All Questions
Tagged with blackbody or thermal-radiation
1,722 questions
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Is the total number of photons in a cavity meaningless?
The gran-canonical partition function for an ideal gas of bosons can be written as
$$\mathcal{Z}=\prod_{(\vec{r},\vec{p})\in\mathbb{R}^{6}}\sum_{N=0}^\infty e^{-\beta E(\|\vec{p}\|)N+\mu\beta N}=\...
- 3,975
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What's the disconnect between blackbodies and lived experience? Do they violate the laws of thermodynamics? [closed]
My understanding of the 2nd law of thermodynamics is, partly that, basically a 'cold' object cannot heat a 'hot' object.
Case in point: if I take a 1500W hot plate and put it on full, the plate will ...
- 1,277
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How to identify the composition of sun if it is treated like a blackbody? [duplicate]
The sun is usually assumed to be approximately very close to a blackbody, but using spectroscopy it is concluded that the sun is made up of Hydrogen and Helium because the lines corresponding to those ...
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Does the gravitational redshift obey the Stefan-Boltzmann law?
Here is a non rotating neutron star emitting perfect black body radiation from its surface. Supposing that the radiation is redshifted by a factor of 2 for distant observers (which is chosen purely ...
- 1,537
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Why won't hydrogen gas heated via conduction/convection emit a blue light / how can it emit infrared light?
According to the European Space Agency:
Every object with a temperature above absolute zero (that corresponds to 0 K, or -273 degrees C) emits electromagnetic (EM) radiation over virtually all ...
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Why does the CMB have a spectrum like a black-body radiation?
Equilibrium distributions of particles (Maxwell, Boltzmann, Saha) are achieved by the particle collisions. On the other hand, photons do not interact with each other. From the introductory course in ...
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Why can't a reflective barrier raise an object's temperature past a heat source's temperature?
Say I have a 1 $m^2$ source of visible light emitting 1,000W worth of light. This is shining down upon 1 $m^2$ of ground.
If we treat the ground as a blackbody, my understanding is that eventually it'...
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Why can't fire heat something hotter than itself, but electromagnetic waves can heat something indefinitely?
Part of my question on Can a low-energy source/object heat a higher-energy object via radiative heat transfer? asked if a 100W lightbulb could heat a blackbody in a vacuum indefinitely, presuming ...
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Why does UV light feel warm on my skin? Whereas infrared light heats up space around me plus my skin?
Noticed something weird today.
I have an infrared space heater that is pretty good at heating up my desk at work (as well as my skin obviously).
I also have a UV flashlight. I noticed the UV ...
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Would an object travelling close to the speed of light gather a lot of energy?
Quick disclaimer: I don't know much about physics, so I don't really know what I'm talking about.
The idea
The idea is that an object traveling fast enough in space will be receiving more radiation ...
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111
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Can a low-energy source/object heat a higher-energy object via radiative heat transfer?
Say we have a blackbody sphere in a perfect vacuum with surface area of $1 m^2$ at temperature 5.1205 C = 278.2705 K. Let's say inside the sphere it has its own energy source that is outputting enough ...
- 1,277
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What determines the particular frequency of infrared any given object emits?
Infrared (IR) includes EM waves between 780nm and 1mm in wavelength. (Source) As an object gets hotter, it emits a greater amplitude of infrared. What determines the particular frequency(s) of IR an ...
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How does fire heat air?
I understand that fire heats its surroundings via conduction, convection and radiation. I've read that conduction is nearly irrelevant to this process as air is a poor heat conductor. In descriptions ...
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Does a blackbody always appear black?
By definition an ideal black body ⚫️ is a complete absorber that is no radiation in any spectrum goes reflected by it , which suggested that it should appear dark or black
On the other hand by ...
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210
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Does thermal energy include the energy of thermal radiation as part of its definition?
I can't get a simple answer to this simple question online, so I thought I'd ask here.
Thermal radiation is usually meant to be the energy associated with a given temperature of a material body. Now ...
- 8,776
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Why the blackbody's spectral emittance isn't a growing exponential in the wavelength?
