alpha2cen Posted January 5, 2011 Share Posted January 5, 2011 When photons collide with the surface electron of the solid surface, electrons are released from the surface. We know the photons energy is transformed into electron release. Then, Where are the photons gone? Link to comment Share on other sites More sharing options...
ajb Posted January 5, 2011 Share Posted January 5, 2011 (edited) There is no conservation of photon number or similar in electromagnetism, so photons can "just disappear" when interacting with charged particles. Edited January 5, 2011 by ajb Link to comment Share on other sites More sharing options...
alpha2cen Posted January 5, 2011 Author Share Posted January 5, 2011 There is no conservation of photon number or similar in electromagnetism, so photons can "just disappear" when interacting with charged particles. Then what's the difference between the temperature rising and electron releasing? Einstein's photoelectric effect considers the light as particle. The kinetic energy of the photon is transfered to electron, and the electron is released form the surface of the solid. If the photon were disappeared, how we would tell the light as a particle? Link to comment Share on other sites More sharing options...
swansont Posted January 5, 2011 Share Posted January 5, 2011 Then what's the difference between the temperature rising and electron releasing? Einstein's photoelectric effect considers the light as particle. The kinetic energy of the photon is transfered to electron, and the electron is released form the surface of the solid. If the photon were disappeared, how we would tell the light as a particle? Not sure I understand the first question. Temperature is a collective property, of an ensemble of particles. We can tell it's a "particle" (quantized energy) because the wave description fails to explain the result, and the quantum one does. Link to comment Share on other sites More sharing options...
alpha2cen Posted January 5, 2011 Author Share Posted January 5, 2011 Not sure I understand the first question. Temperature is a collective property, of an ensemble of particles. This means the transform form light energy to solid state heat energy . Light energy to intermolecular vibration energy, or light energy to electron moving energy. Do we know this step more detail? Link to comment Share on other sites More sharing options...
lemur Posted January 5, 2011 Share Posted January 5, 2011 Then what's the difference between the temperature rising and electron releasing? I'm no expert, but I think you should look at the relationship between electricity- and heat-transfer through a conductor. Heat is caused by vibrations that include the atomic nuclei, I believe, whereas electricity leaves the nuclei relatively immobilized (cold) while energy necessarily transfers through the electrons. When photons hit atoms, they only have limited options of how to dissipate their energy: 1) they can generate heat by vibrating the nuclei 2) they can generate electricity by vibrating the electrons without that energy transferring to the nuclei to generate heat 3) they can be absorbed and re-emitted by the electrons as new photons. Are there any other options? Maybe passing through the atom without striking any particle? Maybe resulting in direct re-configurations of particles in the form of chemical changes? I can't think of anything else. Link to comment Share on other sites More sharing options...
mississippichem Posted January 5, 2011 Share Posted January 5, 2011 I'm no expert, but I think you should look at the relationship between electricity- and heat-transfer through a conductor. Heat is caused by vibrations that include the atomic nuclei, I believe, whereas electricity leaves the nuclei relatively immobilized (cold) while energy necessarily transfers through the electrons. When photons hit atoms, they only have limited options of how to dissipate their energy: 1) they can generate heat by vibrating the nuclei 2) they can generate electricity by vibrating the electrons without that energy transferring to the nuclei to generate heat 3) they can be absorbed and re-emitted by the electrons as new photons. Are there any other options? Maybe passing through the atom without striking any particle? Maybe resulting in direct re-configurations of particles in the form of chemical changes? I can't think of anything else. Yeah the photons can induce a chemical change, but that's just the result of an electron absorbing a photon, reaching a higher energy state to facilitate a chemical reaction, and then emitting a photon as the new molecule relaxes to the ground state through various channels. Some bonds are so weak they can be broken just by excitement to a higher vibrational level. Link to comment Share on other sites More sharing options...
lemur Posted January 5, 2011 Share Posted January 5, 2011 Yeah the photons can induce a chemical change, but that's just the result of an electron absorbing a photon, reaching a higher energy state to facilitate a chemical reaction, and then emitting a photon as the new molecule relaxes to the ground state through various channels. Some bonds are so weak they can be broken just by excitement to a higher vibrational level. Is there a difference between a chemical change that occurs through heat (vibration of the atoms/molecules) and one that occurs specifically due to absorption of photons and the associated change in energy-state/level? Link to comment Share on other sites More sharing options...
