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Why does light not pass through voids within atoms?

  1. Jul 27, 2008 #1
    Why does light not pass through voids within atoms??

    Wow, i luuuuuvvvvv this site. for years i've had a fascination but rarely found many answers on many things. so a BIG thanks to some of you have been answering some of my questions so far.

    Here's another...

    When doing a fibre optic course, i asked the tutor why light could not pass through the wall, but could pass through air and glass, as essentially the atoms of the wall are mainly vacuum.

    I have never had a satisfactory answer to this, and i hold the incorrect opinion that everything of finite density should be allowing light to pass through.

    now i may be far too inept on the quantum side of things, to ever fully understand why things aren't transparent. but when i think about the space within the atom, my basic understanding tells me light should be passing through the space in atoms in a similar way as it travels between planets in our solar system.

    note that for this i am addressing light as photons in particle form.

    an added query following on from this would be that when atoms reflect a wavelength thus giving colour, why do the remaining wavelengths not pass through but are trapped, and what is atomically different between transparent and non transparent atoms.
  2. jcsd
  3. Jul 27, 2008 #2


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    Re: Why does light not pass through voids within atoms??

    Light can pass through the wall, the wall is made of almost the same glass as the core. It is just arranged so that the light which enters the wall is reflected back into the core.

    The reason light doesn't pass through the spaces between atoms is that light is rather large and the spaces between atoms in a solid are rather small.
    Since light is an electromagnetic wave and atoms contain charged electrons the light interacts with the atom.
    In a gas the atoms are much further apart and so most of the light doesn't get a chance to interact with them.

    Trasnaprent and non-transparent materials (at least solids) depends on howthe atoms are arranged. Incoming light excites atoms which then emit new light, which then interacts with the next atom and so on. If the atoms are arranged so that the outgoing light looks the same as the incoming light then the matererial appears transparent - it isn't the same light going through the matial.
  4. Jul 27, 2008 #3


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    Re: Why does light not pass through voids within atoms??

    Electromagnetic radiation (light, radio, microwaves) can go through holes that are larger than the wavelength of the radiation. That's why satellite dishes, radio telescopes, etc. ( http://en.wikipedia.org/wiki/Image:Parkes.arp.750pix.jpg ) aren't necessarily solid. They only need to have a screen with holes small enough that the radiation can't pass through. That's also how the screen covering the window of your microwave oven works (wavelength ~2cm).
  5. Jul 27, 2008 #4


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    Hi azzkika! :smile:

    I take it you're completely happy with the wave explanation?

    I think the answer is that, as a particle, the photon's position is uncertain … alternatively, it "sees" the positions of the gaps as uncertain … and so it can't avoid the atoms. :smile:
  6. Jul 28, 2008 #5
    Re: Why does light not pass through voids within atoms??

    yes thanks, some very good replies. and wow, i never realised atoms were creating their own light by interaction -( i always thought they absorbed the frequencies of colour they weren't so to speak and reflected the remaining frequencies). glass has a whole new concept for me now. lol
    Last edited: Jul 28, 2008
  7. Jul 28, 2008 #6
    Re: Why does light not pass through voids within atoms??

    I'm asking you to clarify the context, because said in this way doesn't seem right to me: em radiation should go even through smaller holes than its wavelenght.
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