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Thread: Electromagnetic absorption

  1. #1 Electromagnetic absorption 
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    So I just read about absorption of electromagnetic radiation. Won't the electron that absorbed the energy of the radiation and jumped to the higher energy level relax again to release another photon?


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    Quote Originally Posted by molecool View Post
    So I just read about absorption of electromagnetic radiation. Won't the electron that absorbed the energy of the radiation and jumped to the higher energy level relax again to release another photon?
    Not necessarily -- it depends on the scenario. Note that, when you sunbathe, you just get warmer. You don't re-emit the photons you absorbed.


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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by molecool View Post
    So I just read about absorption of electromagnetic radiation. Won't the electron that absorbed the energy of the radiation and jumped to the higher energy level relax again to release another photon?
    Not necessarily -- it depends on the scenario. Note that, when you sunbathe, you just get warmer. You don't re-emit the photons you absorbed.
    Yes you do.. You emit heat RADIATION, which is basically infrared light. This heat radiation will not have enough energy to change electron energy, so it will just vibrate (heat) the core.
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    Quote Originally Posted by Zwolver View Post
    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by molecool View Post
    So I just read about absorption of electromagnetic radiation. Won't the electron that absorbed the energy of the radiation and jumped to the higher energy level relax again to release another photon?
    Not necessarily -- it depends on the scenario. Note that, when you sunbathe, you just get warmer. You don't re-emit the photons you absorbed.
    Yes you do.. You emit heat RADIATION, which is basically infrared light. This heat radiation will not have enough energy to change electron energy, so it will just vibrate (heat) the core.
    I worded my statement with care. No need to shout that you are a sloppy reader and thinker. The photons you absorbed are not re-emitted. As you yourself pointed out, you emit some IR. But the process is more complex and subtle than mere emission. There is also a big change in entropy. Obviously, the broad spectrum of what we emit tells us that something far more complicated than re-emission is taking place.

    You are not a simple mirror. You are not fluorescent (which would involve a spectral shift -- the Stokes shift -- in any case).

    Now do you see why your "correction" is fundamentally flawed?
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    So the thermal energy produced by a flowing electric current in a wire is actually generated by the changes of energy levels of electrons in the wire?
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    tk421, while I would normally bow to your much better grasp of physics than I enjoy, I think I need to nitpick your nitpick. (I stand ready to be corrected and thereby learn something.)

    Photons are never re-emitted. The photon that is emitted when an electron drops to a lower level energy level never existed before. But is is convenient to simplify things and refer to that as re-emission. I see no distinction, in the simplified overview that is present in this thread, between that and the thermal radiation we all agree occurs. What am I missing?
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    My take on it (but as you are I'm open to correction) is it can only be simplified as "re-emission" if the emitted photon and the absorbed photon have the same energy and so the ingoing and outgoing photons are indistinguishable, this is not the case in the emission of thermal radiation from the skin that tk421 was referring to.
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    I think that is what tk421 is getting at. My argument is that - at the level of simplification appropriate to this thread - it is reasonable to call thermal radiation a re-emission. I feel he has attacked zwolver for making a point that - to me - seems reasonable. It may be a little loose, but if we insisted on precision on every post at every level only Markus would emerge unscathed.
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    Quote Originally Posted by John Galt View Post
    tk421, while I would normally bow to your much better grasp of physics than I enjoy, I think I need to nitpick your nitpick. (I stand ready to be corrected and thereby learn something.)

    Photons are never re-emitted. The photon that is emitted when an electron drops to a lower level energy level never existed before. But is is convenient to simplify things and refer to that as re-emission. I see no distinction, in the simplified overview that is present in this thread, between that and the thermal radiation we all agree occurs. What am I missing?
    Your en pointe statement that photons are never re-emitted is at the heart of the matter. This question falls into the category of the age-old "what constitutes a good answer" conundrum. At one level of explanation, it would seem to be perfectly fine and innocuous to say that "re"-emission occurs. Many students would be satisfied by that answer and never ask another. Others, though, would then note that a logical consequence of that answer would be that all stimulations by photons should result in the "re"-emission of photons of precisely the same wavelength. That is, of course, at odds with observation except, perhaps, in the case of an ideal mirror. The example of a sunbathing human gives us an opportunity to trace the conversion of low-entropy sunlight into high-entropy blackbody radiation. So, too, does the study of how a microwave oven's nearly monochromatic radiation heats up a leftover slice of pizza, causing the latter to emit over a broad spectrum. I wanted to avoid leaving molecool the impression that absorption and emission are perfectly symmetrical phenomena in the general case.
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  11. #10  
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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by John Galt View Post
    tk421, while I would normally bow to your much better grasp of physics than I enjoy, I think I need to nitpick your nitpick. (I stand ready to be corrected and thereby learn something.)

