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Old Jan 23rd 2010, 05:48 AM   #1
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Is all light that we see comes from electron "falling"?

I was wondering, is all visible ( and non visible ) light that we see comes from electron falling from high energy level to lower one ?

So for example what is the nature of light that we see in a light bulb? is it current that flow in the filament that cause the material to heat up--> electron move ---> light emitted?
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Old Jan 23rd 2010, 08:25 AM   #2
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According to me, you are light. When you passes current through bulb filament, It got heated up due to resistance. Due to heating, electrons get excited to a higher energy level and when they return to their ground state they emit light (or more accurately i should say electromagnetic waves of some wavelength which may lie in visible as well as other regions of electromagnetic spectrum) and we see it.

But still , I want to listen from any other forum member about it.

waiting...
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Old Jan 23rd 2010, 09:16 AM   #3
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if this is the case then,,

Then, let's take it one step further, the reason I radiate in IR is because my electrons in my body getting energy to go to some level up, and then "fall" down while radiating in IR ?

Last edited by Hbar; Jan 23rd 2010 at 11:53 AM.
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Old Jan 24th 2010, 09:22 AM   #4
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ya, this is the case.... you are right
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Old Jan 24th 2010, 09:31 AM   #5
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I c..

So this is Thermal radiation ?
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Old Jan 24th 2010, 09:44 AM   #6
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not sure!!!

I am not sure about it.....
need to look some standard text.
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Old Feb 8th 2010, 06:31 AM   #7
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Originally Posted by Hbar View Post
I was wondering, is all visible ( and non visible ) light that we see comes from electron falling from high energy level to lower one ?

So for example what is the nature of light that we see in a light bulb? is it current that flow in the filament that cause the material to heat up--> electron move ---> light emitted?
All light can be considered to be composed of alternating electric and magnetic fields at right angles to each other and at a right angle to the path it travels. So considering light as a wave solves more problems in electrical engineering than considering it to be composed of a number of photons. Nonetheless, the energy of the wave is composed of a number of photons whose individual energy is a product of Planks constant and the frequency of the photon. Together a number of them sum to equal the energy contained within a light wave. So even the wave theory of light can be linked with the particle theory of light through the energy of the wave and the number of photons needed to sum to that same energy; getting that value one can say that the incoming light is either a wave with a certain amount of potential energy or a number of photons all of which sum to that same amount of energy and have the same frequency as the wave.

If all light can be considered to be photon emitted particles then yes these photons must come from an electron dropping from a higher orbital level to a more stable one, emitting the photon in the process.

In the case of your light bulb, incoming electron flow runs into electrons within the filament causing them to be excited and jump up a level. Upon dropping back down to a more stable level, which they will always do unless continually hit with energy to keep the electron from falling, it will emit photons of particular frequencies that are a function of the energy they have when emitted.

Even radio waves can be considered to be emitted photons. As the charge is accelerated from one pole of the antenna to the other, that charge will run into the free electrons within the antenna causing them to jump up a level from the energy input, upon which they are unstable and fall back emitting a photon in the process.

So one can consider all light to be photon emission and photon emission only comes from an electron dropping from an unstable higher orbital level to a lower more stable orbital level.

Of course what you will find considering all light to be photon based emissions is that a number of electromagnetic radiation problems will be very difficult, to impossible, to solve using the particle theory of light. Light waves are best explained in most situations as waves of potential energy that are governed by Maxwell’s equations. The wave theory of light doesn't consider light to be a particle, only a wave. When we calculate the power received from an incoming source of light energy we use wave theory to find that power. When we design antennas to emit radiation we consider that radiation to be in the form of EM waves and design antenna lengths based on wavelength emission of the wave.

Wave theory, in my opinion, is just a far better method to describe the nature of light. It can't describe how and why the photoelectric effect works, particle theory can do that, but in most cases wave theory beats particle theory in describing the outcome of an event better and with more ease than with particle theory. Nonetheless, if every wave of light can be considered to be a number of photons emitted whose energy sums to that of the wave, then all emitted light waves must come from electrons dropping in orbital levels such that they emit the photons that compose the wave. Again, as far as I know, photon emission only comes from an electron with too much energy in a higher unstable orbital level dropping to a stable orbital level emitting a photon in the process.

Hope that's what you were looking for.

Many Smiles,
Craig
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Old Feb 8th 2010, 07:20 AM   #8
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Dear Clombard,
thank you for your detailed answer. However I have a doubt. Can photons be emitted say by nuclear reactions rather than by an electron changing its orbital level? What about the electron-positron annihilation? I think it emits a photon, but I'm unsure we can talk about the electron orbit level in this case. What do you think?
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Old Feb 8th 2010, 08:38 AM   #9
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Originally Posted by arbolis View Post
Dear Clombard,
thank you for your detailed answer. However I have a doubt. Can photons be emitted say by nuclear reactions rather than by an electron changing its orbital level? What about the electron-positron annihilation? I think it emits a photon, but I'm unsure we can talk about the electron orbit level in this case. What do you think?
You are correct I do believe that photons can be emitted from nuclear reactions, but I think it may still come from electrons dropping from a higher orbital level to a lower one. Let's take nuclear fission first. Essentially incoming neutrons break apart say uranium which splits and releases two more neutrons, and so the process repeats; ignoring alpha and beta radiation as those are just protons and electrons, then we are only concerned with the high frequency EM radiation that occurs from fission. As I'm sure you know the mass of the two parts of the split uranium atom and the two neutrons it emitted are less than the mass of the atom before being split apart, and that tiny amount of mass is what is converted into energy. I'm thinking that during the splitting of the atom process, the electrons that surround the atom in the outer band in particular must get pretty excited about being separated from their atom. If so they must jump up a certain number of orbital levels and upon falling back down emit radiation of great frequency and energy; I'll admit I'm by no means positive of that statement, it just seems to make sense to me. Although the energy emitted seems to be far greater than that which would come from the photons if emitted from dropping electrons, besides which there is less mass and that mass has been converted to energy, so perhaps in the process of fission, positrons are generated that annihilate some electrons emitting photons and decreasing the mass of the atom in the process. I know that's a bit of a leap, but if photon emission doesn't completely come from electrons, how else is it created? Not knowing I'm just taking some guesses.

