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Refractive index is a function of velocity in the medium.How is this related to deviation angle inside the medium? I am not asking for the known formula,but for the mechanism behind it.

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  • $\begingroup$ I would have said it's the other way around, but no matter. Either way, Fermat's Principle as in Wolphram's answer applies. $\endgroup$ – Carl Witthoft Dec 6 '14 at 19:44
  • $\begingroup$ First of all, that's not what "begs the question" means. Next, there is no "why" in physics, just "how." We observe the principles of Least Action and discover that these models match observed phenomena. $\endgroup$ – Carl Witthoft Dec 6 '14 at 23:09
  • $\begingroup$ I agree,and I also notice that the concept of a "massy" photon matches the observed phenomena. $\endgroup$ – elias2010 Dec 11 '14 at 11:23
  • $\begingroup$ ORLY? PLease explain how seawater is somehow exempt from the laws of physics? $\endgroup$ – Carl Witthoft Jan 5 '15 at 12:31
  • $\begingroup$ I have asked a question instead. $\endgroup$ – elias2010 Jan 8 '15 at 7:16
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In optics, Fermat's principle or the principle of least time is the principle that the path taken between two points by a ray of light is the path that can be traversed in the least time. A more modern statement of the principle is that rays of light traverse the path of stationary optical length with respect to variations of the path. In other words, a ray of light prefers the path such that there are other paths, arbitrarily nearby on either side, along which the ray would take almost exactly the same time to traverse. Fermat's principle can be used to describe the properties of light rays reflected off mirrors, refracted through different media, or undergoing total internal reflection. Fermat's principle allows one to derive Snell's law of refraction and the law of reflection. Fore more details see here

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  • $\begingroup$ A light ray is the fastest route between two points P and Q,but what if Q is at the bottom of the sea so that light cannot reach it?Fermat's theorem is an attempt to explain the path of a light ray that progresses from P to Q, but if the light isn't going from P to Q then it doesn't apply. $\endgroup$ – elias2010 Jan 10 '15 at 23:31
  • $\begingroup$ Wave is spread due to Huygens law;ray is a photon's linear orbit,what else? $\endgroup$ – elias2010 Jan 24 '20 at 12:24
  • $\begingroup$ We didn't know beforehand the two points.We only know the incident point A.It is exactly the final point B we are looking for. $\endgroup$ – elias2010 Apr 16 '20 at 0:01
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Provided that the electron & the atomic beams also exhibit refraction,it seems that this is a particle's property.Deflection angle is proportional to particle's mass/size for specific medium.Photon behaves as particle in this effect.Mass is given by de Broglie equation:m=hv/c^2 , v=frequency

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    $\begingroup$ Dear Nikos Binis. It is usually frown upon to directly copy-paste identical answers. (The problem is if everybody start to copy-paste identical answers en mass.) In general in such situations, please consider one of the following options: (i) Delete one of your answers. (ii) Flag for duplicate posts and delete one of your answers. (iii) If you think the three posts are not duplicates, then personalize each answer to address the three different specific questions. $\endgroup$ – Qmechanic Dec 7 '14 at 16:21

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