    Photons are never re-emitted. The photon that is emitted when an electron drops to a lower level energy level never existed before. But is is convenient to simplify things and refer to that as re-emission. I see no distinction, in the simplified overview that is present in this thread, between that and the thermal radiation we all agree occurs. What am I missing?
    Your en pointe statement that photons are never re-emitted is at the heart of the matter. This question falls into the category of the age-old "what constitutes a good answer" conundrum. At one level of explanation, it would seem to be perfectly fine and innocuous to say that "re"-emission occurs. Many students would be satisfied by that answer and never ask another. Others, though, would then note that a logical consequence of that answer would be that all stimulations by photons should result in the "re"-emission of photons of precisely the same wavelength. That is, of course, at odds with observation except, perhaps, in the case of an ideal mirror. The example of a sunbathing human gives us an opportunity to trace the conversion of low-entropy sunlight into high-entropy blackbody radiation. So, too, does the study of how a microwave oven's nearly monochromatic radiation heats up a leftover slice of pizza, causing the latter to emit over a broad spectrum. I wanted to avoid leaving molecool the impression that absorption and emission are perfectly symmetrical phenomena in the general case.
    Yes, I have to say I am with you on this one. If one reads the OP, he explicitly mentions the electron relaxing back from its excited state. So it seems to me the required response should explain the alternative modes of relaxation of excited electronic states, as this is the key to why you don't just get re-radiation at the same frequency - which is what he or she is asking about.

    In fact I think it's rather a penetrating question, as the explanation of how molecular collisions and similar influences can enable the electron to jump down again into its ground state is far from trivial.
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    Quote Originally Posted by molecool View Post
    So the thermal energy produced by a flowing electric current in a wire is actually generated by the changes of energy levels of electrons in the wire?
    Nono, that`s a bit different process. In conductor electrons (or holes) that conduct electric charge are excited to conduction band. That is very similar to electronic sate of atom or molecule but for large systems (such as wire) these isolated states became bands. When such excited electron is moving through wire it interacts with ions in such way that it loses a small portion of its energy (moving lower in the band) while creating a phonon (quantum of vibration of crystal/molecule/...). These phonons are basicaly what you call heat.

    In general you have only three ways how electron may be deexcited. 1) By emitting photon (or photons) 2) By emitting phonon (more likely cascade of phonons) eg. heat 3) By Auger-like process when excited electron hits another electron/hole and transfers its excitation energy to the other particle. To be clear combinations of 1) and 2) may also occur but they are heavily diminished.
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    Quote Originally Posted by exchemist View Post
    In fact I think it's rather a penetrating question, as the explanation of how molecular collisions and similar influences can enable the electron to jump down again into its ground state is far from trivial.
    Well just for you Imagine you have two two-level systems with excited state and ground state . Wavefunction of such system can be generally written as



    When these systems are in vicinity (not necessary colliding) they interact throu electromagnetic field described by interaction hamiltonian. It is usefull to write this operator as projector like this



    Interaction hamiltonian is of course offdiagonal operator. is strengh of interaction (depending typicaly on dipole moment) and A is some term that turns interaction on and off (not important here but worth mentioning as we don`t want systems to interact when they are 1 km away).

    What you do now is plug this into Schrodinger equation in interaction picture. You get



    When you solve this with apropriate initial condition (wavefunction at time 0 or before interaction) you get that system is in superposition of states and depending whose aplitudes depend on phase factors (which depend on time like ) and initial conditions. I would write down full solution but Im too lazy atm.
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    Quote Originally Posted by molecool View Post
    So the thermal energy produced by a flowing electric current in a wire is actually generated by the changes of energy levels of electrons in the wire?
    Gere explains what's going on in a conducting wire.

    Molecool, you are raising a very good question, but unfortunately the answer is complicated. I think possibly the key thing to grasp is that in most everyday situations, one is not dealing with isolated atoms, i.e. the "clean" situation that gives rise to a tidy line spectrum of electrons jumping between different atomic orbitals. In most everyday situations, atoms are combined with other atoms, whether in the form of molecules, or crystalline or metallic materials.