As far as nuclear fusion goes, when we squeeze together two deuterium (or tritium, or some Hydrogen isotope) atoms into a Helium isotope atom, again as I'm sure you know, the mass of the Helium atom is a little less than the mass of the two deuterium atoms had before being squeezed together. Again, being concerned with only light waves emitted from the source let's again ignore alpha and beta radiation, I believe the combining of the two atoms causes some of those atoms electrons to fall into a more stable orbit emitting photons of a high frequency in the process; once more I'll state I don't know that for a fact it is again just a guess on my part. Also, positrons may be created in this process as well which annihilate some electrons emitting photons and decreasing the mass of the Helium isotope in the process. Again, just pure speculation on my part.

So even in nuclear reactions, the actual EM radiation that is emitted from these reactions may well come from electrons dropping from an excited state to a stable state emitting a high frequency photon in the process, or from combining an electron with a positron, in which case one may argue that the potential energy of the electron combined with the positron is what created the photon, so indirectly photon emission is still due to electron energy transfer.

As far as an electron and a positron annihilating each other and essentially "becoming" a photon in the process, I believe the electron and positron pair is a photon by themselves. If they are a photon, that doesn’t tell anything about how the photon was created, but rather that a photon can also be considered as an electron positron pair. That photon may well have come from an electron and could be continually alternating between the states of a photon and an electron positron pair. Even if we just consider an electron to be floating around somewhere out in space and it comes into contact with a positron annihilating it and creating a photon in the process, one might argue that the photon created was done so by the conversion of potential energy to light energy between the electron and positron coming together, in which case it may well follow that the created photon was due directly to the conversion of electron potential energy; granted the electron gets destroyed in the process, but it (along with the positron) did create the photon, much like an electron dropping from a higher orbital level to a lower one imparting that potential energy into a packet of energy it emits as a photon.

I don't know for certain about anything I have said. I am speculating to be honest. I found the question interesting and I thought I'd weigh in on it and see what kind of responses I saw from my reply. Responses like yours is exactly what I was hoping to see. You bring up some very good points, and at the time I couldn’t think of any other way that may be possible for photons to be emitted other than by electron emission. Your ideas may well be a different means by which photons can be created and emitted, or they may be linked back to electron emission, I just don't know to be honest, but it is exactly the kind of response I was hoping to see as it gets me thinking about the other possible ways for photon emission that may occur. Do nuclear reactions emit photons by a means other than from electron emission? I don't know. Can a photon be considered as just a photon or an electron positron pair, in which case the combining of the electron and the positron doesn't create a photon, but is itself a photon in a different state and that would say nothing to as how it was generated.

Your points are interesting ones, and my replies to them are simply my guesses to as to how it may still be possible for all photon emission to be caused from the electrons. Are they? I don't really know, but I thought I throw in the ideas and see if they make sense, or if not why not; then the question becomes if all photon emission doesn't not come from an electron changing orbital levels, what other sources or events can cause photon emission and by what process does that creation occur? For instance, you said what about nuclear reactions. I said it still may be possible for both fission and fusion reactions to generate photons from electron emission due to the greatly excited state the electrons find themselves in by either being attached to an atom that is split apart or attached to an atom that is squeezed together with another one creating a whole new atom. If the photon generating process is not created by electron emission, then by what means is it created by?

Interesting questions, unfortunately I don't know for certain the answer to them. Thanks for the reply though. I do enjoy the stimulation I get from facing the unknown (unknown to me anyway).

Many Smiles,
Craig
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Old Feb 8th 2010, 10:06 AM   #10
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Ok Craig.
I must say I'm just a second year physics student and I didn't took Modern Physics yet. Although I knew that the mass of the atom before the fission is greater than after the fission to due a conversion of mass into energy which can be described by the famous Einstein's formula E=mc˛, if I remember well from high school.
I'm glad the question made you think, as it made me think. I'm generally a guy who pop up with many questions and I can't sleep well if I don't know the answer. All this to say that you could be my E&M professor I guess. So I have much respect to you.
On one hand, your guesses make sense to me, but on the other hand as you know in Physics one cannot always trust his thoughts. I don't have a great knowledge in physics, much less when it comes to fission in atoms. It would be nice if another physicist that knows well this topic could enlighten us on how the photons are emitted.

I'll say what I think regarding the electron+positron pair a photon.
I do not believe them as being a photon. Because say you accelerate them into an accelerator of particles, there will be moments where they are meters, maybe hundreds of meters apart from each other. And then they collide. I think one would have thus to define a minimum distance between the 2 leptons to consider them as being a photon, if it makes any sense.
Or what about an electron in a galaxy and a positron in another?
Also I didn't took any QM yet, I'm not really sure what a photon is, apart the fact that they are generated by electromagnetic field variations. Hence I see your intervention in this thread as a little lecture.
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