black body

in modern physics the teacher mentioned that gasses emit certain wavelengths of light when they are heated depending on the gas. my question is why doesn't it just emit black body radiation.

It has to do with the electron states.  From what I recall, when radiation strikes an atom's electrons, they will absorb specific quantities of energy and move into a different state.  There is no "middle ground" between electron states, so when the electron eventually falls back to a stable state, it emits a specific quantity and wavelength of EM radiation.

It has to do with the electron states.  From what I recall, when radiation strikes an atom's electrons, they will absorb specific quantities of energy and move into a different state.  There is no "middle ground" between electron states, so when the electron eventually falls back to a stable state, it emits a specific quantity and wavelength of EM radiation.

that part makes sense. but then why don't solid objects emit specific wavelengths? why do they emit black body radiation?

Quote from: EnigmaZV on March 05, 2010, 12:01:10 PM

It has to do with the electron states.  From what I recall, when radiation strikes an atom's electrons, they will absorb specific quantities of energy and move into a different state.  There is no "middle ground" between electron states, so when the electron eventually falls back to a stable state, it emits a specific quantity and wavelength of EM radiation.

that part makes sense. but then why don't solid objects emit specific wavelengths? why do they emit black body radiation?

I may be mistaken, but I believe thermal energy in solid objects is stored in the atoms or molecules themselves and not in the electrons. This is why heating up a solid causes it to turn to liquid (it reduces the strength of intermolecular forces), whereas heating up a gas causes it to turn to plasma (it reduces the strength of the binding force on the electrons).

Quote from: optimisticcynic on March 05, 2010, 04:13:55 PM

Quote from: EnigmaZV on March 05, 2010, 12:01:10 PM

It has to do with the electron states.  From what I recall, when radiation strikes an atom's electrons, they will absorb specific quantities of energy and move into a different state.  There is no "middle ground" between electron states, so when the electron eventually falls back to a stable state, it emits a specific quantity and wavelength of EM radiation.

that part makes sense. but then why don't solid objects emit specific wavelengths? why do they emit black body radiation?

I may be mistaken, but I believe thermal energy in solid objects is stored in the atoms or molecules themselves and not in the electrons. This is why heating up a solid causes it to turn to liquid (it reduces the strength of intermolecular forces), whereas heating up a gas causes it to turn to plasma (it reduces the strength of the binding force on the electrons).

First of all, electrons ARE part of the atoms, and atoms MAKE UP molecules, so lets not get anybody confused about terminology here, as so often happens.

The explanation of electron-photon interaction is adequate for most circumstances. A photon will strike an atom and cause one or more electrons to change states. Eventually the electrons will decay back to their original states, and a photon of a specific spectra will be emitted. However, look at the major difference between solids and gasses...namely the close proximity of the atoms and the overall density in a solid. The photon-electron interactions happen differently in a gas because of the ease of interaction a low density condition provides. A photon has to be absorbed and emitted many times in a solid before it reaches the interior, whereas in a gas it does not have this problem.

First of all, electrons ARE part of the atoms, and atoms MAKE UP molecules, so lets not get anybody confused about terminology here, as so often happens.

Any confusion as to terminology in this discussion would require a lack of high school physics education, in which case the person getting confused probably shouldn't be a part of this discussion in the first place.

The explanation of electron-photon interaction is adequate for most circumstances. A photon will strike an atom and cause one or more electrons to change states. Eventually the electrons will decay back to their original states, and a photon of a specific spectra will be emitted. However, look at the major difference between solids and gasses...namely the close proximity of the atoms and the overall density in a solid. The photon-electron interactions happen differently in a gas because of the ease of interaction a low density condition provides. A photon has to be absorbed and emitted many times in a solid before it reaches the interior, whereas in a gas it does not have this problem.

That didn't answer his question, but nice try. Maybe later you can brush up on your reading comprehension if you have time.

ITT: parsifal doesn't understand the difference between nucleus and atom

Quote from: EireEngineer on March 07, 2010, 11:28:27 AM

First of all, electrons ARE part of the atoms, and atoms MAKE UP molecules, so lets not get anybody confused about terminology here, as so often happens.

Any confusion as to terminology in this discussion would require a lack of high school physics education, in which case the person getting confused probably shouldn't be a part of this discussion in the first place.

Quote from: EireEngineer on March 07, 2010, 11:28:27 AM

The explanation of electron-photon interaction is adequate for most circumstances. A photon will strike an atom and cause one or more electrons to change states. Eventually the electrons will decay back to their original states, and a photon of a specific spectra will be emitted. However, look at the major difference between solids and gasses...namely the close proximity of the atoms and the overall density in a solid. The photon-electron interactions happen differently in a gas because of the ease of interaction a low density condition provides. A photon has to be absorbed and emitted many times in a solid before it reaches the interior, whereas in a gas it does not have this problem.

