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B A question of timing in a light bulb

  1. Mar 23, 2016 #1
    Is there any physical law that prevents the electrons in the filament of a light bulb from emitting light? How come we always see light? What are the probabilities that all the electrons in the filament fail to emit light at the same time? I suppose there is a conservation law somewhere preventing this from happening. I'm not proposing that the electrons hold their higher orbit forever without releasing the photon/energy back, just that they fail to do do it at the same time. Has this ever happened (excluding a broken light bulb of course)?

    When I turn on the switch, do all the electrons emit light at the same time, or is this a random process were all the electrons emit a photon randomly but the overall effect is that we see the light bulb light up?
  2. jcsd
  3. Mar 23, 2016 #2
    the emission of light is a random process , obviously not all electrons can get the energy at the same time , its a random process , there are over 10^27 or even more electrons on outer shell in a filament even if you say that 1/1000th of electrons only emit light then also 10^24 are there so you see the light source as constant and also not all electrons emit light of same wavelength ,what you see is a mixture of light. considerable amount of electrons can fail to emit light if either energy supplied to them is high or too low ,, but energy supplied by electric current is almost in visible range so the probability of failing is tending to zero ,, also if they fail ,, the next nanosecond they will emit light as they will gain energy and it becomes near to that of visible range.
  4. Mar 23, 2016 #3
    Burner1234, thanks. So let me see if I understand. There is no law that prevents all the electrons in the filament from not emitting a photon, but it's highly unlikely from happening? Sorta like the thermodynamic scenario in Maxwell's demon?

    Suppose all the electrons in the filament receive a pulse of energy that sends them into a higher orbit. Once there, what says that they should immediately release it in the form of a photon? Is it theoretically possible for the electron to hold on to that energy for an undetermined amount of time? Couldn't the electron just ignore the rest of the electric pulses since it is already at the top of the orbit?
  5. Mar 23, 2016 #4
    yes that can again happen but you must remember that every atom in the filament in unique with respect to its position , although there is metallic bonding but atoms which are far apart can behave as incoherent sources of energy so if an electric pulse energizes electrons of say (n) atoms and they reach mth orbit and (p) of them emit energy simultaneously while n-p are still waiting for another pulse , they get it and they energize to even higher orbit and then emit radiation this is what happens , probability of p being zero is quite low and you can calculate it easily, it is of order 10^(-26) which is almost none so what you think can happen but every atom is unique and independent so probability of such happening is almost none.​
  6. Mar 23, 2016 #5
    How many orbits can there be in the atoms of a filament? My lamp, for example, has a halogen bulb. Don't all the electrons get exited to their maximum orbit when the current flows through the filament in order for them to radiate? I tell you I find the workings of my lamp enthralling. Whenever I turn it on, light irradiates my room, but how? Wanting to know more, I searched Wiki. This is what it says about emission:

    What physics law control this action? What says that an exited electron must radiate the energy back? If for example, the electron were to keep the excited state, would it be a violation of energy? I say it isn't because the energy is still there. Is not like it disappeared or anything. Anyway, I would be happy to know which specific law controls the emission of photons by electrons.
  7. Mar 23, 2016 #6


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    I think there is a misunderstanding of the nature of light creation in heated tungsten here.

    Here's something you can try for yourself if you have the equipment to demonstrate my point, If you have a prism, look at the spectrum emitted by an incandescent light bulb, and then look at the spectrum given out by, say, a mercury lamp (those bright white fluorescent lamp). If you have a good enough resolution, you'll see a distinct difference between the two.

    When I run my class for an experiment at using spectroscopes to look at light from discharge lamps (i.e. atomic gasses), I always throw a wrench by telling the student to also look at the light coming from an incandescent light bulb (maybe everyone should be made to look at this type of demonstration to hammer in the differences). They never fail to be amazed at the glaring (no pun intended) differences. For atomic gasses, you get to see clear, distinct lines, whereas the light from an incandescent bulb gives a rather continuous spectrum!

    So already, one can suspect that the emission process here may not be identical!

