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] nawazorg<<<<<<
                                    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"...

Post a reply to this message

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:

> Gail Shaw escribió:
>> "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

Post a reply to this message

>> 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

Post a reply to this message

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. :-}

Post a reply to this message

"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.

Post a reply to this message

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?

Post a reply to this message

"Orchid XP v7" <voi### [at] devnull> wrote in message
news:4734c9d3$1@news.povray.org...
> 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?

That's an odd question. Why would my experience with databases preclude
knowledge of science? I could as well say you're a system admin, why do you
know about Fourier Transformations?

I have a B.Sc in Physics. Wanted to go into physics as a career, but there's
no jobs other than teaching in this country.
I still read articles on astrophysics, quantum physics and relativity for
fun (when I can get the time)

I actually saw Cherenkov radiation once. Was during a trip to a nuclear
research institute, as part of a prize for coming in the top 50 in the
country's science olympiad.
It's eery to see.

btw, it's also possible to see Cherenkov radiation in the upper atmosphere
(though diffuclt to see from earth) when high velocity cosmic
particles/solar wind particles impact the atmosphere at speeds very close to
c.

Post a reply to this message

Darren New nous apporta ses lumieres en ce 2007/11/08 19:28:
> Alain wrote:
>> A wave guide have ior <1 for radio waves. You can't find the 
>> equivalent for IR and visible light.
> 
> Huh. Why not?  Just because of the size of the atoms you'd have to build 
> it from or something?
> 
A wave guide ior tend to go higher as the wave length go shorter. There is a 
wave length rhere it's ior is = 1, and at shorter wave length, it goes > 1.
If you reduce the openings, the critical wave length diminish, but only by a 
diminishing fraction of the change.

-- 
Alain
-------------------------------------------------
It is the passion that is in a kiss that gives to it its sweetness; it is the 
affection in a kiss that sanctifies it.
~Christian Nevell Bovee

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Orchid XP v7 nous apporta ses lumieres en ce 2007/11/07 16:50:
> Warp wrote:
>> Invisible <voi### [at] devnull> wrote:
>>> Mmm, I wonder if POV-Ray can do this?
>>
>>   Probably not. AFAIK povray has a very specific refraction formula, 
>> which
>> it converts to total internal reflection when needed. I'm all but certain
>> that this formula does not support the concept of negative IOR.
> 
> That was more or less my diagnosis, yes. ;-)
> 
> It's not something any typical implementation would support unless the 
> designer purposely had this in mind, I would think.
> 
> Now negative light sources........ ;-)
And negative colours, and negative diffuse, ambient, filter,  transmit, specular 
and phong.
Why not! Perfectly possible, try it!
Negative light on a negative pigment returns a positive colour.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you think 80s movies have the 
funniest special effects.
Aaron Gage a.k.a Slartibartfast

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Invisible nous apporta ses lumieres en ce 2007/11/08 07:30:
> scott wrote:
>>> I find it rather bizare that electronic properties should actually 
>>> affect optical ones, but there we are.)
>>
>> Well yeh, what's light?
> 
> It's a phenomenon that has something to do with electricity, magnetism, 
> waves and particles, but nobody really understands what exactly. ;-)
> 
> Specifically, light is an electromagnetic wave (or is it a subatomic 
> particle?) in a particular frequency range (or is that particle energy?) 
> that registers in our eyes due to the chemical transformations it 
> induces in certain protein groups.
Light is BOTH a wave AND a particle. Some times, it act more like a particle, 
other, more like a wave. So does electrons and protons.
> 
> However, it's really damn unusual for a material's electrical or 
> magnetic properties to have any bearing at all on its optical properties.
Unusual, yes. DAMN unusual, no.
> 
> * Impure water is an excellent conductor, while pure water is a very 
> good insulator. Yet both substances have almost identical optical 
> properties.
ABSOLUTELY pure water is a prety good insulator, but just the tyniest impurety 
will change it into a conductor.
> 
> * Iron is highly magnetic, while aluminium isn't. Good luck telling the 
> two metals apart by their appearence!
Prety easy just looking. Alu is much "whiter".
Telling cobalt apart from iron from platinum by apearance is much harder.
> 
> * Electricity does not, under any remotely "normal" conditions, produce 
> light or affect it in any way. (E.g., you can't bend light using 
> electricity.) The same goes for magnetism.
Since when electricity don't produce light under "normal" conditions?
> 
> Sure, theoretically they're related. But it's not something you see in 
> the real world very often. ;-)
> 
> (I still can't figure out why you can use an oscilator to make radio 
> waves, but not light rays...)
Wait till we manage to create an oscilator that can ossilate fast enough... That 
would require the construction of a nano-scaled magnetron plunged in a magnetic 
field of a few K teslas.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you think 80s movies have the 
funniest special effects.
Aaron Gage a.k.a Slartibartfast

