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B Do all light waves move at the same speed?

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  1. Nov 23, 2016 #1
    I know photons all move at the speed of light and they move in a wave like pattern. So the question is. Do we take into account the up and down motion of the wave when we measure how fast it's moving or do we just measure the forward movement ?? For example, if the wave has higher and lower ups and downs would the wave cover more "ground" than a wave with lower ups and downs in the rate of speed forward? Please be kind with any response and if anyone is confused with what i'm asking I will try to draw out what i'm asking.



    and a big thank you ahead of time to anyone that responds.
     
  2. jcsd
  3. Nov 23, 2016 #2

    DrClaude

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    Light moves in a straight line. What has an oscillation is the electric and magnetic fields. When someone draws light like this
    lightwave1.gif
    notice that only one of the axes represents space.

    In vacuum, the speed on light is constant, whatever the frequency and amplitude of this oscillation.
     
  4. Nov 23, 2016 #3
    I was under the idea that light traveled in a spiral, slinky, corkscrew like wave or at least that what I have been able to learn off the net so far....
    so the photon travels strate and it gives off electric and magnetic fields with different frequency and amplitude of this oscillation.
    am I getting the right idea maybe ??
     
  5. Nov 23, 2016 #4

    DrClaude

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    That corkscrew picture probably corresponds to circular polarization of light. But there is nothing doing that motion in space.

    It doesn't "give off" electric and magnetic fields, it has electric and magnetic fields. And you should not thing of light in terms of tiny particles called photons zipping about. You can see it has a wave of electromagnetic ration propagating in space.
     
  6. Nov 23, 2016 #5
    ok maybe I should start out with does a photon have a shape???
     
  7. Nov 23, 2016 #6
    This really depends on the photon's energy. All photons have the shape of the picture above. But all photons can also be treated as a particle (and higher energy photons are more particle-like). This is called wave-particle duality and you should read more about it.
     
  8. Nov 23, 2016 #7

    Drakkith

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    No, you cannot think of a photon as having a shape. It is not a particle in the sense that it is a little ball or some other shape. It is simply a quantized interaction between the EM wave and matter or another EM wave.
     
  9. Nov 24, 2016 #8
    Wave-particle duality is an outdated concept and you shouldn't get that much into it. And what you wrote about shape of photon is completely not true. There is no meaningful way to talk about shape of elementary particles.
     
  10. Nov 24, 2016 #9
    There have been a few articles recently about 'twisted light' - for example:
    http://phys.org/news/2016-03-optical-slower.html
    I am not sure whether the light here is actually following a curved path or if it is an interference pattern. This article implies that it is actually twisted so its straight line speed is marginally slower.
     
  11. Nov 24, 2016 #10

    CWatters

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    So the short answer is no because they don't physically "move in a wave like pattern".

    The speed of light is only a constant (c) in a vacuum. The speed of light in glass is about 2/3rds of the speed in a vacuum.
     
  12. Nov 24, 2016 #11

    russ_watters

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    Even for waves that really do propagate in a wavelike pattern, you don't take into account the "up and down motion" when working with its speed.
     
  13. Nov 24, 2016 #12
    What if the photon doesn't have anything to interact with and is just propagating through space? Would it not be like the picture in post 2?
     
  14. Nov 24, 2016 #13

    Nugatory

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    No. However, you've asked a very similar question in another thread: https://www.physicsforums.com/threa...er-interacts-with-matter.894667/#post-5628310
    so we should continue the discussion there.

    As the question that started this thread has been answered, we can close it.
     
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