All Questions
Tagged with blackbody or thermal-radiation
1,722 questions
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Does the radiation spectrum of bodies depend on it composition or not?
In the second edition of Quantum Physics by Robert Resnick and Robert Eisberg, they write
"Matter in a condensed state (i.e., solid or liquid) emits a continuous spectrum of radiation. The ...
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What's the smallest signal to noise ratio for which a signal has been extracted?
Suppose we have some physical variable $y$ that is changing in some way and we want to detect this change in the presence of noise (e.g. white noise) in that same physical quantity. For example $y$ is ...
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Question about unit for intensity
The picture is from one physics textbook about treating sun as a blackbody and compare the electromagnetic radiation spectrum. Note the unit used for Intensity in the picture shown, it's Watts / (...
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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
$$I_\nu = I_\nu(0) e^{-\tau\nu} + I_\...
- 1,391
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Should heat conduction not always be accompanied by heat radiation?
Consider two solid elements exchanging heat due to the temperature gradient between them by heat conduction. Such problems are always modelled with one mechanism only. Example: The transient behaviour ...
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Are there any time irreversible processes on earth which aren't due to the sun?
The sun is very hot. The earth is cold. Energy always flows from hot to cold systems. Due to the temperature difference, useful energy can be imparted onto earth (i.e., blackbody radiation from the ...
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Planck's Black Body Radiation and Einstein's Quanta
Planck described blackbody radiation as quantized resonances in a cavity.
It was not until five years after Planck made his heuristic assumption of abstract elements of energy or of action that ...
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How is black body radiation from sample eliminated when measuring absorption coefficient?
I wonder how absorption spectra of a sample (e.g. gas with some $CO_2$ absorbing strongly at $\approx 15\mu m$) is measured by IR spectroscopy, thereby having in mind the following arrangement, ...
- 1,391
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A function for the percentage of heat lost by an object immersed in a fluid due to conduction versus blackbody radiation
Is there a way to derive an equation for the amount of heat lost by an object immersed in a fluid due to blackbody radiation versus conduction using equations such as Planck's law, and the heat loss ...
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$Q$ Transfer via Radiation Formula
According to the formula:
$$
\frac{\Delta Q}{\Delta t}=\sigma\epsilon A T^4
$$
What does $T$ refer to in a situation where I am modelling the power of radiation from air of temperature to surface of ...
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What radiation spectra does neon glow at 2500 K?
A neon gas tube, when passed with high voltage electric current, will emit a characteristric spectrum of color.
This spectra lines are explained by the different combinatorial paths that electrons ...
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Do all objects at the same temperature glow the same color?
Does Kirchhoff's law for heat radiation imply that all objects at the same temperature will glow the same color?
In other words, if a piece of molten iron glows the same color as my body, which ...
- 627
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Can low energy photons in equilibrium with a black body absorber create a high temperature in the absorber?
With enough flux can low energy photons warm a black body to any temperature?
eg a solar furnace can approach the surface temperature of the sun, but could it in theory go to any temperature? If all ...
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What is the power emitted by a black hole for an observer located near its horizon?
The power emitted by a Schwarzschild black hole via Bekenstein-Hawking radiation is usually given for an observer at spatial infinity.
What is the emitted power for an observer hovering just above its ...
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Why can Einstein coefficients be derived based on thermodynamically equilibrium relations when they are basically intrinsic?
Einstein coefficients for emission and absorption ($A_{21}$, $B_{12}$, $B_{21}$) are often derived from a consideration of thermodynamic equilibrium using Boltzmann statistics and comparison with ...
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Spectral Irradiance of a Blackbody
This website states that the spectral irradiance of a Black Body is
$$F(\lambda) = \frac{2 \pi h c^2}{\lambda^5 (\exp (hc/k\lambda T)-1)}.$$
What does it mean to talk about "the" spectral ...
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Would a dense city impact the radius of a nuclear bomb?
There’s plenty of sites out there where you can choose a nuclear bomb, pick a location, and see the radius of destruction.
I noticed that the radius size of a bomb dropped in the heart of NYC is ...
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Spectral Irradiance of a Black Body
This website states that the spectral irradiance of a Black Body is
$$F(\lambda) = \frac{2 \color{red}{\pi} h c^2}{\lambda^5 (\exp (hc/k\lambda T)-1)}.$$
Other sources, however, state that it is
$$F(\...
- 2,740
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121
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Radiation of an object with a temperature gradient
Case 1: Suppose I have an infinite slab of thickness $D$ connected on one end to a heat bath at temperature $T_B.$ The other end of the slab is exposed to a vacuum, and is at temperature $T_E.$ The ...
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Question on black body radiation
In black body radiation at thermal equilibrium, the absorptivity is equal to emissivity (to conserve energy). Is it fair to say that all of the photons falling on the body are absorbed and emitted? If ...
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How can Kirchhoff's law of radiation be proven more rigorously and what does it really mean?
Kirchhoff's law of radiation states that emission factor equals absorbtion factor for any material body: $\epsilon = a$
I never understood this really: Lets say there a body which reflects totally any ...
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Confusion with spectral density of the emitted power of blackbody radiation
I'm reading a book discussing electrons' velocity fluctuations, which would cause electronic noise when detecting signals.
Velocity fluctuations originate from thermal motion. Superimposed on the ...
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If charged particles have Brownian motion, would this motion be associated with (or produce) heat or electricity?
If we have charged particles having Brownian motion, would this motion be associated with (or produce) heat or electricity? Would it produce electromagnetic radiation (and if it would produce it, what ...
