Emission spectra of a hot body vs. atomic emission spectra

Click For Summary

Discussion Overview

The discussion revolves around the presence of atomic emission spectra, specifically the sodium (Na) yellow band, in the thermal emission spectra of a hot body, such as pure iron (Fe) at high temperatures. Participants explore the relationship between thermal spectra and atomic emission, considering both theoretical and experiential perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that the Na yellow band will be present in the thermal spectra of pure Fe, suggesting that a black body radiates energy at all frequencies.
  • Others argue that the characteristic Na doublet should not be present in the emission spectra of Fe, noting that white light from hot metals encompasses almost all colors in the visible region, with stronger emissions at the ultraviolet end.
  • A participant mentions that thermal spectra are produced by closely packed atoms, which distort energy levels and lead to broader spectral lines compared to atomic emission spectra.
  • Some contributions include anecdotal evidence from everyday experiences of heating metals, illustrating how the color of emitted light changes with temperature.
  • There is a discussion on thermal broadening, where participants note that at high temperatures, the emitted frequencies become closely spaced due to energetic excitations of states.
  • One participant raises a question about the underlying reasons for the observed phenomena, indicating a desire for deeper understanding.

Areas of Agreement / Disagreement

Participants express differing views on whether the Na yellow band is present in the thermal spectra of pure Fe, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Participants reference concepts such as blackbody radiation, thermal broadening, and the effects of atomic interactions on spectral lines, but do not reach a consensus on the implications for the presence of atomic emission lines in thermal spectra.

afcsimoes
Messages
59
Reaction score
2
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.
 
Physics news on Phys.org
afcsimoes said:
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
 
  • Like
Likes   Reactions: Simon Bridge
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.
 
  • Like
Likes   Reactions: drvrm
afcsimoes said:
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.
 
A black body radiates energy at all frequencies.
That's why i say Yes, the Yellow Na characteristic radiation also will be there.
 
The "why it is like that" question is the next level to answer.
Someone knows?
 
afcsimoes said:
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.
 
  • Like
Likes   Reactions: afcsimoes

Similar threads

Replies
8
Views
5K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 19 ·
Replies
19
Views
18K
  • · Replies 9 ·
Replies
9
Views
1K
  • · Replies 12 ·
Replies
12
Views
3K
  • · Replies 19 ·
Replies
19
Views
9K
  • · Replies 4 ·
Replies
4
Views
16K
  • · Replies 21 ·
Replies
21
Views
5K
  • · Replies 1 ·
Replies
1
Views
3K
Replies
23
Views
13K