All Questions
Tagged with absorption thermal-radiation
27
questions
0
votes
2
answers
70
views
Regarding the absorption property of a blackbody
Consider a blackbody of surface area $S_b$ and at temperature $T_b$. It is placed inside an evacuated chamber (to neglect all the effects of convection), with walls of chamber at temperature $T_c$ and ...
- 378
0
votes
1
answer
56
views
Heating of a metallic 'gray body' by radiation
I am interested in a realistic model for calculating the heating of a metallic body by solar radiation.
Assumption (0) is vacuum, so neither conduction nor convection.
Assumption (1) is integration ...
- 917
2
votes
2
answers
349
views
If all matter can emit at all wavelengths, can all matter absorb at all wavelengths too?
Based on Planck’s law all matter can emit at all wavelengths at different intensities dependent of temperature. I was wondering if this holds true, does all matter absorb all wavelengths too, at ...
- 647
2
votes
1
answer
123
views
Is a layer of gas with sufficiently large optical thickness really radiating as a black body?
Can a parcel of gas with large value of optical thickness really radiate like a black body?
I have in mind a simple (most likely oversimplified) model which yields
$$I_\nu = I_\nu(0) e^{-\tau\nu} + I_\...
- 1,299
1
vote
0
answers
51
views
How is black body radiation from sample eliminated when measuring absorption coefficient?
I wonder how absorption spectra of a sample (e.g. gas with some $CO_2$ absorbing strongly at $\approx 15\mu m$) is measured by IR spectroscopy, thereby having in mind the following arrangement, ...
- 1,299
9
votes
4
answers
1k
views
Why can Einstein coefficients be derived based on thermodynamically equilibrium relations when they are basically intrinsic?
Einstein coefficients for emission and absorption ($A_{21}$, $B_{12}$, $B_{21}$) are often derived from a consideration of thermodynamic equilibrium using Boltzmann statistics and comparison with ...
- 1,299
7
votes
1
answer
879
views
Could the solar shield on the James Webb telescope have been pitch black or does it need to be highly reflective?
When I look at pictures of the sun shield on the James Webb Space telescope (JWST), I see something that looks highly reflective (and hence must have a very low emissivity). My intuition tells me that ...
- 1,581
0
votes
1
answer
67
views
Absorption & emission spectrum [closed]
Thermal radiation is visible - infrared - part of ultraviolet.
I wanted to know and more importantly have reference materials related to
What formula decides absorption spectrum of a substance.
And ...
- 101
0
votes
1
answer
60
views
Doubt regarding rate of loss of heat due to radiation
My doubt is with regards to radiation emitted by a body and how we define the rate of loss/gain of heat due to the same.
For my question, let us consider a body of: * surface area A
...
1
vote
0
answers
28
views
Absorption spectra Oxygen vs temperature
Whilst recently commissioning a spectroscopic Tunable diode laser "Oxygen Analyser" on a waste-to-energy plant, I wondered how the Analyser (which fires a narrow wavelength laser across the ...
1
vote
2
answers
432
views
Absorption vs emission not in thermodynamic equilibrium
I have read that good absorbers are good emitters. The argument goes that at thermodynamic equilibrium, the amount of radiation a body emits must be the same as it absorbs, otherwise the body will ...
- 307
3
votes
0
answers
580
views
What is the relationship between emissivity $\varepsilon$ and the imaginary part of relative permittivity constant $\epsilon^{''}_{\rm r}$ if any?
In terms of the Stefan-Boltzmann law a body that does not absorb all incident radiation emits less total energy than a black body and is characterized by an emissivity $0<\varepsilon <1$ such ...
- 703
3
votes
2
answers
160
views
How do we know that the Sun absorbs most of the radiation that falls on it?
The sun is generally considered to be an approximate blackbody. A blackbody has to be a perfect absorber. How do we know that the sun absorbs most of the radiation that falls on it?
- 337
1
vote
1
answer
482
views
Thermal radiation vs emission spectra of gases
I am a high school student and I am very confused in absorption and emission spectrum of gases, for e,g take hydrogen at room temperature for simplicity, so that we can talk in terms of Bohr's model ...
- 470
5
votes
0
answers
83
views
What causes materials like Vantablack to have their high optical absorption properties?
As per the title of this post. From reading, I understand that blackbody radiation is a factor I should consider here, with light being absorbed and converted to heat etc.
However, what I want to ...