That didn't answer his question, but nice try. Maybe later you can brush up on your reading comprehension if you have time.

You were the one confusing atoms, electrons, and molecules, so it is quite obvious that you are a product of the American educational system. Care to explain how the nucleus of an atom stores the energy of a photon, or how a molecule stores energy without interaction of its constituent components, namely atoms? Your first post seemed to be really confused about the subject, and that was the point I was making. I also noticed you had no answers for him either, while I at least was trying to pint him in the proper direction.

You were the one confusing atoms, electrons, and molecules, so it is quite obvious that you are a product of the American educational system.

wat

Care to explain how the nucleus of an atom stores the energy of a photon, or how a molecule stores energy without interaction of its constituent components, namely atoms? Your first post seemed to be really confused about the subject, and that was the point I was making. I also noticed you had no answers for him either, while I at least was trying to pint him in the proper direction.

I don't actually know the answer to his question, so I made an educated guess. Certain classes of solids have lattice structures which would, I expect, be perturbed by exciting an electron to a higher energy state, increasing the size of an atom or ion. Your post didn't point him in the proper direction at all; you simply stated that solids use the same mechanism of absorbing and transmissing light energy as gas without then elaborating as to how the difference in structure would alter the emission spectrum.

Quote from: EireEngineer on March 08, 2010, 03:41:01 PM

You were the one confusing atoms, electrons, and molecules, so it is quite obvious that you are a product of the American educational system.

wat

Quote from: EireEngineer on March 08, 2010, 03:41:01 PM

Care to explain how the nucleus of an atom stores the energy of a photon, or how a molecule stores energy without interaction of its constituent components, namely atoms? Your first post seemed to be really confused about the subject, and that was the point I was making. I also noticed you had no answers for him either, while I at least was trying to pint him in the proper direction.

I don't actually know the answer to his question, so I made an educated guess. Certain classes of solids have lattice structures which would, I expect, be perturbed by exciting an electron to a higher energy state, increasing the size of an atom or ion. Your post didn't point him in the proper direction at all; you simply stated that solids use the same mechanism of absorbing and transmissing light energy as gas without then elaborating as to how the difference in structure would alter the emission spectrum.

Wow, you are way off. When an electron absorbs a photon, it doesnt really make a huge change in "orbit", but it does make a huge change in energy. Any positional change in the cloud is negligible, and far to tiny to cause any change in the structure of any lattice. You are thinking of it as changing its orbit height, which is a primitive way of looking at it to teach valence to middle schoolers.
As for re-emmison spectra:
When electrons in an atom get excited, they jump to higher energy levels. In order for them to do this, they must absorb energy. However, when electrons "calm down", they drop back down and thus release emit energy in the form of photons (the quanta of light). This emission of energy is the light that we see. The color of the light we see depends on the distance the electron drops--the longer the drop, the higher the energy.

@ eireengineer: it would be wrong to say that there's no difference in "height" either. the change in energy is linked to a shift of the peak value in the radial part of the wavefunction. the angular part has no big impact on the energy. its change just compensates the angular momentum of the photon.

i'll have a try at explaining the initial question:
in a gas we can neglect any intermolecular (or interatomic for noble gases) interaction. this leaves us with the sharp spectral lines that result from discrete energy states of the electrons.
these lines can get wider if the gas is very hot and/or under huge pressure because of doppler shifts. additionally scattering between molecules can cause a lower mean lifetime of the excited states which also results in widened spectral lines. (result of the uncertainty principle)

solid objects: now we can't treat the atoms independantly as they are bound to each other. the electrons feel a periodic potential caused by the nuclei of the atoms. solving the schoedinger equation for this system yields a electronic band structure. depending on the material we get forbidden states that can't be occupied by electrons and continuous distributions of allowed states. the electrons are no longer bound to the "classical" orbitals. this results in a more or less continuous black body spectrum. if you want to learn more about that you should grab a introductory book on solid state physics.

@ eireengineer: it would be wrong to say that there's no difference in "height" either. the change in energy is linked to a shift of the peak value in the radial part of the wavefunction. the angular part has no big impact on the energy. its change just compensates the angular momentum of the photon.

i'll have a try at explaining the initial question:
in a gas we can neglect any intermolecular (or interatomic for noble gases) interaction. this leaves us with the sharp spectral lines that result from discrete energy states of the electrons.
these lines can get wider if the gas is very hot and/or under huge pressure because of doppler shifts. additionally scattering between molecules can cause a lower mean lifetime of the excited states which also results in widened spectral lines. (result of the uncertainty principle)

solid objects: now we can't treat the atoms independantly as they are bound to each other. the electrons feel a periodic potential caused by the nuclei of the atoms. solving the schoedinger equation for this system yields a electronic band structure. depending on the material we get forbidden states that can't be occupied by electrons and continuous distributions of allowed states. the electrons are no longer bound to the "classical" orbitals. this results in a more or less continuous black body spectrum. if you want to learn more about that you should grab a introductory book on solid state physics.

