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As we know, light is reflected by a mirror, so we can see our image, it is mostly reflected by a white wall (that does not get hot) but we cannot see our reflection, it is absorbed by a black wall, and it goes through glass. Moreover, depending on the wave-length of the light (infrared, ultraviolet) it may behave differently (x-rays will go through objects that regular visible light will not). Is there a general law we can use to understand what is the light's behaviour, given its wave-length, and a physical object? In other words, how can we predict, given the photon's energy, how it travels through the physical world?

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You predict how it travels by understanding the medium by which it travels and how it reacts with different objects. For example with your comment on a mirror and a white wall, the mirror reflects the light back in a predictable manner, however a white object will scatter the light in all directions, and hence you see no image reflected back at you. Understanding how light reacts with different colours just requires knowledge of the colour of the light itself (the wavelength), and of the object.

Also to do with materials is how the light reacts with charged particles (it is, after all, electromagnetic radiation). For example, in glass the electrons are tightly bound to the atoms and hence are not free to move, but in a metal the bonding is metallic, so the atoms are surrounded by a 'sea' of delocalised electrons which are free to move, so the electrons can absorb the light, causing reflection.

Hope this answers your question :)

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  • $\begingroup$ +1 You might think of expanding this slightly , as the question asks about prediction, to include progagation and it's correlation with initial momentum? $\endgroup$ – user163104 Aug 6 '17 at 17:21
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    $\begingroup$ Noted, I'll edit later as I have to go out now. $\endgroup$ – CooperCape Aug 6 '17 at 17:30

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