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Invisible wrote:
> Solar cells work by using strange chemistry rather than directly turning
> light into electricity. (Presumably that's why they're so inefficient.)
From a basic perspective, the photon is absorbed by an electron and
excites it to the conduction band. Pretty direct...
> I have no clue why LEDs work. But apparently they do. ;-)
You set the conditions for an electron to drop down the band gap and
lose energy - that lost energy is the photon that is emitted.
> Electricity can be used to excite atoms in such a way that they release
> photons. So can heat energy, chemical energy, and all kinds of other
> energy. It's hardly unique to electricity. Basically if you get atoms
> excited enough, they glow.
One of the reasons people produce photons this way is probably because
it's a lot more practical and cheaper than doing it the way you want...
--
Sarchasm: The gulf between the author of sarcastic wit and the person
who doesn't get it.
/\ /\ /\ /
/ \/ \ u e e n / \/ a w a z
>>>>>>mue### [at] nawaz org<<<<<<
anl
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Mueen Nawaz wrote:
> Invisible wrote:
>> It's a phenomenon that has something to do with electricity,
>> magnetism, waves and particles, but nobody really understands what
>> exactly. ;-)
>
> Actually, I'm sure physicists believe they understand electricity
> and magnetism to the letter.
As one physicist once put it, "you never really 'understand' new
theories of physics; you just get used to them". I'm sure they have a
complete mathematical model that explains all known observations, but
that's not quite the same thing. ;-)
>> (I still can't figure out why you can use an oscilator to make radio
>> waves, but not light rays...)
>
> Just needs to oscillate at the frequency of light - I have no idea
> if it's practical, though.
Would need to be many THz - so I'm guessing "no"...
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Mueen Nawaz wrote:
> One of the reasons people produce photons this way is probably
> because it's a lot more practical and cheaper than doing it the way you
> want...
Yes. ;-)
It's also not terribly practical or cheap to make a grape levitate above
a magnet. Damn cool though...
(See what I did there?)
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And lo on Fri, 09 Nov 2007 15:19:00 -0000, Nicolas Alvarez
<nic### [at] gmailisthebestcom> did spake, saying:
>> "Invisible" <voi### [at] devnull> wrote in message
>> news:47342cbb$1@news.povray.org...
>>> For light, the velocity varies a little, but it's roughly 300,000 km/s.
>> Ur, no. The speed of light in a vacuum doesn't vary at all. It's a
>> universal
>> constant.
>> 299 792 458 m.s^-1
>
> ...
>
> How the HECK did they measure that o_O
A stopwatch and an astronaut with really quick reflexes.
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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>> Ur, no. The speed of light in a vacuum doesn't vary at all. It's a
>> universal
>> constant.
>>
>> 299 792 458 m.s^-1
>
> ....
>
> How the HECK did they measure that o_O
It's defined that way: one meter is the 1/299 792 458 part of what light
travels in one second in vacuum...
(Well one meter was defined differently in former times...)
kk
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KalleK wrote:
>> How the HECK did they measure that o_O
>
> It's defined that way: one meter is the 1/299 792 458 part of what light
> travels in one second in vacuum...
>
> (Well one meter was defined differently in former times...)
Sweet!
So how do they define 1 second? (IIRC, isn't it the amount of time it
takes for the Sodium D-line to go through some defined number of
oscilations or something?)
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"Orchid XP v7" <voi### [at] devnull> wrote in message
news:4734b5ac$1@news.povray.org...
> KalleK wrote:
>
> >> How the HECK did they measure that o_O
> >
> > It's defined that way: one meter is the 1/299 792 458 part of what light
> > travels in one second in vacuum...
> >
> > (Well one meter was defined differently in former times...)
>
> Sweet!
>
> So how do they define 1 second? (IIRC, isn't it the amount of time it
> takes for the Sodium D-line to go through some defined number of
> oscilations or something?)
Hyperfine transition of the Caesium-133 atom, iirc
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Gail Shaw wrote:
> "Orchid XP v7" <voi### [at] devnull> wrote in message
> news:4734b5ac$1@news.povray.org...
>> KalleK wrote:
>>
>>>> How the HECK did they measure that o_O
>>> It's defined that way: one meter is the 1/299 792 458 part of what light
>>> travels in one second in vacuum...
>>>
>>> (Well one meter was defined differently in former times...)
>> Sweet!
>>
>> So how do they define 1 second? (IIRC, isn't it the amount of time it
>> takes for the Sodium D-line to go through some defined number of
>> oscilations or something?)
>
> Hyperfine transition of the Caesium-133 atom, iirc
...or Caesium, yes. :-}
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"Invisible" <voi### [at] devnull> wrote in message
news:47347b15$1@news.povray.org...
> Gail Shaw wrote:
> > "Invisible" <voi### [at] devnull> wrote in message
> > news:47342cbb$1@news.povray.org...
> >> For light, the velocity varies a little, but it's roughly 300,000 km/s.
> >
> > Ur, no. The speed of light in a vacuum doesn't vary at all. It's a
universal
> > constant.
> >
> > 299 792 458 m.s^-1
>
> Yes, the speed of light *in a vacuum* doesn't vary.
>
> The speed of light in other mediums varies though. ;-)
Kinda. Maybe. Not really. Depends on your definitions. *g*
From wiki
(http://en.wikipedia.org/wiki/Speed_of_light#Interaction_with_transparent_ma
terials)
In passing through materials, the observed speed of light can differ from c.
The ratio of c to the phase velocity of light in the material is called the
refractive index. This apparent contradiction to the universality of the
constant c is a consequence of sloppy (but universally practiced)
nomenclature: what is referred to as light in a medium is really a
light-like hybrid of electromagnetic waves and mechanical oscillations of
charged or magnetic particles such as electrons or ions, whereas light in
the strict sense is a pure electromagnetic wave
---
And it is possible for particles to travel faster than the 'speed of light'
in a particular material. (Though, of course not faster than c)
This is most commonly seen around submerged nuclear reactors and is called
Cherenkov radiation. If you've ever seen a picture of a submerged reactor,
it's that eery blue glow.
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Gail Shaw wrote:
> And it is possible for particles to travel faster than the 'speed of light'
> in a particular material. (Though, of course not faster than c)
> This is most commonly seen around submerged nuclear reactors and is called
> Cherenkov radiation. If you've ever seen a picture of a submerged reactor,
> it's that eery blue glow.
Gail... You're a DBA. Why do you know about Chernkov radiation?
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