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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Black bodies, energy per unit volume

While reading about black bodies, I found that the average energy per mode per unit volume is $KT$ classically, but I don't understand why this is per unit volume. The linear oscillators are ...
6
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2answers
266 views

Does the Cosmic Microwave Background obey $\sigma T^4$?

The fact that the CMB has a temperature of 2.7 degrees Kelvin is well publicized, but I have a harder time finding a measure of the wattage per unit area. The Wikipedia article on the CMB is totally ...
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2answers
237 views

Polar ice caps and thermal radiation

I was reading an article on global warming and it said that the polar ice caps, because they are white, reflect a lot of the sun's radiation. The article also has a picture of some houses in England ...
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1answer
219 views

Do bifacial solar panels operate at lower temperature than normal solar panels?

Bifacial solar panels have a glass backplane instead of the usual aluminum and are designed to absorb and convert to electricity light incident on either face. Many manufacturers claim that their ...
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0answers
40 views

Nuclear Weapon Effects: Cloud Rise [closed]

I am interested in modeling the rise of a nuclear cloud to stabilization height post detonation. I am interested in any ideas you may have on the approach. I have collected some research on the topic ...
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0answers
51 views

Can we make any substance that will produce ions at low temprature

I am talking about thermal ionization, Is to possible to make any material or is there any element that can be ionized at let say 20 degree centigrade Temperature? I am a computer engineer and into ...
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3answers
4k views

2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...
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3answers
4k views

Which color of an umbrella is more effective against sunlight?

It's usually said that black umbrellas are best against sun, since black absorbs most of the radiation . The common umbrellas in market(atleast in India) are painted black outside and silvery inside. ...
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2answers
269 views

Do green stars exists?

I asked a university lecturer why we don't observe green stars, and he said the blackbody curve averages at that frequency such that the cones in our eyes don't recognise it. I have a hunch that ...
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1answer
214 views

Study of Black-body Radiation

Why did scientists study black body radiations from something as complicated as a hollow container rather than the radiation from something simple like a thin solid cylinder?
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1answer
2k views

Kirchhoff law of thermal radiation

Kirchhoff's law of thermal radiation states that for thermal equilibrium for a particular surface the monochromatic emissivity $\epsilon_{\lambda}$ equals the monochromatic absorptivity ...
106
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1answer
46k views

Why does NASA use gold foil on equipment and gold-coated visors?

I've read several websites about equipment covered with gold foil and astronaut helmet visors are coated with gold. However, their explanations are devoid of almost all physics content. Can someone ...
5
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1answer
236 views

Measuring temperature at a distance

http://www.youtube.com/watch?v=gKYrXHZwtPw In this video it is explained that Land Skin Temperature (LST) are measured by NASA's Aqua and Terra satellites. It seems it works by collecting the ...
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1answer
182 views

On the atomic level, how is incandescent light structured?

I want to know from the smallest possible originating structures how the light I see generated from heat is made by atoms themselves.
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1answer
249 views

Can't understand a thing about emissivity concept

I can't understand something about emissivity. Emissivity is defined as the ratio of the radiant energy of an object, to radiant energy of blackbody at a temperature $T$. So, The vegetation has ...
7
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2answers
424 views

Planck's Law-Where does it come from?

It seems that Planck's constant was made from fitting a curve for blackbody radiation, is it just experimental-further more his assumption that energy comes in quanta seems to have been a guess. Why ...
6
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3answers
218 views

Can visible light be emitted from a non-thermal source?

I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?
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1answer
196 views

Blackbody radiation force (link), what are the fundamental forces behind it?

Here is a link to an article from phys.org describing what the scientists (M. Sonnleitner at the University of Innsbruck and Innsbruck Medical University in Austria, M. Ritsch-Marte at Innsbruck ...
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2answers
443 views

Cooling down a container in outer space

If I have two containers filled with very hot water(~210F) with one in outer space and one on earth, which one has a higher rate of cooling initially? Imagine the containers are single wall metal ...
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2answers
817 views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
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1answer
147 views

What cause scientists to study Black Body Radiation?

After spending hours understanding what exactly Black Body radiation and Ultraviolet catastrophe is, I cannot help myself asking what was the reason that make scientists such as Wilhelm Wien and Max ...
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2answers
1k views

What causes a blackbody radiation curve to be continuous?

The ideal blackbody radiation curve (unlike the quantized emission seen from atomic spectra), is continuous over all frequencies. Many objects approximate ideal blackbodies and have radiation curves ...
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0answers
124 views

Intensive radiative heat transfer in very hot gas ( >5000K, gas core nuclear reactor related )

The question: At temperatures above ~5000K are not stable any solid or liquid materials or even more complex molecules (such as fullerenes and Polycyclic aromatic hydrocarbons) which emit/absorb ...
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2answers
117 views

Extreme heating by Sun on Earth- Can eggs be fried?

Will it be possible to fry eggs in Sahara desert by just keeping them under the sun? If so, then will the radiated eggs be any different? Or will we have to use the solar cooking concept to some ...
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1answer
117 views

Heat preserving performance of container relative to content

This question has been addressed in the case of a thermos bottle: Performance of a thermos bottle relative to contents I am asking the question again without the hypothesis that it is a thermos ...
11
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1answer
482 views

Thermodynamically possible to hide a Dyson sphere?

