All Questions
13 questions
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2
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79
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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 ...
- 393
0
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1
answer
60
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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 ...
- 947
2
votes
1
answer
142
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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_\...
- 1,391
9
votes
4
answers
2k
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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 ...
- 1,391
7
votes
1
answer
887
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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 ...
- 1,599
0
votes
1
answer
63
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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
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0
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29
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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
507
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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 ...
- 317
1
vote
1
answer
569
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
1
vote
2
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933
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If black is the best absorber and radiator, why does it get hot?
I can guess that it’s emission peaks at a higher temperature than white. So when a light is turned onto a black and white piece of paper, the initial condition is not at equilibrium. As black absorbs ...
- 1,729
0
votes
0
answers
51
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Black hole absorbing photons?
If a black hole has a radius that is not that much smaller than the wavelength of light emitted by the sun, and is at the same temperature, shouldn't it be able to absorb photons as well as emit them? ...
- 36
0
votes
1
answer
174
views
Are these statements about different emissivities correct?
I'd like to verify if my concluded statements regarding different emissivities are correct or not. And if not, why.
1
Two objects, one with an emissivity of 1 (object A) and one with a very low ...
- 471
1
vote
1
answer
521
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Why do high altitudes have larger diurnal temperature variation than lower altitudes?
It seems like the lack of atmosphere should not be playing a role in the diurnal temperature variation because that's what makes it colder. Mountains are not that dry, usually.
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