All Questions
Tagged with blackbody or thermal-radiation
1,722 questions
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Different methods for measuring intensity of IR wavelengths
I am proposing a teaching experiment at my university for undergraduates to learn about black body radiation and part of it will involve measuring intensities of different near - mid IR wavelengths. ...
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What would the RGB color value of an infinitely hot blackbody be?
In other words, what is the limit of the rgb values of color temperature as temperature approaches infinity? Put differently, what is the terminal point of the Planckian locus? Is there an exact value?...
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Differential form of Planck's Distribution Law interpretation
So I didn't encounter differentials that often until now, I was taught that the seperate parts of $dy/dx$ for example are not supposed to have any sort of independent existence - ok.
(Calculus, 4th ...
- 65k
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Is the spectrum of Hawking radiation identical to that of thermal radiation?
Hawking radiation is frequently described as a form of black-body radiation, the same as non-black hole objects emit, except with the black hole's temperature defined solely by its mass.
But is this ...
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The derivation of the Planck distribution
I am trying to understand the derivation of the Planck distribution and black body radiation. In the Wikipedia derivation of the Planck distribution, the photons confined within a cubic box, are ...
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Effect of coloring on emissivity at temperatures below 150C?
I'm working on Aluminum/Copper heat sink design optimization and came across this thought.
The heat source on which the heat sink is going to be placed is approx 100C. Forced convection is absent, so ...
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Is thermal EMR just another form of Fluorescence / Phosphorescence?
Normally when thinking about Fluorescence one only deals with visible light, but is it fair to say that the thermal EMR (heat) that's generated from a light source is also a fluorescent effect? For ...
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How to estimate thermal conductivity of a sample?
There is a rectangular sample whose emissivity is known, and I want to estimate its thermal conductivity. A heater with a known heat flux is applied to one end of the sample and a fixed temperature is ...
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Underlying mechanism for black body radiation [duplicate]
I understand that every body of some temperature above the absolute zero radiates EM waves. When we heat it up enough it enters the visible spectrum and than proceeds to go upwards to higher and ...
- 213k
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Converting between $F_{\nu}$ and $F_{\lambda}$ spectral density
In papers, spectral energy distributions are given either in $F_\nu$, $\nu F_\nu$, $F_\lambda$ or $\lambda F_\lambda$.
$F_\nu$ has units of Janskys, for example.
Is there a clear explanation online I ...
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When can we expect a black-body radiation?
During the pandemic last few years, the Infrared thermometer is widely used to measure the body temperature.
However, the fundamental question or the question in the first place is, why do we expect ...
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How can the air be warmer than both the floor and the glass ceiling of an aluminum foil-lined box in the sun?
I've constructed a styrofoam box, with the insides spray-painted black, on top of which I placed five layers of borosilicate glasses, air-gapped with a bit of cork. It is diagrammed below:
The box ...
- 13.2k
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3
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Is it true a cloud of free electrons emits no radiation?
We all know that atomic matter emits blackbody radiation according to its temperature even if no electrons are excited within that matter, however as far as I know no mechanism exists for blackbody ...
- 26.6k
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Is a hotter heat source always necessary for an object to be heated?
Heat always moves from a high-temperature object to a low-temperature object. Therefore, a low-temperature object cannot become hotter than the relative high-temperature object from which it is ...
- 387
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How to build a reverse greenhouse?
So basically, I stumbled across this concept of radiative cooling. There are a couple of YouTubers who posted videos on this topic.
What I understood, was that in passive daylight radiative cooling, ...
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Radiation from a 2D mirrored box
I came across an elegant maths proof here1, which is related to "black body" radiation. It's a kind of "toy thought experiment".
A unit square has perfectly mirrored sides but ...
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Extracting heat energy without a heat engine
Is it possible to extract the molecular kinetic energy from a system directly (without the use of a heat engine / temperature gradient) and convert that to
another form of energy, such as electricity, ...
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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 ...
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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 ...
- 136k
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Nocturnal freezing of water: Calculation of radiation through atmosphere?
I recently came across an article in Wikipedia, which claimed that medieval civilizations used to leave water out overnight in an insulated pot during clear and calm nights, which results in the ...
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3
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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 ...
- 41.2k
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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 ...
- 65k
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Why does canola oil heat up in the microwave?
Introduction: I read on Wikipedia's list of common misconceptions that microwaves work not by emitting the resonant frequency of water, but as a result of dielectric heating. As I understand it, this ...
