All Questions
Tagged with blackbody or thermal-radiation
1,722 questions
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Can heat radiate from a cold to hot body?
if you have 2 bodies (A,B), with Temperature of B>A, can you have heat transfer from A to B through radiation?
In particular if A reflects the wavelengths that B is emitting the radiation at would ...
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Finding the temperature of the glass envelope in an incandescent light bulb
I've been trying to evaluate the temperature of an incandescent light bulb, using radiation for the filament and convection for the bulb, the radiation's equation works fine, but the problem is the ...
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Planck's Law frequency vs wavelength [duplicate]
I was plotting planck's law today and attempted two different implementations. I took both from this table on Wikipedia. They are:
In terms of wavelength:
$$
B_{\lambda }(\lambda ,T)={\frac {2hc^{...
- 213k
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How can I calculate the temperature at a distance $r$ from a neutron star?
I am looking for an equation that can take into account the strong magnetic fields of neutron stars and the affect they have on the radiation of heat. So far, I have been unable to find anything more ...
- 213k
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How did Planck derive his formula $E=hf$?
Some time ago I asked my quantum physics lecturer the question:
How did Planck derive his formula, the Planck–Einstein relation
$$E=hf$$
with constant of proportionality $h$, the Planck constant.
I ...
- 213k
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Is there a function for how hot an object would have to be to compensate for the drop off after SSR is exceeded using a microbolometer?
I am wondering if there is a clean formula for how much hotter a given object would have to be to register at the same temperature after the spot-size ratio has been diminished for a given thermal ...
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Why is there a colour difference between stars and hot objects since they are both black-body radiators? [duplicate]
I have a question about the color of a black-body radiator that has been baffling me for a few years now, and I haven't been able to find a satisfactory answer. So, we know that a star's color depends ...
- 213k
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Blackbody emission from $N$ parallel & infinite 2D planes
This is something that's been bothering me. A solid object will emit radiation with a flux surface of $\sigma T^4$, but what about a plane?
Here is a thought experiment I came up with to help me make ...
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Event Horizon vs. "Interior" of a black hole from perspective of distant oberserver
From the perspective of a faraway observer watching an object fall into a black hole, they will see the object approach the black hole's horizon at a slower and slower rate until eventually "...
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Pair of polarizers as a black body
Let a system be composed of two perfect linear polarizers, where the axis of the first one is perpendicular to the axis of the other, so they do not let any light pass through the second polarizer. ...
- 16.2k
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What is the purpose for the blackbody radiation graph to be graphed using the below parameters?
If you observe the above graph, for y axis, "intensity per wavelength" is used as the parameter. I am aware we use "per wavelength" because it is hard to measure and graph isolated ...
- 51.6k
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Experiments carried out to determine the energy of photons of different wavelengths
I imagine it would be very difficult to experimentally determine the energy per photon of monochromatic EM radiation. Since every material reflects/absorbs differently at different wavelengths, I can ...
- 29.5k
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Does Stefan's law give the intensity of all the electromagnetic radiation or just infrared radiation?
The Stefan–Boltzmann law, also known as Stefan's law, describes the intensity of the thermal radiation emitted by matter in terms of that matter's temperature. (WIKIPEDIA)
The Stefan-Boltzmann Law ...
- 3,162
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Wien on Temperature and Entropy
As far as I understand, Wien defines entropy, which he uses in his derivation, as
$$ S = \text{v} \int\limits_0^{\infty} \varphi(\rho, \nu) d \nu, $$
where $\text{v}$ is the volume occupied by ...
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Physics behind gold+silver space blanket placement
In the first aid and mountaneering, "space blanket" or "astro foil" is used for protection against cold enviroment or as first aid after burns. There are many different versions of ...
- 42k
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How is a black body 'radiating' light different from 'reflecting' it?
Light falls on a black body and its oscillating electric field causes the electrons to start vibrating, thus gaining kinetic energy which contributes to rise in temperature and, simultaneously, the ...
- 3,162
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Calculating new temperature of an object when air temperature changes
I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time.
Basically I get periodic readings from an air temperature sensor in a ...
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How can I apply Planck's law to calculate the photon energy density of a warm room?
I am trying to calculate the rate at which photons of any particular frequency will pass through a volume in a room illuminated by black body radiation only.
I've found a couple of starting points ...
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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 $\ R_1=...
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Volume dependence on quantization of the electromagnetic field
I'm studying a non-additive formalism where volume dependencies play a crucial role, and I am particularly interested in applying these models to electromagnetic radiation, which has a well-defined ...
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Lambertian emitter law contradicts black body radiation
I'm really worried about "Lambert's law": A blackbody emitter is supposed to be "Lambertian" but I know from blackbody radiation that its radiance L (W/m²/Sr) is independent of ...
- 136k
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Can nonimaging optics concentrate heat to a higher temperature than the source? [closed]
Practical goal:
I'd like to concentrate the low-grade heat from the back of solar panels, which I've measured is in the range of 20-50F greater than the ambient temperature throughout the day, and ...
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What are the Planck's "resonators" on his solution on the Black Body problem?
On his paper "On the Theory of the Energy Distribution Law of the Normal Spectrum" from 1900, in wich M. Planck presents an overview on his prescription to obtain the expression for the ...
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Planck's law in terms of flux [duplicate]
The Stefan-Boltzmann law describes blackbody radiation in terms of radiant flux per unit area i.e. how much energy passes through a 2D surface per unit time. I find this very simple and I understand ...
- 213k
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Does night sky cooling need clear sky and why?
I think I understand what radiative cooling is in general. Each body which is at a non absolute zero temperature would emit electromagnetic waves and loose energy.
