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Refraction and splitting of a photon

  1. May 26, 2012 #1
    I wonder if someone could help with me with this.

    I understand Snells Law and I can also work out various refractions in different media by using C.

    But “why” does refraction occur.

    Every website I look at (inc Wiki) gives the results of refraction (e.g. Snell’) not the reason. They will talk about what happens when light with XYZ refractive Index inter-reacts with another at ABC RI.

    But none of them explain “Why”.

    I assume that a photon is an elemental particle (not getting into duality here by the way). So if it elemental “how” can it be split/dispersed.

    At the interface some wavelengths will pass through the intersection at a certain speed and other wavelengths will pass at others – so you get bending. OK I can understand this “if” the photon could be split, as it meant to be elemental it should really, should it?

    I wonder if someone would be kind enough to the offer a clear and simple explain of “why” refraction occurs (not the results of it).

    What is actually happening?

    Or is there a website that would give this and do you have a link.

    Thank you
  2. jcsd
  3. May 26, 2012 #2


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    hi karen! :smile:

    "why" depends on the level of detail you want

    the simplest "why" is that light follows the quickest possible path, and you can easily prove that that means it must follow snell's law at any boundary

    the most complicated "why" involves considering the quantum effects of each individual molecule

    in between, we can assume that media are continuous … then the quantum effects boil down to the all-possible-paths approach, which in turn (feynman's description of this is best) favours the quickest possible path :wink:
  4. May 27, 2012 #3

    Simon Bridge

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    He needs the quantum version because of:
    ... which means go watch the feynman lectures on youtube.

    The descripton of reflection is easier to follow but refraction works the same way.
    The photon don't need to be split at all - some go one way and some go another way and when they all add up at some detector the brightest bit is what's predicted by Snell's law. Some photons travel the other ways as well which can be demonstrated by carefully blocking off some of the material.

    With mirrors it's dramatic - you can get a stronger refection by removing most of the mirror (but only for one colour).
  5. May 28, 2012 #4
    What is difference b/w unpolarized light and depolarized light????
  6. May 28, 2012 #5


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    Nothing, really, in this instance. The sums work for radio waves, which are, very often plane polarised. Birefringence makes things more complicated but that's the next level up, I think.
  7. May 28, 2012 #6
    The explanation really does depend on the level you are interested in !!!
    You do not need to know anything about photons to come up with (discover by experiment) the laws of refraction.
    Basically waves change speed when they travel from one medium to another medium.
    Different wavelengths change speed by different amounts.... this is called 'dispersion'
    One fascinating feature (mentioned by tiny tim) is that the paths taken by waves fits with the principle that the waves will take the least time to get from one point to the next. It is easy to prove that this fits with observed effects and the best BY FAR book to read to get you deeper into this is Feynman's .....title escapes me... I will find the title.
    Found it...''QED- the strange theory of light and matter.''
    Last edited: May 28, 2012
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