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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 ...
- 136k
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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 ...
- 58.5k
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1
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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 ...
- 109k
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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 ...
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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,...
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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 ...
- 213k
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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?
- 363k
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396
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Should I hold a baby formula bottle to cool it down faster?
This is an interesting and somewhat surprising physics problem - holding a hot object in your hand will cool it down faster, even if the air around is colder. I guess that 90% of people would be ...
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Why did the air not heat up in this experiment demonstrating the atmospheric greenhouse effect?
In the paper "Experimental Verification of the Greenhouse Effect", the authors (Hermann Harde, Michael Schnell (2022)) describe an experimental setup that they say demonstrates the ...
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Derivation of $P$ representation of the thermal density operator
I'm trying to derive the P representation for the thermal state
$$
\rho = \sum_{n=0}^\infty \frac{\mathrm{e}^{-\beta \omega n}}{Z} |n\rangle \langle n |
$$
where $\beta$ is the inverse temperature, $...
- 15.1k
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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 ...
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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 ...
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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
- 97.8k
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Intuitive understanding of the derivation of the Rayleigh-Jeans law
I know the Rayleigh-Jeans law and how the formula predicts UV catastrophe. Without getting into the exact derivation, I am trying to get some intuitive understanding of it by using some of the broad ...
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7
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Why is methane considered an important greenhouse gas?
Methane’s absorption bands are centered at 3.2 and 7.2 microns -- far off the peak of the Planck spectrum for a 290 K blackbody near 16 microns. Moreover, its absorption bands overlap with the water ...
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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 ...
- 41.2k
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Is the Virial Theorem dependent on the classical Equipartition Theorem?
The Wikipedia entry for the Virial Theorem states:
"*The significance of the virial theorem is that it allows the average total kinetic energy to be calculated even for very complicated systems ....
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2
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Is it possible to explain the Ultraviolet Catastrophe as a manifestation of the Riemann-Lebesgue Lemma? [closed]
Is it possible to explain the Ultraviolet Catastrophe as a manifestation of the Riemann-Lebesgue Lemma?
I don't fully understand any of both topics, but reading about the Ultraviolet Catastrophe on ...
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What do we mean when we say the CMB has a temperature and how do we measure it?
I have read this:
An object without any internal degrees of freedom, like a single photon, can't really have a temperature. But an ensemble of photons can have a temperature. If you put an ensemble ...
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Why can't we see green color in the sky? [duplicate]
From sunrise to sunset we can see a variety of colors in the sky.
For example, during morning the most dominant color is blue whereas during sunset orange,red,yellow and there shades are more dominant....
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In a universe with no photons, will everything necessarily be at absolute zero temperature?
Imagine a universe governed by the same physical laws as ours, i.e., the same fundamental forces, with the only caveat that there are no photons, hence no electromagnetic radiation in this universe. ...
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Why are good absorbers also good emitters?
I read that good absorbers are good emitters - hence a blackbody, that absorbs all kinds of radiation, also emits all kinds of radiation? I'm not able to get my head around this.
What does it mean to ...
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How does blackbody radiation suggest the quantization of energy?
I have read about Wein's law and Rayleigh-Jeans law which were apparently based on classical mechanics and couldn't explain the radiation spectrum of a blackbody.
Then Planck came up with the ...
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Can I find the surface temperature of the Sun using a spectrometer?
So I have a high school physics project and I essentially have this experiment idea where I use spectroscopy to find the surface temperature of the sun. Now I'm essentially going to assume the Sun is ...
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Wavelength and frequency of the peak of the black body radiation [duplicate]
Why does the product of the peak wavelength and the peak frequency of Planck's black body radiation not equal to the speed of light?
$$λ_{\mathrm{max}}=\frac{hc}{4.97\mathrm{kT}},$$ while $$ν_{\mathrm{...
- 213k
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Is this an error in deriving the Rayleigh-Jeans law? Kunstatter and Das's Symmetry SR and QM Ultraviolet Catastrophy
My question regards G. Kunstatter and S. Das, A First Course on Symmetry,
Special Relativity and Quantum Mechanics, Undergraduate Lecture Notes
in Physics, https://doi.org/10.1007/978-3-030-92346-4\_8
...
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Blackbody Radiation Simulation Software [closed]
I am trying to model the effective radiating temperatures of various three-dimensional solids (Tetrahedron, cube, octahedron, etc.) given a specific incident radiation. Are there any (free) softwares ...
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