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HOW do radio waves form at the subatomic level?

  1. Apr 10, 2010 #1

    taylaron

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    Hello,
    I've been puzzling over how radio waves and other EMR are formed at the subatomic level. I understand how to produce radio waves using a function generator but I do not understand how an antenna can emit a radio wave (among other types of EMR).
    I've asked several people this, but all I've received is "It just does!" Well, that's not good enough for me. How do electrons flowing through a series of atoms produce EMR like radio frequencies? What steps are involved?

    Regards,
    -Tay
     
  2. jcsd
  3. Apr 11, 2010 #2

    Claude Bile

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    Radio waves are typically produced by oscillating free electrons inside conductors. Free electrons, by definition, are not bound to an atomic nucleus and thus do not involve any atomic energy level transitions.

    Claude.
     
  4. Apr 11, 2010 #3

    Dale

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    Except in very specific circumstances* there is really no advantage to thinking of radio waves at the subatomic or quantum level. For one thing, radio waves are much bigger than atoms. Even for Extremely High Frequency (EHF) radio waves, the shortest wavelength radio waves, you are talking about wavelength in the 1-10 mm range. This is so far above the size of an atom that it is just not useful to describe in quantum terms.

    You are much better off sticking with a classical (Maxwell's equations) analysis for radio waves.

    *EDIT: the very specific circumstances is what is called "hyperfine splitting" which is basically due to the interaction of the nuclear magnetic moment with the magnetic field due to the electrons. The energy difference between a "parallel" and "anti-parallel" is very small and corresponds to a single photon in the RF range (e.g. the famous 21 cm line). This is NOT the way that radio waves are generated in practical applications.
     
    Last edited: Apr 11, 2010
  5. Apr 11, 2010 #4

    taylaron

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    How can one not begin with formation of EMR at the subatomic level? Radio waves can not just appear from nowhere. They must be given birth to.
     
  6. Apr 11, 2010 #5
    truth is no one here knows the answer so they'll give you the run around. I tried to post an answer but my post was deleted by moderators apparently for being too 'speculative' but in reality your standard definitions are speculative as well because no one knows the real answer so to answer this person's question how else can we do so without being "speculative"?
     
  7. Apr 11, 2010 #6

    taylaron

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    It see. The situation seems as bad as I feared.
     
  8. Apr 11, 2010 #7

    Andy Resnick

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    If I understand your question, then I would answer it this way:

    Different portions of the EM spectrum derive from different energy transitions in matter. Starting with x-rays, that involve ionization of inner-shell electrons, through UV (ionization of more loosely-bound electrons), visible (electronic transitions), IR (vibrational and rotational transitions), THz, MMW, radio, all correspond to smaller and smaller energy differences. Most materials emit very little radio-wave energy naturally- the energies are too *small*, but we are able to "synthetically" create radio waveband photons by macroscopic control of a conducting device (as mentioned in another post).

    Here's a more interesting question: fluorescent molecules are ~10 nm in size, yet the radiation they emit is 50 times that size. Similarly, radio antennas are a small fraction of the wavelength of emitted light. How can this be? How does the photon 'fit' inside the emitter?
     
  9. Apr 11, 2010 #8

    Dale

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    This is a complete non-sequitir. Just because something cannot just "appear from nowhere" does not in any way imply that it must therefore appear from the subatomic level.
     
  10. Apr 11, 2010 #9

    Dale

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    Complete BS. There is no experimental observation in electromagnetism which is not in agreement with modern theory.
     
  11. Apr 11, 2010 #10
    That's funny. You've posted about 5 or 6 posts in this thread alone and not a single one of them answers the question. You just proved my point right, i.e. you have no clue what the answer to the thread starter's question is.
     
  12. Apr 11, 2010 #11
    Are you asking that last question rhetorically, or in a Socratic way because you know the answer?

    I would like to know that as well.

    For example ELF waves are a hundred thousand miles in wavelength yet can be emitted by things far smaller. How does that work? The only explanation I've had in that regard is from an electrical engineer who told me that just because a small emitter can emit something of a far huger wave length doesn't mean that it is an efficient transmission. But I have no idea what he meant by the fact that the wave will not be anywhere near as "efficient" as it would be if the emitter was close to the size of the wave.


    Anyway, the first portion of your explanation was good and eye opening however it still fails to explain how the actual EM wave is emitted in the most fundamental way possible. Ok so an electron gets ionized and this creates an EM emission according to your theory but how exactly does it do that? Can science explain this process in more detail? Does a EM wave just "magically" fly out of the round shiny electron? This is not a substantial explanation.
     
