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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27 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.
...
4
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0answers
52 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 ...
4
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1answer
51 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
52 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
64 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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0answers
32 views
Angular distribution of radiation
I have a problem in which I'm asked to calculate the radiancy of a black body which consists of a hole in a body, and they ask me for the angular distribution of the radiation that comes out of it.
...
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1answer
45 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 ...
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2answers
164 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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2answers
70 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 ...
4
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1answer
84 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 ...
2
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1answer
124 views
Find temperature of surface (Blackbody Radiation)
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 ...
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6answers
606 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 ...
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1answer
58 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
35 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
238 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 ...
0
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1answer
99 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 ...
2
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2answers
243 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 ...
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0answers
109 views
Different versions of Planck's law
For a presentation in physics I am going to talk about black body radiation since our book just mentions Planck's law, Wien's displacement law and Stefan-Boltzmann's law. I want to derive Wien's law ...
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0answers
140 views
Classical blackbody radiation 'solution'
I never understood how the equipartition theorem was applied electromagnetic waves inside the metallic blackbody. As hyperphysics puts it ...
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1answer
147 views
Hawking Radiation: how does a particle ever cross the event horizon?
The heuristic argument for Hawking Radiation is, that a virtual pair-production happens just at the event horizon. One particle goes into the black hole, while the other can be observed as radiation.
...
4
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1answer
242 views
Historic derivation of Wien's law
Every book I've read, including a lot of websites, Wikipedia, etc, say that Wien derived this:
$$\rho_\nu(T)=\rho(\nu,T)=\nu^3f\left(\frac{\nu}{T}\right)$$
Being $\rho_v(T)$ the spectral enegy ...
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1answer
69 views
The equilibrium temperature distribution of a pan in vacuum
If a rectangular pan has a constant and uniform temperature $T$ first, then put it in a vacuum. Considering the effect of thermal radiation, the temperature distribution of the rectangular blackbody ...
2
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3answers
198 views
Why aren't the graphs for black body radiation straight lines?
We know that a wave which has greater frequency will have low wavelength and high energy. So, by decreasing the wavelength, the frequency and consequently energy (intensity) of that wave will increase ...
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2answers
146 views
Radiation pressure on a Dyson sphere
To find the outward pressure from the sun's light on an enveloping spherical shell (Dyson sphere), one can simply divide the insolation by $c^2$. Using the entire system, we can specify the power of ...
13
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2answers
266 views
Why aren't gas planets and stars fuzzy?
The edge of Jupiter looks very sharp.
Even more bothersome, the edge of the sun looks sharp, aside from kind of a soup of particles floating above it.
The sun's surface has an incredibly low ...
2
votes
1answer
99 views
Commercial Infrared lights
I purchased an infrared light. It's a 100 W Philips infrared lightbulb. Says it's infrared, but I haven't done any spectrum analysis so I don't know for sure if it's just red or really infrared.
As I ...
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1answer
141 views
Do gases reflect some IR radiation?
The usual definition given for a greenhouse gas is that it absorbs infrared radiation. Of course, then the gas emits its own thermal radiation, and it does so without preference for direction ...
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1answer
66 views
Equations for the two-plane model of the greenhouse effect
I'm trying to understand this "toy model" of the greenhouse effect.
http://www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model
The model predicts the surface temperature of ...
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2answers
200 views
Radiated power and energy density for a black-body
I am having an hard time trying to understand why the radiated power per unit area $P$ of a black body is given by
$$P=\frac{c}{4} u$$
in terms of the energy density $u$ and the velocity of light.
I ...
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3answers
94 views
What's the physical difference between a convective heater and an infrared heater?
Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air?
...
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1answer
295 views
Calculate temperature of the earth through blackbody radiation
I don't understand the solutions to a problem about blackbody radiation and was wondering if anybody could help me out.
Here is the question:
The sun can be considered as a blackbody radiation ...
0
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1answer
156 views
Energy loss in pipe/hose with hot water (how its affected by pipe/hose size, temperature)?
I'm working on low budget small solar power project.
I want to transport heat (peak heat power about 1kW) over ~10 meter (~30ft) long pipe or hose.
