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Generating EM radiation

  1. Aug 5, 2008 #1
    What are the ways (both natural and artificial) in which em radiation is generated?

    Here is one of the methods: We take a point charge (or more practically a charged sphere with uniform charge distribution) such that we can voluntarily fluctuate the amount of charge on it. We fluctuate the charge of the particle sinusoidally and hence fluctuate the electromagnetic field associated with it. We have by definition an electromagnetic wave.

    Let us discuss some more ways. I would like to know all the natural ways and also the artificial techniques.

    In particular, can somebody explain to me how actually is an em wave generated when an electron in an atom, falls from a higher energy state to a lower one? I mean, alright I understand that the electron, when it falls back, loses energy in the form of em wave, but what is the mechanism of its generation?
  2. jcsd
  3. Aug 5, 2008 #2


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    In what level in physics are you? Do you want a delicate argument from QED? For what purpose are you asking?
  4. Aug 5, 2008 #3
    Apart from moving electrons (which can be done by fluctuating charge as the example that you gave), I believe the only other way is through the electrons jumping back into inner shells after undergoing excitation. These two methods are, I would say the basis of all forms of em production.

    Some not so common ways:
    Accelerating electrons produce em waves due to synchotron radiation which is essentially moving electrons.

    A charged particle entering a medium at a speed faster than the speed of light in that medium gives arise to Cerenkov radiation, which results in a nice blue glow around nuclear reacters. (this one is caused by electrons falling from higher orbitals after excitation)
  5. Aug 5, 2008 #4
    I am an undergraduate student. But I would like to have the most accurate answer no matter what level. Even if the explaination happens to go over my head initially, I'll try my best and understand it.

    Thank you.
  6. Aug 5, 2008 #5
    About the moving electrons that you mentioned- I think we need to specify that the motion be accelerated. Right? As, as far as I know, uniformly moving charge particles do not produce(or emit) em radiation, only the accelerated ones do.

    Well, I would like to point out another thing in this situation. Tell me if I'm correct or wrong-- The em waves generated due to accelerating charges are not spherically symmetrical.

    Secondly, just to remind you that I also asked for the explaination of the actual mechanism of the generation of em radiation during the transition of electron from a higher energy state to a lower one.(don't worry about the level of the explaination. I just want to have it. I'll see if I can understand it or not. If not, I'll keep it in mind until I have enough knowledge to come back to it).

    Thank you and have a good time.
  7. Aug 5, 2008 #6
    Yup, you are right about that point about accelerating charges. (even a circular motion counts)

    I am not sure about the spherical assymetry of em waves from accelearting charges, but I should think it would be correct since the em waves produced from such a situation are symmatrical usually about one axis only.

    As for the mechanism of the generation, I do not know it, so thats why i did not answer that question.

    EDIT: I dunno if u trust Wiki, but here's an explanation to the mechanism using quantum field theory: Spontaneous emission -Wikipedia
    read the part labled "Theory"
    Last edited: Aug 5, 2008
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