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Thread: What makes glass TRANSPARENT ?

  1. #1 What makes glass TRANSPARENT ? 
    owl
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    Hello freinds !

    Can any one kindly explain me what properties of the molecules or atoms that make up the glass OR what phenomenon makes glass to transmit all light through them without being blocked as other solid materials do ?

    I have searched for it on the web. But the explanations were too technical to understand (I am not a Physics person). Some sites explained it like this ----- " an absence of electronic transition states in the range of visible light" -------- What does this mean. Can any one explain it to me in simple language ?

    Thank you very much !


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    Forum Professor Zwolver's Avatar
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    glass lets some wavelenghts of energy trought.. known as visible light..

    other substances let infrared (heat) and most let gamma radiation trough..

    can't explain exactly.. sorry for that..


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    Forum Freshman Captain_Anubis's Avatar
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    I think that it might be because the particles in glass are small (I'm not sure if that's true but if it is it explains the transparency my way) and the wavelengths of visible light are too big to be effected, they simply pass through the glass as though nothing happened. I don't know if this is true but that is why air is transparent so it might be true for glass too.
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    Glass is not transparent.
    It depends on the angle of incidence, but glass has a certain amount of reflection. Hence, when you look out the window, you not only see outside, but your reflection as well.

    Additionally, glass can be considered a liquid, however, a very slow moving one. Possibly it contains some of the same properties that make water, at times, "transparent." I'm sure the refractive indexes are very different though.
    For proof of the glass = liquid, take a look at windows in an old home (new windows are coated in material that prevents the following phenomenon). If you take the glass out and measure the base, it is thicker than the rest of the pane. A graduated decrease in thickness applies as you move up to the top of the window.
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    Usually when light is absorbed it raises something in the material to a higher-energy state. For example, it might raise an electron to a higher energy level. There doesn't happen to be anything in glass that can be raised in energy by visible wavelengths of light, so light goes through it without being absorbed.
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    When a photon, a "unit2 of light, hits an atom, it may run into an electron. thne the photon is absorbed and tis nergy is used to "lift" the electron farther from the atom, yet this si a usntable condiiton and the electron will "dump2 the extra enrgy it got by absorbing the photon. Then several things may happen; in a transparent body what happens is that most of the times the electron "dumps" the energy by emitting a photon with the same energy as the one that entered it, and does it in a direction opposite to the one where the photon was coming... that is, seen from outside, a photon enters a electron, the electron "soars" above the nucleus, then goes down and a photon exits the electron traveling in the same angle and direction as the one that entered it. If this happpens often enough, the body will be "transparent", although nothing is perfectly transparent -an ordinary window glass will absorb about 1 to 3% of the photons entering it.

    BTW, it takes a time to abosorb and emit a photon, and this causes photons to be "delayed" when they move through transparent bodies. This is why there things such as "speed of light in glass", "in the air" or "in the water" -they always will be "delayed"by the absobtion-emisison rpcoess and thsu will mvoe slower than across vacuum. This different "transmisison speeds" cause the phenomenon of refraction...
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    hmm, yeah, that's a good explanation. but how does this theory prove how a prism works? or is that a density thing combined with the angle.. but i still think there is more than just passing electrons trought..

    and for glass beeing a liquid.. :? ehh.. all materials (elements) can be liquid.. depends on the amount of energy they contain.. but glass being liquid isn't possible because it has a liquid state as well.. and the liquid state of glass is a lot different.. also.. if glass is a liquid state, we can't form a solid state..

    ahw..
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    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    Evidently, upon further research, it seems I am one of many victims of a farily common old wives tale.
    Thanks, Zwolver.

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    Gaaaa...people's commonts on this thread are killing me.
    Additionally, glass can be considered a liquid, however, a very slow moving one. Possibly it contains some of the same properties that make water, at times, "transparent." I'm sure the refractive indexes are very different though.
    For proof of the glass = liquid, take a look at windows in an old home (new windows are coated in material that prevents the following phenomenon). If you take the glass out and measure the base, it is thicker than the rest of the pane. A graduated decrease in thickness applies as you move up to the top of the window.
    No, this is an urban myth. Glass is solid by pretty much any definition of "solid" that you can come up with. Glass sometimes appears thicker on the bottom of old windows because the old, imperfect processes used for making sheets of glass often resulted in sheets that were thicker on one side than the other.