    When atoms combine in this way, the outer electrons (in the "valence" shell) occupy orbitals that are mixtures with those of the other atoms. This often allows them to occupy a one of range of microstates, forming a band of energy levels. This arises because the "orbitals" in that situation are defined, not only by how the atoms would be positioned if their positions were fixed, but also by the fact they are in dynamic motion relative to one another, vibrating, rotating etc, all of which motions affect the energy of the orbital slightly at any given instant. Furthermore the motion also means there are transient, dynamic electric fields, from the approach and retreat of other atoms. These things can allow electrons to lose or gain energy and move up or down within the bands, or even to jump from the bottom of one excitation band to the top of another and thus descend a kind of ladder back to the ground state, without emitting a photon that corresponds in energy to the one that caused the initial excitation. In fact there may be no emission of radiation at all, a "non-radiative" relaxation pathway. In this case the energy thereby released goes into thermal motion.

    People tend to brush all this off by saying light gets absorbed and turns into heat, but actually the precise way this happens is very complicated (and interesting) at the atomic level.
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    Quote Originally Posted by Gere View Post
    Quote Originally Posted by exchemist View Post
    In fact I think it's rather a penetrating question, as the explanation of how molecular collisions and similar influences can enable the electron to jump down again into its ground state is far from trivial.
    Well just for you Imagine you have two two-level systems with excited state and ground state . Wavefunction of such system can be generally written as



    When these systems are in vicinity (not necessary colliding) they interact throu electromagnetic field described by interaction hamiltonian. It is usefull to write this operator as projector like this



    Interaction hamiltonian is of course offdiagonal operator. is strengh of interaction (depending typicaly on dipole moment) and A is some term that turns interaction on and off (not important here but worth mentioning as we don`t want systems to interact when they are 1 km away).

    What you do now is plug this into Schrodinger equation in interaction picture. You get



    When you solve this with apropriate initial condition (wavefunction at time 0 or before interaction) you get that system is in superposition of states and depending whose aplitudes depend on phase factors (which depend on time like ) and initial conditions. I would write down full solution but Im too lazy atm.
    Yes, in non-mathematical language I recall you get a mixing of states, which allows transient pathways back to the ground state to be possible. I seem to recall this explains how electrons can make "forbidden" transitions in Inter-System Crossing and so forth….if I recall….it was a very long time ago…..
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    Quote Originally Posted by exchemist View Post
    When atoms combine in this way, the outer electrons (in the "valence" shell) occupy orbitals that are mixtures with those of the other atoms.
    Don't you mean valence electrons? I heard valence shell is a less accurate way of calling the outermost shell of an atom which can participate in chemical bonds.

    And BTW, the heat generated by absorption of electromagnetic radiation is caused by phonons?
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by exchemist View Post
    When atoms combine in this way, the outer electrons (in the "valence" shell) occupy orbitals that are mixtures with those of the other atoms.
    Don't you mean valence electrons? I heard valence shell is a less accurate way of calling the outermost shell of an atom which can participate in chemical bonds.

    And BTW, the heat generated by absorption of electromagnetic radiation is caused by phonons?
    Yes indeed, fair enough. Any electrons in orbitals that are of the energy to take part in bonding are potentially subject to having their states mixed and disturbed in the way I have been describing. Whereas those in the "core" inner orbitals more or less retain their atomic line spectra (X ray spectra for example).

    Phonons are a characteristic of solid lattices, in which the modes of vibration of the structure necessarily involve the whole lattice. As you may know, you get IR spectra due to excitation of vibrational modes of motion - and electronic spectra of molecules also contain vibrational "fine structure" due to this, leading to "band spectra" , which is what I was trying to describe to you earlier. In substances made of free molecules (e.g. polyatomic gases) these are comprised of vibrational modes of individual molecules, but in ordered solids phonons come into it.
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    Quote Originally Posted by John Galt View Post
    tk421, while I would normally bow to your much better grasp of physics than I enjoy, I think I need to nitpick your nitpick. (I stand ready to be corrected and thereby learn something.)

