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Rotating EM source

  1. Feb 28, 2015 #1
    Hello,

    There is an omni-directional and coherent light source rotating at the frequency of EM waves. If you think of the wave model, there will be nothing unexpected that you can imagine the space is rotating around the source. However, if it is quantized I can't tell what happens since photons consist of multiple waves. So if the same thing happens, I need to know why.

    Thank you.
     
  2. jcsd
  3. Feb 28, 2015 #2

    Drakkith

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    I'm sorry I can't make any sense of what you're saying.
     
  4. Feb 28, 2015 #3
    Wave model: One wave is completed in one rotation of the source.
    Quantum model: Waves are not emitted continuously, how do I know the -say- electric field in an arbitrary point at time t?

    edit: I know this is not clear, so let's say that, a time t will pass for a photon to be emitted after the previous, thus the source will have rotated a bit. Now, this is hard to visualize but it contradicts with the wave model.
     
  5. Feb 28, 2015 #4

    Drakkith

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    I can't even begin to understand what you're trying to say except something about contradicting the wave model. Can you try to simplify your example a bit?
     
  6. Feb 28, 2015 #5
    Alright, I found how to make it easy to understand:

    A very long wavelength light source is rotating very quickly. One photon is emitted. Is the photon distorted?
     
  7. Feb 28, 2015 #6

    Drakkith

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    No, the photon isn't a particle in the normal sense of the word. It is simply the quantized energy of an EM wave. When the emitted EM wave interacts with something, an amount of energy equal to one photon's worth is transferred. That's it. Until the wave interacts with something you can't even localize the photon. In other words, a photon has no size and no shape.
     
  8. Feb 28, 2015 #7
    Isn't photon simply a package of waves? If you write down the time dependence function can't you tell the electric field at a certain point?
     
  9. Feb 28, 2015 #8

    Drakkith

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    Not as far as I know.

    When talking about energy levels on the order of single photons, I don't think so. But I'm not very familiar with the details of quantum physics, so I'm not certain. I'm under the impression that you can only do that when you have so many photons that the wave can be approximated as a classical EM wave.
     
  10. Feb 28, 2015 #9
    OK, thank you. Is there somewhere that I can read about this approximation?
     
  11. Mar 1, 2015 #10

    Drakkith

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  12. Mar 1, 2015 #11

    Simon Bridge

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    I'm going to agree with everything Drakkith says ... suspect I know what you are trying to talk about though.
    I'll start slow.

    For a uniform monochromatic spherical light source:
    In the wave model, it is continuously emitting spherical EM radiation

    In the particle model, it is equally likely to produce a photon headed in any direction.

    The thing to remember is that the particle model is statistical. You go from the particle to the wave model in the limit of large numbers of photons.
    More generally, classical mechanics is what quantum mechanical things do on average.

    I suspect you are thinking of how a beam of light "distorts" when it is fired from the surface of a rotating sphere ... it appears as a spiral. (Though you cannot see light without something for it to interact with - so, if the source were in a large dusty room, the locus of scattered light could be rigged to be a spiral by artful rotations... when most people think of beams of light they are actually imagining the pattern of light scattered from dust or something.)

    If you imagine the photon as a short burst of light or a wave-train of some kind - as some popular pictures show you - then you'd probably think that the photon would have a similar curve to it. i.e. that the photon were distorted by the rotation.

    This is not the case - photons are not thought of as having an extent in space like that.
    The spiral beam is what the particles look like when there are lots of them.

    For more on how the particle model works, try the historic but accessible:
    http://vega.org.uk/video/subseries/8
     
  13. Mar 1, 2015 #12
    Simon Bridge, then what exactly does a photon do when it "hits" an electron. Doesn't it oscillate the electron through changing electric field?
     
  14. Mar 1, 2015 #13

    Simon Bridge

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    No.

    This is a particle model.
    What normally happens when two particles collide?
    Hint: what happens when a marble hits another marble?

    Did you watch the lectures I linked for you?
     
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