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Invisible nous apporta ses lumieres en ce 2007/11/08 08:08:
> M_a_r_c wrote:
> 
>>> (I still can't figure out why you can use an oscilator to make radio 
>>> waves, but not light rays...)
>>
>> Is not a laser an excitated resonant optical cavity eg a oscillator?
> 
> Actually, I thought it was a tube full of extremely hot gas with some 
> mirrors at the ends? (I don't know a huge amount about lasers.)
There are laser diodes, no gas at all and barely any heat. How about crystal 
lasers, the ruby ones been the archetype of all lasers: the famous RED laser 
beam! Gas lasers use cool, and idealy COLD low presure gas, and may NOT have ANY 
mirror at all, and often only one if they have any.
Usualy, heat is the enemy of lasers: they need to stay cool to stay 
monochromatic and keep a parallel beam.
You can build a nitrogen UV laser in your kitchen! You need a large 2 faces 
project board, some coper fold, some palstic, a screw, a bunch of capacitors and 
diodes, an ossilator, a nitrogen source, a cheap water jet vacuum pump, a 
welding iron and welding strip. ANYBODY can gather all components.
I have the plans if you want. They where published in the Scientific America 
magazine, with all needed instructions, as well as the working principles.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you've ever "lost" a Julia fractal 
because you're not quite sure how to align things in four dimensions.
Dylan Beattie

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Invisible nous apporta ses lumieres en ce 2007/11/09 04:47:
> Darren New wrote:
>> Invisible wrote:
>>> However, it's really damn unusual for a material's electrical or 
>>> magnetic properties to have any bearing at all on its optical 
>>> properties.
>>
>> That's why mirrors made out of wood work so well, after all. :-)
> 
> Well, you know, there are conductive materials that are reflective, and 
> ones that aren't. There are insulators that are reflective, and ones 
> that aren't. There seems to be little correlation here.
> 
>>> * Iron is highly magnetic, while aluminium isn't. Good luck telling 
>>> the two metals apart by their appearence!
>>
>> Magnetism is a field of photons at a frequency you just can't see.
> 
> What an interesting concept...
> 
>>> * Electricity does not, under any remotely "normal" conditions, 
>>> produce light or affect it in any way. (E.g., you can't bend light 
>>> using electricity.) The same goes for magnetism.
>>
>> Except for photoelectric effects, LEDs, solar cells, florescent light 
>> bulbs, all that sort of thing.
> 
> Solar cells work by using strange chemistry rather than directly turning 
> light into electricity. (Presumably that's why they're so inefficient.)
There is NOTHING chemical about solar cells, it's all a purely physical effect.
> 
> Florescent light bulbs work by stimulating atoms to release photons, not 
> by directly turning electric oscilations into light.
> 
> I have no clue why LEDs work. But apparently they do. ;-)
They convert electrical energy directly into light without heat.
> 
>> Don't you use a computer? What do you think you're looking at?
> 
> 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.
> 
>>> (I still can't figure out why you can use an oscilator to make radio 
>>> waves, but not light rays...)
>>
>> You can. It just has to osscilate a lot faster.
> 
> I think I've found an answer for this one.
> 
>   frequency = velocity / wavelength
> 
> For light, the velocity varies a little, but it's roughly 300,000 km/s. 
> That means that even if each wave is 1 km long (pretty damn long wave!), 
> it's going to have a frequency of 300 kHz. If you make that wave 1 m 
> long, that becomes 300 MHz, and by the time you get down to an utterly 
> *microscopic* wavelength, you're well above the THz range.
> 
> AFAIK, nobody has ever made an oscilator that goes that fast... (Indeed, 
> maybe there's even a quantum-mechanical reason why you *can't* do this? 
> Don't electrons have a "frequency" after all?)
> 
> So it seems that unless you can find a material with an index of 
> refraction of several thousand, you aren't going to make light with an 
> electric oscilator.


-- 
Alain
-------------------------------------------------
Agnostic: Shit might have happened; then again, maybe not.

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Nicolas Alvarez nous apporta ses lumieres en ce 2007/11/09 10:19:
> Gail Shaw escribió:
>> "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 stationary mirror and a spinning rotor holding 8 others. Shine a light on the 
spining mirror so it encounter the stationary one. With the spining mirror 
stoped, mark where the return beam goes. Start the rotor and look as the return 
beam move.
At stop, the light hit rotor mirror #1, reatch the stationary one, return on 
rotor mirror #3. When the rotor is spining, it have moved before the light that 
hit the frist surface can return, so, it's reflected in a slightly different 
direction.
I've redone the experiment in colege. The aparatus is not that large, nor 
costly, and you only have to look in the eye piece to clearly see the movement.
You could do it yourself. You need: some mirrors, 2 razor blades, a drill, an 
eye piece, a light source, a plank of wood and some nails or screws, a dark room 
or the night. Some flat black paint is recomended.