    Photons are never re-emitted. The photon that is emitted when an electron drops to a lower level energy level never existed before. But is is convenient to simplify things and refer to that as re-emission. I see no distinction, in the simplified overview that is present in this thread, between that and the thermal radiation we all agree occurs. What am I missing?
    I didn't mean the exact same photon was reëmitted, i meant for the energy to be released, in the form of another photon. So i do understand his reaction to this. But yeah, it didn't break down my point.
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    Quote Originally Posted by John Galt View Post
    I think that is what tk421 is getting at. My argument is that - at the level of simplification appropriate to this thread - it is reasonable to call thermal radiation a re-emission. I feel he has attacked zwolver for making a point that - to me - seems reasonable. It may be a little loose, but if we insisted on precision on every post at every level only Markus would emerge unscathed.

    I wouldn't quite go that far. Me and Markus have has different opinion on things, never anything drastic.
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    Quote Originally Posted by tk421 View Post
    Quote Originally Posted by molecool View Post
    So I just read about absorption of electromagnetic radiation. Won't the electron that absorbed the energy of the radiation and jumped to the higher energy level relax again to release another photon?
    Not necessarily -- it depends on the scenario. Note that, when you sunbathe, you just get warmer. You don't re-emit the photons you absorbed.
    Were all producing small amounts if light...yes kids you are glowing.
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    Quote Originally Posted by frumpydolphin View Post
    Were all producing small amounts if light...yes kids you are glowing.
    I'm not aware of human bodies emitting visible light. Infrared EMR, sure. Maybe even a bit of radioactivity because one out of every 8,550 potassium atoms is radioactive potassium-40.
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    Quote Originally Posted by Chucknorium View Post
    Quote Originally Posted by frumpydolphin View Post
    Were all producing small amounts if light...yes kids you are glowing.
    I'm not aware of human bodies emitting visible light. Infrared EMR, sure. Maybe even a bit of radioactivity because one out of every 8,550 potassium atoms is radioactive potassium-40.
    Well……just for the sake of a bit of pedantry, we do fluoresce under UV illumination, though. Especially the teeth, though I am unable to discover from web searches what compounds are responsible…....
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    Quote Originally Posted by Gere View Post
    Quote Originally Posted by molecool View Post
    So the thermal energy produced by a flowing electric current in a wire is actually generated by the changes of energy levels of electrons in the wire?
    Nono, that`s a bit different process. In conductor electrons (or holes) that conduct electric charge are excited to conduction band. That is very similar to electronic sate of atom or molecule but for large systems (such as wire) these isolated states became bands. When such excited electron is moving through wire it interacts with ions in such way that it loses a small portion of its energy (moving lower in the band) while creating a phonon (quantum of vibration of crystal/molecule/...). These phonons are basicaly what you call heat.

    In general you have only three ways how electron may be deexcited. 1) By emitting photon (or photons) 2) By emitting phonon (more likely cascade of phonons) eg. heat 3) By Auger-like process when excited electron hits another electron/hole and transfers its excitation energy to the other particle. To be clear combinations of 1) and 2) may also occur but they are heavily diminished.
    There is no "conduction band" in a conductor. By the definition of a conductor, there is no bandgap near the fermi level. If there was, the material in question would be either a semiconductor or an insulator. You are correct about the phonons, however.
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    Quote Originally Posted by exchemist View Post
    Quote Originally Posted by Chucknorium View Post
    Quote Originally Posted by frumpydolphin View Post
    Were all producing small amounts if light...yes kids you are glowing.
    I'm not aware of human bodies emitting visible light. Infrared EMR, sure. Maybe even a bit of radioactivity because one out of every 8,550 potassium atoms is radioactive potassium-40.
    Well……just for the sake of a bit of pedantry, we do fluoresce under UV illumination, though. Especially the teeth, though I am unable to discover from web searches what compounds are responsible…....
    We also reflect light and other frequencies of EMR. I know we reflect some frequencies of radio waves. Not sure if we reflect micro waves, infrared, or UV. Gotta believe our bodies don't reflect x-ray and gamma waves -- these must pass right thru or are absorbed. But I really don't know.
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    Quote Originally Posted by ajarjour View Post
    Quote Originally Posted by Gere View Post
    Quote Originally Posted by molecool View Post
    So the thermal energy produced by a flowing electric current in a wire is actually generated by the changes of energy levels of electrons in the wire?
    Nono, that`s a bit different process. In conductor electrons (or holes) that conduct electric charge are excited to conduction band. That is very similar to electronic sate of atom or molecule but for large systems (such as wire) these isolated states became bands. When such excited electron is moving through wire it interacts with ions in such way that it loses a small portion of its energy (moving lower in the band) while creating a phonon (quantum of vibration of crystal/molecule/...). These phonons are basicaly what you call heat.

