Questions tagged [thermal-radiation]
The temperature-dependent emission of electromagnetic waves. Combine this tag with the [thermodynamics] tag for a macroscopic view or the [quantum-mechanics] tag for a microscopic explanation.
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Thermal gravitational waves vs thermal radiation
A body at temperature $T$ has both an electromagnetic emission spectrum and a gravitational emission spectrum, are there any temperatures or conditions where the gravitational one could be comparable ...
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Question about Rayleigh-Jeans law derivation
I'm trying to understand the derivation of Rayleigh-Jeans law of this following video:
https://youtu.be/rCfPQLVzus4?t=1142
And there are some parts that I'm still not clear:
When he derive the number ...
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Photoelectric effect and heating an absorptive body
As we know, two bodies undergo radiative heat exchange due to each emitting a spectrum of light according to its temperature (blackbody radiation).
When one body is hotter than the other, it emits a ...
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How is Hottel's method of crossed strings valid? [duplicate]
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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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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How does a blackbody heat up if it emits all radiation that it absorbs?
How does a blackbody actually heat up and change temperature if it emits all the radiation that it absorbs by definition? And by extension, if the absorptivity and emissivity of a body are equal, then ...
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Standing Waves are formed by an Electromagnetic radiation inside a cavity
While seeing the derivations of the Rayleigh Jeans law and the Planck's Law for a Blackbody Radiation, I came across a fact that they assumed that Electromagnetic Radiation inside a cavity would form ...
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Effect of having infrared reflective paint on a room with and without a heat source
I am trying to check if my understanding is correct. This is not really a question but a request for validation. I hope this is allowed.
When painting with a heat reflective paint there are two ...
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Convert radiation density into temp in degrees kelvin
in the 1948 paper by Alpher he gives a present radiation density in gm per cm cubed. how is that converted to a temp of 5 degree kelvin
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Blackbody temperature in special relativity?
This is from Gravitation Foundations and Frontiers - Padmanabhan
Consider an observer moving with a velocity v through a radiation bath of temperature $T_0$. The observer will see an anisotropy in the ...
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How is the average energy, $k_BT$, associated with each mode of electromagnetic radiation confined in a cavity described in Rayleigh-Jeans Law?
From Rayleigh-Jeans law we can get an expression for the energy density of black-body radiations confined in a cavity.
When blackbody radiations i.e. electromagnetic waves are confined into a cavity ...
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Is there a way to completely stop energy losses due to thermal radiation?
If all bodies emit thermal radiation, does it mean that it's impossible to build something that can retain all of its energy - and last indefinitely? i.e. is everything in our world, including a ...
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How can we prove mathematically that a body not at zero kelvin emits radiations of all wavelengths?
Well, today our teacher was taking up the topic Radiation under the chapter Properties of Matter. And he said that all bodies with a temperature above zero kelvin emit EM waves with all wavelengths ...
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Emissivity Relation Between viewing angle, wavelength and temperature
I am trying to find the relation between emissivity of a material, viewing angle(from normal) and temperature of a grey body. Is there a formula that gives us this relation. This is to create an ...
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Why does a blackbody cavity with a hole emit black body radiation?
Why could we use nearly every material in a cavity with a hole to absorb/ emit every wavelength?
If the material doesn't have the exact energy gap, g, for example, it couldn't absorb a photon with ...
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Blackbody Radiation vs Emission Line spectrum
A perfect blackbody has a predicable emission pattern in terms of both intensity and color, given by Planck´s law.
Similarly, elements such as Hydrogen or Helium will emit specific wavelengths when an ...
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Color temperature and space
I often think about the universe and lately about the color spectrum. so I wanted to ask how much the temperature of the body depends on the color. the hottest star I've found is 200,000 k and its ...
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Equation-of-state for a photon gas
What is the equation-of-state for the photon gas ?
Remarks:
Here Photon gas = Black body radiation. For more background see How does radiation become black-body radiation?, Does thermal energy ...
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Writing a Monte Carlo radiative transfer simulation for computing the observed blackbody radiance due to the environment
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I'm attempting to determine the power observed at some antenna immersed in some perhaps highly anisotropic scattering and absorbing medium due to the blackbody radiance of the environment. ...
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Is Sun not the biggest source of energy to us?
Probably in my 5th or 6th grade, I learnt in my science classes that sun is the biggest source of energy to us.
However, I was watching this youtube video according to whom the energy of earth is ...
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Are there any material coatings that would currently be effective to counter the rise of directed energy weapons?
I've been reading into directed energy weapons recently, and they seem like they're going to be a gamechanger. I'm just curious as to material countermeasures. I've learnt that some dielectric mirrors ...
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Can something become hot enough that it stops glowing?
So I understand that matter emits EM waves when hot. And that the higher the temperature, the shorter the wavelength, so cooler flames start off orange and the hotter flames reach light blue and white....
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Relationship between blackbody radiation and double slit experiments
What are the intrinsic properties of the two phenomena that makes them part of the same lets say "universe"?
I'm just a graduate mathematician trying to gain physical intuition behind ...
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Surface Temperature vs Body Temperature in Stefan-Boltzmann Law
In many tutorials in atmospheric physics, I have seen a basic method used to calculate Earth's surface temperature, assuming it was a black body in equilibrium. The method follows this outline:
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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=\...
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Why does a blackbody object emit light if it only absorbs light?
I have learned that a blackbody object only absorbs light and thus does not reflect any light. The blackbody object will, however, emit light, and none of this light is due to reflection. Where does ...
