The temperature-dependant 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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Absorption cross section and absorption coefficient

What is the absorption cross section, how is it measured? How to convert it to the absorption coefficient (measured in cm$^{-1}$)?
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31 views

Absorption coefficient from HITEMP or HITRAN [closed]

How to calculate the absorption coefficient (for radiation) from HITEMP or HITRAN databases? Or where can I find some tables or plots for the absorption coefficient?
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1answer
32 views

Frequency-averaged (gray) radiative transfer

The equation for radiative transfer is $$ \omega \cdot \nabla I = \kappa(B - I) $$ where $I$ is the intensity of radiation, $\omega$ is the ray direction, $\kappa$ the absorption coefficient, $B$ the ...
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47 views

Sun radiation in England

I used to live in Italy, and when it was sunny, well, as expected it was pretty hot. Both under the direct light of the sun through the atmosphere, and in the shade, where the temperature was of ...
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How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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7answers
755 views

How does heat actually stay kept in the carbon molecules in the atmosphere? [duplicate]

We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their ...
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2answers
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If black and white object are in isolated space will the black absorb heat from the white?

This question has come to me from my friend in fact: he noted that the heating in the pub is painted black. I replied that it's better for heat emission. I don't know where did I know that from. And ...
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24 views

Thermal Conduction through sphere

In general, a sphere with conductivity $\kappa$, heat capacity per unit volume $C$ and radius $R$ obeys the differential equation at time t: $$C\frac{\partial T}{\partial t} = \kappa \frac{\partial^2 ...
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Question on luminosity of a radiant source and its dependence on temperature, and involvement of Doppler Effect

A few days ago, I happened to go through the chapters on Radiation, and Photometry, studying them at quite an elementary level. I studied Wien's displacement law, and the dependence of luminous flux ...
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Can the hot combustion products from a large flame be in “non-local thermal equilibrium”

Question: Does it take some time for the hot combustion products from a flame to reach local thermodynamical equilibrium (i.e. for the energy state populations to follow the Boltzmann distribution)? ...
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Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate?

Does a surface in front of a radiator (not in contact) have a significant effect on the room's temperature or heating rate? Some time ago I had a discussion about it, and despite none of us knowing ...
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45 views

What's wrong with this simple derivation of energy flux in a photon gas?

In a photon gas, we know that pressure, $P$, and energy density, $u$, are related by: $$P=\frac{u}{3}$$ We also know from relativity that the momentum of a photon is $$p=\frac{E}{c}$$ Finally, the ...
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Is darkness really light?

According to this wikipedia article "Consequently, most objects that absorb visible light reemit it as heat. So, although an object may appear dark, it is likely bright at a frequency that humans ...
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3answers
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Does one square centimenter of the sun core really radiate this amount of energy?

I have been thinking that since the core of the sun maintains its temperature at 15 million degrees Kelvin, then every cubic centimeter of this core is receiving a certain amount of energy to keep it ...
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1answer
47 views

Could airport security devices detect differences between printed and written documents?

If airport security scanners of any kind (xray, thermal, whatever else they use) looked at two items: A printed paper textbook The same printed paper textbook into which we have inserted a regular ...
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33 views

Quantum Temperature?

I was thinking if temperature is proportional to the rate at which energy is transferred then does it exist on a quantum as well as a classical scale? If so what is it proportional to exactly?
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Thermal AdS and the Hawking Page phase transition

I have some difficulty understanding the concept of pure thermal radiation, as described in Hawking and Page's paper on the Hawking-Page phase transition. The four-dimensional thermal AdS solution ...
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3answers
74 views

Gas vs electric cooking

I've heard it said many times that you're more likely to burn food on an electric stove than a gas one, but I can't tell a difference. This seems to me to be a fallacy perpetuated by the natural gas ...
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photoelectric cell

In the photoelectric cell my teacher says that the electron emission from the cathode depends on the frequency of the incident photon and it doesn't depend on the light intensity (I = nhU/ta , Right?) ...
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Black body radiation curve [closed]

In the black body radiation curve, why is the wavelength directly proportional with the intensity before the peak and inversely proportional after the peak.
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The origin of the colour of the sun

I have learned so many concepts under astrophysics and unfortunately, I have muddled everything together... Let me try to illustrate my problem: When a star is in main sequence, it fuses hydrogen to ...
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0answers
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Radiation heat transfer

I'm looking at the radiosity equations for heat transfer http://en.wikipedia.org/wiki/Radiosity_(heat_transfer)#Radiosity_method Specifically, I'm hesitant to accept the equation: $$ \dot Q_i = ...
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2answers
45 views

Heating a black body

By definition, Black body has absotivity=emmisstivity=1. This means the black body radiates all energy it accepts. Does this mean the black body cant be heated?
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1answer
102 views

Examples to illustrate temperature dependant radiation by examples of temperature to color relation

I'm looking for a set of examples to illustrate the relation of temperature and color of "glowing" bodies. It should allow to build an intuitive understanding of this relation, so it's not about ...
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Thermography time evolution

I have an imaging problem. I essentially have a metallic plate with a number of holes through it. I am looking at the number of holes with a thermal camera. While looking at the plate I have two ...
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Radiation pressure at high temperature

I am reading a book on the history of the hydrogen bomb. The author describes the Teller-Ulam design and explains that the liquid deuterium charge was compressed by the radiation pressure generated by ...
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2answers
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Why don't the derivatives of the blackbody spectrum over frequency and wavelength match?

