All Questions
Tagged with thermal-radiation radiation
150 questions
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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 ...
2
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1
answer
108
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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 ...
2
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1
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71
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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 ...
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How well does a cavity with a hole approximate a black body?
Cavity with a hole is a frequently cited approximation to a black body (more precisely, it is the hole that is the black body here):
Is there a simple estimate of how well such a cavity approximates ...
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2
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Regarding the absorption property of a blackbody
Consider a blackbody of surface area $S_b$ and at temperature $T_b$. It is placed inside an evacuated chamber (to neglect all the effects of convection), with walls of chamber at temperature $T_c$ and ...
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1
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Radiation power emmited by a material with two different temperatures [closed]
Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
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1
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0
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How to measure light intensity in a room?
Does anyone know how I would go about measuring the light intensity in a room? I'm not interested in knowing the lux reading, I would like to measure the $W/m^2$ due to thermal radiation in my ...
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0
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How were luminous intensity changes for each EM frequency measured in the blackbody experiments of the late 19th c., which led to up to Planck’s Law?
If in today’s parlance it would be either ‘spectral density’ or ‘spectral radiance’ that was in fact measured then as opposed to ‘luminous intensity’ please feel free to clarify.
Kindly note that my ...
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0
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What are the benefits/weaknesses of different diffusion models in radiation transport?
Can anyone summarize or point me toward references for why someone would choose one diffusion model over another, particularly in relation to radiation transport during a nuclear blast? The diffusion ...
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0
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Heat transfer and Stefan-Boltzmann law and black body radiation [closed]
can there exist a black body (theoretically) which has a cavity in it I don't mean Fery's black body I am referring to a black body which is made of a MATERIAL which has the property to emit and ...
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Can a body be in thermal equilibrium at a different temperature from surroundings?
As per my knowledge bodies attain constant temperature (thermal equilibrium with surroundings) when they absorb and emit energy at equal rates.
Let us say temperature of surroundings is T1.
We have a ...
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2
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3
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Why does the color of a body only depend on absorptive power and not emissive power?
In the numerous explanations on nets and books, all give the reasoning as follow. If you see a red shirt, it's because that pen had a higher absorptive power for all colors except red, causing its ...
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2
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0
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How did Kurlbaum and others measure the intensity of each wavelength to get blackbody radiation curve?
In 1900 Plank was faced with data that didn't agree with the Plank-Wien law. This data that plots different temperature curves - wavelength on the horizontal and intensity on the vertical (or rather ...
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1
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Jumps between energy states of harmonic oscillators
I have recently read that in perfect harmonic oscillators to go up or down in energy state you have to go, using the simile of a staircase, step by step, emitting or absorbing a photon of energy $E=\...
0
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2
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Cavity radiation and number of modes
Cavity radiation says the number of modes in the cavity increases with frequency, or shorter wavelength, because more modes can fit in. But consider a square box with sides L with a small hole. EM ...
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4
answers
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Do blackbodies emit gravitational waves?
It was previously my understanding that the reason blackbodies only emit light was because light was the only massless particle, so there exist excitations of the electromagnetic field of arbitrarily ...
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21
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6
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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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4
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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 ...
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0
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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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1
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64
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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 ...
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2
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1
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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 ...
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1
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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 ...
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2
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1
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Is a layer of gas with sufficiently large optical thickness really radiating as a black body?
Can a parcel of gas with large value of optical thickness really radiate like a black body?
I have in mind a simple (most likely oversimplified) model which yields
$$I_\nu = I_\nu(0) e^{-\tau\nu} + I_\...
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How is black body radiation from sample eliminated when measuring absorption coefficient?
I wonder how absorption spectra of a sample (e.g. gas with some $CO_2$ absorbing strongly at $\approx 15\mu m$) is measured by IR spectroscopy, thereby having in mind the following arrangement, ...
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What radiation spectra does neon glow at 2500 K?
A neon gas tube, when passed with high voltage electric current, will emit a characteristric spectrum of color.
This spectra lines are explained by the different combinatorial paths that electrons ...
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73
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How can Kirchhoff's law of radiation be proven more rigorously and what does it really mean?
Kirchhoff's law of radiation states that emission factor equals absorbtion factor for any material body: $\epsilon = a$
I never understood this really: Lets say there a body which reflects totally any ...
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1
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How does apparent brightness (or stellar magnitude) change with distance in an expanding universe
Cosmological redshift causes wavelengths of a distant object to stretch by a factor $1/(1-Hr/c)$ where H is the Hubble constant, r is distance, and c is the speed of light. Consequently the received ...
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1
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Diffrence between thermionic emission and photoelectric emission
Thermionic emission involves heat energy to excite the electron and remove it. In the photoelectric effect, a beam of light is involved.
As per my understanding heat and photons, both are energy. Heat ...
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3
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1k
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Cavity and black body radiation
If one speaks of the fact that one gets blackbody radiation in good approximation by a cavity with hole, does one mean as blackbody this hole, i.e. the place where the radiation exits from the cavity? ...
