What makes glass transparent even though it’s in a solid state?
In: Physics
Atoms and molecules can only interact with light if that light has a very specific amount of energy per photon (which also determines its color). The colors they can interact with depend on the arrangement of the atoms and molecules within the material.
Basically, if an atom wants to interact with light, the light has to lift an electron from one energy level exactly to the next one, or it doesn’t do anything at all. Different molecules can alter this by changing how big that energy gap is. In the case of glass, all visible light simply has too little or too much energy for all the energy levels available in glass, so it all passes right through. UV-proof glass, on the other hand, absorbs UV light while letting visible light through; if you looked at that through a UV camera, it would look black. Likewise, black trash bags are opaque to visible light, but let infrared light through just fine.
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