-- 
Alain
-------------------------------------------------
Commercialism: Let's package this shit.

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Invisible nous apporta ses lumieres en ce 2007/11/09 10:21:
> 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. ;-)
Yes. the formula is simply: c = C / ior. "c" been the speed in that medium.

-- 
Alain
-------------------------------------------------
Wars are not paid for in wartime, the bill comes later.
Benjamin Franklin

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Invisible nous apporta ses lumieres en ce 2007/11/09 04:49:
> Darren New wrote:
>> Invisible wrote:
>>> bizare that electronic properties should actually affect optical 
>>> ones, but there we are.)
>>
>> Actually, the only interactions that take place outside the nucleus 
>> are between electrons (and antielectrons, I guess) and photons, so it 
>> seems pretty *necessary* more than *bizarre*. :-)
> 
> Well, sure, at quantum scales perhaps. At macroscopic scales? Well, 
> let's put it this way: there's no simple, easily observable correlation 
> between these variables in everyday life. I'm not denying that whoever 
> wrote this thing knew what they were talking about...
There are real substances that become transparent or opaque or reflective when 
exposed to some electrical field, and some that do the same if a beam of light 
hit them in a sertain way. The later are colour specific: a white beam pass 
trough, a red control beam will cause it to reflect red of the exact same wave 
length as that of the control beam. There are ongoing researches done to create 
a working computer from those. They do have some working prototypes that have 4 
states "bits" for 30 or so independent colours...

-- 
Alain
-------------------------------------------------
   It's tough to stay married. My wife kisses the dog on the lips, Yet she won't 
drink from my glass!
	Rodney Dangerfield

Post a reply to this message

Alain escribió:
>> * Impure water is an excellent conductor, while pure water is a very 
>> good insulator. Yet both substances have almost identical optical 
>> properties.
> ABSOLUTELY pure water is a prety good insulator, but just the tyniest 
> impurety will change it into a conductor.
>

I read on a website about an interesting CPU watercooling technique: 
submerging the motherboard. They still had trouble because of ions on 
the water. It's hard to get *totally* pure water...

Post a reply to this message

Nicolas Alvarez wrote:

> I read on a website about an interesting CPU watercooling technique: 
> submerging the motherboard. They still had trouble because of ions on 
> the water. It's hard to get *totally* pure water...

We have a machine at work that produces "20 mega-Ohm water".

Of course, water reacts with *air* to absorb various ions. (For example, 
CO2 disolves in water to yield carbonic acid.)

But seriously - computers work at 12V. The water's resistance would have 
to plummet to yield any meaningful current.

I would imagine a far bigger problem is water's viscosity; I'd think 
fans wouldn't like that...

Post a reply to this message

Orchid XP v7 escribió:
> I would imagine a far bigger problem is water's viscosity; I'd think 
> fans wouldn't like that...

Not really. They then had much better results with oil.

Post a reply to this message

Nicolas Alvarez nous apporta ses lumieres en ce 2007/11/09 21:28:
> Alain escribió:
>>> * Impure water is an excellent conductor, while pure water is a very 
>>> good insulator. Yet both substances have almost identical optical 
>>> properties.
>> ABSOLUTELY pure water is a prety good insulator, but just the tyniest 
>> impurety will change it into a conductor.
>>
> 
> I read on a website about an interesting CPU watercooling technique: 
> submerging the motherboard. They still had trouble because of ions on 
> the water. It's hard to get *totally* pure water...
Even if you have totally pure, desionised, degazed water, it will never stay 
that way. When you submerge your components, the water comes in contact with 
bare metal parts. Not all of those parts are of the same metal. Some of that 
metal will dissolve in the water, and, while doing so, will produce some 
current, whitch in turn will accelerate the process. Turn the power on and this 
will accelerate 100 folds.
In a few minutes, your inert water will become to conductive.

You need a non-ionic fluid like oils or other organic, non-aquous, fluid.

