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Random reflection question

Why/how do things reflect? It seems such an easy question I know, but I don't *think* I know, so if anyone can enlighten me?
Thank you :smile:
Reply 1
Avatar for Morbo
Morbo
17
From a particle point of view, a reflection is just an energy conserving collision between a relatively light particle and a very massive one e.g. ball bouncing off a wall. If it's perfectly elastic, all the energy the ball has towards the wall must be directed back because the wall hardly moves.

From a wave point of view, a reflection is similar: when the wave hits a rigid surface, for example, the wave's energy must go somewhere. A symmetry argument says that the only way the energy can go is back in the direction it came from.
Reply 2
Avatar for Willa
Willa
11
angel_with_a_mission
Why/how do things reflect? It seems such an easy question I know, but I don't *think* I know, so if anyone can enlighten me?
Thank you :smile:


I think you're asking about what is going on at the atomic scale.

Basically all material will absorb and then retransmit the light that falls on it (or particles or whatever). In shiny things that reflect well, there exists a cloud of electrons at the surface (you get this in conductors, hence why metals shine). The cloud provides lots of accessible energy levels, almost a smooth continuum. This results in almost any incoming photon being absorbed and transmitted almost exactly as it was.

In non-shiny things, the photons will get absorbed as well, but because there isn't the electron cloud, there isn't the same continuous range of energy levels at which they will re-emit the photon. What will happen is the atoms will have a certain "dominant path" which they return via on their way from their excited state back down to their ground state. This dominant path will only have certain energy jumps, and so we will only see certain colours!

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