I was thinking about thin hose (6-8mm / about 1/4 ...
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1answer
165 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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2answers
194 views
What are thermal energy distributions?
I am trying to understand the photoelectric-effect deeply. My teacher used the Planck's law and integrated it to deduce the Stefan-Boltzmann law. He somehow showed some quantum-physical ...
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1answer
67 views
What is the relation between surface area and radiation, if any?
Basically I wonder what happens to emitted radiation by douubling a light e.g. twice the surface area of the sun will emit how much more radiation? 4 times more? Is there a formula?
3
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0answers
42 views
Photon pumping in Laser
Let's consider a ring laser where the laser must pass through the gain material before it is sent toward a partially reflective surface $\ R=1-T $. The other mirrors are perfect reflectors with $\ ...
3
votes
2answers
291 views
How to interpret Stefan-Boltzmann's law?
The Stefan-Boltzmann equation states $e=\sigma T^4$, but how do we interpret this?
Is this completely wrong: A body of size $s^2$ generates the radiation/temperature $T^4$ for a given size and a ...
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3answers
107 views
Why is the planck function continuous and not discrete?
If we imagine a object made up of Hydrogen gas that is optically thick to all radiation, and is in thermal equilibrium, then, microscopically, photons will be emitted and absorbed as ...
11
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1answer
283 views
Quantum uncertainty of particle falling in black hole
A stationary observer at infinity sees a particle of mass m falling in a supermassive Schwarzschild black hole. He observes an increasing redshift and sees the particle ceasing to progress when it ...
2
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1answer
213 views
What really is Planck's constant and what are its origins?
In the physics texts I have read and other info online, they says Planck's constant is the quantum of action or that it is a constant of the ratio of the energy of a particle to its frequency. Im ...
2
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2answers
276 views
Possible colors of fire?
I have learnt that depending on the various gases those are involved in the reaction that produces fire, different colors (yellow, red or blue) of flames become visible.
I have a question .. what are ...
5
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4answers
198 views
what is the basic form of the 'fire'? [duplicate]
Possible Duplicate:
Is fire matter or energy?
What is the basic form of fire? physics defines every entity by a basic form either solid or liquid or as a gas,
example: water is liquid,
ice ...
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1answer
105 views
Is the Unruh radiation isotropic?
The Unruh effect is the prediction that what appears to be a Minkowski vacuum to an inertial observer, would appear to be a thermal bath of particles to an observer accelerating uniformly in the same ...
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1answer
62 views
Is synchrotron radiation considered incandescent?
Synchrotron radiation is produced via the acceleration of charged particles, much like incandescence.
However, all information I've seen state that incandescent light is produced exclusively from the ...
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2answers
117 views
Temperature of a black-body in LEO on the dark side of the Earth
Questions about the temperature of something in space are often very hard to pin down (example), since there is radiative transfer to/from many different regions in the field of view at dramatically ...
1
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1answer
79 views
What would the spectral distribution of a greenbody look like?
Suppose you had a body that behaved like a blackbody for all wavelengths except some range that we would call "green". For those wavelengths it reflects all radiation incident upon it.
Am I just ...
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1answer
2k views
How do you change Planck's law from frequency to wavelength?
I have to derive Wien's displacement law by using Planck's law. I've tried but I come to a unsolvable equation (well I can't solve it) anywhere I look online it comes to the same conclusion, you need ...
4
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0answers
131 views
How do I measure the temperature of a tiny water droplet?
How do I accurately (+/- 0.1 degrees Celsius or better) measure the temperature of a small (5 to 50 microliter) water droplet without noticeably affecting its temperature?
The mass of a thermistor or ...
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1answer
164 views
Mathematical derivation of $N(\lambda)d\lambda$
We all know that in Rayleigh-Jeans law,
$$N(f)df ~=~ 8\pi f^2 df/c^3.$$
How do you derive $N(\lambda)d\lambda$?
I am sort of confused...
2
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1answer
104 views
What is the diameter of the sun as a function of wavelength/frequency (around 10GHz)?
I have this vague recollection of being told that the diameter of the apparent surface of the sun is a function of what band you observe it in. I'm looking for a model of this that works for bands in ...
