Physics Stack Exchange
Physics Stack Exchange

Questions tagged [blackbody]

A black body is an object that absorbs all electromagnetic radiation regardless of frequency, and emits black body radiation. Such an object is just theoretical, but nevertheless, it is a useful model.

A black body is an object that absorbs all electromagnetic radiation regardless of frequency or angle of incidence, and emits black body radiation. Such an object is just theoretical, but nevertheless, it is a useful model. Questions that deal with the emission of black body radiation or with black bodies themselves should use this tag.

62 questions
69
votes
8 answers

What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium is a statement of the mean behaviour of the…
Douglas B. Staple
  • 1,566
37
votes
5 answers

Is it possible to focus the radiation from a black body to make something hotter than that black body?

My previous question wasn't specific enough. I'll try to be more specific. Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative power falls on on a m². Now if we use a lens with 1m²…
Calmarius
  • 8,428
31
votes
1 answer

Why is black the best emitter?

Why are emitters colored black better emitters than other colors? Why is white a worse emitter?
Brinn Belyea
  • 425
28
votes
3 answers

How can it be that the sun emits more than a black body?

As far as I know, a black body is an ideal emitter. So how can it be that a non-ideal emitter emits more radiation than a black body? This happens only in a very limited area at around 500nm, but it still happens: it looks like at the maximum it is…
Stefan
  • 293
21
votes
5 answers

How does the concept of a "black body" make any sense?

In my introductory chemistry class, we are learning about the basics of quantum mechanics. We were introduced to the concept of emission and absorption spectra. Our textbook describes how electrons can only exist at certain energy levels, and the…
Raiden Worley
  • 315
16
votes
5 answers

If a black body is a perfect absorber, why does it emit anything?

I'm trying to start understanding quantum mechanics, and the first thing I've come across that needs to be understood are black bodies. But I've hit a roadblock at the very first paragraphs. :( According to Wikipedia: A black body (also, blackbody)…
Vilx-
  • 3,501
15
votes
8 answers

How can the black body radiation formula be so general?

In the derivation of the black body radiation formula, there is nothing whatsoever that relates to a particular/specific material. But we nonetheless use this formula for several distinct sources in nature, such as the Sun and the CMB. How can it be…
SuperCiocia
  • 25,602
15
votes
3 answers

Is frequency quantized in the black body spectrum?

I'm aware that there're some questions posted here with respect to this subject on this site, but I still want to make sure, is frequency quantized? Do very fine discontinuities exist in a continuous spectrum like the black body spectrum? The…
arax
  • 1,208
  • 1
  • 15
  • 33
13
votes
2 answers

How can a metal heated at 600° emit thermal photons at 4000°+?

Suppose we have a cube of metal inside a room at temperature 27°. If we heat the metal up to 600° using uniform radiation of that energy, no part of it should have higher T°, but nevertheless it will start emitting visible light, that is thermal…
bobie
  • 5,862
11
votes
2 answers

Why doesn't diamond glow when hot?

In an answer to this SE question, the respondent explains that heating a perfect diamond will not cause it to glow with thermal blackbody radiation. I don't quite follow his explanation. I think it comes down to: there is no mechanism for diamond…
garyp
  • 22,633
10
votes
2 answers

Conservation of energy when focusing black body radiation on another black body

This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics and/or the fact that etendue cannot be reduced are…
M.Herzkamp
  • 1,488
10
votes
3 answers

How is temperature related to color?

I spent some time studying about temperatures and color of objects. It turns out that as we heat something it turns to red, then yellowish white and if we heat it more it turns to bluish-white. Like we can say a blue star is hotter than a red…
lastman93
  • 211
  • 1
  • 2
  • 6
9
votes
4 answers

Light formed by the sun?

This is an extract from the astrophysics chapter in my book: Hydrogen atoms fuse to form helium. At the same time, lots of of gamma photons and neutrinos are produced. The photons take thousands of years to "fight" their way to the surface of the…
Eliza
  • 2,187
8
votes
2 answers

Radiation emission and absorption

Any object can emit and absorb radiation and the power of emission can be represented by the Stefan-Boltzmann law: $$P=A\epsilon\sigma T^4$$ In many texts the net power radiated is the difference between the power emitted and the power…
Kelvin S
  • 1,185
8
votes
1 answer

Is temperature discrete

Because an object's temperature is inversely proportional to the wavelength of blackbody radiation which it emits, physicists have theorized the existence of Planck temperature at around $1.4×10^{32}$ K. Does this imply that temperature must be…
patstuart
  • 185
1
2 3 4 5