in reply to Re: I'm not a PhD but...
in thread How many colors does a rainbow have?
Thanks for answering my post jdporter. You've let yourself in for it a bit though, as you've generated more questions :) If you or anyone else can help me understand this I'd be grateful. I realise it's hideously OT in terms of perl, so feel free to ignore me, but here goes(!)
Whilst I agree that without a definitive definition of 'colour' (or 'color' :P) we won't agree how many colours are in the rainbow, I am proposing that part of the definition of 'colour' should include 'wavelengths of light that humans can see'. By definition (at least any that I've ever seen) infra-red and ultra violet are outisde the visible spectrum. That's all :)
As to the rest of my post.. I am bad at expressing myself with physics! Let me try again.. for one it should have sounded more like a (series of?) question(s):Firstly, am I right in thinking that a blackbody doesn't just require not to 'reflect or transmit' (I am not quite sure what you mean by this) any of it's radiation? It must also have a continuous spectrum which is dependent only on temperatue, and is determined by Planck's law? And it must be able to absorb and emit radiation at any (and all) wavelengths? Given that the Sun is (approximately at least) a blackbody radiator, doesn't that mean that it's spectrum is continuous, and it (absorbs and) radiates EM waves at all frequencies? If the previous is correct, is the mechanism for the sun's radiation atomic exctitation/de-excitation? Or plasma recombination, I would've thought more likely.
If the main mode of EM emission by the sun is through atomic excitation/de-excitation, is that true of all black bodies? What other modes (if any) of photon emission are there from materials? (Thinking about it, the only other ones I know would be the acceleration of charged particles---relevant to a plasma? and annihiliation of matter-antimatter pairs---plausible in something pretty hot I would have thought). If so, how is it that a theoretical black body has a continuous spectrum, dependent only on temperature if the main mode of anything's EM emission is through de-excitation? Wouldn't you expect the spectrum to be concentrated around spectral lines?
It also appears that whatever "fuzzing out" is happening, it is not enough to completely smooth out the spectrum. Far from it!
My point is though, shouldn't it? If the main mode of EM emission from a black body is by atomic excitation/de-excitation, shouldn't black body theory take account of this, or use it as its starting point?Thanks!
Those are my principles. If you don't like them I have others.
-- Groucho Marx
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Re^3: I'm not a PhD but... (models, approximations, Planck)
by moritz (Cardinal) on Feb 04, 2009 at 12:04 UTC
by why_bird (Pilgrim) on Feb 04, 2009 at 15:51 UTC