- 2,878
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Why is Wien's displacement law not discrete? [duplicate]
We are taught that the electrons emit electromagnetic waves/photons when transitioning from one quantum level to another in a discrete manner. This is what causes the spectral line of specific ...
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110
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What does a Space radiator/cooler look like exactly? [closed]
I understand the principles of radiating heat to space using heat pipes and whatnot but what exactly do these devices look like in real world applications? The closest example for a space base ...
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165
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What is the maximum temperature gradient between two points? [closed]
What is the maximum temperature gradient between two points?
If the environment material affect the solution, you can assume that the environment is vacuum.
For example, can we change the temperature ...
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139
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How does the density of the air affect our perception of temperature?
The classic experiment where you have someone put one hand in a bowl of hot water and the other in a bowl of cold for a while then move their hands to a warm bowl is a classic demonstration that our ...
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Radiation Graphs and their meaning
I am looking a two graphs, the first one is radiation vs $\frac{1}{x^2}$ (Inverse Square Law) and the second one is radiation vs $T^4$(Stefan-Boltzmann Law).
The equations of my inverse square graph ...
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How does apparent brightness (or stellar magnitude) change with distance in an expanding universe
Cosmological redshift causes wavelengths of a distant object to stretch by a factor $1/(1-Hr/c)$ where H is the Hubble constant, r is distance, and c is the speed of light. Consequently the received ...
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Thermalization of two gases at different temperatures [closed]
Consider a box with partitions $A$ and $B$ each filled with a (possibly different) gas at temperature $T_A$ and $T_B$, and is separated by an adiabatic barrier. Each partition is in thermal ...
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331
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What physical property defines how fast a material loses thermal energy? [closed]
I was thinking about the following - let's say, I want to heat a 100 ml of vegetable oil in a 30 cm stainless steel pan (which weighs 1 kg) to 220°C. How should I proceed to reach the desired ...
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106
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Will a black hole disappear?
Reading The brief history of time by Stephen Hawking and the chapter 7 BLACK HOLES AIN’T SO BLACK has below.
Does it mean if his theory is correct, a black hall can disappear on its own?
Because ...
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229
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Black Body Radiation and Tungsten Filament?
I’m trying to understand Black Body Radiation and a specific case of tungsten filament light bulb. I read that these filaments have a color temperature of 4,400 degrees F yet a thermal image of a ...
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How long before the Sun has given off enough energy=mass for a one meter thick Dyson Sphere at earths orbit?
Just for fun: As energy can be converted into mass - what if we had some kind of magic technology which can convert photons into carbon atoms with 100% efficiency. I realize its not as easy as just ...
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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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Why spontaneous emission?
From what I have understood Einstein somehow deduced the A and B coefficient for spontaneous respectively stimulated emission to match the observed blackbody radiation/Planck spectrum. How did he come ...
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Is stimulated emission an excluded possibility in blackbody radiation?
From what I have understood spontaneous emission is what causes most of the light around us. And that lasers are made by stimulated emission, one photon "stimulating" an atom to drop to a ...
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Is the emitted radiation that succeeds to run away from a blackbody cavity represents what is inside of it identically?
I mean to say if a blackbody ( the one represented by a cavity with a hole) emits at equilibrium a radiation at the same temperature as the cavity walls, and some of that radiation succeeds to run ...
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How the Stefan's law will change if the body isn't a black body?
The Stefan's law for black body radiation where energy varies with the forth power of the temperature but what will happen if the body isn't black body? Would it be still forth power of temperature ...
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What the black body radiation stand for?
i'm having hard time to figure out what is happening in a black body in thermodynamic equilibrium. Let me tell what i know so far: by definition the black body emits and absorb all radiation from and ...
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Is passive cooling below ambient temperature using a spacecraft radiator possible?
Consider the following set-up: a spacecraft radiator is placed inside a vacuum chamber with transparent walls, on the surface of the Earth. The radiator acts as a heatsink touching one of the walls of ...
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How does Kirchoff's law of Thermal radiation explain that to cool below ambient temperature have to radiate through atmospheric transparency window?
Kirchhoff's law of thermal radiation is "a body emits radiation at a given temperature and frequency exactly as well as it absorbs the same radiation." Is this law valid only at thermal ...
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What percentage of sunlight isn't scattered by the atmosphere?
What percentage of sunlight isn't scattered by the atmosphere and instead will arrive at your eyes directly from the sun.
It's been aksed here before but a proper answer hasn't been given.
I was ...
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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 ...
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Why do dark objects absorb visible light but only emit infrared radiation?
What is it about the molecular structure of dark coloured objects that means they absorb most of the visible light that falls on them, but radiate infrared?
Naively I would think that if a molecule ...
- 523
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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 ...
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53
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Why does the Planck curve drop below the Rayleigh-Jeans curve for blackbody radiation when Planck quantized the energy?
This has been a research topic of mine for days now. I understand the Rayleigh-Jeans law and how it leads to the ultraviolet catastrophe. I have been searching for a clear, conceptual explanation of ...
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682
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What is the meaning of a thermal equilibrium between matter and radiation?
I understand that the thermal equilibrium between two bodies means that the two bodies attain the Same temperature. Therefore,there is no flow of a thermal energy between them. However, I don't know ...
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What would a piece of high emissivity polished metal inside a blackbody cavity look like? Darker than the walls of the cavity but the same color?
I'm trying to work out the challenges to using an infrared pyrometer to measure the temperature of a piece of shiny metal. This device has no user-accessible emissivity setting, and my sample will ...
- 6,101
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Diffrence between thermionic emission and photoelectric emission
Thermionic emission involves heat energy to excite the electron and remove it. In the photoelectric effect, a beam of light is involved.
As per my understanding heat and photons, both are energy. Heat ...