  13. Apr 11, 2010 #12

    Dale

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    Post 3 answers it at the subatomic level and also mentions that Maxwell's equations are more useful for a practical understanding.
     
  14. Apr 11, 2010 #13
    Yes I noticed you went back and "edited" your post after I called you out on trolling the thread with 5 posts that all failed to even address the actual thread topic.

    However after reading your post I don't think it answers the question at all. At least not in a way easily visualized. Which is what I believe thread starter is asking, for a fundamental understanding of how the process occurs not for obscure equations that do nothing but obfuscate the understanding of the fundamental natural process.

    Let me try to analyze it with my limited understanding:

    "*EDIT: the very specific circumstances is what is called "hyperfine splitting" which is basically due to the interaction of the nuclear magnetic moment with the magnetic field due to the electrons. The energy difference between a "parallel" and "anti-parallel" is very small and corresponds to a single photon in the RF range (e.g. the famous 21 cm line). This is NOT the way that radio waves are generated in practical applications."

    Ok so the magnetic moment is the tendency for the nucleus to align with the magnetic field...of what? The electrons or of the nucleus? This part is not clear.
    The energy difference between a parallel and anti-parallel "corresponds" to a single photon you said. But where does the actual photon get generated? No where did you mention that. You said it only "corresponds" to a photon. I'm not even sure what that means. It's not very clear.
     
  15. Apr 11, 2010 #14

    f95toli

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    We DO have a complete theory for this: quantum electrodynamics (QED).
    The "problem" is that it is a very complicated theory and unless you know a fair amount about graduate level quantum mechanics there is no way to explain what is going on (this stuff is so specialized that it is not even covered in "normal" graduate level QM).
    Morever, QED is very "abstract" so there really no way to explain it using words, you simply have to use math.

    If you want to know more about the physics I would recommend Feynmann's pop-sci book about QED.
     
  16. Apr 11, 2010 #15

    Andy Resnick

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    Well first off, the photon is emitted when the ionized electron re-joins the atom, not when it is liberated- that's an absorption event. The most fundamental explanation I can think of is 'conservation of energy'.
     
  17. Apr 11, 2010 #16
    Surely even you must realize how utterly insufficient this explanation is?

    That's like you asking me how does a car brake work at its most fundamental level? And me responding: "it stops the car"

    Can anyone here actually explain how a wave is generated without diverting to obscure mathematical equations? For example how about a descriptive diagram of some sort, anything?
    For instance, I can quite easily explain the gestalt of how a sound wave works, and how the pressure wave propagates, there are even numerous animated diagrams and such on the internet that can be found. But the same is not true for EM waves.

    I'm watching the youtube video on quantum electro-dynamics and even its own creator Richard Feynman said he doesn't understand it so I think we can all admit that while they were able to create accurate equations to predict the exchanges at this subatomic level, NO ONE actually understands the process and no one can explain descriptively how it works.
    But I do look forward to someone attempting to prove me wrong.
     
  18. Apr 11, 2010 #17

    Dale

    Staff: Mentor

    This is completely disingenuous. Look at the timestamps. I edited that before the following post landed and certainly before you started your nonsense. Whenever I edit a post I always make sure that there were not any posts afterwards. If there were then I remove my edits and make a new post.
     
  19. Apr 11, 2010 #18
    Please stay on the topic or moderators will be forced to delete your posts. We're discussing EM waves here and how they are formed. Thus far you have failed to explain this phenomenon.
     
  20. Apr 11, 2010 #19

    Dale

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    That wasn't a stipulation of the OP and if it were I would have said that it is a nonsense stipulation. Being "easy to visualize" is not a requirement of a scientific theory. All we ask of scientific theories is that they accurately predict the results of experiments. Modern theories of electromagnetism (QED at the subatomic level and Maxwell's at the classical scale) accurately predict all EM phenomena encountered thus far.

    The electrons.

    By "corresponds" I was referring to the Planck-Einstein equation E=hf. The energy of a photon is proportional to its frequency. So if an atom makes a transition from one energy state to a lower energy state then, by conservation of energy, it must emit a photon with a frequency which corresponds to that energy by the above equation.
     
  21. Apr 11, 2010 #20

    Dale

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    To the OP, do you understand the generation of a radio wave in the context of Maxwell's equations?

    If so, then that is sufficient for all practical "technology" applications. If not, then I would be glad to answer questions about Maxwell's equations, which I think will be much more useful than answering questions about QED.
     
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