    BTW, it takes a time to abosorb and emit a photon, and this causes photons to be "delayed" when they move through transparent bodies. This is why there things such as "speed of light in glass", "in the air" or "in the water" -they always will be "delayed"by the absobtion-emisison rpcoess and thsu will mvoe slower than across vacuum. This different "transmisison speeds" cause the phenomenon of refraction...
    No, refraction is caused by changes in the electric and magnetic permitivity and permeability of the material, which is basically the material's resistance to changes in electric and magnetic field strengths. The Maxwell equations predict that the speed of light in any medium will depend on the permitivity and permeability of the medium; when those change, the speed of light changes.

    The time needed for an electron to absorb a photon, be promoted to a higher energy level, and drop back to a lower energy level by reemitting the photon is on the order of microseconds - far too long to explain the slowing down of light in glass. Glass has a refractive index of around 1.5, so it should take a pulse of light around 10^-9 seconds to travel through a sheet of glass 20 cm thick - far faster than the order of about 10^-6 seconds that one would expect from electron absorption/emission.
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    Phew!
    I'm sure glad you were there to correct me. Of course, after Zowler, and then myself.

    Good job, juinor, thanks again.
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    I go for the concept that glass is a super cooled liquid. It is just a fluid that has near zero viscosity. So it just has the same props. as water and oil and lke that.
    Always remember Murphy's Law - anything that can go wrong will go wrong.
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    Forum Radioactive Isotope mitchellmckain's Avatar
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    Quote Originally Posted by Scifor Refugee
    No, this is an urban myth. Glass is solid by pretty much any definition of "solid" that you can come up with. Glass sometimes appears thicker on the bottom of old windows because the old, imperfect processes used for making sheets of glass often resulted in sheets that were thicker on one side than the other.
    Well this is not that simple. As a cause for the non-uniformity of old church windows it may be a myth. But there are several reasons for classifying glass as neither a liquid nor a solid but somewhere in between.

    The basic difference between a liquid and a solid is that while the molecules in a liquid have fixed distances between them, the molecules in a solid also have fixed positions. But the difference usually also includes, as in the case for water, prefered angles at which the molecules position themseves (which is the cause of crystaline structure) and a latent heat or energy barrier between the states. The molecules in glass do have fixed positions, but no prefered angles and no latent heat. Therefore as glass cools there is no crystalization and there is no easily identified point of transition between liquid and solid. The molecules of the glass just slow down and stop pretty much in what ever position they find themselves. There is a transition point but it only seems to effect the thermal properties such as thermal expansion and heat capacity.

    As a result glass is often considered to be in an intermediate state called glass, naturally.
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  14. #13  
    Forum Isotope Zelos's Avatar
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    the reason y glass is transperent is cause the energy levels in it is either to great, or to low to absorb visible light. This counts for both electron energies, orbital energies and vibration energies
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    Quote Originally Posted by mitchellmckain
    Well this is not that simple. As a cause for the non-uniformity of old church windows it may be a myth. But there are several reasons for classifying glass as neither a liquid nor a solid but somewhere in between.

    The basic difference between a liquid and a solid is that while the molecules in a liquid have fixed distances between them, the molecules in a solid also have fixed positions. But the difference usually also includes, as in the case for water, prefered angles at which the molecules position themseves (which is the cause of crystaline structure) and a latent heat or energy barrier between the states. The molecules in glass do have fixed positions, but no prefered angles and no latent heat. Therefore as glass cools there is no crystalization and there is no easily identified point of transition between liquid and solid. The molecules of the glass just slow down and stop pretty much in what ever position they find themselves. There is a transition point but it only seems to effect the thermal properties such as thermal expansion and heat capacity.

    As a result glass is often considered to be in an intermediate state called glass, naturally.
    True, but normal glass also contains large networks of covalently bonded silicon and oxygen. Although they are irregular, the covalent networks extend over very large distances in the material. That makes them distinctly different from liquids, which are typically help together by weak interactions.
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