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While investigating Wikipedia, I came across a fleeting suggestion that
a material's optical properties are somehow related to its electrical
and magnetic properties.
Obviously, this seems *highly* implausible, given the abundance of
materials with similar optical qualities but highly disimilar electrical
properties, and vice versa. On the other hand... light is supposedly
related to both electricity and magnetism in some mysterious way. So, in
principle, it seems as if it *could* be true...
Unfortunately, the article states that the parameters of interest are
"permitivity" and "permeability". I've checked the articles for both of
these, and they are entirely beyond my ability to comprehend. (But then,
so were Wikipedia's articles on DSP and filter design - which actually
turns out to be quite simple when explained _properly_.)
Does anybody here know anything about this curios idea?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> Does anybody here know anything about this curios idea?
GIYF?
http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
seems to have a pretty good summary.
As the man says, these measurements are an average of what happens when
photons run into electrons, so it's kind of like "heat" is an average of how
fast individual atoms are moving that are otherwise unrelated.
--
Darren New, San Diego CA, USA (PST)
The NFL should go international. I'd pay to
see the Detroit Lions vs the Roman Catholics.
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Darren New wrote:
> GIYF?
Pfff. Yeah, and what do you suggest I search for? "Electricity is
somehow related top optics"? :-P
> http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
> seems to have a pretty good summary.
Mmm, OK. Still not really understanding, but...
> As the man says, these measurements are an average of what happens when
> photons run into electrons, so it's kind of like "heat" is an average of
> how fast individual atoms are moving that are otherwise unrelated.
Well, yeah, but "light" as we usually thing of it is a macroscopic
phenominon too. ;-)
I'm just intrigued by the idea that measuring the electronic properties
of a substance will tell you all of its optical properties...
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> Pfff. Yeah, and what do you suggest I search for? "Electricity is
> somehow related top optics"? :-P
I searched on permitivity permeability.
>> http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
>> seems to have a pretty good summary.
>
> Mmm, OK. Still not really understanding, but...
Light reacts primarily with electrons, which absorb it, then later emit it.
Permittivity is the extent to which charges of different signs go different
directions. If an electron tends to go left more than right, it builds up a
charge on the left, which tends to make electrons keep farther away from the
left, until it's full. Like a capacitor getting full. Clearly, if optics is
affected by photons interacting with electrons, and there are more electrons
going one way than the other, you're going to get different optical properties.
Permeability is how easily a magnetic field affects the material. If it
tends to make the atoms line up, the magnetic field inside the substance
will get stronger than the magnetic field that's causing things to line up.
The "electric" field is caused by charges, i.e., protons and electrons,
which interact with photons. The "magnetic" field is caused by photons
(primarily virtual photons) flooding an area and moving charges around.
Hence the interactions between them, and the ways in which they affect optics.
> I'm just intrigued by the idea that measuring the electronic properties
> of a substance will tell you all of its optical properties...
Sure. The light you see is coming from the interactions between photons and
electrons. *Everything* outside the nucleus except gravity is interaction
between photons and electrons. All of chemistry, optics, magnetism,
electricity, heat, biology, etc is the "electronic" properties of
substances. Measuring the electronic properties of a substance will tell you
how much weight it will support, what temperature it will melt, how sticky
it is, and what color it is. :-)
It's hard to measure things that complicated, tho, at that level, because
the calculations are all infinite sums of hard-to-measure stuff. The nuclear
interactions appear to follow the same sort of rules, except with
coefficients on the factors of the infinite sums that converge much more
slowly, so you have to take many many more terms into account before you can
come up with a number that's close to what you measure.
--
Darren New, San Diego CA, USA (PST)
The NFL should go international. I'd pay to
see the Detroit Lions vs the Roman Catholics.
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> While investigating Wikipedia, I came across a fleeting suggestion that a
> material's optical properties are somehow related to its electrical and
> magnetic properties.
Of course they are, "optical" properties are just how a material responds to
a certain frequency band of electro-magnetic waves. We just think of the
optical wavelengths differently to the others because that's what our eyes
respond to.
For example, you know how light "bends" when it enters eg glass, well how
much it bends is related to the refractive index of the material. And if
you know the "electrical" properties you can calculate this refractive index
exactly (it's the square root of permittivity times permeablility of the
material).