    I'll go even further by asking you to look at the atomic energy level of tungsten. Even if you don't get an exact series of energy states, you'll find that the transition lines do not give you the continuous spectrum that you observe with our spectroscopic measurement. So this is another hint that maybe, this is not an "atomic transition" light, but rather from something else. The issue of electrons in "orbits" may not hold in this case.

    A very common idea that most people often miss is that atoms in solids can behave VERY DIFFERENTLY than when they are isolated. Case in point: graphite and diamond. Both are composed of carbon atoms. Yet, how they are arranged to produce the solid can dramatically alter their properties! If you don't know that both are made up of carbon atoms, you'd think that they are very different elements!

    The "tungsten" that has been formed into a wire has different properties than isolated tungsten atom! This is now no longer in the realm of atomic physics, but rather solid state physics, because in a wire, there are a gazillion tungsten atoms all connected together as a conglomerate! There are behaviors of tungsten wires that are not present in isolated tungsten atoms! So simply looking at the characteristics of tungsten atoms in trying to explain all the properties of the wires will miss a lot of extra physics! The vibrational states (i.e. phonon states) that is present in the wire is severely missing in the isolated atoms. Yet, these phonon states are responsible for a zoo of properties of the solid.

    We have addressed in this forum the QM explanation for light from such sources, and there is even a rather decent explanation for it that can be found elsewhere.

    As Phil Anderson used to say, More Is Different! That should be the take-home moral of the story here.

  8. Mar 23, 2016 #7
    ZapperZ has summarized it well enough for me.
  9. Mar 23, 2016 #8
    Yes, there are many ways to produce a photon of visible light, but there must be a law that controls this action. And this is what I'm asking. Whether the photon in produced by thermal or resistive heating, I'm no closer to understanding the mechanism that instructs the electron to release a photon rather than to hold that energy. Is it something to do with thermodynamics? Something to do with conservation laws? Is it a random action for which we currently have no explanation?
  10. Mar 23, 2016 #9
    Yes, just like as with atomic half life there is no known way of predicting which particular atom in a mass of say Uranium will be the next to spontaneously fission.
    What we do know though is that statistically some of them will do that at a measurable and predictable rate.
  11. Mar 23, 2016 #10
    But I thought we knew the mechanism by which atoms decay. Something to do with the weak-force. Is there an analog to the weak-force for the spontaneous release of a photon?
  12. Mar 23, 2016 #11


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    Yes, conservation of energy!

    Here's something else to throw a wrench into your limited view of how we can created EM radiation. Take a clump of charge, say electrons, and then shake it vigorously. Guess what? You've just created light!

    This is not uncommon either. The radio waves that you are so familiar with are created from transmission antenna in such a way. And if you ask to look at a synchrotron light souce or a free-electron laser, you'll see bunches of electrons jiggling back and forth producing a range of EM radiation from IR all the way to hard x-rays! In all of this, there is NOTHING resembling an atomic transition whatsoever!

    You will get nowhere if you think that there is just ONE mechanism that will create ALL of the EM radiation that we have.

  13. Mar 23, 2016 #12
    I get where you are coming from, Zapper, I really do. Is not that I'm fixated with atomic orbits or anything. What I want is the mechanism by which electrons release or not release photons. All of those examples you gave speak of an excitation of the electron. Yes, there are many ways to excite an electron, or the electron field, but ultimately, there is a mechanism that says to the electron or the electron field ''release that energy back in the form of a photon.'' Please, Zapper, just give me the name of the mechanism. The equation that control this process. Is it a quantum field theory equation?
  14. Mar 24, 2016 #13


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    It's conservation of energy and momentum!

    Can we go home now?

  15. Mar 24, 2016 #14


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    Spontaneous emission.
  16. Mar 24, 2016 #15
    lol. Yes, thank you.
  17. Mar 24, 2016 #16
    DrClaude. Thank you. The Wiki page on spontaneous emission says that:

    But I'm not sure if the atoms in the filament of my lamp's bulb could be considered free space?
    If it is, then is this the equation I'm looking for? Meaning the equation that controls the emission of photons in my lamp:

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