Alchool could be used, as well as glycerin.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you call in sick in order to render.
David Kraics

Post a reply to this message

Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 04:19:
> Nicolas Alvarez wrote:
> 
>> I read on a website about an interesting CPU watercooling technique: 
>> submerging the motherboard. They still had trouble because of ions on 
>> the water. It's hard to get *totally* pure water...
> 
> We have a machine at work that produces "20 mega-Ohm water".
> 
> Of course, water reacts with *air* to absorb various ions. (For example, 
> CO2 disolves in water to yield carbonic acid.)
> 
> But seriously - computers work at 12V. The water's resistance would have 
> to plummet to yield any meaningful current.
> 
> I would imagine a far bigger problem is water's viscosity; I'd think 
> fans wouldn't like that...
Main power is 5V for all the electronics. The 12V is for the fans and drives motors.

A good deal of the currents are counted in miliamps or less. In particular, the 
data transmition use very low curents at 5V. A leak of less than a 1 miliamp can 
easily cause malfunctions. And then, those 12V going to various motors can push 
or pull some curents into the data and address paths...

You don't need fans on a submerged system, if you keep them, it's only for the 
show with a clear case. Convection does all of the work.

-- 
Alain
-------------------------------------------------
Keep your eyes wide open before marriage, half shut afterwards.
Benjamin Franklin

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Alain wrote:
> Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 04:19:
>> Nicolas Alvarez wrote:
>>
>>> I read on a website about an interesting CPU watercooling technique: 
>>> submerging the motherboard. They still had trouble because of ions on 
>>> the water. It's hard to get *totally* pure water...
>>
>> We have a machine at work that produces "20 mega-Ohm water".
>>
>> Of course, water reacts with *air* to absorb various ions. (For 
>> example, CO2 disolves in water to yield carbonic acid.)
>>
>> But seriously - computers work at 12V. The water's resistance would 
>> have to plummet to yield any meaningful current.
>>
>> I would imagine a far bigger problem is water's viscosity; I'd think 
>> fans wouldn't like that...
> Main power is 5V for all the electronics. The 12V is for the fans and 
> drives motors.
> 
> A good deal of the currents are counted in miliamps or less. In 
> particular, the data transmition use very low curents at 5V. A leak of 
> less than a 1 miliamp can easily cause malfunctions. And then, those 12V 
> going to various motors can push or pull some curents into the data and 
> address paths...

My point was more that at a mere 12V, the resistance has to drop *very* 
low indeed for any noticable current to happen. (Ohm's law, and all that...)

Post a reply to this message

Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 17:17:
> Alain wrote:
>> Orchid XP v7 nous apporta ses lumieres en ce 2007/11/10 04:19:
>>> Nicolas Alvarez wrote:
>>>
>>>> I read on a website about an interesting CPU watercooling technique: 
>>>> submerging the motherboard. They still had trouble because of ions 
>>>> on the water. It's hard to get *totally* pure water...
>>>
>>> We have a machine at work that produces "20 mega-Ohm water".
>>>
>>> Of course, water reacts with *air* to absorb various ions. (For 
>>> example, CO2 disolves in water to yield carbonic acid.)
>>>
>>> But seriously - computers work at 12V. The water's resistance would 
>>> have to plummet to yield any meaningful current.
>>>
>>> I would imagine a far bigger problem is water's viscosity; I'd think 
>>> fans wouldn't like that...
>> Main power is 5V for all the electronics. The 12V is for the fans and 
>> drives motors.
>>
>> A good deal of the currents are counted in miliamps or less. In 
>> particular, the data transmition use very low curents at 5V. A leak of 
>> less than a 1 miliamp can easily cause malfunctions. And then, those 
>> 12V going to various motors can push or pull some curents into the 
>> data and address paths...
> 
> My point was more that at a mere 12V, the resistance has to drop *very* 
> low indeed for any noticable current to happen. (Ohm's law, and all 
> that...)
Not that much. When the distance is short and the surface relatively large, even 
10K ohm can let pass to much durrent.
On a typical computer mother board, there are 1000's of places where the 
distances are less than 0.5mm, with neigoing surfaces in the 2~3 mm square 
range. Have some 200 MHz signal passing there and you can easily get currents in 
the 0.1 miliamp range, and a parasitic current of about 0.01 miliamp is 
sometimes enough to cause malfunctions.
So, no, you don't have to have a big drop in resistivity at all.
The 20 Mohm water quickly drop to the 100Kohm range. And that's for a 1cm cube 
of water. A 1 cm travel trough a 1 cm square section. In a case where it's 0.5mm 
with a section of 2 mm square, you divide the resistance by 4! Add some 
contaminant buildup to the mixture, whose concentration is the greatest near 
those conductors, and you easily get a HUGE resistivity drop.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you stop using a protractor to 
measure angles because you can do it just by looking.
Taps a.k.a. Tapio Vocadlo

Post a reply to this message

Alain wrote:
> A wave guide ior tend to go higher as the wave length go shorter. There 
> is a wave length rhere it's ior is = 1, and at shorter wave length, it 
> goes > 1.