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How was the black body intensity vs wavelength (or frequency) radiation curve historically produced?
I have read that Wilhelm Wien gave his formula to match the radiation curve of a black body as shown in the picture; which works well in high frequency region. Another formula by Rayleigh-Jeans is ...
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1
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Black body side of the Moon
A few closely related questions regrading the Moon thermodynamics:
The Moon is clearly not a black body, as it reflects a great deal of radiation incident on it. Still, it does absorb some radiation ...
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1
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1
answer
154
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Equipartition theorem for radiation in black body?
In Planck distribution of energy density for black body he solved the uv catastrophe by association of descrete energy to each mode, and by the equipartition theoreme from statistical mechanics we ...
1
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1
answer
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Interference of standing waves inside black body?
Does electromagnetic wave inside a cavity (modeling black body ) interfere with each other?
And why in the derivation of Rayleigh law of black body radiation we add energy of different modes (are we ...
1
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1
answer
308
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Do the pupils of an eye emit blackbody radiation?
A blackbody, by definition is an ideal system that absorbs all radiation incident on it.
If a good approximation of a black body is a small hole leading to the inside of a hollow object, then am I ...
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Solar constant and Energy received by the Earth
I've been reading about black body radiation and I came across the topic of solar irradiance.
If we consider the sun to be a perfect blackbody, then the intensity of the solar radiation at a distance ...
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1
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665
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Calculate the heat energy absorbed by an object without knowing its specific heat?
Say we know the mass of the object, the surface area, the temperature change, the time taken for the temperature to change and that all heat exchange happened through radiation
Can the stefan boltzman ...
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0
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It seems a stove top coil / burner element defies black body radiation
Most glow charts say that incipient red Heat is 1000 Fahrenheit or 540 Celsius , and bright orange is just shy of 2,000 Fahrenheit or 1093 celsius . But my fluke thermocouple rated at over 2,000 ...
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4
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Can we feel heat in outer space? [duplicate]
Is there air outside of earth atmosphere? If not, could we feel heat coming from sun?
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Entropy Change in Radiation and Convection
When a system loses it's internal thermal energy by emitting radiation or by convection what is change of the systems entropy mathematically?
I saw this question's answers for radiation only but still ...
user310884
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0
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38
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Objects react different to different types of radiation
I am a bit confused about the different types of radiation and how objects react to it. In class, the professor showed us a cube with white, black and reflecting sides (the Leslie cube). Inside the ...
2
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1
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605
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What truly is spectral blackbody emissive power?
I read that a blackbody at a temperature T, would emit thermal energy in the form of Electromagnetic waves. This thermal energy emitted per unit the area per unit time is called blackbody emissive ...
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2
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Area under the Wien's Law graph
Before I proceed, in the Wien's law graph is the Y-axis Emittance[$E=Q/(A*t)$] or Power density ($Watt/M^3$)?
According to several Google pages, The Y-axis is Power density but my book has used ...
user294573
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1
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What is the difference between thermal and electromagnetic radiation?
In my understanding thermal radiation and electromagnetic radiation is same, for example suppose we heat up a knife to high temperature then it glows red. This means the thermal radiation / ...
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Spectral Radiation Intensity and Energy Density
I'm trying to prove the following relation
$$ I_{v} = \frac{c}{n} u_{v} $$
where $I_{v}$ is the (spectral) radiation intensity and $u_{v}$ is the respective energy density, $n$ is the refractive index ...
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4
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1
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Picturing Photon Gas
Consider a photon gas inside a cavity with diathermal walls which is held at temperature $T$.
I want to picture everything that's going on. More like the picture, We have for molecular gas.
So I can ...
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1
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569
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Thermal radiation vs emission spectra of gases
I am a high school student and I am very confused in absorption and emission spectrum of gases, for e,g take hydrogen at room temperature for simplicity, so that we can talk in terms of Bohr's model ...
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2
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What is black-body equivalent of UV part of solar spectrum?
If all non-UV light was filtered from sunlight, does this approximate a different type of black body radiation? Regular sunlight has a black-body temperature of 5777 K.
This is in relation to the ...
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2
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What is thermal radiation on a molecular level? [duplicate]
I’ve recently been scouring my Finnish high school level textbooks and online physics forums for an answer to the following question: ”How is thermal radiation created on a molecular level?” or ”What ...
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2
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What was the question to which Max Planck gave an explanation and how is it related to blackbody radiation?
Quoting from my text book - "several attempts were made to predict intensity as a function of temperature/wavelength". This line was preceded by the explanation for blackbody radiations and ...
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What does it mean when we say "a blackbody is in thermal equilibrium with it's surroundings"?
Quoting from my text book - "a blackbody is a perfect radiator of radiant energy. It is in thermal equilibrium with it's surroundings and radiated as much energy per unit area as it absorbs from ...
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