mississippichem Posted January 5, 2011 Share Posted January 5, 2011 Is there a difference between a chemical change that occurs through heat (vibration of the atoms/molecules) and one that occurs specifically due to absorption of photons and the associated change in energy-state/level? Short answer, yes. A lot of the photon initiated reactions result in homolytic cleavage of bonds (one electron of the bond goes with one molecular fragment while the other electron goes with the other fragment). Most common chemical reactions are thermally driven though and bonds are cleaved heterolytically, (broken into + and - ions). There are many exceptions. Many thermo-initiated reactions result in a homolytic event. Spectroscopy and computation have just now, in the last twenty years or so, become sensitive enough to really study the mechanisms of many photochemical and homolytic reactions. The advent of single molecule EPR spectroscopy as well as the advent of DFT in the chemistry world have done wonders. Photochemistry is a field that I think will become more and more valuable as time goes on and energy needs become more dire. There is a lot of rich and interesting QM in photochemistry as well. *Just because a reaction is photo-initiated doesn't mean it isn't thermodynamically favored though. Link to comment Share on other sites More sharing options...
lemur Posted January 5, 2011 Share Posted January 5, 2011 *Just because a reaction is photo-initiated doesn't mean it isn't thermodynamically favored though. what do you mean by "thermodynamically favored?" Link to comment Share on other sites More sharing options...
mississippichem Posted January 5, 2011 Share Posted January 5, 2011 what do you mean by "thermodynamically favored?" A good question with a lengthy answer that risks me hijacking the thread so here are some links: fundamental thermodynamic relationship Gibb's free energy enthalpy Basically if something is thermodynamically favored, then the universe "wants" this action to take place. That borders on a gross oversimplification though. One really needs the math to comprehend it well. Language is hot air, equations speak concisely. Link to comment Share on other sites More sharing options...
lemur Posted January 5, 2011 Share Posted January 5, 2011 Basically if something is thermodynamically favored, then the universe "wants" this action to take place. That borders on a gross oversimplification though. One really needs the math to comprehend it well. Language is hot air, equations speak concisely. I don't think in equations OR language. I think in concepts and I use language to describe them. I am not skilled or practiced in the language of math so I usually use English. By thermodynamic favoring, it sounds like you're talking about the tendency for energy to disipate in the direction of less energy. You basically are saying that a chemical reaction is prone to react due to something that could be described loosely as potential energy, which has a tendency to become kinetic and chain-react once initiated/catalyzed, no? Link to comment Share on other sites More sharing options...
mississippichem Posted January 6, 2011 Share Posted January 6, 2011 (edited) I don't think in equations OR language. I think in concepts and I use language to describe them. I am not skilled or practiced in the language of math so I usually use English. By thermodynamic favoring, it sounds like you're talking about the tendency for energy to disipate in the direction of less energy. You basically are saying that a chemical reaction is prone to react due to something that could be described loosely as potential energy, which has a tendency to become kinetic and chain-react once initiated/catalyzed, no? Yes, you've got the general idea. Don't take me too seriously on the equation/language comment. I just get a bit uneasy explaining somethings in prose because there is a lot of room for misinterpretation or misleading syntax on my part. The last thing I wish to do is mislead. Have a look at the "Gibb's energy" Wikipedia article though. You may not fully comprehend the math, but there should be some "low hanging fruit" that is well within your reach and is interesting enough to make it worthwhile. Interesting for me anyway; I'm in chemistry, I've been told we delight in the dry and mundane by more than one physicist Edited January 6, 2011 by mississippichem Link to comment Share on other sites More sharing options...
lemur Posted January 6, 2011 Share Posted January 6, 2011 (edited) Yes, you've got the general idea. Don't take me too seriously on the equation/language comment. I just get a bit uneasy explaining somethings in prose because there is a lot of room for misinterpretation or misleading syntax on my part. The last thing I wish to do is mislead. Have a look at the "Gibb's energy" Wikipedia article though. You may not fully comprehend the math, but there should be some "low hanging fruit" that is well within your reach and is interesting enough to make it worthwhile. Interesting for me anyway; I'm in chemistry, I've been told we delight in the dry and mundane by more than one physicist I get defensive about math because it seems like it always becomes an issue to exclude me from thinking about science if I don't practice equation discourse. Anyway, don't worry so much about misleading - math illiterates are at varying levels of critical rigor and any descriptions that mislead us should get criticized by someone else in a way that gives us a good lesson. I am much more comfortable with the simple elegance of physics than the complexity of configurations in chemistry, but it would be my greatest dream to be able to understand any and every possible chemical reaction using only my intuitive sense of how subatomic particles interact. Probably that is impossible, but chemistry is the practical holy grail of particle-physics, imo. Edited January 6, 2011 by lemur Link to comment Share on other sites More sharing options...
