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Thermal (blackody) radiation

  1. Nov 2, 2005 #1
    When we realize what is temperature (kinetic energy) and what is radiation (photons), we find out that thermal radiation is process transforming kinetic energy of particles to electromagnetic waves.

    But I cannot understand this process on microscopic scale. (How does it run exactly in some small time.) ................(just radiating of charged particles in atoms with accelaration by atom collisions get on my mind)

    thanks.................:tongue:
     
  2. jcsd
  3. Nov 4, 2005 #2
    please......I cannot find this anywhere.............:frown:
     
  4. Nov 4, 2005 #3

    Tide

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    You're leaving something out! Yes, atoms emit radiation but they also absorb radiation. Blackbody radiation refers to the the radiation field under special conditions - namely, there is a complete balance between emission of radiation and absorption of radiation. Every photon that is emitted is eventually absorbed.

    It represents an idealization wherein the radiation field is in thermodynamic equilibrium with matter.
     
  5. Nov 4, 2005 #4
    hmmm....thanks.......but I still cannot understand sth.....

    you say, blackbody radiation is radiation of some body that is absorbing everything and continuously emiting all absorbed photons. And this is process running in electron clouds around atoms according to Bohr postulates....

    ok.....I understand this..........

    but I thought that thermal radiation of some body of high temperature (quick atoms) in NO surrounding radiation (!) has to be process of transforming the kinetic energy of atoms to photons.....................
    ....................so, it isnt truth that such body radiates or what is wrong?????????????????????

    thanks...........
     
  6. Nov 4, 2005 #5

    Mk

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    Black bodies absorb all electromagnetic radiation in its way. No radiation gets through and none is reflected; although, despite the name, black bodies radiate energy as well. How much depends on their temperature.

    I don't think we understand what you are trying to ask very well?
     
  7. Nov 4, 2005 #6
    I will try again :smile:

    OK. At first, does (black) body with temperature higher then its environment radiate if there is no radiation around it to absorb???????????
    (now the expression black is useless)

    IF SO (!!!), I am trying to ask how is described this process........(because it has to be change of kinetic energy to electromagnetic energy).................

    I hope you can understand me now :-)))
     
  8. Nov 4, 2005 #7

    Tide

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    The process is straightforward. When particles collide with each other they exchange momentum with the more energetic particle giving up some of its energy to the one with less energy and vice versa. In a large collection of particles (such as a gas) the result of a very large number of collision the cumulative exchange of energy results in, e.g., a Boltzmann distribution of the energies. The material is said to have thermalized.

    When radiation is taken into account, photons exchange energy with the particles. An absorbed photon is eventually re-emitted and its frequency is modified by the Doppler effect due to the motion of the particle. The cumulative exchange of energy after MANY such exchanges is a Blackbody spectrum for the radiation.
     
  9. Nov 4, 2005 #8
    THANKS A LOT............................

    I think I am starting to understand at last............:!!)

    SO, let there be an absolutely isolated body or gas.........let the atoms MOVE and let ALL the atoms to be NON-excited.
    Now, the collisions between atoms can be INELASTIC what results such atoms are excited (like in Franck-Hertz experiment with electrons-atoms) and then spontaneously emited..................
    ............and this is that !!!!!transforming process!!!! of kin.energy of atoms to electromagnetic energy described in microscopis scale using inelastic collisions and Bohr postulates (and principle that everything in our Universe wants to have minimal potencial energy).


    AM I RIGHT WITH ALL OF THIS NOW????????????
     
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