Are electrons the only thing that emits light?


by um0123
Tags: electrons, emits, light, thing
um0123
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#1
Aug3-09, 01:08 AM
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WARNING NOOB QUESTION FOLLOWS:

Well this has been bugging me lately, as i have been doing research on maxwells equations. In chemistry i was taught that light from chemical reactions comes from electrons jumping from a higher orbit to a lower one. But is ALL light emitted this way, or only light that comes from chemical reactions? For instance, are the electrons in my desk always jumping to create the brown color of wood?

In my research i found that a changing electric field creates a magnetic field that also is changing to create an electric field. And this creates light.

I do not doubt that the electrons jumping down an orbit gives off light, but is the only thing that gives off light? This would mean all object's electrons jump from the exact same point to give off the exact same color at all times.
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vanesch
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Aug3-09, 02:14 AM
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For visible light, I think you can say safely that most of visible light you will ever see has to do with moving electrons, yes.
In principle, every charged particle can emit light by moving, but from the top of my head, I can't think of many that produce actual *visible* light and aren't electrons.
um0123
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Aug3-09, 02:17 AM
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Quote Quote by vanesch View Post
For visible light, I think you can say safely that most of visible light you will ever see has to do with moving electrons, yes.
In principle, every charged particle can emit light by moving, but from the top of my head, I can't think of many that produce actual *visible* light and aren't electrons.
So i was right when i said that the electrons on my desk (or any other object) always jump from the the same place on one orbit to the same place on the lower orbit to produce the same color frequency?

That just doesnt seem right to me.

Lok
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Aug3-09, 04:33 AM
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Are electrons the only thing that emits light?


Quote Quote by vanesch View Post
For visible light, I think you can say safely that most of visible light you will ever see has to do with moving electrons, yes.
In principle, every charged particle can emit light by moving, but from the top of my head, I can't think of many that produce actual *visible* light and aren't electrons.
Not sure... but I thought that black body radiation was the result of vibration of the atomic nucleus.
Vanadium 50
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Aug3-09, 04:49 AM
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Quote Quote by Lok View Post
Not sure... but I thought that black body radiation was the result of vibration of the atomic nucleus.
It's not. A nucleus will radiate if you shake it hard enough, but that's not where black body radiation comes from.
Lok
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Aug3-09, 04:52 AM
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Thanks. This time I'll remember it.

Weird how that turns the light off in neutron stars :P
chi22
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Aug3-09, 08:42 AM
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"In 1965, Antony Hewish and Samuel Okoye discovered "an unusual source of high radio brightness temperature in the Crab Nebula." - Wikipedia


Some more info could be found here, have fun
sylas
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Aug3-09, 09:23 AM
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Quote Quote by Vanadium 50 View Post
It's not. A nucleus will radiate if you shake it hard enough, but that's not where black body radiation comes from.
Quite right... but I think I know where the mix up comes.

Light and electromagnetic energy comes from vibrations of molecules and lattices, which is not vibration of a single nucleus, but of one nucleus in relation to another. Stuff is generally held together by electromagnetic forces of one kind or another, and the distributions of charge in a substance are not uniform from nucleus to nucleus. For example, a co-valent bond often has a disparity of charge to one of the nuclei involved, and so oscillations of the particles produce and absorb electromagnetic radiation. The charge differences are still about how the electrons are shared in the bonds.

Cheers -- sylas
Bob S
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Aug3-09, 12:40 PM
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This is a very good question. Everything we can see outside of cosmology is based on radiation from electrons in some way or another. The only thing atomic nuclei do is by holding electrons together in atomic states and by neutralizing the huge Coulomb forces of electrons alone.
I can name two sources of light created by atomic nuclei (outside of radioactive decay).
Any charged particle traveling faster than c/n in a material (water, glass, plastic, etc.) with index of refraction n will radiate. This is called Cerenkov (also spelled Cherenkov) radiation. Electron Cerenkov radiation is easily seen in pool-type reactors and in used radioactive fuel rods stored under water. I have used equipment to detect visible photons from Cerenkov radiation from protons, kaons, muons, and pions.
Any relativistic charged particle that is deflected with a strong magnetic field will radiate synchrotron radiation. Electrons do it. In the Superconducting Super Collider (cancelled), proton synchrotron radiation was a serious problem, This might also be true in the CERN LHC.
vanesch
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Aug3-09, 01:18 PM
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Quote Quote by Bob S View Post
This is a very good question. Everything we can see outside of cosmology is based on radiation from electrons in some way or another. The only thing atomic nuclei do is by holding electrons together in atomic states and by neutralizing the huge Coulomb forces of electrons alone.
But even within cosmology... do you know many light (visible) sources where the emission is not due to the motion of electrons ?

