Simply: what happens to the electric(and magnetic) fields when it enters the medium? How does it interact with the molecules and how this interaction leads to the bending of light?
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asked Oct 29, 2019 at 6:42
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$\begingroup$ You have to keep in mind that the classical electromagnetic light is studied in a different frame than molecules, which are quantum mechanical entities and interact with the quantum mechanics layer of classical light. The bending of light is more easily understood in the classical frame, waves in a medium, even though the classical emerges from the underlying quantum, a lot of complexity enters. Similar to using thermodynamics variables rather than statistical mechanics to study the emergent temeperatures pressure etc behavior of matter. $\endgroup$– anna vCommented Oct 29, 2019 at 6:50
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$\begingroup$ Where can I go through the quantum mechanical explanation? $\endgroup$– Swaroop JoshiCommented Oct 29, 2019 at 7:02
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$\begingroup$ For a simple explanation of why the light bends see en.wikipedia.org/wiki/Refraction#General_explanation $\endgroup$– Adrian HowardCommented Oct 29, 2019 at 7:02
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1 Answer
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Light bends due to the difference in refractive index to fulfill the property that light travels the fastest way from point a to point b.
A good example i heard in a lecture was that of a life guard at a beach. The lifeguard can run significantly faster than he can swim. If a person is in the water in distress x meters along the beach and y meters into the water away from the life guard, the life guard is not going to run first x meters on the beach and then y meters in the water, but he will instinctively run at an angle and cross the water at some point between them.
When a wave interacts with a thicker medium for example it will slow down inside this medium. When the wave approaches the interface at an angle, part of the wave will slow down before the other parts and this is one way of imagining why it tilts. This change in direction and speed is governed by the law of refraction.
$$ \frac{\sin\theta_1}{\sin\theta_2} = \frac{v_1}{v_2}$$
You also have to keep in mind that what anna v said, this theory of refraction is composed of a different set of physics and that classical electromagnetic theory is enough to fully describe this phenomenon and that quantum physics is not required.
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$\begingroup$ I get the meaning but as examples should clarify things, that of the life guard is almost senseless. At least if running speed is assumed much greater than the running one the angle at which s/he enter must be indistinguishable from perpendicular. $\endgroup$ Commented Oct 29, 2019 at 9:28
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1$\begingroup$ @Alchimista I dissagree, i believe it is a perfect example. $\endgroup$ Commented Oct 29, 2019 at 9:43
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$\begingroup$ Might be that I am not a fast swimmer :) I agree that he won't swim x and y but still the difference between running and swimming implies that he runs the full x then he swims the full y. Not that he goes along any hypotenuse, more or less. Coastal features would change the situation. Anyway the meaning* is clear. *of the answer $\endgroup$ Commented Oct 29, 2019 at 13:58