alpha2cen Posted January 6, 2011 Author Share Posted January 6, 2011 When photons hit atoms, they only have limited options of how to dissipate their energy: 1) they can generate heat by vibrating the nuclei 2) they can generate electricity by vibrating the electrons without that energy transferring to the nuclei to generate heat 3) they can be absorbed and re-emitted by the electrons as new photons. Are there any other options? Maybe passing through the atom without striking any particle? Maybe resulting in direct re-configurations of particles in the form of chemical changes? I can't think of anything else. Let's think about again photons hit the surface atoms. Some of them hit the surface electron and the electron leave the surface, and photoelectric current flows. But I' don't know the photons' position. The other photons hit the surface atoms, and give them heat(I' don't know the detail energy transfer mechanism microscopically). The heat energy is like this, you said, atomic vibration, fast of free electron movement, crystal vibration, re-emitted as new photons -- black body radiation, etc. Link to comment Share on other sites More sharing options...
Nikolay Posted January 9, 2011 Share Posted January 9, 2011 Hi I have a theory that suggests photon are just electrons which are moving through dark energy. When a photon hits an atom, the photon joins with the electron and moves to a higher orbit, since the photon and electron are essentially the same thing, that is a quantized amount of dark energy, they simply mix together as if they were one while they sit in the higher orbit. The electron will site in this orbit mixed with the photon, but this is not very stable as the electron wants to drop to a lower orbit which will release the photon again. So the answer is the photon haven't gone anywhere, they are trapped with the atom for a while until they are release again. Best Regards Nick When photons collide with the surface electron of the solid surface, electrons are released from the surface. We know the photons energy is transformed into electron release. Then, Where are the photons gone? Link to comment Share on other sites More sharing options...
swansont Posted January 9, 2011 Share Posted January 9, 2011 So the answer is the photon haven't gone anywhere, they are trapped with the atom for a while until they are release again. The photon doesn't exist as a stored entity. It doesn't exist after it's been absorbed, and new ones are created when the system releases energy via EM radiation. Link to comment Share on other sites More sharing options...
J.C.MacSwell Posted January 10, 2011 Share Posted January 10, 2011 The photon doesn't exist as a stored entity. It doesn't exist after it's been absorbed, and new ones are created when the system releases energy via EM radiation. So the photon's energy and momentum is absorbed...what happens to it's spin??...is this absorbed as well?...I'm thinking this should be conserved as well...somehow... Link to comment Share on other sites More sharing options...
alpha2cen Posted January 10, 2011 Author Share Posted January 10, 2011 (edited) The photon is an electromagnetic wave particle. How to disappear after colliding with the electron in the solid surface? Is It changed into electric current frequency variation? Electric current variation in a conductor <=========> electromagnetic wave(photon) Edited January 10, 2011 by alpha2cen Link to comment Share on other sites More sharing options...
swansont Posted January 10, 2011 Share Posted January 10, 2011 So the photon's energy and momentum is absorbed...what happens to it's spin??...is this absorbed as well?...I'm thinking this should be conserved as well...somehow... It is conserved, And some interactions aren't possible because of this; this gives rise to "selection rules" which tell you what transitions are possible. Since the photon has spin 1, the angular momentum of the atom changes by 1. (a combination of spin and orbital terms) Link to comment Share on other sites More sharing options...
J.C.MacSwell Posted January 10, 2011 Share Posted January 10, 2011 It is conserved, And some interactions aren't possible because of this; this gives rise to "selection rules" which tell you what transitions are possible. Since the photon has spin 1, the angular momentum of the atom changes by 1. (a combination of spin and orbital terms) Thanks... the angular momentum referred to is quantized and also non-classical, correct? In String theory it would be assumed to be in extra dimensions? Any room for the photon to be hiding in there? (I know the last answer is no, because that is not what we call a photon...but all the little quantized bits and pieces seem to be conserved) Link to comment Share on other sites More sharing options...
swansont Posted January 10, 2011 Share Posted January 10, 2011 Right. Spin 1 means it has 1 unit (hbar) of angular momentum. I can't speak to the way string theory handles things. Link to comment Share on other sites More sharing options...
alpha2cen Posted January 12, 2011 Author Share Posted January 12, 2011 The interaction between photon and surface electron, I know, is related to photon frequency and it's energy. How do we explain it? Link to comment Share on other sites More sharing options...
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