> Obviously, this seems *highly* implausible, given the abundance of
> materials with similar optical qualities but highly disimilar electrical
> properties, and vice versa.
There is no fixed standard rule, but you can see patterns. For example how
good electrical conductors also tend to be good thermal conductors, and
completely opaque to light. Finding a good conductor that is transparent or
soft is difficult. Ditto things that are soft tend to not conduct
electricity. An exception is ceramics, which are hard and opaque, but very
good insulators, that's why they are used on electricity pylons (rubber or
plastic would suffer much worse weathering). As always, it's all in the
atomic level detail, but you can make higher level generalisations.
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scott wrote:
>> While investigating Wikipedia, I came across a fleeting suggestion
>> that a material's optical properties are somehow related to its
>> electrical and magnetic properties.
>
> Of course they are, "optical" properties are just how a material
> responds to a certain frequency band of electro-magnetic waves. We just
> think of the optical wavelengths differently to the others because
> that's what our eyes respond to.
It's more that, in everyday life, there is no way of turning light into
either electricity or magnetism. I'm sure theoretically it must be
possible somehow, but it's not something you typically observe.
> For example, you know how light "bends" when it enters eg glass, well
> how much it bends is related to the refractive index of the material.
> And if you know the "electrical" properties you can calculate this
> refractive index exactly (it's the square root of permittivity times
> permeablility of the material).
So that's the magic relationship? Those two measurements allow you to
determine the index of refraction?
Presumably knowing the *colour* of an object still requires you to
compute electron energy band gaps and weird crap like that though?
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> It's more that, in everyday life, there is no way of turning light into
> either electricity
Solar panels.
> So that's the magic relationship? Those two measurements allow you to
> determine the index of refraction?
Yes, but bear in mind those two properties will likely not be constant over
frequency (maybe one of them will be, I don't know).
> Presumably knowing the *colour* of an object still requires you to compute
> electron energy band gaps and weird crap like that though?
Probably, I don't know the details, I just know that for eg car paint there
is *a lot* of this sort of research to get colour pigments that don't fade
or change colour after 20 years in the sun. You certainly need to know your
chemistry and physics!
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>> It's more that, in everyday life, there is no way of turning light
>> into either electricity
>
> Solar panels.
And when do you *ever* see those in everyday life? ;-)
>> So that's the magic relationship? Those two measurements allow you to
>> determine the index of refraction?
>
> Yes, but bear in mind those two properties will likely not be constant
> over frequency (maybe one of them will be, I don't know).
Yeah, fair enough. This, presumably, is why we also have the index of
dispersion! :-D
>> Presumably knowing the *colour* of an object still requires you to
>> compute electron energy band gaps and weird crap like that though?
>
> Probably, I don't know the details, I just know that for eg car paint
> there is *a lot* of this sort of research to get colour pigments that
> don't fade or change colour after 20 years in the sun. You certainly
> need to know your chemistry and physics!
Heh. You know, all I was *actually* trying to find out in the first
place is whether the reflections on a coloured surface are themselves
coloured.
It seems I get rather side-tracked. Again.
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On Mon, 01 Dec 2008 11:11:43 +0000, Invisible <voi### [at] dev null> wrote:
>>> It's more that, in everyday life, there is no way of turning light
>>> into either electricity
>>
>> Solar panels.
>
>And when do you *ever* see those in everyday life? ;-)
http://www.nef.org.uk/renewableenergy/solar.htm
PV applications today are more common place than we might expect. Domestic
burglar alarm systems are now fitted with PV panels to charge the battery for
the system. In Milton Keynes, parking meters are powered by solar panels. ;)
--
Regards
Stephen
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>>> Solar panels.
>> And when do you *ever* see those in everyday life? ;-)
>
> PV applications today are more common place than we might expect. Domestic
> burglar alarm systems are now fitted with PV panels to charge the battery for
> the system. In Milton Keynes, parking meters are powered by solar panels. ;)
LOL! Like I'd know about parking meters - I never go outside, remember? ;-)
(Damnit, suddenly I feel like I'm in a Monty Python sketch. "All right,
but apart from the sanitation, the medicine, education, wine, public
order, irrigation, roads, a fresh water system, and public health, what
have the Romans ever done for us?")
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