Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Mr.Bhanu. on 01/03/2011 13:30:03
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Mr.Bhanu. asked the Naked Scientists:
Why does glass allow light to pass through it?
What do you think?
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Because it doesn't interact with the glass.
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It has to do with the specific wavelengths and frequency's and so black body radiation, about the discrete energy quanta / frequency's needed for exciting different electrons/orbitals in the glasses atoms. The ratio of 'speed of light in a vacuum' relative its speed in a material is called the "refractive index" of the material (like glass). When light goes through glass the general idea is that its frequency/energy (number of wavelengths per second) stays the same, but its wavelength (horizontal distance between consecutive peaks/vibrations) contracts and becomes 'choppier'.
"There are charges – electrons – in glass that are able to oscillate in response to an applied external oscillating electric field, but these charges are tightly bound to atoms, and only oscillate at certain frequencies. It happens that for ordinary glass none of these frequencies correspond to those of visible light, so there is no resonance with a light wave, and hence little energy absorbed. Glass is opaque at some frequencies outside the visible range (in general, both in the infrared and the ultraviolet). These are the frequencies at which the electrical charge distribution in the atoms or bonds can naturally oscillate. A piece of metal has electrons free to move through the entire solid. This is why metals can conduct electricity. It is also why they are shiny. These unattached electrons oscillate together with large amplitude in response to the electrical field of an incoming light wave. They themselves then radiate electromagnetically, just like a current in an antenna. This radiation from the oscillating electrons is the reflected light. In this situation, little of the incoming radiant energy is absorbed, it is just reradiated, that is, reflected."
"When light hits matter and gets absorbed, matter uses this light energy and does something with it. This includes exciting electrons to different levels, flipping particles' quantum mechanical "spins" (pretty much where they point), making molecules change their arrangements ("cis" or "trans" configurations) or whether they are vibrating or not. These different processes, the transitions between these states of matter require different amounts of energy, which they get from specific frequencies of electromagnetic radiation."