Huh. Very cool. Thanks for explaining.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Invisible wrote:
> Well, you know, there are conductive materials that are reflective, and 
> ones that aren't. There are insulators that are reflective, and ones 
> that aren't. There seems to be little correlation here.

I suppose if you don't understand what makes something a conductor or 
what makes it reflective, that could be the case, yes.

>>> * Electricity does not, under any remotely "normal" conditions, 
>>> produce light or affect it in any way. (E.g., you can't bend light 
>>> using electricity.) The same goes for magnetism.
>>
>> Except for photoelectric effects, LEDs, solar cells, florescent light 
>> bulbs, all that sort of thing.
> 
> Solar cells work by using strange chemistry rather than directly turning 
> light into electricity. (Presumably that's why they're so inefficient.)

Depends on the solar cell, but in general, I think when you say "strange 
chemistry", you don't understand that "chemistry" is an electromagnetic 
effect.

> Florescent light bulbs work by stimulating atoms to release photons, not 
> by directly turning electric oscilations into light.

And what is it that stimulates atoms to release photons?

> I have no clue why LEDs work. But apparently they do. ;-)

You have a crystal of semiconductor (i.e., 4 valence electrons), one 
side of which is doped with a mild concentration of atoms with 5 valence 
electrons, one with a mild concentration of 3 valence. (Say, gallium and 
arsinide.) You put negative voltage (i.e., an excess of electrons) on 
the side with 5 electrons, and it pushes them across the gap to the side 
with waiting "holes", into which they fall. As they fall, they release a 
photon of a color specific to how far they fall.

Originally, the cheapest chemicals to do this with had holes deep enough 
to emit red light. Hence the traditional red LEDs.

For bonus: A light sensitive diode is the same thing, basically, with 
less electricity. When light hits it, it knocks an electron free, which 
can then migrate across the junction and into the + side of the voltage, 
causing current that can be detected.

So LEDs both turn electricity *directly* into photons and vice versa.

>> Don't you use a computer? What do you think you're looking at?
> 
> 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.

Nope. Heat doesn't stimulate atoms to release photons. The electrons in 
atoms banging into electrons in other atoms generates photons. When you 
heat atoms up, they bang into each other much more.

But take a bunch of atoms that are very hot but going all the same way, 
and you won't get much light out, until they hit something.  You know, 
like a cosmic ray.

And, as I said, "chemical energy" is energy in the valence electrons of 
atoms. Hence, it's electromagnetic.

> So it seems that unless you can find a material with an index of 
> refraction of several thousand, you aren't going to make light with an 
> electric oscilator.

Well, no, not like that sort of thing. You'd have to use a quantum-scale 
ossilator.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Phil Cook wrote:
> A stopwatch and an astronaut with really quick reflexes.

You're not joking. The first evidence that light had a speed was someone 
(galileo?) noticing that the shadows cast by jupiter's moons on 
jupiter's clouds were not where they should have been.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Mueen Nawaz wrote:
> Darren New wrote:
>> Magnetism is a field of photons at a frequency you just can't see.
> 
> ???

I'm not sure what your question is.

What do you think carries the magnetism from the magnet to the item 
influenced by that magnet?

I'll give you a hint: It isn't electrons, and it isn't gravity, and it's 
not the strong or weak nuclear force. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Phil Cook wrote:
> And lo on Fri, 09 Nov 2007 00:41:46 -0000, Darren New <dne### [at] sanrrcom> 
> did spake, saying:
> 
>> Phil Cook wrote:
>>> On a more serious note can anyone explain refraction in terms of 
>>> particles.
>>
>> Yes.
>>
>>
http://www.amazon.com/QED-Strange-Princeton-Science-Library/dp/0691125759/ref=pd_bbs_1

>>
> Thanks, though I note one commentator said "The problem is that we never 
> get an explanation for why the vectors point the way the do, are rotated 
> just so, etc. 

That's the wrong book for *that* question. You asked "can anyone explain 
refraction in terms of particles". That's what the book answers.

That person is complaining that we don't know why the laws of physics 
are the way they are. Well, yes. But I don't think you'll ever solve 
that for the most current theories.

The book for that is this:

http://www.amazon.com/Character-Physical-Law-Modern-Library/dp/0679601279/ref=pd_bbs_10/105-9307687-6115653

I also recommend "six easy pieces" and "six not so easy pieces".

 > Without that it's simply voodoo, and nothing has been
> explained." 

He gives you a handful of rules (simplified to ignore polarization) to 
tell you how to figure out what's going to happen. This is stuff you 
determine by making measurements. He doesn't explain why the universe 
picked those rules, no.

never mind. Amazon UK stocks it, but I'll check out my local
> store first.