I have read multiple paragraphs about why we do get the bell shaped curve and the tale goes like this, oscillators with high frequency aren't paying the bell getting excited as they would require ...
- 1,035
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Is the emitted spectrum is that of a blackbody when the blackbody is in thermal equilibrium with the ambient or with its interior or either?
I have came across the following paragraph in Wikipedia
A perfectly insulated enclosure which is in thermal equilibrium internally contains blackbody radiation, and will emit it through a hole made ...
- 1,035
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140
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Cooling of a solid vs hollow sphere
We have a solid and a hollow sphere made of same material, and of same dimensions.
We have to compare the temperatures of the sphere after a long time of cooling.
So initially I can safely say that ...
- 2,062
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Photon statistics for thermal light?
I know that the variance $\Delta^2$ of the number of photons $n$ for thermal light is:
$\Delta^2 n = \bar{n} + \bar{n}^2 \hspace{2 cm} (1) $
where $\bar{n}$ is the average number of photons.
This ...
- 454
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Why doesn't the accretion of ice, cause the ice to melt?
I was reading about the accretion of ice which describes the rate at which the ice layer above a lake thickens. It said that in order for the water just below the ice to solidify,heat had to be ...
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60
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If a satellite is shut down, will it eventually reach the high temperatures of the exosphere?
If a satellite is shut down so that it neither generates additional heat from whatever internal energy source it might have, nor is able to dissipate heat by an active cooling system, will it ...
- 1,964
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Focusing blackbody light simulation
As an honest citizen, I do not intend to violate the laws of thermodynamics by concentrating the light emitted by a blackbody on a smaller area. However by playing with this wonderful 2d ray online ...
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161
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Temperature estimate from eclipsing binary
So assuming perfect edge on eclipsing binary, we can estimate the temperature ratio of the two stars because the "blocked area" is the same, and thus the amount of light "dimmed" ...
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Can a thermal radiating surface be replaced by an equivalent antenna with proper current distribution?
Thermal radiation is EM waves generated by electrons movements due to a non-zero absolute temperature. Given a certain material with such an emission at temperature T, is it possible to see it as an ...
- 1,329
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What fraction of heat is exchanged by thermal radiation (by ordinary objects)? [closed]
I understand that heat can be transferred by conduction, convection and thermal radiation.
So, lets say when I bring a cold glass of milk in a room at room temperature, then what fraction of heat is ...
- 1,306
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3
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344
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Power emitted during thermal radiation
How does the power emitted during thermal radiation depend on time (if it does)? What are some sources refering to the particular relation between the power emitted during thermal radiation and time? ...
- 4,157
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Derivation of Planck's Formula: Why summing over maximal number of linear independent modes and NOT over all modes?
Here I have a question about the Derivation of Planck's formula in this text. On page 5 is derived the differential expression
$dN= 2 \times \frac{4\pi \nu^2 V}{c^3} d\nu $
for the number of modes of ...
- 1,555
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How is black-body radiation affected by recoil?
In a semi-relativistic framework, which accounts for the mass of an energetic photon ($=h\nu/c^2$), a black body cannot emit a photon whose relativistic mass is greater than its own. So the higher the ...
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When the radiation spectrum of two bodies will be undistinguishable?
While reading my book I came a cross the question that .
Suppose there is solid sphere of radius $r$ inside a spherical shell of radius $R$.
If a heating source is connected to the inner solid sphere ...
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When a gas is in thermodynamic equilibrium, does it emit like a black-body? [duplicate]
Black-body radiation is said to be the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment or emitted by a black body. For the first case ...
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How a piece of metal put in the oven reaching a constant temperature of 3000 K fit the model of a hole in a cavity?
The common and practical model for a blackbody is a hole inside a cavity, and even stars can be made to fit into this model. My question is how to make anything else like a piece of metal at some ...
- 1,035
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391
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If all matter can emit at all wavelengths, can all matter absorb at all wavelengths too?
Based on Planck’s law all matter can emit at all wavelengths at different intensities dependent of temperature. I was wondering if this holds true, does all matter absorb all wavelengths too, at ...