The question is: The radiation emitted by a black body can be represented either by the energy distribution over the wavelength or by that over the frequency. In the first case the maximum energy ...
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59 views

Refrigerator cooling power usage

I have a refrigerator, that makes a lot of noise, and we have therefore set a time on it will limit the run time to when we are not at the office. But this is where our discussion begins, should we ...
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52 views

Why doesn't diamond glow when hot?

In an answer to this SE question, the respondent explains that heating a perfect diamond will not cause it to glow with thermal blackbody radiation. I don't quite follow his explanation. I think it ...
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Radiation and absorption

Can thermal radiation from a cooler object (B, which emits longer wavelength radiation) ever ADD to the overall thermal energy level of a warmer object (A, which emits shorter wavelength radiation)? ...
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What would Planck's Radiation Law look like if there were only two modes of oscillation, $n = 0, 1$?

I have an idea that the law (since it's based on average energy, number of modes per volume, and a constant) would be shortened to something that would eliminate the summation terms in average energy. ...
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1answer
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Quantum physics and black body

I'm a high school student, I just read something about black body. So I wanna know if I understand it correctly that black body is an ideal perfect absorber and emitter in sense that a normal object, ...
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88 views

Thermodynamics of thermometer

Mercury is used in thermometers because it increases in length significantly due to rise in temperature, However, mercury has high density relative to water, which means more inter-molecular forces ...
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172 views

How would a physicist measure temperature of molten metals in 1850-1920s?

How would a physicist measure temperature of molten metals in 1850-1920s? What equipment would be used?
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1answer
48 views

Photon number conservation during scattering

I was reading this writeup on the Kompaneets equation and the Sunyaev-Zel'dovich effect. On page 3, section 2 the author states There is no way to increase the mean energy of a planckian ...
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Realistic calculation of heat loss for pipe

Good day everyone, I am new on this site and I hope to find here help, since I am not going anywhere with the literature I have found. I try to calculate realistically the heat loss of a hot, ...
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2answers
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Temperature of relic radiation and thermal equilibrium

The temperature or relic radiation is 2.7 K. Does it mean that any flying body sufficiently far from any stars will reach this temperature? As I understand it, you can warm up water with sufficient ...
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Radiation pressure thermodynamic paradox

Could the radiation pressure of a black body (theoretically) perform work on the perfectly reflecting apparatus in the figure below? Assume that the block does not hinder the passage of light through ...
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76 views

Temperature of thermally isolated space region

If we thermally isolate a region in space, say using a hypothetical material of $0$ conductivity, and measure the region's temperature, will it be 2.7K?
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The strange thing about the maximum in Planck's law

I read that it makes a difference whether you calculate $\frac{d \omega}{d \lambda}=0$ or $\frac{d \omega}{d \nu}=0$ in the sense that the maximum energy densit with respect to the wavelength does not ...
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Radiative cooling time for a black body

Okay, so this is confusing me a bit. How can I calculate the time it takes to cool a perfect black body from an initial temperature $T$ down to equilibrium temperature (say, 3 K for space)? I know ...
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2answers
403 views

Planck's distribution and Bose-Einstein distribution?

If the application of the Bose-Einstein distribution is in blackbody radiation, then what is Planck's distribution? Are they same? How did Planck know that he should use a Bose-Einstein distribution ...
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160 views

What is “number degrees of freedom for frequency ν”. Frequency is 1D right?

The book QM Demystified states this about black body radiation spectrum: An attempt to explain these results using classical theory was codified in the Rayleigh-Jeans formula, which is an ...
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159 views

Does coffee with cream cool slower than black coffee?

At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the ...
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324 views

How to derive Stefan constant from Planck's Blackbody radiation?

How to derive Stefan constant from Planck's Blackbody radiation? Consider the following expression relating to blackbody radiation: $$\phi(\lambda) d\lambda= E({\lambda}) \, ...
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3answers
760 views

All objects radiate energy, but we cannot see all objects in the dark. Why?

We claim that all objects radiate energy by virtue of their temperature and yet we cannot see all objects in the dark. Why not?
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2answers
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Energy loss of Earth

How does the Earth lose the energy that it gains from the sun's radiation if it is surrounded by - and in contact with - nothing?
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171 views

Why is spectrum obtained by sunlight, said to be continuous?

My sir spoke about atomic spectra today. Sir said that, unlike the spectrum obtained by analyzing the sunlight, the spectra of atoms are not continuous. I got a doubt here, i,e even the sunlight ...
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1answer
97 views

Continous spectrum of black body radiation [duplicate]

I am wondering why black body emission spectrum is continous. Assuming only quantum effects that is electrones falling to less energetic orbitals it should be discrete. Is the continous part emerging ...
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196 views

Wien's Displacement Law for real bodies

It is known that for perfect blackbodies, $$\lambda T= c$$ where $\lambda= \text{peak wavelength}$ $T= \text{Absolute temperature}$ $c= \text{Wien's constant}$ ...