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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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2 Answers2

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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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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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