It's cool. Check out the two "six pieces" parts too.

The lectures on computation are from a very physical POV, fwiw. Stuff 
like explaining the quantum tensors that would let you build a truly 
quantum computer. I got very little out of it except for one or two 
insights that aren't really very useful unless you're arguing about 
turing machines or perfect randomness or some such.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Darren New wrote:
> Mueen Nawaz wrote:
>> Darren New wrote:
>>> Magnetism is a field of photons at a frequency you just can't see.
>>
>> ???
> 
> I'm not sure what your question is.
> 
> What do you think carries the magnetism from the magnet to the item 
> influenced by that magnet?
> 
> I'll give you a hint: It isn't electrons, and it isn't gravity, and it's 
> not the strong or weak nuclear force. :-)

	Fair enough. I incorrectly thought the term photon was used only for 
electromagnetic phenomena.

-- 
First Rule of Intelligent Tinkering - Save all parts.


                     /\  /\               /\  /
                    /  \/  \ u e e n     /  \/  a w a z
                        >>>>>>mue### [at] nawazorg<<<<<<
                                    anl

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>>> (I still can't figure out why you can use an oscilator to make radio 
>>> waves, but not light rays...)
>>
>> Lasers?
>
> I don't actually know how those work. I was under the impression that it 
> works by exciting atoms so that they emit photons - much the same way a 
> lump of iron glows if you put it in a hot fire. (But with some mirrors in 
> there to ensure the light only travels in one direction...)

Photons from a glowing lump of iron (or even an LED) have all different 
wavelengths and all different polarisations.  Photons from a laser all have 
virtually the same wavelength and polarisation, it's very different.

Post a reply to this message

And lo on Sun, 11 Nov 2007 23:00:37 -0000, Darren New <dne### [at] sanrrcom>  
did spake, saying:

> Phil Cook wrote:
>> A stopwatch and an astronaut with really quick reflexes.
>
> You're not joking. The first evidence that light had a speed was someone  
> (galileo?) noticing that the shadows cast by jupiter's moons on  
> jupiter's clouds were not where they should have been.

I seem to recall something about a moon being eclipsed when it shouldn't  
have been.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

Post a reply to this message

And lo on Sun, 11 Nov 2007 23:19:35 -0000, Darren New <dne### [at] sanrrcom> 
 

did spake, saying:

> Phil Cook wrote:
>> And lo on Fri, 09 Nov 2007 00:41:46 -0000, Darren New <dne### [at] sanrrco
m>  

>> did spake, saying:
>>
>>> Phil Cook wrote:
>>>> On a more serious note can anyone explain refraction in terms of  

>>>> particles.
>>>
>>> Yes.
>>>
>>> http://www.amazon.com/QED-Strange-Princeton-Science-Library/dp/06911
25759/ref=pd_bbs_1
>> Thanks, though I note one commentator said "The problem is that we  

>> never get an explanation for why the vectors point the way the do, ar
e  

>> rotated just so, etc.
>
> That's the wrong book for *that* question. You asked "can anyone expla
in  

> refraction in terms of particles". That's what the book answers.
>
> That person is complaining that we don't know why the laws of physics 
 

> are the way they are. Well, yes. But I don't think you'll ever solve  

> that for the most current theories.

so he's *describing* refraction in terms of particles not *explaining* i
t  

:-)

> The book for that is this:
>
> http://www.amazon.com/Character-Physical-Law-Modern-Library/dp/0679601
279/ref=pd_bbs_10/105-9307687-6115653
>
> I also recommend "six easy pieces" and "six not so easy pieces".
>
>  > Without that it's simply voodoo, and nothing has been
>> explained."
>
> He gives you a handful of rules (simplified to ignore polarization) to
  

> tell you how to figure out what's going to happen. This is stuff you  

> determine by making measurements. He doesn't explain why the universe 
 

> picked those rules, no.
>
> never mind. Amazon UK stocks it, but I'll check out my local
>> store first.
>
> It's cool. Check out the two "six pieces" parts too.
>
> The lectures on computation are from a very physical POV, fwiw. Stuff 
 

> like explaining the quantum tensors that would let you build a truly  

> quantum computer. I got very little out of it except for one or two  

> insights that aren't really very useful unless you're arguing about  

> turing machines or perfect randomness or some such.

Nada at various stores looks like I'm Amazon bound.