    In general you have only three ways how electron may be deexcited. 1) By emitting photon (or photons) 2) By emitting phonon (more likely cascade of phonons) eg. heat 3) By Auger-like process when excited electron hits another electron/hole and transfers its excitation energy to the other particle. To be clear combinations of 1) and 2) may also occur but they are heavily diminished.
    There is no "conduction band" in a conductor. By the definition of a conductor, there is no bandgap near the fermi level. If there was, the material in question would be either a semiconductor or an insulator. You are correct about the phonons, however.

    Not true. Only difference between conductor and semiconductor is that Fermi level in conductor is in conduction band. Also semiconductor is the same as insulator.
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    Quote Originally Posted by Chucknorium View Post
    We also reflect light and other frequencies of EMR. I know we reflect some frequencies of radio waves. Not sure if we reflect micro waves, infrared, or UV.
    We do reflect those, although to varying degrees. Since we're not that many microwave wavelengths in extent, diffraction is also a big part of what happens there. Our IR reflectivity is not large, but it is readily detectable -- shine a television remote control's beam on your skin, and view the result with a cellphone camera. Indeed, you can light up the night with IR lamps and watch what happens outdoors. The nocturnal world is extremely interesting!

    We also do reflect UV (again, we're not perfect mirrors there, but neither are we perfect absorbers).

    Gotta believe our bodies don't reflect x-ray and gamma waves -- these must pass right thru or are absorbed. But I really don't know.
    You are right -- there is no appreciable reflection there.
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    Quote Originally Posted by Gere View Post
    When such excited electron is moving through wire it interacts with ions in such way that it loses a small portion of its energy (moving lower in the band) while creating a phonon (quantum of vibration of crystal/molecule/...). These phonons are basicaly what you call heat.
    Wait, that means the electron has to transfer heat to the nucleus of the atom before the whole atom creates a phonon?
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    Quote Originally Posted by molecool View Post
    Quote Originally Posted by Gere View Post
    When such excited electron is moving through wire it interacts with ions in such way that it loses a small portion of its energy (moving lower in the band) while creating a phonon (quantum of vibration of crystal/molecule/...). These phonons are basicaly what you call heat.
    Wait, that means the electron has to transfer heat to the nucleus of the atom before the whole atom creates a phonon?
    Not really, it just means it excites a lattice vibration. This involves movement (vibration) of the atomic nuclei about their mean rest position in the lattice, a bit like when an IR photon is absorbed my a molecule and give rise to a molecular vibration. But there is no nuclear process. Don't forget the positions of the nuclei in a molecule or lattice are determined by the bonding electrons, not the nuclei.
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    Then when an electron absorbs a photon and turns it into thermal energy, the whole atom then has the converted thermal energy even though it was the electron that absorbed the photon?
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    Quote Originally Posted by molecool View Post
    Then when an electron absorbs a photon and turns it into thermal energy, the whole atom then has the converted thermal energy even though it was the electron that absorbed the photon?
    Exactly.
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    Seems legit enough. Thanks. Why is that, though?
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    Quote Originally Posted by molecool View Post
    Seems legit enough. Thanks. Why is that, though?
    Again, like your question around 28th April, on how absorption of a photon by an electron leads ultimately to heat in molecules, this is good and not simple question. I may get the answer a bit (or totally) wrong, as I am not a solid state physicist.

    My understanding is that the lattice of ions in which the electrons move is vibrating, in a range of resonant vibration modes that we call phonons. The conduction band electrons are not in discrete, molecular "orbitals". They are instead occupying the continuum of energy levels formed by the merging of an almost infinite series of delocalised "orbitals" that extend throughout the metal. However the vibration of the ions causes perturbations in the energy levels, just as in a molecule the orbital's energy level is modified by the vibrational state of the molecule. So I imagine an electron can jump down in energy, from a higher energy state of a level with little vibrational excitation to a lower energy state of a a level with higher vibrational excitation, in a similar way - giving up its energy to the lattice in the process. The problem conceptually is that there is a virtually infinite number of of all these vibrational states, making a continuum. I feel fairly sure a physicist's explanation would use a formalism relating to these continua rather than imagining individual electrons and bits of vibrating lattice.

