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Black bodies are considered as emitting all wavelengths. A incandescent light bulb has (nearly/almost) also the continuous blackbody spectrum near-perfect color rendition.

In this bulb is only one element: tungsten producing all those different wavelengths. By running a current through it, it will start to glow and gives heat and light.

But what is happening with the atoms of tungsten that those different wavelengths are produced? Isn't the radiation depending on the 'orbit jumps' of the electrons which has one 'solid' quantum value? From that point of view there should be just of couple of wavelengths. But it isn't so what produces the other waves?

Marijn
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  • "Perfect color rendition" is not a physical but a physiological statement about the evolutionary adaptation of the human eye to sunlight. A tungsten filament melts at 3695K, far below the necessary 5800K to get "perfect color rendition" that would be (almost) achieved in sunlight. – CuriousOne Jun 24 '16 at 18:53

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You are correct that quantum mechanics is the basic framework of nature, but not everything in this basic level is quantized, in the sense of coming in a discrete spectrum. Even the spectrum of the hydrogen atom at very high n has such close spacing where it can be called a continuum.

The first quantum level is bound atoms. The second level is bound molecules. The third level is molecules bound into crystals and lattices in general. The energy levels in this last case are so dense that they cannot be separated from the continuum . On top of that there are vibrational degrees of freedom within the lattice, again not separable from the continuum. Thus can one element have an almost continuous spectrum when in the solid phase.

The derivation of the black body radiation simulates all these states as quantized harmonic oscillators and the radiation curve is continuous because of the large number of oscillators. For real bodies the fit is always approximate, and often one can see spectral lines coming out over the fit or below.

anna v
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  • Still it is a bit curious. You say: "the radiation curve is continuous because of the large number of oscillators". But if all oscillators are the same (tungsten atoms) and there is the same current running through how do they get their continuous differences? It looks like though they only emit in the visible spectrum is it known why that is? And how do they know where stars are made of, because they are also BB radiators; so every element would be possible?? – Marijn Jun 24 '16 at 19:41
  • I am talking of the quantum mechanical model used to derive the black body curve. It is based on the quantum mechanical oscillator model. It is a successful model because most potentials are symmetric and when expanded in a series have as a first term the x^2 of the harmonic oscillator. Real material is made out of other potentials, still the x^2 is a good first order approximation and that is why the black body curve is more or less followed. So the tungsten atoms are not the only potentials entering, also the lattice vibrations enter, it is not one type of oscillator. – anna v Jun 25 '16 at 03:34
  • Currents have no meaning in the quantum frame; it is the kinetic energy of the vibrations and the kinetic energy of the electrons which make up the current, which raise the temperature of the body and shape the bb radiation curve approximately. They emit in the whole spectrum subject to the temperature and the shape. It is easier to measure light than microwaves, (but it is done in the comsmic microwave background for example.) – anna v Jun 25 '16 at 03:37
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The continuum radiation from a material is the conversion of thermal energy into electromagnetic energy. As per Wikipedia

All matter with a temperature by definition is composed of particles which have kinetic energy, and which interact with each other. These atoms and molecules are composed of charged particles, i.e., protons and electrons, and kinetic interactions among matter particles result in charge-acceleration and dipole-oscillation. This results in the electrodynamic generation of coupled electric and magnetic fields, resulting in the emission of photons, radiating energy away from the body through its surface boundary

The radiation comes from electronic transfer inside the medium is known as characteristic radiation (usually this term is used with inner shell line radiation in x ray regime) which is a property of the material.

The thermal oscillation of the dipoles and charged particle at the surface of a material is responsible for the continuum radiation. The radiation can come from the volume if the medium is transparent to the radiation, this is known as corona emission.

Regards,

hsinghal
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  • Do you think that all elements can be BB radiators like tungsten? If not why can tungsten and other not? – Marijn Jun 24 '16 at 19:56
  • I don't know the answer but for it to be BB there has to be thermalization. One wavelength would have it as coherent as lasers, or at least as narrow BW. So it must be free charges or dipoles around, the electrons going tru as current colliding with atoms etc. can't be the atomic state change emissions. I have not seen yet a clear, complete, correct and authoritative answer – Bob Bee Jun 24 '16 at 23:37
  • @Marijn actually there is no perfect black body in this world. The ideal black body absorb all the energy given to it and radiate only from its surface. The light emitted by tungsten is thermal radiation. To get good light we need a wire which can sustain high temperature and can conduct appriciably. Tungsten might be the best by far. Originally Edison used carbon filament for this purpose – hsinghal Jun 25 '16 at 07:24