-- 

Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

Post a reply to this message

scott wrote:
>>>> (I still can't figure out why you can use an oscilator to make radio 
>>>> waves, but not light rays...)
>>>
>>> Lasers?
>>
>> I don't actually know how those work. I was under the impression that 
>> it works by exciting atoms so that they emit photons - much the same 
>> way a lump of iron glows if you put it in a hot fire. (But with some 
>> mirrors in there to ensure the light only travels in one direction...)
> 
> Photons from a glowing lump of iron (or even an LED) have all different 
> wavelengths and all different polarisations.  Photons from a laser all 
> have virtually the same wavelength and polarisation, it's very different.

True. But - at least according to Wikipedia - it's still due to making 
electrons jump between different energy levels in atoms (rather than 
building an electronic oscilator). It's just a lot more controlled than 
a whitehot lump of iron...

Post a reply to this message

Gail Shaw wrote:
> "Orchid XP v7" <voi### [at] devnull> wrote in message
> news:4734c9d3$1@news.povray.org...
>> Gail... You're a DBA. Why do you know about Chernkov radiation?
> 
> That's an odd question. Why would my experience with databases preclude
> knowledge of science? I could as well say you're a system admin, why do you
> know about Fourier Transformations?

Hey, I was being playful, not spiteful. ;-) (Just wanted to get that 
part straight...)

> I have a B.Sc in Physics. Wanted to go into physics as a career, but there's
> no jobs other than teaching in this country.
> I still read articles on astrophysics, quantum physics and relativity for
> fun (when I can get the time)

I generally read about abstract mathematical constructs and computer 
algorithms, especially to do with 3D graphics, sound synthesis, 
cryptology, data compression... wait. OK, basically about *anything*!

> I actually saw Cherenkov radiation once. Was during a trip to a nuclear
> research institute, as part of a prize for coming in the top 50 in the
> country's science olympiad.
> It's eery to see.

o_O

I thought the whole "glowing bars of radioactive stuff" was a myth...

Post a reply to this message

"Invisible" <voi### [at] devnull> wrote in message
news:47381d18$1@news.povray.org...
>
> Hey, I was being playful, not spiteful. ;-) (Just wanted to get that
> part straight...)

I didn't think you were been spiteful. Just struck me as a strange question.
But them a lot of people wonder anout some of the things I know. Wide
interestes

> > I actually saw Cherenkov radiation once. Was during a trip to a nuclear
> > research institute, as part of a prize for coming in the top 50 in the
> > country's science olympiad.
> > It's eery to see.
>
> o_O
>
> I thought the whole "glowing bars of radioactive stuff" was a myth...

It is, generally. The blue glow comes from electons emitted at very, very
high speeds passing into the surrounding water. If  the water hadn't been
there, there would have been no glow.

Some radioactive stuff does glow, most doesn't

Post a reply to this message

Gail Shaw wrote:

> Some radioactive stuff does glow, most doesn't

So... is it really true that the Earth's core is so hot due to neuclear 
reactions?

Post a reply to this message

"Invisible" <voi### [at] devnull> wrote in message
news:47382526@news.povray.org...
> Gail Shaw wrote:
>
> > Some radioactive stuff does glow, most doesn't
>
> So... is it really true that the Earth's core is so hot due to neuclear
> reactions?

I believe that the current theory is that the heat is partially a leftover
from the planet's formation, and partially from the natural decay or
radioactive elements.

I may be wrong. Geology isn't my forte.

Post a reply to this message

"Gail Shaw" <initialsurname@sentech sa dot com> a écrit dans le message de 
news: 4738267c@news.povray.org...
> I believe that the current theory is that the heat is partially a leftover
> from the planet's formation, and partially from the natural decay or
> radioactive elements.
>
> I may be wrong. Geology isn't my forte.
>
That's the theory I read in some papers as well.
They say that if there was no radio-activity, the core and the mantle  shoud 
be solid and no more magnetic field and no more protection from Van Hallen 
belt thus no more life on Earth

Marc

Post a reply to this message

And lo on Mon, 12 Nov 2007 10:12:11 -0000, Gail Shaw sa dot com>  
<"<initialsurname"@sentech> did spake, saying:

>
> "Invisible" <voi### [at] devnull> wrote in message
> news:47382526@news.povray.org...
>> Gail Shaw wrote:
>>
>> > Some radioactive stuff does glow, most doesn't
>>
>> So... is it really true that the Earth's core is so hot due to neuclear
>> reactions?
>
> I believe that the current theory is that the heat is partially a  
> leftover
> from the planet's formation, and partially from the natural decay or
> radioactive elements.
>
> I may be wrong. Geology isn't my forte.

