: "Have you ever considered becoming a vet?"
Epstein: "Uh...Uh no. My brother Sanchez was in the army. Didn't like it 
a bit."

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Neeum Zawan <m.n### [at] ieeeorg> wrote:
>         I find it disturbing that Wikipedia's article on refraction has no 
> actual physical explanation

  Does science even fully agree on the physics of refraction?

-- 
                                                          - Warp

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On 08/02/09 10:01, Warp wrote:
> Neeum Zawan<m.n### [at] ieeeorg>  wrote:
>>          I find it disturbing that Wikipedia's article on refraction has no
>> actual physical explanation
>
>    Does science even fully agree on the physics of refraction?

	Don't really know. However, I think it does agree on the physics behind 
refractive index. It's just a function of the permittivity, which 
electromagnetics precisely describes (in terms of waves). I don't know 
if there's a "particle" explanation.

-- 
Kotter: "Have you ever considered becoming a vet?"
Epstein: "Uh...Uh no. My brother Sanchez was in the army. Didn't like it 
a bit."

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Neeum Zawan wrote:
>     Don't really know. However, I think it does agree on the physics 
> behind refractive index. It's just a function of the permittivity, which 
> electromagnetics precisely describes (in terms of waves). I don't know 
> if there's a "particle" explanation.

IIRC, it's accurate enough that predictions of refraction based on 
permittivity yield correct results, even for fringe cases like negative 
or really high indices of refraction.

-- 
Chambers

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:4a75aa3e@news.povray.org...
> Neeum Zawan <m.n### [at] ieeeorg> wrote:

> >         I find it disturbing that Wikipedia's article on refraction has
no
> > actual physical explanation

>   Does science even fully agree on the physics of refraction?

Yes, AFAIK, but the "problem" is that there are many levels of
understanding. Our everyday experiences can be a hindrance when trying to
understand things at a more "fundamental" level. Refraction (reflection,
dispersion, ...etc) are all emergent and not fundamental processes in QFT,
for instance. There, all you have are 1) emission of a photon  2) absorption
of a photon and the boring case of 3) unhindered transmission of a photon.
There's practically no common ground as far as the fundamental processes go
with classical wave mechanics. But it turns out, that within applicable
domains, their conclusions/predictions agree, and where they don't, we
realize we are out of the respective applicable domains.

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Darren New <dne### [at] sanrrcom> wrote:
> Light is (essentially) a traverse wave[1], which is why your microwave oven
> has little holes in the screen so you can see in without getting fried. It's
> working like you think - the light has a frequency high enough that it fits
> thru the holes, while the microwaves are bigger and bounce off.

Even this is only the case because the screen is conductive.

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