Where does the continuous spectrum of photons from blackbody radiation comes from?

Question

I know that electrons can emit photons when they release energy but only at certain characteristic wavelenghts since they are bound to orbital levels within the atom. So how does the blackbody curve become continuous?

Listen people. I'm not looking for you to list random facts about blackbody radiation or to copy and paste information from other sites. If you can answer my question please do but don't waste my time with off topic information.

My comment refers to the first two entries...the other are great ...I'm getting closer to understand but not quite there.

Answer 1

The amount and type of electromagnetic radiation a black body emits is directly related to its temperature. Black bodies with temperatures below 700 K (426.85 ºC) produce very little radiation at visible wavelengths and appear black (hence the name). Black bodies above this temperature, however, begin to produce radiation at visible wavelengths starting at red, going through orange, yellow, and white before ending up at blue as the temperature increases.

The continous spectrum of a black body is not produced at one particular temperature, but over a large range of temperatures. So your concept of the electrons in an atom emitting a photon of a particular frequency due to their bound orbital levels is correct, since as the temperature increases, the atoms within the black body will have higher kinetic energy and thus the electrons will emit higher frequency photons.

Answer 2

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RE:
Where does the continuous spectrum of photons from blackbody radiation comes from?
I know that electrons can emit photons when they release energy but only at certain characteristic wavelenghts since they are bound to orbital levels within the atom. So how does the blackbody curve become continuous?

Answer 3

That's an interesting question.

The idea of a "blackbody spectrum" is an idealization, where all the emitting objects are the same (single) temperature, and all wavelengths are "optically thick", so that any photon emitted in any direction at any wavelength is re-absorbed within the blackbody cavity. Think of a hot oven, with the door closed and no window.

The material in the oven walls is made of atoms, and the atoms do indeed have quantized energy levels. However, the emission and absorption of the photons do not happen only on precise wavelengths---the spectral lines have some width, and in fact the strength of the spectral lines is non-zero even for wavelengths far from the line center. The requirement of "optical thickness" for the blackbody cavity assures that every photon will be absorbed eventually, even if it is far from the resonance wavelengths of the material making up the oven walls. The "wings" of all the spectral lines overlap somewhat so that all wavelengths have non-zero probability of being absorbed. The "infinite" optical depth of the definition of the blackbody then assures that all photons will eventually be absorbed in the oven walls.

Since the radiation in the cavity does not change with time, the photon emission processes in the walls must precisely balance the absorbtion. This is basically required by the laws of thermodynamics---if there were irregularities in the spectrum, they could be exploited to extract energy from a system whose temperature was constant and whose entropy was maximal. Every photon absorption process in the oven walls is, in detail, balanced by emission processes.

The net result is that the spectrum of photons is continuous.

Answer 4

I would say that the blackbody is not a uniform substance but rather a composite of various materials that are at different temperatures so there is no quantized look to the graph of it's radiation.
I'm no expert though.

I entered
blackbody radiation spectrum
on yahoo and a bunch of interesting sites came up, none had the exact answer explicitly, but they had some interesting info that might help you extrapolate a good answer.

Answer 5

First let me refer to the details of your difficulty. What you say would be true if atoms are considered as electrically neutral entities. But in practice they are not They may have permanent electric dipole moment or instantaneous dipole moment. You may be knowing that these instantaneous dipole moments give rise to so called Van der Waal forces between atoms. At high temperature or any temperature above 0 K these atoms vibrate and along with them the instantaneous electric dipoles vibrate. amounting to acceleration of charged particles. Under thesecircumstances the accelerated charges emit electromagnetic radiation as per the classical electromagnetic theory and frequency distribution of such radiation is continuous in nature and not discrete.

Answer 6

Each particular wavelength can only appear in certain discrete energies, but every wavelength can appear. The black body radiation does not only come from orbital excitations, it comes from excitations of kinetic energy modes also. The kinetic energy levels have a continuous spectrum.