That may be a bit above Parsi's head there, but good job. Its a balancing act in here.

Quote from: iznih on March 08, 2010, 06:28:55 PM

@ eireengineer: it would be wrong to say that there's no difference in "height" either. the change in energy is linked to a shift of the peak value in the radial part of the wavefunction. the angular part has no big impact on the energy. its change just compensates the angular momentum of the photon.

i'll have a try at explaining the initial question:
in a gas we can neglect any intermolecular (or interatomic for noble gases) interaction. this leaves us with the sharp spectral lines that result from discrete energy states of the electrons.
these lines can get wider if the gas is very hot and/or under huge pressure because of doppler shifts. additionally scattering between molecules can cause a lower mean lifetime of the excited states which also results in widened spectral lines. (result of the uncertainty principle)

solid objects: now we can't treat the atoms independantly as they are bound to each other. the electrons feel a periodic potential caused by the nuclei of the atoms. solving the schoedinger equation for this system yields a electronic band structure. depending on the material we get forbidden states that can't be occupied by electrons and continuous distributions of allowed states. the electrons are no longer bound to the "classical" orbitals. this results in a more or less continuous black body spectrum. if you want to learn more about that you should grab a introductory book on solid state physics.

That may be a bit above Parsi's head there, but good job. Its a balancing act in here.

You should read Parsifal's work in math. Your explanation hints at perhaps a second semester understanding of physics at best. I'm sorry to say but he's smarter than you and understood the question much better than you did. At most you restated the OP's understanding of the issue and threw a little bs in to make it sound like he didn't understand it well enough. Sadly enough it's impossible to bs in physics unless the person is much dumber than you.

@ eireengineer: it would be wrong to say that there's no difference in "height" either. the change in energy is linked to a shift of the peak value in the radial part of the wavefunction. the angular part has no big impact on the energy. its change just compensates the angular momentum of the photon.

i'll have a try at explaining the initial question:
in a gas we can neglect any intermolecular (or interatomic for noble gases) interaction. this leaves us with the sharp spectral lines that result from discrete energy states of the electrons.
these lines can get wider if the gas is very hot and/or under huge pressure because of doppler shifts. additionally scattering between molecules can cause a lower mean lifetime of the excited states which also results in widened spectral lines. (result of the uncertainty principle)

solid objects: now we can't treat the atoms independantly as they are bound to each other. the electrons feel a periodic potential caused by the nuclei of the atoms. solving the schoedinger equation for this system yields a electronic band structure. depending on the material we get forbidden states that can't be occupied by electrons and continuous distributions of allowed states. the electrons are no longer bound to the "classical" orbitals. this results in a more or less continuous black body spectrum. if you want to learn more about that you should grab a introductory book on solid state physics.

thanks for this. I asked the question to the teacher. unfortunately going to a community college and having a math professor teaching modern physics has its negatives. I figured I would learn about it next year but I wanted to learn about it now.

When electrons in an atom get excited, they jump to higher energy levels. In order for them to do this, they must absorb energy. However, when electrons "calm down", they drop back down and thus release emit energy in the form of photons (the quanta of light). This emission of energy is the light that we see. The color of the light we see depends on the distance the electron drops--the longer the drop, the higher the energy.

Everybody in this thread understands this already. Even if they didn't to begin with, it was explained quite clearly in the first reply. Again, you have completely failed to understand the question being asked and simply repeated what has already been said in the hope that somebody will pay attention to you.

Also, thanks iznih. This thread actually got me curious as well, and your explanation makes a lot of sense.

Quote from: EireEngineer on March 08, 2010, 05:41:10 PM

When electrons in an atom get excited, they jump to higher energy levels. In order for them to do this, they must absorb energy. However, when electrons "calm down", they drop back down and thus release emit energy in the form of photons (the quanta of light). This emission of energy is the light that we see. The color of the light we see depends on the distance the electron drops--the longer the drop, the higher the energy.

Everybody in this thread understands this already. Even if they didn't to begin with, it was explained quite clearly in the first reply. Again, you have completely failed to understand the question being asked and simply repeated what has already been said in the hope that somebody will pay attention to you.

Also, thanks iznih. This thread actually got me curious as well, and your explanation makes a lot of sense.

Then why was your first reply to him so horribly confused?

Then why was your first reply to him so horribly confused?

You've already given me more than sufficient reason to doubt your reading comprehension ability, so I'm sure you'll excuse me if I don't take your opinion of my posts entirely seriously.

Also, thanks iznih. This thread actually got me curious as well, and your explanation makes a lot of sense.

it raised my interest, too. a simple question but if you have a close look at it, it gets quite complicated.