White Yeti
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World's most expensive light bulb?
I had a strange idea dating back to two years ago and didn't have the will to look further into it, until now. It's a little more physics than
chemistry.
In high school physics, you learn about the origin of electromagnetic waves and photons. Photons as quanta of energy, originate from the energy
transitions of electrons in exited atoms. Electromagnetic waves can also be created as a result of the flow of an alternating current through a wire
(or antennae). The frequency of the alternating current would correspond to the frequency of electromagnetic radiation emitted.
So theoretically, could you have a source of light resulting from electrons oscillating in a superconductor rotating 4x10^14 times every second in a
magnetic field?
This is far beyond anything I could ever try in my crummy little lab, but as a challenge, how could you get a superconductor to spin fast enough in a
magnetic field to emit visible light?
Does anyone know how you could make "gears" that would not introduce friction? Magnetic coupling of some kind that would also serve as a mechanical
advantage?
Any friction or heat losses at these speeds means the self destruction of the whole thing; hence the use of a superconductor rather than a regular
conductor.
Any ideas?
Armchair speculation is welcomed, so long as it is relevant to the topic.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Endimion17
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You can suspend it in a magnetic field in transparent glass chamber immersed in some cryogenic cooling liquid (let's use liquid helium to put an even
worse price tag on it).
Even if you could spin it by using different set of alternating magnetic fields and even if it does emit visible wavelength (not exactly my area, so
bear with me), the problem isn't the setup, but the forces involved. There's no material of any kind, let alone superconductive, that would be
able to withstand the centrifugal forces that would arise when the frequency of spinning is 10e14. Even the strongest materials we know, not
neccessarily superconductive, would burst to schrapnels way before the frequency reaches that value. Even with small spheres spinning, the
forces and velocities would be fantastically huge.
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Lambda-Eyde
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Try to calculate the largest possible diameter such a sphere would be required to have in order for the radial speed not to exceed c... 
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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phlogiston
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You are about to discover that the setup you imagine pretty much describes an atom!
In the bohr model, an electron revolves around the nucleus at a rate of approximately 2 million meters/sec. Let's use this number in a simple
calculation. One rotation in your setup takes 10^-14 seconds, so the length of one lap = 2*10^6/10^14 = 2*10^-8 meters.
A circular lap has a radius of 2*10^8/(2*pi) = 3.18 *10^-9, or 31 Angstrom.
The diameter of a real hydrogen atom is 1.1 Angstrom, so I would say the dimensions are of similar magnitude...
You can't design a device of visible dimensions by assuming faster speeds. Even if your superconductor (or the electron) were traveling at the speed
of light, the maximum radius of the rotation will turn out to be only 119 nm, invisibly small and quite a bit smaller than the light it would emit
(your rotational rate corresponds to 750 nm, or just barely visible red light)
In the days before quantum mechanics, this is exactly what puzzled phyisists: why does the electron not radiate light, losing energy in the process
and eventually fall onto to the nucleus? So your idea would work if classical physics were true. In real life, this problem led to the development of
Quantum mechanics, in which there can only be certain orbit(al)s around the nucleus, and once the electron is in the lowest energy orbital, it can't
radiate its energy to fall any closer to the nuclus.
[Edited on 27-1-2012 by phlogiston]
[Edited on 27-1-2012 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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turd
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Gosh. Is it me or is the quality of threads worsening significantly lately?
In any case, these are the expensive "light bulbs" big girls and boys play with:
https://en.wikipedia.org/wiki/Synchrotron#List_of_installati...
| Quote: | | The diameter of a real hydrogen atom is 1.1 Angstrom |
Interesting. After 1.1 Å the atom suddenly stops or how are we to understand the diameter of an atom? (Maybe you are talking about the VdW
radius or the radial electron density maximum?)
