Emission spectra of a hot body vs. atomic emission spectra

  • #1
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Main Question or Discussion Point

Consider a piece of pure Fe hot enough to have a bright white color (about 2 000 ºC, e.g.) and the characteristic yellow narrow yellow emission of the Na atom.
Does the Na yellow band will be present at the thermal spectra of the pure Fe?
My guess: Yes.
 

Answers and Replies

  • #2
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Does the Na yellow band will be present at the thermal spectra of the pure Fe?
characteristic Na doublet should not be present in Fe emission spectra -regarding yellow color band -in a white light emission from hot metals one expects almost all the colors in the visible region but the ultravoilet end will be stronger
 
  • #3
Simon Bridge
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In addition to above:
How atoms produce spectra - includes a section on thermal (ie. blackbody) spectra.
http://www.astronomynotes.com/light/s8.htm
"A thermal spectrum is produced by atoms that are closely packed together. The energy levels of the atoms are distorted by their neighboring atom's electrons. This smears out the normally sharp spectral lines (they become fatter)."
Related: band structure of solids.
 
  • #4
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My guess: Yes.
some general info;

From everyday experience we know that heated solid objects emit light, and as a their temperature increases, their dominant color moves increasingly towards the blue end of the spectrum.

A blacksmith handling hot iron makes it glow a dull red, then if the coals are fanned and the temperature increases, orange.

The filament of a light bulb fed by a fading battery also glows orange, while a fresh battery makes the light bulb glow yellow-white.
 
  • #5
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A black body radiates energy at all frequencies.
That's why i say Yes, the Yellow Na characteristic radiation also will be there.
 
  • #6
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The "why it is like that" question is the next level to answer.
Someone knows?
 
  • #7
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A black body radiates energy at all frequencies.
That's why i say Yes, the Yellow Na characteristic radiation also will be there.
characteristic emission lines are signature of energy levels participating in the the transition of electron -the lines will be sharper if the levels are sharp.
in thermal emission as the states are so much energetically excited and have all possible oscillations the the lines will get broadened - thermal broadening is an area being explored by spectroscopists.
i feel that that at high temperatures the photons of all possible energies get emitted and the intensity of various frequency range get to the wien's curve of black body radiation and its a continuous curve ,so the emitted frequencies are closely spaced.
these bands are also observed in 'molecular spectra' where the degrees of freedom of molecules lead to to rotation -vibration frequencies.something of this nature is happening in thermal motion of various types leading to closely spaced energy levels.
 

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