Most of the heat is stored in the mantle which is the bit between the  
crust that we live on and the moving outer liquid core that provides the  
magnetic field. As you said the heat is made up of gravitational heat  
(friction at the Earth's creation), latent heat (the inner core cooling  
and expanding) with the majority being the decay of radioactive elements.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

Post a reply to this message

Invisible wrote:
> True. But - at least according to Wikipedia - it's still due to making 
> electrons jump between different energy levels in atoms (rather than 
> building an electronic oscilator). It's just a lot more controlled than 
> a whitehot lump of iron...

It's light amplified by stimulated emission of radiation.  The photons 
are in phase because each photon is created when another photon knocks 
an electron between energy levels. And because when that happens, they 
come out in phase.  The math isn't even that hard for someone who knows 
what a dot product is.

The light from a hot lump of iron isn't emitting stimulated light. It's 
emitting light randomly and spontaneously.

It's the same difference between a lump of plutonium sitting there 
giving off radiation and a lump of plutonium exploding in a bomb.

Hi FBI!

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Phil Cook wrote:
> And lo on Sun, 11 Nov 2007 23:00:37 -0000, Darren New <dne### [at] sanrrcom> 
> did spake, saying:
> 
>> Phil Cook wrote:
>>> A stopwatch and an astronaut with really quick reflexes.
>>
>> You're not joking. The first evidence that light had a speed was 
>> someone (galileo?) noticing that the shadows cast by jupiter's moons 
>> on jupiter's clouds were not where they should have been.
> 
> I seem to recall something about a moon being eclipsed when it shouldn't 
> have been.

Yeah, that sounds more likely. I knew it was something like that.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Mueen Nawaz wrote:
>     Fair enough. I incorrectly thought the term photon was used only for 
> electromagnetic phenomena.

Could be. But isn't that kind of what we're talking about? :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Phil Cook wrote:
> so he's *describing* refraction in terms of particles not *explaining* 
> it :-)

He explains why things work the way they do in terms of the underlying 
science.  He explains the mechanism whereby particles can refract like 
waves, which is what I thought the original question was.

It's like buying a book on how to program in C, and then complaining 
that nobody tells you why "*" is for pointers or why you need commas 
instead of spaces between the arguments to a function. Do you want to 
know how C works, or do you want to know why K&R made the decisions they 
did while designing it?  The latter is a bit more difficult when you're 
talking about fundamental physics.

> Nada at various stores looks like I'm Amazon bound.

Well worth it. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

M_a_r_c wrote:
> "Gail Shaw" <initialsurname@sentech sa dot com> a écrit dans le message de 
> news: 4738267c@news.povray.org...
>> I believe that the current theory is that the heat is partially a leftover
>> from the planet's formation, and partially from the natural decay or
>> radioactive elements.
>>
>> I may be wrong. Geology isn't my forte.
>>
> That's the theory I read in some papers as well.
> They say that if there was no radio-activity, the core and the mantle  shoud 
> be solid and no more magnetic field and no more protection from Van Hallen 
> belt thus no more life on Earth
> 
> Marc 
> 
> 
While protection from Van Hallen sounds like a good idea, it is the Van 
Allen radiation belt that you might be referring to :)

Post a reply to this message

"Paul Fuller" <pgf### [at] optusnetcomau> a écrit dans le message de news: 
4738ce31@news.povray.org...
>>
> While protection from Van Hallen sounds like a good idea, it is the Van 
> Allen radiation belt that you might be referring to :)

Ooops you're right. Protection from van Halen only requires good earplugs, 
of course :-)

Marc

Post a reply to this message

Darren New wrote:
> Mueen Nawaz wrote:
>>     Fair enough. I incorrectly thought the term photon was used only 
>> for electromagnetic phenomena.
> 
> Could be. But isn't that kind of what we're talking about? :-)

	I use the term electromagnetic only when there's an electric field 
coupled to a magnetic one. But I suppose that's merely my idiosyncrasy.

-- 
Give a man a fish and you feed him for one day. Teach him to use the Net 
and he won't bother you for weeks.


                     /\  /\               /\  /
                    /  \/  \ u e e n     /  \/  a w a z
                        >>>>>>mue### [at] nawazorg<<<<<<
                                    anl

Post a reply to this message

Mueen Nawaz wrote:
> Darren New wrote:
>> Mueen Nawaz wrote:
>>>     Fair enough. I incorrectly thought the term photon was used only 
>>> for electromagnetic phenomena.
>>
>> Could be. But isn't that kind of what we're talking about? :-)
> 
>     I use the term electromagnetic only when there's an electric field 
> coupled to a magnetic one. But I suppose that's merely my idiosyncrasy.

Probably more like because you actually studied physics. :-)

What do you call the photons that aren't coupled with both an electric 
and magnetic field?  Or no field at all, for that matter, such as 
exchange particles inside molecules?

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message