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Why is snow white?

  1. Jul 20, 2006 #1
    Ice cubes do not have a colour but snow (which is claimed to be frozen water or ice) is white. Why?
     
  2. jcsd
  3. Jul 20, 2006 #2
    Snow crystals have many facettes.
    Each facette reflect a small part of the light.
    An ice cube basically shows two facettes. You can observe easily that each do reflect some light.
    Consider now the same volume of ice. The physical properties are the same (refractive index is the same) but you have maybe millions of facettes and the reflection is then a million times larger. The reflexion can become so large that in the end snow looses transparency and attenuate light quite a lot. The theory is a little bit more complicated because of multiple reflexions and attenuation, but the principles remain.

    Another effect of the powder structure of ice is the diffusion of light.

    You can observe the same effect on any transparent material, like glass or even sand.
    Crush it fine and it will look whiter and brighter. Whitheness and brightness is something to be discussed also in more detail: take a book on color perception or colorimetry.

    White cement (prepared with whiter raw materials) appears brighter when it is grinded finer.

    Michel
     
    Last edited: Jul 20, 2006
  4. Jul 20, 2006 #3
    Actually, ice cubes will also have a white color if the water freezes quickly and has impurities in it. The impurities contribute to irregularities in the crystal structure and make thousands of little bubbles.

    If the water freezes slowly, however, then the impurities are more likely to fall away from the crystalline structure, and you will have clear ice.
     
  5. Jul 20, 2006 #4

    HallsofIvy

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    "claimed to be" ? Do you doubt that? Have you ever carried a handful of snow into the house? What happened?
     
  6. Jul 20, 2006 #5
    White is not a color. So snow doesn't have a color either. :smile:
     
  7. Jul 20, 2006 #6

    Danger

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    Because she makes the dwarves shower first. :uhh:

    Sorry, mentors. Feel free to delete it, but I just couldn't let that go by. :redface:
     
  8. Jul 21, 2006 #7
    I should have mentioned that I have never had the opportunity to touch snow before because I have never been to a place that has snow.
     
  9. Jul 21, 2006 #8
    Haven't you seen the inside of a freezer?
     
  10. Jul 21, 2006 #9
    Could you say more specifically what you mean by 'facettes'? Is this a proper word because it dosen't appear in the dictionary http://en.wiktionary.org/wiki/Special:Search?search=facettes&go=Go
     
  11. Jul 21, 2006 #10
    Good one. I have seen the frost in my fridge and I can remember that it is white. But would you call it snow? Altough they are very related, if not the same. I'd rank from most to least transparent ice cube, frost, snow.
     
  12. Jul 21, 2006 #11

    Danger

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    Pivoxa, it's spelled 'facets' in English. It simply means 'faces', as in the flat bits on a diamond.
    If you shave an ice cube, or put some of that frost in a blender for a while, you'll have snow. You can surprise someone with a snowball upside the head. :devil:
     
  13. Jul 21, 2006 #12

    Gokul43201

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    The answer is in post#4 of the Physics FAQ (particularly in the moral at the end).
     
  14. Jul 21, 2006 #13
    Sorry, wrong thread, post deleted.
     
    Last edited: Jul 21, 2006
  15. Jul 22, 2006 #14
    Could you give me a link to it?
     
  16. Jul 22, 2006 #15
  17. Jul 22, 2006 #16
    This explanation is pretty much what is contained in post#4 of the Physics FAQ except in less technical detail and applied specifically to ice and snow. The collective behaviour of ice cube and ice snow are slightly different and so light interacts with them slightly differently, even though they are made out of the same combination of atoms.

    Could you take a little bit of snow and make it so it has the physical features of ice again i.e. become more transparent?
     
  18. Jul 23, 2006 #17

    russ_watters

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    Sure, you could rearrange the crystal structure by releasing and reforming the bonds that hold the water molecules in place.

    In other words, melt it and re-freeze it.
     
  19. Jul 23, 2006 #18
    You would assume that the way water was fozen in the atomsphere is different to the re-freeze (i.e. done in the fridge)? Hence get different structures the second time round (i.e. more ordered structures).
     
  20. Jul 23, 2006 #19

    Danger

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    Pivoxa, the pressure inside of a refrigerator is exactly the same as that outside of it. It's not air-tight to that extent (which is not to say that it would make a good play-pen).
     
  21. Jul 23, 2006 #20

    russ_watters

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    Absolutely. When it forms in the atmosphere, it is suspended in the air.
     
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