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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207 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 ...
2
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3answers
121 views

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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5answers
2k views

Entropy of radiation emitted into space

In several papers I see something equivalent to the following expression for the entropy of radiation given by an astronomical object such as the Sun (assuming the object can be approximated as a ...
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1answer
37 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?
4
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0answers
140 views

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
96 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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1answer
23 views

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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0answers
80 views

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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2answers
1k 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 ...
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1answer
218 views

How does heat energy travel in space?

How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us?
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1answer
237 views

Wien's Displacement Law for real bodies

It is known that for perfect blackbodies, $$\lambda T= c$$ where $\lambda= \text{peak wavelength}$ $T= \text{Absolute temperature}$ $c= \text{Wien's constant}$ ...
3
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1answer
83 views

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
45 views

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
50 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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2answers
239 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 ...
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0answers
35 views

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 ...
3
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3answers
341 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. ...
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0answers
18 views

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 ...
3
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3answers
365 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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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
136 views

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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1answer
73 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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1answer
75 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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6answers
7k views

Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
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1answer
82 views

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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0answers
33 views

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
390 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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1answer
47 views

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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1answer
1k views

Wien's displacement law in frequency domain [duplicate]

When I tried to derive the Wien's displacement law I used Planck's law for blackbody radiation: $I_\nu = \frac{8 \pi \nu^2}{c^3} \frac{h \nu}{e^{h\nu/k_bT}-1}$ Asking for maximum: $\frac{dI_\nu}{d ...
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2answers
156 views

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 ...
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0answers
67 views

A problem concerning the change of temperature and spectrum of a filament

The spectrum of a filament has been given before, the left one having the lowest temperature, the middle with a medium temperature and the right one with the highest. My question is this: Why does ...
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2answers
615 views

At the atomic level, is heat conduction simply radiation?

Radiation and conduction are two ways that heat is transferred. Convection isn't really a mode of transfer as the actual heat transfer really occurs through radiation/conduction and not by some other ...
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3answers
80 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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2answers
117 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 ...
7
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1answer
206 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
60 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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2answers
53 views

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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1answer
62 views

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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0answers
188 views

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 ...
0
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2answers
516 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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1answer
182 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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1answer
123 views

What's the relationship between the energy density of a black-body and its radiant exitance?

Through a bit calculation we can derive that in a cavity, the energy density $$u(f,T)=\overline{E(f)}\times G(f)=\frac{8\pi h}{c^3}\frac{f^3}{e^{h\nu /kT}-1}$$ If we take the integral over all ...
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0answers
197 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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3answers
1k 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
68 views

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?
8
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1answer
291 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, ...
3
votes
1answer
108 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 ...
0
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1answer
175 views

Filament in a lightbulb, thermal radiation

I'm trying the following: The filament inside a 100 W lightbulb has an absorption coefficient of 0.25, and while operating, it is at a temperature of 2,573 K. What's the size of the surface of the ...
8
votes
2answers
411 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 ...
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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 ...