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Mechanics of refraction

I know light refracts because of changes in speed at media boundaries, but what is the actual mechanism that makes the path change? Why does a photon slowing down make a turn in towards the more-dense medium?

I presume part of a photon can't slow down without all of it slowing down, but if all of it slows down instantaneously, why should it turn at all rather than just carry straight on at reduced speed?

Narbadingi Fri 18/07/08 23:33

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baylisst111
Sat 19/07/08
12:50

If you think of the ray of light as a wave instead of a beam of photons, you can think of it as the same as sound; sound travels much faster through a denser material. Similarly light travels faster through less dense materials, i.e. a material with fewer atoms/particles to "get in the way" of the wave, which explains why the speed of light is greater in empty space than in air/water/perspex/whatever.

As for the light turning/bending/refracting, this, again, is because of the light acting as a wave. When it slows down the wavelength becomes shorter. For the wave to carry on as normal it needs to turn into the material. If anyone else can explain this bit better please do, haven't done this for a good 3/4 years now!

Narbadingi
Fri 25/07/08
15:15

Question Author

Thanks. I can understand if I think about it as a wave, but I can't understand it if I think about photons. What is the quantum mechanical explanation of refraction?

Also, why does the refractive index depend on wavelength? I cannot find an explanation for this anywhere - it seems it 'just does', which I don't like. Advice welcome.

baylisst111
Wed 30/07/08
14:26

Sorry for such a late reply! The first question I don't know I'm afraid - my knowledge of this doesn't go beyond A level stuff. The second question, it's not the refractive index depending on the wavelength, rather the wavelength depending on the refractive index, which depends on what material is.. Again I don't know why any further than I've explained, sorry :(

Narbadingi
Wed 30/07/08
15:24

Question Author

Thanks anyway. Appreciate it. Maybe we'll never know.

Cheers.

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