You build a Dyson sphere around a star to capture all its energy. The outer surface of the Dyson sphere still radiates heat at much higher temperature than the cold space background, so you're easy to ...
8
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2answers
225 views

radiation thermodynamics paradox

This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape. Consider two nested shells that are axisymmetric ellipsoids with the same ...
3
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2answers
169 views

What are the largest thermal gradients achievable in a lab environment?

I am looking for a system capable of creating a gradient of $100\, \mathrm{K}/\mathrm{\mu \textrm{m}}$ on a $30\, \mathrm{\mu}\textrm{m}$ spacing of a system mounted on a Si-N membrane. My so-called ...
3
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1answer
193 views

How thermally conductive is a black body?

Does a black body (imagine like a square of solid black-body-matter) thermally conduct well at room temperature?
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2answers
251 views

Black body radiation

I have a few questions related to the emission of electromagnetic radiation by black bodies. Consider the following image: On the above image I have drawn the rays of light that are emmited by ...
8
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1answer
294 views

Graphene as optical and UV mirrors

One usually hears about graphene as a good thermal conductor, and good light absorber due to its tunable bandgap properties. But i haven't heard about its aplicability as an optical mirror. In fact, ...
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2answers
111 views

Photon gas kinetic theory

Suppose a black body as an enclosure of volume $V$ with a hole of section $A$. In the interior there is a photon gas, whose energy density $u$ is, at temperature $T$. $$ u=cT^4$$ How can I show that ...
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1answer
62 views

heat spread from hot coil: diffusion, radiation?

When modeling the heat spread from a hot object through a vacuum (or a gas), what is the dominant physical process for heat energy transportation? Thermal diffusion, thermal radiation, a mix of the ...
3
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0answers
500 views

How do you estimate colour temperature based on the position of the sun in the sky?

I'd like to estimate the colour-temperature of sunlight (as applied in photography) based on the position of the sun in the sky for a mobile phone app I'm working on (app link from a more appropriate ...
3
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3answers
373 views

Leap from photon gas energy distribution to black body radiation?

I remember considering in class in college, the case of a photon gas trapped in a d-dimensional box as a subject of interest, whose energy distribution, heat capacity, etc. should be calculated. ...
5
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0answers
141 views

Gravitational redshift of Hawking radiation

How can Hawking radiation with a finite (greather than zero) temperature come from the event horizon of a black hole? A redshifted thermal radiation still has Planck spectrum but with the lower ...
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1answer
261 views

Bunsen Burners and the Sun

Why do Bunsen burners burn blue in the center? What element is being burned? Why does the sun glow yellow, and not blue-a Bunsen burner is much cooler and yet it burns blue. Is it because the ...
5
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1answer
171 views

Temperature of glowing materials

As I understand it, Stars emit visible light, OBAFGKMRNS, in the range of $10^3 - 10^4 K$. Yet materials such as steel emit similar frequencies at much lower temps; red is around 800K. Why the ...
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1answer
205 views

How to understand the thermal radiation?

I am studying the thermal radiation (Stefan–Boltzmann law) by myself $$P = \epsilon \sigma A T^4$$ here $\epsilon$ is the emissivity, $\sigma$ is Stefan-Boltzmann constant, $A$ is the surface area ...
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1answer
106 views

Electromagnetic field to cool a substance?

I saw somewhere that an electromagnetic field would cause a substance to let off thermal energy, ultimately resulting in the substance to cool really quickly. If this is possible, does the strength ...
5
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2answers
2k views

Is a black hole a perfect black body?

A black body absorbs all light/radiation in its reach. According to basic laws of physics, the more energy a body absorbs the more it can emit. Therefore, a black body absorbs all energy directed at ...
2
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2answers
216 views

Does the black body emit more than any other type of body?

I found this on Wikipedia article on black bodies: A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic radiation called black-body radiation. The ...
6
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1answer
313 views

How is the index of refraction dependence in Planck's law compatible with thermodynamics?

In various formulae for black-body radiation where $c$ appears, there is an implicit index of refraction dependence, since $c=c_0/n$, where $c$ is the speed of light, $c_0$ is the speed of light in ...
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1answer
2k views

Find temperature of surface (Blackbody Radiation) [closed]

An astronomer is trying to estimate the surface temperature of a star with a radius of $5 \times 10^8\ m$ by modeling it as an ideal blackbody. The astronomer has measured the intensity of ...
19
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6answers
2k views

What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
0
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1answer
100 views

Landauer's principle vs Wien's displacement law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of kTln2? If it is so, can we also argue ...
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0answers
86 views

Landauer's principle vs Rayleigh–Jeans law

Can we argue based on Landauer's principle that if one bit information is changed inside a blackbody, the total radiated energy should be at least or in order of $kTln2$? If it is so, can we also ...
2
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2answers
1k views

Why does Planck's law for black body radiation have that bell-like shape?

I'm trying to understand Planck's law for the black body radiation, and it states that a black body at a certain temperature will have a maximum intensity for the emission at a certain wavelength, and ...
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1answer
2k views

Calculating the amount of heat energy radiated by sun

How do I calaculate the amount of heat energy radiated from the sun in one minute?? Well, i tried some stefan method, but the answer seems far off from the correct one....well, i would thus strongly ...
3
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2answers
2k views

Are Newton's law of Cooling and Stefan's law related?

Many of Indian school textbooks claim a proof of Newton's law of cooling from Stefan's law of black-body radiation. As far as I am aware of, Newton's law is based on cooling from convection currents ...