I can name two sources of light created by atomic nuclei (outside of radioactive decay).
I don't know any radioactive decay which gives rise to light. Of course, radioactive decay can give rise to ionisation and excitation, which produces light, but we're back to electrons, no ?

Any charged particle traveling faster than c/n in a material (water, glass, plastic, etc.) with index of refraction n will radiate. This is called Cerenkov (also spelled Cherenkov) radiation. Electron Cerenkov radiation is easily seen in pool-type reactors and in used radioactive fuel rods stored under water. I have used equipment to detect visible photons from Cerenkov radiation from protons, kaons, muons, and pions.
Ok, that's true in high energy physics. Indeed, when I think of Cherenkov radiation, I think of fast electrons, but you can have Cherenkov radiation from particles when the particles are *really* fast. This is the first example I see.

Any relativistic charged particle that is deflected with a strong magnetic field will radiate synchrotron radiation. Electrons do it. In the Superconducting Super Collider (cancelled), proton synchrotron radiation was a serious problem, This might also be true in the CERN LHC.
I didn't know that proton synchrotron radiation was ueberhaupt even noticeable in existing machines. I'm a bit surprised because I thought that synchrotron radiation goes as the fourth power of mass (inversely), so for a proton which is about 2000 times heavier than an electron, for the same state of motion, a proton emits about 10^13 times less radiation than an electron. That said, in LHC, the energy is also about 100 times higher for the protons than for the electrons in LEP.
Second example indeed !
jtbell
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Aug3-09, 01:28 PM
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Quote Quote by um0123 View Post
In my research i found that a changing electric field creates a magnetic field that also is changing to create an electric field. And this creates light.

I do not doubt that the electrons jumping down an orbit gives off light, but is the only thing that gives off light? This would mean all object's electrons jump from the exact same point to give off the exact same color at all times.
The emission of light when an atomic electron makes a transition between two orbitals (not "orbits") is not described by classical electrodynamics. The classical formulas for radiation by a moving charge do not apply here. This is a quantum mechanical phenomenon.

QM tells us that the electron has a definite energy before the transition, according to which orbital the electron is in; but it does not tell us where, precisely, the electron is. It gives us only a probability distribution for finding the electron in various locations near the nucleus. Similarly after the transition, QM tells us that the electron has a definite (different) energy, according to which orbital the electron is now in; but again it gives us only a (different) probability distribution for the location of the electron.
LeonhardEuler
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Aug3-09, 01:43 PM
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Quote Quote by um0123 View Post
So i was right when i said that the electrons on my desk (or any other object) always jump from the the same place on one orbit to the same place on the lower orbit to produce the same color frequency?

That just doesnt seem right to me.
That isn't quite right. Each individual electron in your desk does not always make the same exact transition every time. If they did, your desk would not be brown since there is no such thing as a brown photon. What you see is the result of a vast number of electronic transitions of different types. The reason you don't see the color of your desk changing very quickly as different frequencies are emitted is that you what you see is averaged over a period of time and averaged over a range of space so that the number of emitted photons is so large that the average effect is constant to within the precision your eye can perceive.

To be clear, I'm not saying this is true only of brown objects, I'm just saying it is especially obvious in that case because the color brown could not possibly be produced by a stream of a single type of photon.
Dadface
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Aug3-09, 02:06 PM
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Quote Quote by um0123 View Post
WARNING NOOB QUESTION FOLLOWS:

Well this has been bugging me lately, as i have been doing research on maxwells equations. In chemistry i was taught that light from chemical reactions comes from electrons jumping from a higher orbit to a lower one. But is ALL light emitted this way, or only light that comes from chemical reactions? For instance, are the electrons in my desk always jumping to create the brown color of wood?

