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Balckbodies and black body radiation - please enlighten me!

  1. May 15, 2014 #1
    Hi as far as I have understood: Blackbodies are physicsl objects which absorb electromagnetic waves at ALL frequencies. And the only light they radiate is determined by their temperature which means They don't reflect any light shined on them, they only emit Energy from their temperature.

    Here is my confusion and some questions i can't understand,

    a) What happens when a blackbody absorbs Electromagnetic waves? Where and how are the waves stored/absorbed in physical material ? When light is reflected it's because an Electron is excited and jumps to a higher orbit and back again, but how is light stored in physical objects - I can't understand that, because it seems impossible that an object can store infinite light -it must emmit it somehow?
  2. jcsd
  3. May 15, 2014 #2


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    The absorbed energy would be stored as internal energy in the blackbody. Now internal energy can mean many things, but in many cases would boil down to the thermal motion of whatever constitutes the blackbody. The thing to note here is that this will be a thermal distribution, which is why you get out a thermal spectrum and not a discrete one. When monochromatic light is absorbed by the blackbody it is true that it would momentarily imply a non-thermal distribution of the blackbody constituents. However, the time for this deviation from equilibrium to decay would typically be very short (depending on the interaction rate among constituents).

    The light "stored" in the blackbody will change the blackbody temperature depending on its heat capacity. The blackbody will radiate accordingly, which boils down to emission of light (and thus loss of temperature).
  4. May 15, 2014 #3
    Yes, you're correct, the energy stored in the blackbody must be emitted somehow and that emitted energy IS the blackbody radiation. But you're not correct that reflected radiation is radiation absorbed by an electron that jumped to a higher orbit and then emitted when the electron jumps back. The reflected radiation is never absorbed by the object to begin with.
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