Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Kryptid on 23/10/2008 14:09:01
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I've done some research in regards to incandescence, but I don't seem to have been able to get to the root of its cause. "Light generated by heat" just isn't descriptive enough for me. I want to know how heat can generate light. I doubt that it is just caused by friction between molecules. Is the light a result of electron excitation and subsequent photon emission as in other forms of light generation like fluorescence? If so, how is the kinetic energy of molecules transformed into this electron excitation state? Also, how does the inverse occur? If a beam of light strikes an object, how does it cause it to get hotter? How is the energy of photons converted into the kinetic energy of molecules?
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An element's 'emission spectrum' is the relative intensity of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited).
When the electrons in the element are excited, they jump to higher energy orbits. As the electrons fall back down, and leave the excited state, energy is re-emitted, the wavelength of which refers to the discrete lines of the emission spectrum
http://en.wikipedia.org/wiki/Emission_spectrum
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At a high enough temperature there are a significant number of molecules with kinetic energies (energy levels) which correspond to visible light. Each molecule will have its own level of KE and a transition can produce the emission of a photon. Because we are dealing with Fermions, there is not necessarily one set of energy levels, with spaces between. You will first get 'energy bands'which spread the spectral lines. Then, once the medium becomes dense enough, there is a continuum of levels which can produce a continuous spectrum - so called 'black body radiation'.
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If you consider light as electromagnetic waves, rather than photons, then it's merely a matter of moving charges creating an EM wave (emission), or an EM wave exerting a force on charged particles (absorption).
It's a very small version of the case of moving electrons in a radio transmitter aerial creating an EM (radio) wave.
Awww... missed the point of the question which says "what quantum effect..."
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In 'electrical' situations we are always dealing with a condensed medium. There is a continuum of energy levels and the transitions are particularly small so the photon energies are low (RF frequencies). This makes it much more convenient to take the wave approach. There is nothing to be gained but aggro by using quantum - except in some device design theory.