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White Yeti
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What if the magnets were also spinning in the opposite direction to that of the superconductor, thereby cutting the speed down to half (2x10^14
revolutions per second). It doesn't help out much but it's better than nothing. It might make the set-up more complex than it already is.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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phlogiston
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| Quote: | | Interesting. After 1.1 Å the atom suddenly stops or how are we to understand the diameter of an atom? (Maybe you are talking about the VdW radius or
the radial electron density maximum?) |
Not that it matters for this discussion in any way, but I took double the most probably distance between the nucleus and the electron (aka the bohr
radius) as the number for the diameter of the hydrogen atom.
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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bbartlog
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| Quote: | | What if the magnets were also spinning in the opposite direction to that of the superconductor |
If you want to move electrons around in order to see some sort of moving-electrical-charges phenomenon, you're a million times better off *just moving
the electrons* (i.e creating a current or even an arc, beta ray beam or w/e) than trying to move the heavy matter that they're attached to. In this
case, I believe that something sort of similar to what you're proposing has already been done: http://en.wikipedia.org/wiki/Free-electron_laser
The less you bet, the more you lose when you win.
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turd
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Quote: Originally posted by Lambda-Eyde  | | Try to calculate the largest possible diameter such a sphere would be required to have in order for the radial speed not to exceed c... |
Actually I expect all members to be able to do that in their head without pen and paper (at least the order of magnitude). It's bigger than I had
estimated at first.
More interesting calculations: What is the acceleration of particles at the equator of the sphere? And what kind of radiation do you expect from
charged particles subjugated to that acceleration? That's the kind of thing the poster should have worked out on paper before posting and
included in the original post. You know, showing that you have put some thought into your question. We demand that from people posting in organic
chemistry and I think the same level should be required for all Fundamental forums with the exception of Beginnings.
| Quote: | | Not that it matters for this discussion in any way, but I took double the most probably distance between the nucleus and the electron (aka the bohr
radius) as the number for the diameter of the hydrogen atom. |
Oh, I think this is more interesting than the rest of this thread, since it shows how flimsy the concept of atom size is. Your definition is a bit
like saying the border of our solar system is somewhere in the sun (I'm guessing - the highest radial mass density could also be somewhere else).
| Quote: | | If you want to move electrons around in order to see some sort of moving-electrical-charges phenomenon, you're a million times better off *just moving
the electrons* (i.e creating a current or even an arc, beta ray beam or w/e) than trying to move the heavy matter that they're attached to. In this
case, I believe that something sort of similar to what you're proposing has already been done: http://en.wikipedia.org/wiki/Free-electron_laser |
Sigh. And why do you think I have posted a link the the Wikipedia page of synchrotrons? Wigglers and undulators are not some "has already been
done"-kind of technology. It's routine "performed in numerous locations around the world 24/7"-technology. Used extensively in academia and business:
Your sample is too complex (often an euphemism for too crappy)? Send it to the synchrotron. Need a publication? Send random sample to the synchrotron.
It's that common. Beta rays? What's wrong with a CRT? 
And of course the other way to "move electrons around in order to see some sort of moving-electrical-charges phenomenon" is to apply a high frequency
electromagnetic field. Commonly know as "light". That's how these things work:
http://en.wikipedia.org/wiki/Dispersion_%28optics%29
http://en.wikipedia.org/wiki/Non-linear_optics
http://en.wikipedia.org/wiki/Second-harmonic_generation
http://en.wikipedia.org/wiki/Diffraction
The basics for all that are known for over a century:
http://en.wikipedia.org/wiki/Maxwell%27s_equations
http://en.wikipedia.org/wiki/Special_relativity
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IrC
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No it's not you. Not only that the drive through window people are getting worse if this is possible. While watching 'night of the comet' I started
thinking maybe genetic altering space dust really is coming down.
"Science is the belief in the ignorance of the experts" Richard Feynman
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phlogiston
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| Quote: |
Quote:
Not that it matters for this discussion in any way, but I took double the most probably distance between the nucleus and the electron (aka the bohr
radius) as the number for the diameter of the hydrogen atom.