- 647
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Doubt on the radiated heat of a black spheric shell
Consider a black spheric shell of radius $R$ manteined at temperature $T$ in an empty space. By Stephan-Boltzmann's Law we know that the power radiated is given by $\dot{Q} = 4\pi R^2 \sigma T^4$ but ...
- 402
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Do gases emit radiation at all wavelength? [duplicate]
According to Planck's law, all matter emits radiation at all wavelengths but is this statement true for gases and pure elements? Gases like hydrogen and helium have specific emission spectrums and I ...
- 647
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112
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Do all matter emits radiation at all wavelengths? [duplicate]
Does all matter emit radiation at all wavelengths? Do gasses also emit radiation at all wavelengths since they have a specific emission spectrum? Shouldn't they only emit radiation according to their ...
- 647
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Estimating the climate sensitivity parameter
Temperature changes $\Delta T$ are related to radiative forcing $\Delta F$ linearly (to a first approximation):
$\Delta T = \lambda \Delta F$
I was thinking how to estimate the climate sensitive ...
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Is the Sun considered to be a black body as a whole or it is only the photosphere which is a black body?
I am having some difficulties understating how fusion inside the Sun is connected to the Sun being a blackbody. How do the photons transfer to the photosphere? Is the amount of transferred energy less ...
- 647
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128
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Why doesn't a black body absorb its own radiation?
If black bodies absorb all the radiation and emit radiation by themselves, why don't they absorb their own emitted radiation? We shouldn't see the sun for example, since it's a black body.
- 647
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Different radiation intensities from a black body
I am a high school student and was wondering about the radiation curve of a black body. Why do the emitted wavelengths from a black body have different intensities? What happens at the atomic level ...
- 647
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4
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368
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How does blackbody radiation suggest the quantization of energy?
I have read about Wein's law and Rayleigh-Jeans law which were apparently based on classical mechanics and couldn't explain the radiation spectrum of a blackbody.
Then Planck came up with the ...
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Blackbody radiation and the quantization of energy?
If the energy spectrum is continuous, a blackbody would radiate shorter wavelengths with higher intensity with no upper limit (the "ultraviolette catastrophe") for any temperature.
How can ...
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What is the temperature of a greenhouse gas?
The temperature of a gas is usually the sum of the kinetic energy of its particles, right?
Whereas the temperature of a solid object is given by the Stefan-Bolzmann equation, as a function of how much ...
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Elementary question about quanta
I've been trying to read about the origins of quantum physics, and I have not found a very satisfactory answer to this question.
The ultraviolet catastrophe resulted from, as I understand it, the ...
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Can an evaporating black hole emit protons with an energy beyond the GZK limit?
There are protons reaching the earth with energies that exceed what their interaction with the cosmic microwave background should allow, the so-called GZK limit.
Could an evaporating black hole emit ...
user353451
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Temperature of copper block inside a metal container
I have one cylindrical metal container : ~20 cm in length; ~15 cm in diameter.
I have kept one small copper block inside this container. Copper block is thermally
insulated from all other components ...
- 1,034
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2
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Photoionization by black-body radiation
I am trying to solve the question:
"Show that if an atom is photoionized by black-body radiation with the
temperature $T^*$ such that $kT^*\ll I_H,$ the average kinetic energy acquired by an ...
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233
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Is the Drapers point inaccurate?
Is the Drapers point faulty since an oven glows visibly red without it actually reaching Drapers point? When the Drapers point blackbody radiation frequency is calculated by Wien's law it results ...
user348071
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598
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How does anodization increase emissivity?
In articles devoted to the study of the contribution of radiation to heat dissipation, it is often mentioned that an anodized heatsink has better emissivity compared to a bare heatsink.
Since the ...
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Is there a relationship between the electrical power supplied to a material and the emitted wavelength?
I have a graphite bar that is used in a vacuum furnace that serves as a heating resistor and the heat is provided by radiation, so I would like to know by knowing the electrical input power (240kW), ...
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112
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If mass is just energy, how does thermal or kinetic energy transfer happen? [closed]
If mass is just energy, as it's excitations on quantum fields that when they vibrate together a certain way, they end up a particle, then how does energy transfer work?
Specifically kinetic energy ...
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