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Why are metals shiny?

  1. Jul 12, 2009 #1
    Just want to make sure my understanding is correct...
    Here it goes:

    1. Metals have free electrons, which can be in a myriad of energy levels, including those corresponding to the full range of frequencies in the visible region of the spectrum.

    2. Light shone on a piece of metal thus strongly absorbed by the free electrons on its surface.

    3. Tiny currents are produced (why? Can it be said that the electrons are excited?), and the energy they carry is soon re-emitted as visible light


    Thanks for your help :smile:
     
  2. jcsd
  3. Jul 12, 2009 #2

    Ranger Mike

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    Why are metals shiny? depends on the one looking at it...i do know that two specimens of the same metal will have differnet degrees of shiny....due to the surface texture ofthe metal...light is reflected by the surface of the metal..technically called Surfcae texture by ANSI/ASME B 46.1 standard...
    so it ultimately depends upon the light source ( nothing going to be shiny in the dark..right) and the amount of reflection ofthe surface roughness
     
  4. Jul 12, 2009 #3
    Ok, ok...
    Assuming adequate light and a piece of smooth metal, structurally why the metal is shinny?
     
  5. Jul 12, 2009 #4
    Would it not be shiny in the dark if you could perceive the correct wavelenght, such as infrared reflection???
     
  6. Jul 12, 2009 #5

    ZapperZ

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    One of the main reasons why metals are shinny is the existence of conduction electrons, forming what is often called surface "plasmon". These conduction electrons are able to reflect light, especially in the visible spectrum.

    The ability to make metal surfaces as very smooth surfaces also adds to the "shinyness" of the material.

    Zz.
     
    Last edited: Jul 12, 2009
  7. Jul 12, 2009 #6

    Ranger Mike

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    almost right....it is emperically a fact that a piece of metal with a surface patch finished to a surface roughness of 12 micro inch Ra ( Roughness Average 0 appears dull compared to a patch on the same piece of metal finished to a surface roughness of 112 Ra...the reason is the peaks and valleys on the 12 Microinch patch are a lot shorter than the peak and valley excurisons on the 112 Ra patch..the 112 Ra patch provides more sufaces of reflectivity and thus will reflect light better thna the better finished surface....also the SPACING between the peaks is greater on the 112 Ra patch
     
  8. Jul 12, 2009 #7

    Ranger Mike

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    also the flatness of the specimen effects "shininess"
     
    Last edited: Jul 24, 2009
  9. Jul 12, 2009 #8
    annatar.....I'm doubtful any of the reasons you state are the reason for "shiny" metal........ plastic is "shiny" too, so is paint....and if I rub a metal with some sandpaper it might be briefly very shiny then get dull via oxidation....and color also must play a part....

    I suspect reflection mechanisms are what's really at play..
    try wikipedia
    http://en.wikipedia.org/wiki/Reflection_(physics)#Reflection_of_light

    for a start....
     
  10. Jul 12, 2009 #9
    Maybe I should be specific : what is the origin of metallic luster?
    How does their reflection mechanism makes them especially shiny?
     
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