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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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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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why do we use energy density in black body radiation instead of only energy? [on hold]

why did we use energy density in the derivation of planks law and also how can we count the number of waves inside a blackbody generated by in internal reflection of waves?
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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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107 views

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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Is there any evidence that 'anthropogenic climate change' greenhouse radiative models describe real atmospheric processes?

The radiative models used by the IPCC predict in case of a doubling of the preindustrial CO2 concentration of 285 ppm in the atmosphere - the current value is 405 ppm - an increase in backradiation or ...
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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. ...
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Is there a difference in the infrared absorption spectrum of a greenhouse gas when pure and when mixed with non-greenhouse gases?

According to the standard IPCC greenhouse climate change hypothesis a doubling of the preindustrial CO2 concentration of 285 ppm in the atmosphere - the current value is 405 ppm - would lead to an ...
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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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Satellite radiance measurements in spectral regions

Q: A satellite measures longwave radiation emerging from a planet with uniform surface temperature T1 and uniform atmospheric temperature T2. What values of radiance does the satellite measure in the ...
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Local equilibrium of slow time varying thermal system

I'm trying to differentiate a thermal system in local equilibrium (and slow time varying) v/s a non-equilibrium system. For a thermal system which is slowly time varying, how does one define local ...
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1answer
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Does a black body in zero gravity emit EM radiation? [closed]

I have just recently thought of this query. However, I can find no evidence of any experiments ever being carried out on the effect of zero gravity on black body radiation.Perhaps someone here has ...
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Do materials approach black body behavior as temperature increases

I have emittance curves of a material (that cannot be shared) that show an increase in emittance values over a wide wavelength range. As the temperature increases, the value for emittance increases, ...
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How far can we track ionic based spaceships if antenna fails

Suppose we send an ionic based spaceship and all the antennas are broken on launch, suppose the spaceship destination is another solar system. Obviously we can track it with optical telescopes, but i ...
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Air gap in a radiant barrier insulation system: why?

It's generally accepted that a reflective surface, when used to insulate a system by reflecting radiant energy back to it, must have an air gap in front of it. Why exactly is this, and what determines ...
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Blackbody photon variance and number of modes [closed]

In an experiment to measure the photon statistics of thermal light, the radiation from a black- body source is filtered with an interference filter of bandwidth 0.1 nm centered at 500 nm, and allowed ...
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Relation between the electric dipole radiation and the black-body radiation at small frequencies?

The electric dipole radiation has a power $\propto \omega^4$, while black-body radiation has the same behavior at low frequency (Rayleigh-Jeans)? Are they the same phenomena?
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How to tie in black body radiation with quantum theory?

I'm having trouble understanding the physical basis for the UV catastrophe in blackbody radiation graphs. Is the source of the drop off past UV because the electrons in a blackbody substance can't ...
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Is placing a fire safe inside a larger fire safe helpful?

If I put a small fire safe (say, one rated for 1 hour at 1700°F) inside a larger, equivalently-rated fire safe, to what degree is the fire/heat protection improved?
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Inferring Properties of Stars from Masses and Radii

I have two questions related to inferring properties of stars from their masses and radii. What properties of a star's spectrum could we deduce? In particular, do all stars emit like black bodies? ...
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Why isn't the emissive power of a black body 1?

My text book has a question which says that the emissive power of a black body isn't one but the answer states that the absorptive power is 1, considering that $$e=a \tag{Kirchoff's law}$$ and a ...
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What is the difference between Wien's Displacement Law for peak frequency vs peak wavelength?

While doing research for a high school report I came across the fact that WDL actually has two forms, one for peak frequency and one for peak wavelength, and that these two forms are not the same and ...
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Calculating rate of heat loss through conduction and radiation

I'm trying to calculate the rate at which a hollow cylinder with a heating element inside will lose heat, specifically through both conduction and radiation. I realize that the total heat loss per ...
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1answer
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Questions on derivation of the Rayleigh-Jeans law

I'm following this derivation of the Rayleigh-Jeans law: https://thecuriousastronomer.wordpress.com/2013/10/28/derivation-of-the-rayleigh-jeans-law-part1/ There are a few points that I don't quite ...
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Width of the Blackbody spectrum

The Planck spectrum, $$ B(\lambda,T) = \frac{2hc^2}{\lambda^5} \frac{1}{\exp(\frac{hc}{k_BT\lambda})-1}, $$ gives the energy density of blackbody radiation at a certain wavelength, $\lambda$, for ...
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Can we see emission lines in stars?

I read that stars show both absorption and emission lines. While how we see absorption lines is clear to me, I don't understand how (and when) we see the emission lines. Based on what I read in ...
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Difference between emission spectrum and black body spectrum

Why is an emission spectrum dependent on the chemical composition of the body's material, but the black body spectrum is independent of the material and only based on the body's temperature? Aren't ...
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Does there exist a notion that generalizes a black body to include other emission processes than electromagnetic ones?

A black body by definition is a perfect absorber for all incident electromagnetic radiation. It isotropically emits electromagnetic radiation whose spectral distribution only depends on the ...
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Black body/Sun radiation - λmax

The Sun's effective temperature is 5778K. Using Wien's law we can calculate the wavelength λmax in which we observe the maximum amount of radiation received from the black body. After doing the ...
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Has there been a quantifed estimate of the thermal impact of human activity? Not to include “greenhouse gasses” [closed]

In 1984 I read a prediction by the biological scientist and Nobel Laureate Konrad Lorenz that heat produced by human activity would necessarily increase Earth's average atmospheric temperature. His ...
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Planck Blackbody Radiation: Is this an error in the textbook?

the textbook I am reading describes two forms of equations of Blackbody Radiation. $$d\rho(\nu, T) = d\rho_\nu(T)d\nu = \frac{8\pi h}{c^3}\ \frac{\nu^3d\nu}{e^{h\nu/k_BT}-1}\ . $$ Substituting $ c = \...
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Planck blackbody radiation

I am reading a chapter about blackbody radiation in my physics textbook, and I encountered the following equation: $$d\rho(\nu, T)=\rho_\nu(T)d\nu=\frac{8\pi k_BT}{c^3}\nu^2d\nu$$ which is a classical ...
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How does temperature correspond to number of particles produced?

I'm looking to calculate the number of particles per unit time produced by a Schwarzschild black hole through Hawking radiation. I know that the temperature of the black hole goes as $\kappa/2\pi$, ...
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Electromagnetic radiation from sun and human body

What is the difference between infrared radiation produced in sun and thermal radiation, in infra red range, by human body in terms of its energy or are they the same?
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Is there an equivalent of black body radiation for other particles?

So all objects composed of matter emit black body radiation, which is photons of various frequencies. Is there an equivalent of black body radiation for other processes? Is there gluon black body ...
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Colour Temperature and the thermal temperature [duplicate]

I understand that Colour Temperature correlates with the object's thermal temperature, such as a red-hot piece of iron being ~360c and the incandescent bulb filament is about 2500c. Why are sources ...
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How to obtain the luminosity of a blackbody disk? [closed]

How do I get the luminosity of blackbody disk (negligible thickness) with temperature $T$ and radius $r$? Also how can one obtain the flux density if the object is at a distance $d$ and an ...
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What determines the timescale for fluctuations in the electromagnetic field from a light source?

Let's say you place an electric field meter some distance from a light bulb. As a function of time the output of the meter would be $\mathbf{E}(t)$. I would guess that the electric field will be some ...
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What is the difference between reflection and emission?

What is the difference between a body that simply reflects the light that falls upon it and a body that absorbs and emits it (like a black body in thermal equilibrium)? How can one experimentally ...