In my research i found that a changing electric field creates a magnetic field that also is changing to create an electric field. And this creates light.

I do not doubt that the electrons jumping down an orbit gives off light, but is the only thing that gives off light? This would mean all object's electrons jump from the exact same point to give off the exact same color at all times.
There is bioluminescence which is displayed by glow worms ,fireflies and many other organisms including, I believe, many deep sea creatures.I think the light is caused by biochemical reactions and therefore I am assuming that these involve electron transitions.
Bob S
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Aug3-09, 02:19 PM
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Quote Quote by vanesch View Post
But even within cosmology... do you know many light (visible) sources where the emission is not due to the motion of electrons ?!
We don't, but cannot rule it out. What is the source of extremely energetic photonic cosmic rays?
I don't know any radioactive decay which gives rise to light. Of course, radioactive decay can give rise to ionisation and excitation, which produces light, but we're back to electrons, no ?!
Are there any nuclear transitions that can emit visible photons (~ 2 to 3 eV), and visible pehaps if we had billions of Curies?
Ok, that's true in high energy physics. Indeed, when I think of Cherenkov radiation, I think of fast electrons, but you can have Cherenkov radiation from particles when the particles are *really* fast. This is the first example I see. !
I have used Cerenkov counters to separate charged muons from pions, and kaons from pions, in beams- it requires 1 ns timing resolution..
I didn't know that proton synchrotron radiation was ueberhaupt even noticeable in existing machines. I'm a bit surprised because I thought that synchrotron radiation goes as the fourth power of mass (inversely), so for a proton which is about 2000 times heavier than an electron, for the same state of motion, a proton emits about 10^13 times less radiation than an electron. That said, in LHC, the energy is also about 100 times higher for the protons than for the electrons in LEP.
Second example indeed !
Proton synchrotron radiation, and by extension anti-proton (anti?) radiation, is visible at the Tevatron. See photo image of proton synchrotron radiation in http://beamdocs.fnal.gov/DocDB/0013/...GapMonitor.pdf
One of the major unsolved problems in the SuperConducting Supercollider was UV proton synchrotron radiation dislodging atoms of residual gas that had adhered to the walls of the 2 Kelvin vacuum tube, thus raising the residual gas pressure to an untenable level..Maybe this will be a problem in the LHC. We shall see......
um0123
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Aug3-09, 03:23 PM
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Woah! lots of good information here. Some of it i didn't umderstand because im only 16 and still havent even taken physics class (taking it this yea when school starts up again, and thats why i said "in my research" instead of "in school").

It seems all my questions spark debates which lead the conversation off topic, but in doing so i learn even more. But i was able to fully understand LeonhardEuler's answer and now i understand. And i am very grateful for everyone else's replies also which gave me more interesting things to research.

I can always rely on Physics Forums for a good answer and more!
vanesch
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Aug3-09, 11:58 PM
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Quote Quote by Bob S View Post
We don't, but cannot rule it out. What is the source of extremely energetic photonic cosmic rays?
Ok, but that's not *visible*

Are there any nuclear transitions that can emit visible photons (~ 2 to 3 eV), and visible pehaps if we had billions of Curies?
I'm not aware of any, but then I don't know all nuclear data by heart either...

I have used Cerenkov counters to separate charged muons from pions, and kaons from pions, in beams- it requires 1 ns timing resolution..
Cherenkov, or transition radiation ?

Proton synchrotron radiation, and by extension anti-proton (anti?) radiation, is visible at the Tevatron. See photo image of proton synchrotron radiation in http://beamdocs.fnal.gov/DocDB/0013/...GapMonitor.pdf
One of the major unsolved problems in the SuperConducting Supercollider was UV proton synchrotron radiation dislodging atoms of residual gas that had adhered to the walls of the 2 Kelvin vacuum tube, thus raising the residual gas pressure to an untenable level..Maybe this will be a problem in the LHC. We shall see......
I believe you, but I'm amazed.


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