Questions tagged [thermal-radiation]
The temperature-dependent emission of electromagnetic waves. Combine this tag with the [thermodynamics] tag for a macroscopic view or the [quantum-mechanics] tag for a microscopic explanation.
1,627
questions
-1
votes
0
answers
34
views
Stefan-Boltzmann's law independence of surface density
One thing about Stefan-Boltzmann's law didn't make sense to me is that the radiated power density is independent of the particle density of a surface. It seems like things have to cancel out amazingly ...
0
votes
0
answers
43
views
How well does a cavity with a hole approximate a black body?
Cavity with a hole is a frequently cited approximation to a black body (more precisely, it is the hole that is the black body here):
Is there a simple estimate of how well such a cavity approximates ...
- 60.3k
6
votes
3
answers
686
views
Trouble understanding the classic approximation of a black body as a hole on a cavity
While studying the Rayleigh-Jeans attempt to explain the spectral energy distribution of black bodies I have trouble understanding the concept of a black body as a small hole on a cavity.
We define a ...
- 85
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
1
vote
2
answers
44
views
Cooling properties of trees and thermal radiation
A question about trees, shading and thermal radiation: Will the shaded area under trees have lower average air temperature than adjacent non-shaded areas?
On the one hand, I've read that the real air ...
- 13
2
votes
1
answer
49
views
Two interacting blackbodies (one inside another) - when will thermal equilibrium be attained? [closed]
As I understand it, an ideal blackbody absorbs (and subsequently starts emitting) all incoming radiation. In typical setups like determining a planet's temperature given its albedo and distance from a ...
- 35
0
votes
0
answers
43
views
Radiation energy and momentum relation [duplicate]
Why is $\rho = 3p$ for radiation? What is the intuition behind this? If we had only 2 spatial dimentions, would it be $\rho = 2p$?
(I came across this relation while studying the state of the universe,...
- 1,161
-4
votes
2
answers
112
views
Surely $\rm CO_2$ reflects incoming solar infrared radiation?
Is the greenhouse effect not cancelled out by the $\rm CO_2$ in the atmosphere reflecting solar infrared radiation back into space? It seems logical to me that, if $\rm CO_2$ reflects infrared shifted ...
0
votes
0
answers
48
views
Does gas have thermal radiation of continuous spectrum?
Related question: Thermal radiation of a nitrogen sphere
What kind of spectrum will a sphere of a heated gas have?
Will this spectrum be continuous or linear? Will it have continuous part?
- 1,732
3
votes
1
answer
114
views
Thermal spectrum of a warmer body in a colder room
Here are a few questions about heat that I've been wondering about.
Suppose I had a piece of glass (just as an example) at room temperature, let's say $T_0 = 293$ K, and I moved it into a dark room ...
- 821
0
votes
1
answer
41
views
Does Kirchhoff's law of thermal radiation fail for optically thin sources?
A box made of any material with a small hole in it will give blackbody radiation. According to my textbook by ARNAB RAI CHOUDHURI, If you place an optically thick source of same temperature as the box ...
2
votes
1
answer
34
views
Spectral Irradiation Plots: Units/ Order of Magnitude
I am hoping to get unconfused about calculations of irradiation vs the many plots I have found online for calculated spectral irradiance from the sun assuming it is a Black Body. I have found that my ...
1
vote
0
answers
45
views
Why is a cavity with discrete modes necessary in the derivation of Planck's law?
In my readings, I have come across the concept that a finite cavity allows for the quantization of electromagnetic modes, leading to discrete energy levels. However, it's not clear to me why this step ...
0
votes
1
answer
41
views
Determine thermal emissivity of material
Is there a practical way of determining it without a lab setup?
interested in Aluminum alloys ADC-10 and ADC-12
- 109
0
votes
5
answers
77
views
Is the radiation from closed boxes blackbody radiation irrespective of the material of the box?
Suppose I have a box made of silver at temperature T, in thermal equilibrium with the surroundings. Silver has very low absorptivity and hence it will have the same low emissivity to maintain thermal ...