Oh, I think this is more interesting than the rest of this thread, since it shows how flimsy the concept of atom size is. Your definition is a bit
like saying the border of our solar system is somewhere in the sun (I'm guessing - the highest radial mass density could also be somewhere else).
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While I must admit there are many possible definitions of 'atom size' that will give widely different numbers and you could call that 'flimsy', it is
perfectly feasible to pick a definition of atom size that is good enough for a given discussion. If you insist that everything in the world has
infinite dimensions because of the Heisenberg uncertainty, ofcourse you are right in a sense but it is not helpful to get a meaningful sense of
dimensions at the atomic level.
The solar system analogy is very poor for several reasons. If you were to apply the definition of bohr radius to the solar system, you would simply
get nearly the same result as what you expect from a classical calculation of its dimensions. The 'most probable distance' of the earth to the sun is
nearly the same as the classically defined distance, as quantum effects are negligable at planetary scales.
The 'radial mass density' you speak of is an entirely different thing. The mass of the nucleus has only a infinitely small effect on the electronic
orbitals as I am sure you are well aware. The bohr radius is not weighted by mass (or electrostatic charge, which would be the equivalent force to
gravity within an atom).
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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White Yeti
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| Quote: Originally posted by bbartlog | | If you want to move electrons around in order to see some sort of moving-electrical-charges phenomenon, you're a million times better off *just moving
the electrons* (i.e creating a current or even an arc, beta ray beam or w/e) than trying to move the heavy matter that they're attached to. In this
case, I believe that something sort of similar to what you're proposing has already been done: http://en.wikipedia.org/wiki/Free-electron_laser |
Thanks that was helpful! I didn't know that some lasers operated on this principle, tuneable too. All you'd need is a high intensity source of beta
rays and some neodymium magnets aligned around an evacuated tube.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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turd
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| Quote: | | I didn't know that some lasers operated on this principle, tuneable too. |
You should have known after the fourth post to this thread. We used to complain about people not going to the library. Too lazy to read Wikipedia
pages is a new low.
| Quote: Originally posted by phlogiston |
While I must admit there are many possible definitions of 'atom size' that will give widely different numbers and you could call that 'flimsy', it is
perfectly feasible to pick a definition of atom size that is good enough for a given discussion. |
Of course - I'm using various size definitions myself on a regular basis: https://www.sciencemadness.org/whisper/viewthread.php?tid=18... My point was not that the different definitions make the concept flimsy, but that
which ever you choose - you're trying to describe a complex (not in the sense of complex numbers, but as in with many parameters) function with a
single real. Impossible. Since many of these aspects have exponential and high order polynomial terms it may be "good enough" but there's always some
grey area. In a way chemistry is not a hard science. It's all about fuzzy similarities.
Take the Van-der-Waals radius: For light atoms it works OK, but you will always find cases where non-bonding atoms are closer than the VdW radius. Now
you could define it as the closest distance that has ever been observed, but that would be quite useless for the common case. And for fatter atoms
(e.g. Barium) - LOL. They are so soft that the whole concept just doesn't make any sense.
So people go from one to two parameters: http://en.wikipedia.org/wiki/Bond_valence_method but even that doesn't work with fat atoms, since the bond length distributions are very broad.
One exception is the scattering length of the neutron diffraction people. That's a nice number. But what is a negative length??
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White Yeti
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| Quote: Originally posted by turd | | You should have known after the fourth post to this thread. We used to complain about people not going to the library. Too lazy to read Wikipedia
pages is a new low. |
I am not lazy, I simply did not know these types of lasers existed. I can't look up something I don't know exists. If I were lazy, I would have asked
you how a synchotron or a FEL works; point out any place that shows evidence of laziness and I will take all this back
I know how synchotrons work, and apparently FELs operate on the same basic principle; deflecting the trajectories of electrons in a beam, thus
converting their kinetic energy into coherent electromagnetic radiation.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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