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What is the entropy increase associated with the absorption and remission of solar radiation? [duplicate]
The average solar irradiance over the Earth is 1361 W/m2 with a wavelength distribution given by Planck's law for a temperature of about 5778 K. Approximately, the same amount of radiation is re-...
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Fluctuation of thermal state of light derivation
I am having trouble following how the expression for the variance of the photon number $$\Delta n = \langle n \rangle^2 + \langle n \rangle $$ is obtained for a thermal state of light (steps below ...
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Properly inserting radiative heat flux into partial differential heat equation for a gas
The heat equation for a gas can be written as:
$$ \mu c_p \left( \boldsymbol{v} . \boldsymbol{\nabla} + \partial_t \right) T = - \boldsymbol{\nabla} . \boldsymbol{j} + \partial_t P + S $$
with $\mu$ ...
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Does radiant barrier work if hidden under timber structure
I am insulating my house roof and I wanted to explore the radiant barrier and if these are actually effective in a real life scenario.
The desired outcome of installing such barrier, would be to ...
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What are the hex color code equivalents for the different classifications of stars?
Stars appear to be of various colors based on the visible light they emit. I am wondering if there is a hex color code that can be considered to be typified or average for the various classifications ...
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Can we redirect the thermal radiation of an object back to itself to heat it more?
Imagine we have a tungsten wire that we heat up to 1000 kelvins inside a tube with a special coating that reflects 99.99% of tungsten's emitted light due to thermal radiation back to the wire.
My ...
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Estimate the Sun's temperature, based on the duration of sunrise
The full problem statement is:
Measured from the time when the first rays of sunshine appear above the horizon until
the moment when the sun is fully visible, sunrise lasts 2.1 minutes. Based on this
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Can stellar wind cause a star to have a Bimodial Radiation spectrum?
Most stars emit Stellar wind, so more then others.
Some stars such as Eta Carinae emit enough stellar wind (0.001 solar masses a year) that most of the radiation they emit will be absorbed and re-...
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Why is the Sun’s emission spectrum shaped like this?
The Sun emits more at $450-600 \,\rm{nm}$ than a black body of the same effective temperature would, it also emits far less UV.
I’ve heard this is due, in part, to the fact that the Sun doesn’t have a ...
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Where does heat go at an atomic level in all phases of matter? [closed]
I'm trying to understand where heat energy goes in a substance. I've seen that mainly it's translation at lower temperatures, rotation at mid range, and vibration at high range, but I'm not sure of ...
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Effect of Sun temperature on the thermosphere
Correct me if I’m wrong here.
The thermosphere is hot due to its absorption of moderately high energy UV radiation. (<200nm)
Cooler stars emit fewer high energy photons. So if the Earth orbited an ...
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A question about colour temperature
This picture from Wikipedia is a table of temperatures vs colour for incandescence, however the problem is that I’ve been told that for a black body, even something with a temperature of say 2000C (E....
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Thermal emission, after equilibrium, of two identical plates?
Take two identical plates at two different temperatures. Thermally isolate the "back" of the plates and connect the other sides via a "vacuum tunnel" with walls made of a perfectly ...
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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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Numerical outputs of experiments which gives spectrum of blackbody
Many books have spectrum of blackbody radiation in some temperatures before result of Planck and say this is result of experiment. But they don't have any table as result of measurements from them we ...
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Power received close to a large black body radiator
I am interested in calculating the power received by an object near a black body radiator. Say, for example, I had a piece of paper perpendicular to the earth's surface normal. If I make assumptions ...
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What is the EM spectrum of the earth seen by a satellite?
I am asking because of the greenhouse effect. It is said that without the atmosphere, the average surface temperatur of the earth would be about -18 celcius. This number is obtained simply by assuming ...
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Modeling radiative transfer in a two-layer, vertically inhomogeneous medium in local thermodynamic equilibrium
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I'd like to determine the power observed by an antenna due to the blackbody radiation emitted by the medium in which it is immersed. I'd like to take into account absorption, emission, and ...
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In the blackbody radiation, would the energy distribution with wavelength take the same curve as the intensity distribution?
Would the energy distribution take the same curve as the intensity distribution? In other words, can I derive the energy distribution by multiplying the Planck's radiation law by the surface area of a ...
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Underestimation of peak wavelength by Wien's law for stellar spectra
I plotted some simulated stellar emission spectrums from PHOENIX which also each came with their respective effective temperatures. With the effective temperatures, I used Wien's law to estimate the ...
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Distribution of Electric oscillator's in Boltzmann's theory
While I was reading the book "In Search of Schrodinger's Cat" I found an interesting excerpt on how Max Planck used Boltzmann's statistical equations to solve the Blackbody radiation problem....
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In simple terms: how does the quantisation of energy solve the Ultraviolet Catastrophe? [duplicate]
I've searched around the site and looked at older posts but none of the answers make sense to me.
For a bit of background: I'm a high school student and don't have a great understanding of the more ...
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How do plasma radiative losses scale with temperature in the range 5kev to 1MeV (holding density constant)?
The $T^4$ blackbody radiation rule breaks down well below 1MeV because of new effects like bremstrahlung, inverse compton scattering, etc. It would be great to have a chart of temperature vs aggregate ...
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How can i find the value of Planck's constant using Black body radiation?
I'm working for a physics project for Highschool, and i'm currently thinking about using black body radiation to measure Planck's constant. I know there is an option using the photoelectric effect but ...
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