What CAUSES black cody radiation?

[mahela007]

What causes black body radiation? I don't think it's the electrons being exited and falling back because the result of that would be the emission spectrum of the element...

 

[Geezer]

Well, the Blackbody Radiation you study in basic physics concerns an "ideal" black body, one that absorbs and re-emits radiation of ALL energies: that is, a perfect, classical black body and not one that preferentially absorbs and emits light at certain frequencies (as a "real-life" black body does).

That said, a real-life blackbody will show spectral lines. In fact, some studies in astronomy use this kind of blackbody analysis--e.g. relative intensities and spectral lines--to infer information about stars.

 

[Dadface]

What causes black body radiation? I don't think it's the electrons being exited and falling back because the result of that would be the emission spectrum of the element...

The ideal black body is in the solid state and to see the emission spectra of the elements from which it is composed these elements must be in the gaseous/vapour state.

 

[sylas]

What causes black body radiation? I don't think it's the electrons being exited and falling back because the result of that would be the emission spectrum of the element...

Most real substances are not perfect blackbodies. You seem to be asking about the actual physics of a real material and how it emits radiation; rather than specifically for an ideal blackbody. It's a very good question.

The sources of radiation depend on the substance. Mostly, as you say, it has nothing to do with electrons changing energy levels in an atom. For thermal radiation, it is mostly from vibrations of molecules, I believe.

Like the emissions spectrum of an atom, this radiation is also has a bunch of characteristic frequencies, corresponding to vibration modes of a molecule.

Cheers -- sylas

 

[mahela007]

I don't want to be ungrateful or rude but only Sylas's answer helped. So.. black body radiation is caused by the atoms themselves vibrating really fast?

 

[Dadface]

I don't want to be ungrateful or rude but only Sylas's answer helped. So.. black body radiation is caused by the atoms themselves vibrating really fast?

Let me elaborate on my answer.The close packing of atoms as in the solid state results in the creation of numerous extra energy levels which are so close together that they can be considered as a continuous energy band.The result is that when the solid is energised there is a continuous range of allowed electron jumps this giving rise to a continuous spectrum which is distinct from the line spectrum observed when the atoms are in the gaseous/vapour state, the energy levels in the latter case being discrete and separated.

 

[mahela007]

oh... So it's like metallic bonding? (By the way.. thanks for your reply)

 

[conway]

I haven't done any detailed calculations on this but I think in a typical engineering calculation, like heat coming off a brick wall or a cement pavement, the motion of the nucleii is more significant than what the electrons are doing. The nucleii are big centers of charge which vibrate thermally, both individually and in bulk modes, and thereby radiate classical e-m energy.