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Questions tagged [thermal-radiation]

The temperature-dependent emission of electromagnetic waves. Combine this tag with [tag:thermodynamics] for a macroscopic view or [tag:quantum-mechanics] for a microscopic explanation.

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How to add protective enclosure around exposed thermal camera

First off, let me state that I'm not entirely sure this is the right forum for this question. This was the only section I found multiple questions pertaining to thermal imaging, however, so I thought ...
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Thermal radiations

everything having temperature above 0 k emits radiation. But those radiations depend upon temperature of the body and not on nature of the body. Why thermal radiations are not material dependent?
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How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
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How many degrees Celsius/Fahrenheit can be reached in 1 square meter area using magnifying glasses?

The magnifying glasses are each 10 meters in diameter, their collected light is concentrated via mirrors into a 1 square meter spot. Is it possible to get a temperature higher than 2000 degrees ...
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Heat transfer on Mars

SCENARIO: I have been tasked with finding the heat transfer across a composite wall on Mars. On the left of the wall there is air maintained at Earth atmospheric conditions and room temperature (101 ...
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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? ...
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How many $\text{watt}$ are required to obtain $500°$$\text{C}$? [closed]

I am using two $1000$ $\text{watt}$ heating elements in a cylindrical chamber of volume $7500$ $\text{cm}^3$ with a limited opening at two sides. The cylinder has a radius of $6$ $\text{inch}$. How ...
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Is thermal coupling to a too cold thermal background impossible?

In (Krauss & Starkman 1999) the authors critique (Dyson 1979), and in one section argues that in the very far future cooling will become impossible because thermal contact with the cosmic ...
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Emissivity and absorptivity relation question

This question is related to another discussion here about emissivity of bodies. What interested me is to verify what extend the wavelength between emissivity and absorption is conserved at thermal ...
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Black body radiation and planck temperature [closed]

We know that for black body analysis, the radiance against wavelength is as shown: We also know that as temperature increases, the wavelength peak shifts to the left with a decrease in intensity, but ...
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What is the reason for the emission of electromagnetic waves from the sun? [duplicate]

What is the reason for the emission of electromagnetic waves from the sun and why curve its in about the visible light is maximum?
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How much change in Earth's orbital distance to change average temperature by 1°C?

How much closer/farther would the Earth need to be to/from the Sun to effect a $1 \sideset{^{\circ}}{}{\mathrm{C}}$ increase/decrease in average temperature?
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What actually causes blackbody radiation? [duplicate]

I've spent a fair bit of time reading up on answers detailing exactly how blackbody radiation is created but I have seen two different explanations for how it is created. The Kinetic Energy (KE) of ...
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Why do we take the derivative of the number of modes with respect to frequency (Rayleigh-Jeans)

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/rayj.html We arrive at this result: $$N(\nu)=\frac{4}{3}\frac{\pi L^3\nu^3}{c^3}.$$ So now we have a function representing the number of ...
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Questions on derivation of Rayleigh-Jeans equation

So it starts by assuming a cube cavity with length $L$ that acts approximately as a black body. [note: the cube length is $a$ but I'm using $L$ instead] Standing waves are formed inside the cavity, ...
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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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Which emits more radiation - a warming blackbody or a cooling blackbody?

My intuition says a cooling blackbody would emit more radiation as any body that emits radiation is itself losing that energy, causing its internal temperature to decrease.
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Factor of 4 discrepancy between integral of Planck's law vs Stefan-Boltzmann law

Consider an absolutely black sphere with unit surface area and temperature $T$. Planck's law states for the power emitted per unit area of the emitter per unit solid angle of emission per unit ...
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Infrared pass material thermal camera

I have a situation in which I need to use a thermal camera in a rain enviroment, the camera is mounted on a gymbal and can rotate 360 degrees, so I tought it may be an option to build a dome in order ...
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Black body problem

What will happen if a black body at room temperature is dropped into a furnace?? What will it look initially and how in the steady state.? I guess initially it should be black as it is absorbing a ...
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If the Sun had a larger surface temperature how would that affect its appearance to us in the sky?

I thought about this when I came across wiens displacement law which says the higher the temperature, the lower the peak wavelength. If the sun was a lot hotter, and its peak wavelength wasn't in the ...
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Is the quantum harmonic oscillator energy $E = n\hbar\omega$ or $E = (n + 1/2)\hbar\omega$? (Feynman Lectures)

Please, read the whole question. I've discussed a few contradictions and so far have not found an explanation for them. I was reading The Feynman Lectures on Physics (vol. 1), the part where he talks ...
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Why does a dense, hot, opaque body produce blackbody radiation?

I read from a textbook that a dense, hot and opaque body produces black body radiation, for example the heated filament of an incandescent light bulb. Why is it so? The explanation given is if a ...
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Given the radiation emited from a black body in a range of wavelength, how to find the temperature of such body?

For a black body that emits a radiance of $5\times 10^5 Wm^{-2}$ between the wavelengths $\lambda_1=520nm$ and $\lambda_2=550nm$, find the temperature of the given body. I think we want to work with ...
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How to develop a model for cooling rate of steel tube in air?

