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Why hotted iron glows?

  1. Feb 9, 2006 #1
    Does it something to do with photons emitted by electrons when going down orbits around the atom?

    And why it glows in red color?

    Is it light and heat two faces of the same thing?

    Sorry if the question is ,apparently, too plain. :biggrin:
     
  2. jcsd
  3. Feb 9, 2006 #2

    ZapperZ

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    When you heat a material, you cause the atoms and molecules that make up the material to vibrate (a solid is made up of a lattice of ions at roughly fixed locations in the material, so they vibrate around these points). This vibration produces EM radiation. A slow vibration produces long wavelength. As you heat the material more, it vibrates faster, the wavelength of the EM radiation becomes shorter until it reaches the visible spectrum. That's why you start seeing this radiation.

    Most people don't realize that this is the reverse of what happens when light hits an opaque material. Here, light hits the solid, gets absorbed by the lattice vibration (see the FAQ in General Physics) and converted to heat. This is exactly the reverse of what is happening here, where heat casues the lattice vibration and results in light emission.

    Zz.
     
  4. Feb 9, 2006 #3
    Ok, I understand, so that EM radiaton comes from photons emitted by electrons?
     
  5. Feb 9, 2006 #4

    ZapperZ

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    No, it doesn't. Notice I didn't mention anything about emission by electrons.

    A "vibration" is not the same as "atomic transition". I think most people are somehow convinced that the only way light can be emitted is when an excited atom makes a transition. That is what I tried to debunk when I wrote the FAQ for photon transport in a solid. The same goes here.

    There is no atomic transition here. The "vibration" causes the lattice ions that are surrounded by the valence electrons to vibrate. At the naive level, these are similar to dipole radiation. You have a chain of + - + - and they start vibrating. This is similar to an oscilating charge, and oscillating charge produces EM radiation.

    Look at the spectrum from your incandescent light bulb. It produces a CONTINUOUS band of light, not discrete like what you expect from an atomic transition (i.e. compare that with what you would get from a He discharge tube, for instance). The spectrum is different. The light emission from each of them comes from different processes.

    Zz.
     
  6. Feb 9, 2006 #5
    Nice focused answer, thanks! :smile:
     
  7. Feb 9, 2006 #6

    Tide

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    Incidentally, a nonheated iron also glows - just with very few photons in the visible range.
     
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