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Why aren't all insulators transparent?

  1. Dec 5, 2007 #1
    As I understand it, conductors interact with EM waves (light) in such a way that
    prevents transmission through the conductive material.

    Given this, why aren't all insulators transparent?

    Why is SiO2 transparent, but Si by itself is not?

    Any and all information helpful.


  2. jcsd
  3. Dec 5, 2007 #2


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    Why should they be? Should insulators have "opposite properties" to every typical property of a conductor? Even if insulators interact with EM waves in a completely different way, can they still not be opaque over the visible range?

    The properties of a compound have nothing to do with the properties of the elements it is composed of.

    PS: You might want to check out post #4 here: https://www.physicsforums.com/showthread.php?t=104715
    Last edited: Dec 5, 2007
  4. Dec 5, 2007 #3

    I am trying to understand why some types of matter are transparent and why
    other types are not, that is my real question.

    Now, there are other questions I have that go along with this.

    For example, are there any known conductors that are transparent?
    Are there insulators that have a luster (like metals) and are reflective (like metal)?
  5. Dec 5, 2007 #4
    I had understood it to be that the "behavior" of the electrons determine the properties of the compound. Metals with free electrons in their outer most shell tend to be the best conductors, stable elements with all electron shells stable (lowest energy state) tend to be good insulators. relection and luster is just another property due to electron behavior.

    My explanation may not be completely correct so I suggest wikipedia and check out the references they use.
  6. Dec 5, 2007 #5
    Transparency is all controlled by the outer shell of electrons.
    There's no transparent conductor except for liquids.
    Luster is other phenonmenon : reflection. It depends more on the surface properties of the material.
  7. Dec 5, 2007 #6


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    Did you read the FAQ that was pointed out to you?

  8. Dec 6, 2007 #7

    I did read the message referred to me, but have not read the FAQ, yet.
  9. Dec 7, 2007 #8


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    Metals are transparent at energies above the plasma energy.
    As mentioned above, it's all to do with electrons in the material.
  10. Dec 13, 2007 #9
    Just a note.

    It is also possible to explain this phenomenon by considering light as a particle.

    The amount of scattering that arises due to photon-electron interactions determines the opacity of the material.

    Correct me if I'm wrong.
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