We have two materials; say glass and wood. Light passes through glass but it doesn't pass through wood. Is it caused by atoms and molecules arranged in glass and wood such that they interact differently with light?

  • $\begingroup$ I heavily modified your question, you can decide if it's OK for you. $\endgroup$
    – Mithoron
    Aug 16, 2015 at 21:33
  • $\begingroup$ There is an excellent video featuring Dr. Phil Moriarity on the Sixty Symbols channel about this very question. I'm sure someone here (or perhaps on Physics SE) will give you a good answer, but that is a very accessible video that doesn't require much background. $\endgroup$ Aug 16, 2015 at 23:09
  • $\begingroup$ Check out Quora $\endgroup$
    – Freddy
    Aug 17, 2015 at 6:50

1 Answer 1


A brief summary: It is caused by the electrons in the particles in the substance. When electrons are orbiting the nucleus of an atom they can move to higher and lower energy levels. They do, however, need energy in the form of photons to do this, this means that when a ray of light hits the atom, the electrons in it will absorb some of the energy from the light ray. It needs a specific amount of energy to move up to the next energy level so will only absorb light from a specific part of the spectrum. This means that in some materials most of the light can pass through it and it may only absorb light waves not of visible light.

So wood, to some frequencies of light, is see through but not to the light waves we can see. That is why we can have mobile and radio signal from inside houses but only see through glass.

(Electrons are actually much more complicated and theoretical than this suggests but this)

Try watching this: https://www.youtube.com/watch?v=Omr0JNyDBI0

  • 5
    $\begingroup$ Doesn't scattering play a role too? $\endgroup$
    – ron
    Aug 17, 2015 at 13:50

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