Now when it comes to night sky ...
- 213k
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3
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Can small solid bodies emit radiation with wavelength larger than the body itself?
It's known that EM waves cannot pass the aperture with a diameter much smaller than the wavelength. How is it for an opposite situation? If, for example, a solid body is a $100 \ \text{nm}$ sphere, ...
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Peak of energy and black body
The tungsten filament of an incandescent light bulb has a temperature of approximately 3000 K. The emissivity of tungsten is approximately
1/3, and you may assume that it is independent of wavelength. ...
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Does water vapour also emit radiation when rising into the air before condensing?
There are topics on how water vapour absorbs radiation ("How does carbon dioxide or water vapour absorb thermal infra red radiation from the sun?"), but what I am looking for is can water vapour also ...
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How to apply symmetries ($q$-points) in the Brilloun Zone on the transmission function of radiation heat transfer?
Basically, I want to find out the near field radiation transmission function between two graphene, set at Temperature $T_1$ and Temperature $T_2$. As you can see in the figure d is the separation ...
- 213k
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What effect does color on the upper and lower side of umbrella have?
This question isn't referring to the general use of umbrella to provide protection from rain rather it concerns the optical effects of the color on lower and upper portion of umbrella.
Umbrella are ...
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Is fire plasma?
Is Fire a Plasma?
If not, what is it then?
If yes why, don't we teach kids this basic example?
UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify the ...
- 1,746
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600
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Technical definition of heat
The other day I asked a question here. The question concerns two separate, radiating spheres that have constant heat generation and a consequent steady state temperature. Since one sphere has a ...
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Why does gold only glow red after flame is removed?
I was at a jewelry workshop today and saw somebody place a gold ring under an intense flame. Weirdly, the ring looked normal when underneath the flame, but glowed "red-hot" as soon as the ...
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Spectral energy density of black body radiation [closed]
$u(\nu,T)$ is known as the amount of energy emitted per unit frequency $\nu$ per unit volume $V$. It is the function of $\nu$ and $T$. In case we would like to know the amount of energy density at ...
- 553
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Why do dark colors absorb light more than light colors?
Black color absorbs light better than any other. The thermodynamics explains the propagation of heat but never really answers why exactly specific spectrum of color has different absorption ...
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How is radiation emitted from a small hole in a box, if the hole is small enough to prevent radiation from escaping in the first place?
So I totally understand how a hole in a box works as a good approximation for a perfect absorber of all incident radiation (a black body). However, a black body is also a perfect emitter of radiation ...
- 16.2k
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Derivation of the solar resource at Earth's surface
I am reading Jenny Nelson's The Physics of Solar Cells and am a bit confused with the derivation of the solar irradiance at the Earth's atmosphere she supplies. I'll outline it here, and I provide ...
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What do Maxwell's equations tell us about the ultraviolet catastrophe?
I have found it that in elementary discussions of black-body radiation, other than justifying electromagnetic waves should exist from Maxwell's equations, those equations are not used for anything ...
- 65k
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Why does not Earth radiate more energy into the space while it gets warmer? [closed]
The earth is getting warmer. By Stephan's law, it should radiate more energy into the universe.
On the other hand, the energy from the sun is a constant. So how to achieve a balance?
- 136k
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3
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483
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Global warming and planetary thermodynamics
To a first approximation, the earth currently radiates out as low frequency thermal radiation the same amount of energy as it absorbs as high frequency solar radiation. (This ignores energy generated ...
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Matter made of neutral charges does not radiate?
We know that any blackbody that has a certain non-zero temperature radiates. This happens due to the jiggling of charged particles (protons and electrons), and accelerated charges create ...
- 26.6k
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If the heat transfer in a particular direction is negligible then is it necessary that the temperature variation will also be negligible?
Imagine having a rectangular block. If the heat transfer is predominant in only one direction (say x) and the heat transfer in the other two directions (say y and z) is negligible, then can I conclude,...
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How can blackbody radiation be explained by quantization?
I don't understand why quantization makes a peak in the blackbody radiation curve (so there is no UV catastrophe) and the concept of a relationship between that peak and quantization.
When the ...
- 136k
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When measuring IR for temperature of shiny surfaces, how is the object own emission added to the reflection?
While discussing measuring temperature of a heated glass plate used in 3D printers, it was pointed out that IR thermometers are not accurate because, for uncoated and shiny glass surface, they measure ...
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How would a three dimensional standing wave created inside a box look like?
While deriving Rayleigh-Jeans law, in order to make a standing inside a cube, a condition is put forward which says electric field must vanish when the EM wave hits a surface of the cube.
I want to ...
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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)$$
Being $\rho_v(T)$ the spectral enegy ...
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How is Hottel's method of crossed strings valid?
Hottel's method calculates the view factor as $ F_{ij} = \frac{1}{2P_i} \times \text{(crossed - uncrossed lengths)} $ and similarly $ F_{ji} = \frac{1}{2P_j} \times \text{(crossed - uncrossed lengths)...
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Do black holes convert 100% of their mass into energy via Hawking radiation?
And if so, does that mean that we do not need matter/antimatter annihilations for 100% mass to energy?
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Wien's displacement law
Wien's displacement law states the following
$$\lambda_{max}\propto\frac{1}{T}$$
However, after learning about redshift and blueshift, it doesn't make sense to me why we can use this law. Supposedly, ...
- 213k
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Why does Sun appear white at noon?
I have found several source citing the reason for the white apperance of sun is due to less scattering of light before sunlight reaches an observer on the Earth (as it is relatively closer to us at ...
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