Blakut t1_jarmjpp wrote on March 3, 2023 at 3:48 PM

Reply to comment by 4a61756d65 in Why does a Thorium gas mantle, when incandescent, emit more light in the visible spectrum than in infrared, when compared with a black body with the same temperature? by [deleted]

>Electron gets excited, likely through atom/atom collision, either through literal collision in a gas or vibrations in a solid.
>
>Electron comes back down and emits a photon

You can have thermal emission only from point charged particle, you don't need electron levels, no? I don't have experience with solids, but this was my understanding, that it is proportional to the distirbution of velocities of atoms in the object, much like the free-free emission is a continuous spectrum too. I understand that different objects have different emissivities, and that emission at different wavelengths is different, but why would that be the case outside electron transitions? Could a possible crystalline lattice play an effect in this, restricting movements of individual atoms?

4a61756d65 t1_jarn8c0 wrote on March 3, 2023 at 3:52 PM

Yeah, you can derive some forms of thermal emission from pretending electrons are classical point charges. That doesn't mean doing it will always explain the real world correctly! That's why we need quantum physics.

Blakut t1_jarouro wrote on March 3, 2023 at 4:03 PM

But the planck spectrum uses quantum physics... It cannot be explained classically.

edit: idk why i considered gases (which i thought i know) and solids (which i know i don't know) as so different. Kirchoffs law applies to solids too, so if a solid is a poor absorber at a wavelength, it must be a good emitter.

4a61756d65 t1_jarq3pl wrote on March 3, 2023 at 4:11 PM

Ah, you're right, but you're not talking too much about the emitter when you show plank, just about the EM field itself (and if you do it somewhat rigorously you at least mumble the words ergodicity/equidistribution, which fail in dilute gases with quantum electrons for example, so you get emission lines) I'm saying classical electrons are not enough to explain emission fully even in solids (that being said I don't know much/anything about the thorium case specifically)

Blakut t1_jars76x wrote on March 3, 2023 at 4:25 PM

no they are not, i was thinking of something completely different. The stuff i work with, astrohysical sources, usually have two kinds of spectra: continuum which can come from a few things, such as free free emission, synchrotron emission, thermal emission from dust, and spectral line emission. The thermal part of the spectrum is usually very close to the ideal black body and deviations happen moslty because of geometry of particles (such as dust) and other stuff along the way, so i can separate the continuum from the spectral part. This of course gave me the wrong impression that most objects (also on earth) must have a spectrum close to a black body, and deviate from that only slightly because of things "around" the emitting body, such as gases absorbing/emitting, without considering that of course, Kirchoffs law applies to solids and everyday objects too (i only studied this in relation to gasses and some line emission scenarios).