I am trying to develop an equation to determine the cooling rate of a steel tube in air. I'm using Fourier's Law, Stefan-Boltzman Law, Newton's Law as well as the specific heat capacity equation. The ...
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Derivation of entropy for ideal vs. photon gas

Here's the standard way of deriving the entropy of the ideal gas (see e.g. here): $$ dQ=dU+PdV=C_VdT+\dfrac{NkT}{V}dV $$ $$ dS = \dfrac{dQ}{T} $$ Integration of the latter gives the correct result. ...
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Unit of Spectral Emissive Power

I understand Spectral Emissive Power as the total amount of energy carried by photons having the same wavelength (energy), and it has the unit of (W/m2.um). I could not grasp the physical ...
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optimal spacing for stove pipe heat shield

Note: Question is DIY'ish, but analysis seems pretty theoretical, if less so than typical for this site (I'm new to it). Should I move to "engineering" site ? The flue for my wood stove transitions ...
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How/Why does heat radiation work, atomically?

In this question the relationship between characteristic spectral lines of elements and the apparently continuous emission of blackbody radiation was examined. It was suggested in the answer that ...
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How does the heat capacity of an object come into play in thermal radiation?

So say there's a cube in space acting as a blackbody. Each side is 2 metres. Initial cube temperature is 400 Kelvin. Mass is 15 kg. Say the heat capacity is 500 J/kgK. How would that affect thermal ...
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Treating stars and planets as a blackbody determine the temperature of a planet that has EM radiation incident upon it from a star

Consider the following question: Power emitted by the star via the Stefan Boltzmann law is as follows: $$4\pi\sigma T_s^4 r_s^2 $$ However the power will drop over distance and so we can say that ...
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Why should blackbody radiation emit all the absorbed energy?

So it is said that a perfect blackbody absorbs all the energy and then emits all of that in the form of blackbody radition. Why should it emit all the absorbed energy? Why can it not emit some and ...
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How do I get energy distribution of radiation (Planck's Law) in terms of frequency?

I have $$u(\lambda) d\lambda = \frac{8\pi hc\lambda^{-5}}{e^{hc/\lambda kT} - 1}d\lambda$$ I want this in terms of frequency. I can start with $\lambda =c/f$ but I will end up with $u(c/f)$ rather ...
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Planck equation in terms of frequency [duplicate]

Given $$u (\lambda) d\lambda = \frac{8 \pi hc \lambda ^{-5}}{e^{\frac {hc}{\lambda k t}}-1}d\lambda,$$ I want to convert this into frequency form $u(\nu)d \nu$. Basically, I want to covert the amount ...
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Thermal equilibrium of objects in space

I've read somewhere (not a reliable source though) that an object in space and far enough away from any heat source other than the CMB would eventually cool to 3K, the CMB's temperature, but no colder....
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Could food be used as heating element?

Could we heat food by flowing electricity through it as a heating element?
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Is the *measured* temperature inside a hollow black body the same if we place a thermometer inside it or let it make contact with the body itself?

Imagine the inside of a black body shell with non-zero thickness. Inside the shell, there is photon gas produced by the shell [at a temperature much higher than zero, say $1000(K)$]. Is there is a ...
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Will a black body placed somewhere around the Sun obtain (eventually) the same temperature as the Sun?

Suppose we look (above the Earth's atmosphere) at the wavelength ($=\frac c f)$ spectrum emitted by the Sun: This shows that the Sun is approximately a black body with a temperature of about $5525(K)....
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Time for black body to cool to a given temperature

I'm trying to figure out the time required for a blackbody to cool assuming it only looses heat via radiation. I can estimate the mass, specific heat, surface area, emissivity, initial temperature, ...
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How to see Planck's radiation law as a consequence of Bose Einstein statistics?

Planck's law comes about from the following ingredients. 1) The mode density per unit volume in a cavity is $8\pi\nu^2/c^3$. 2) Within each mode, assume Boltzmann statistics i.e the probability of ...
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Where is quantization used in deriving Planck's law?

There are several explanations for how Planck used quantization to explain blackbody radiation correctly without the ultraviolet catastrophe. I will follow this explanation. For a cavity, the mode ...
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Why do hot objects tend to emit shorter wavelength? [closed]

So how do the temperature and wavelength related and why do hot objects tend to emit shorter wavelength?
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Difference between color and effective temperature

What is the difference between color temperature and effective temperature of a star? I have gone through the pages at wikipedia, but I still do not understand that. Can anyone please help?
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If perfect blackness violates the Uncertainty Principle, how isn't dark matter a violation?

In a recent tweet, Dr. Michio Kaku stated that perfect blackness would violate the Heisenberg Uncertainty Principle, i.e. every object must emit some radiation. I have two questions regarding this ...
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Missing link re: how does kelvin relate to temperature when talking about color temperature?

I am an electrician at a commercial electrical company. There is an in-house training program that posits the datum that when talking about the designations of color temperature for lights (for ...
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Thermal radiation from molten glass

Molten glass, on photos, appears to radiate light like a black body. However, as cold glass absorbs almost no visible light, I would guess the emissivity for visible light is very low. So I am ...
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How does brightness affect color? [duplicate]

How does brightness affect the color of light? For instance, the sun might be yellow because of the blue scattering when the light travels through the atmosphere - but if you look at it, it seems ...
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Why does the sun always have some whiteness? [duplicate]

So the atmosphere scatters light on its way to earth, making the color of our sky. For example, when the sky is blue on a clear, sunny day, the sunlight appears somewhat yellow because the blue light ...
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Empty container with pinhole - an assumption for a black body

I know that a black body is a hypothetical perfect absorber and radiator. It emits EM radiation with different intensities. But my doubt is, how can an empty container with a pinhole be considered a ...
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Physical Model for a Black Body

I am learning about black body radiation and it was stated in a textbook that The best model for a black body is a large cavity with a very small hole in it which absorbs all incident radiation. ...