    Where is a physicist when you need her, or him?
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    exchemist is right as usual. Electron excited to the middle of conduction band will thermalize releasing cascade of longitudinal optical phonons dropping to lowest possible state in conduction band.
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  34. #33  
    ▼▼ dn ʎɐʍ sıɥʇ ▼▼ RedPanda's Avatar
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    Quote Originally Posted by Gere View Post
    exchemist is right as usual. Electron excited to the middle of conduction band will thermalize releasing cascade of longitudinal optical phonons dropping to lowest possible state in conduction band.
    Yeah - that's what I was going to say.
    Election exited to the middle of construction bond will thermos flash realising a cavalcade of longplayer optimal phonograms dripping to the lowly passable stoat in connection sand.
    SayBigWords.com/say/3FC

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    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by Gere View Post
    exchemist is right as usual. Electron excited to the middle of conduction band will thermalize releasing cascade of longitudinal optical phonons dropping to lowest possible state in conduction band.
    Yeah - that's what I was going to say.
    Election exited to the middle of construction bond will thermos flash realising a cavalcade of longplayer optimal phonograms dripping to the lowly passable stoat in connection sand.
    That's funny. But sadly (for me) both statements make the same amount of sense to me.
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  36. #35  
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    Quote Originally Posted by Chucknorium View Post
    Quote Originally Posted by RedPanda View Post
    Quote Originally Posted by Gere View Post
    exchemist is right as usual. Electron excited to the middle of conduction band will thermalize releasing cascade of longitudinal optical phonons dropping to lowest possible state in conduction band.
    Yeah - that's what I was going to say.
    Election exited to the middle of construction bond will thermos flash realising a cavalcade of longplayer optimal phonograms dripping to the lowly passable stoat in connection sand.
    That's funny. But sadly (for me) both statements make the same amount of sense to me.
    Arf arf.

    You mean we could equally well have said " My hovercraft is full of eels"? Or, "Would you like to come back to my place, bouncy bouncy?" What a pity.

    But it is hard, in the space we have on a discussion forum. Also, I have to rack my brains for what I can recall from 40 years ago.

    I hope molecool gets at least enough out of our replies to be motivated to read further on the full explanation. If we achieve this much I shall be well satisfied.
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    Now, what about electromagnetic fields? Are they real or they are just some mumbo-jumbos about electromagnetic waves since the waves have both electric and magnetic fields. As far as I know, electric fields are produced by stationary charges and magnetic fields moving charges, but there's no way you can have a stationary and moving charge at the same time!
    http://en.m.wikipedia.org/wiki/Electromagnetic_field
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  38. #37  
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    Quote Originally Posted by molecool View Post
    Now, what about electromagnetic fields? Are they real or they are just some mumbo-jumbos about electromagnetic waves since the waves have both electric and magnetic fields. As far as I know, electric fields are produced by stationary charges and magnetic fields moving charges, but there's no way you can have a stationary and moving charge at the same time!
    Electromagnetic field - Wikipedia, the free encyclopedia
    Not sure quite what you mean but "electromagnetic" is just a useful term, as electric and magnetic phenomena tend to go hand in hand - one example indeed being EM radiation, which, as you say, consists of both fields oscillating together at right angles to each other.

    Not mumbo-jumbo at all.

    But have you a more specific concern?
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    Electric fields are produced by stationary charges and magnetic fields by moving charges, so you can't have them 2 fields at the same time?
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    Depends on your frame of reference, if you are at rest with respect to the charge you will see an electric field, someone moving relative to you will see a magnetic field. They are different manifestations of the same "thing" not separate fields as such.
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    Electric field - Wikipedia, the free encyclopedia

    What about electrodynamic fields? (Electric fields that happen when charges are in motion)
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  42. #41  
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    You mean magnetic fields?

    Quote Originally Posted by molecool
    magnetic fields by moving charges
    You see the B term in the equation in your link? That's a magnetic flux, that creates an electric field. I think we need a real physicist to take this any further I don't want to give you any mis-information (this isn't my area of expertise).
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  43. #42  
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    Quote Originally Posted by PhDemon View Post
    You mean magnetic fields?

    Quote Originally Posted by molecool
    magnetic fields by moving charges
    Post #40
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  44. #43  
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    Last sentence post #39. Whether you see an electric or magnetic field (or both) and the strength of the fields depends on relative motion. *A real physicist might correct me here but this is my understanding of it.*
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