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Black and White

  1. Sep 6, 2007 #1
    As I know, a black substance absorbs all light and a white substance reflects all light.

    Can I say, in a black substance, the electrons are in a high energy state, compared to a white substance?
    And how much light energy it can absorb? There has to be a limit to it, right?

    So, shouldn't a black substance turn white after exposing to light for some period of time?

    Thanks,
    .joby
     
  2. jcsd
  3. Sep 6, 2007 #2
    Everything radiates -- at the temperature that they are at. In fact, the radiation profile is exactly that of a perfectly black body. The temperature will be such that the radiated energy equals the absorbed energy.

    Remember that your light bulb filaments are black when the light is off...
     
  4. Sep 8, 2007 #3
    Last edited: Sep 8, 2007
  5. Sep 8, 2007 #4
    All non-ideal substances have frequencies where they are more likely to absorb, and different frequencies where they are more likely to emit. The higher the temperature, the closer the emission spectrum of a macroscopic, non-ideal material approximates that of the ideal blackbody; the lower the temperature, the closer the absorption spectrum of a macroscopic, non-ideal material approximates that of the ideal blackbody.
     
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