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Questions tagged [thermal-radiation]

The temperature-dependent 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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Is a thermal emitter the same thing as a blackbody?

Is a thermal emitter the same thing as a blackbody? It seems that both have the property to absorb all light and re-emit them in the form of thermal radiation. Is a thermal emitter the same thing as a ...
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graph relativistic degrees of freedom

I'm trying to graph the relativistic degrees of freedom, which should look like the figure And I am trying to guide me with this Phys.SE answer: Number $g(T)$ of relativistic degrees of freedom as a ...
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Does the black-body radiation formula (Stefan-Boltzmann) change if the photon turns out to be massive?

The black-body radiation formula, the Stefan–Boltzmann law, is derived treating photons as massless. Questions: What would the Stefan–Boltzmann law look like if derived assuming that photons have ...
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Why do we see black objects if they absorb all frequencies?

Black object absorb all frequencies, yet maybe some light is reflected anyway, but why do we see pitch black?
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Optimal radiator sizes?

Imagine a situation where we need to generate 10 GW of electrical power for about an hour. It would probably require large equipment, which would also produce waste heat. Lets further imagine that ...
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28 views

Spectrum range of black body radiation [duplicate]

Why does a black body emit at all frequencies at thermal equilibrium?
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Thermal radiation measurements: Looking for ~100 Hz BW, broadband (1-20 um) NIR/MIR detector

I am looking for a detector with about 100 Hz bandwidth, that has broad and ideally uniform absorbtance in the 1-20 um range. I need to be able to pickup signals in the 1 uW range with SNR >10, ...
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Units in Representation Of Energy Density Spectrum

In most of the texts, I referred to The Axis being labelled with Units as shown above. But I also found few images with different Notation (1/Units) Being Followed as shown Below. The units of the ...
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How can a solid be thermally transparent?

Thermal cameras designed to image wavelengths between 7-14µm (which is the peak for blackbody radiation around "room" temperatures) use lenses made of germanium, zinc sulfide, zinc selenide, or ...
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Planck's law - spectral radiance per wavelength, wikipedia article [duplicate]

I am looking at the wikipedia article of the Planck's law. Is the second formula correct? $$ B_\lambda (\lambda, T) = \frac{2hc^2}{\lambda^5}\frac{1}{e^\frac{hc}{\lambda k_B T} -1} $$ If $f = \frac{c}...
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Clarifying Planck's law

I've edited this. The 2 answers i've received so far were confused as to my meaning. I'm in an endless argument with a guy who insists that Planck's law predicts that a black body where $T>0$ ...
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Black body wave function non-trivial hole

I'm trying to integrate all the parts of quantum I know to examine in detail solving the Schrodinger equation for classic problems like black body radiation and double slit experiment. So I'm trying ...
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Hritik Nayaran said photons heats us [closed]

and i saw this. "The photons of ionizing radiation that over time can possibly affect evolution, contribute to the more immediate problem of morbidity and mortality of cancer. ... This energy, when ...
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Volume of air required to keep electrical box cool [closed]

I have a steel electrical box that is 15cm x 15cm x 10cm. The weight of the box is 1kg. Inside the box is a relay that loses 30 Watts of heat while in operation (it's attached to a heat sync that ...
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Why is blackbody radiation continuous?

I will preface this by saying I am not a physicist and have not taken a course on spectroscopy but I had some basic questions as I work with IR spectroscopy. Is it accurate that photons are only ...
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407 views

The derivation of the Planck distribution

I am trying to understand the Planck distribution and black body radiation. In the Wikipedia derivation of the Planck distribution, the photons confined within a cubic box, are emitting from and ...
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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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Thermal emission from a metal surface

We know from Kirchhoffs law that at thermal equilibrium the absorbance is equal to the emissivity. Let's consider some opaque layers of Al, Ag, Au for which I found reflectances at google: When I ...
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Thermal radiation of flowing gas inside cilinder

Problem: Understanding the concept of flowing gas radation. For my study i am designing a model of the heat transfer in a large verticale cilinder where flue gas with a temperature of 1400K flows. ...
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Does all thermal energy eventually turn into light?

Any object with a nonzero temperature emits energy as light, right? This means that the kinetic energy of its particles (thermal energy) is being converted to light. As it loses thermal energy, its ...
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190 views

Understanding thermal radiation in a conductor, gas and insulator

Context: I was in my bliss of ignorance and happiness when I was taught that quantum mechanics was about nice discrete values of energies. Now I am introduced the idea of Fermi Energy in a block of ...
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Blackbody radiation source

I have an instrument in the lab which needs to be calibrated. Ideally, it needs to be calibrated using a device that produces near-perfect blackbodies called a "blackbody calibration source". An ...
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1answer
153 views

Synthetic Photometry - Calculating a colour index

I have a theoretical black body spectrum as described by plancks law. I also have the bandpass sensitivity function for various filters. I would like to calculate a colour index from this information, ...
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147 views

Calculating rate of heat loss through conduction and radiation

I'm trying to calculate the rate at which a hollow cylinder with a heating element inside will lose heat, specifically through both conduction and radiation. I realize that the total heat loss per ...
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2answers
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Solid angles in integral?

Could somebody explain why we have to integrate over the solid angle when calculating total luminosity in the following: The integral over the wavelength makes sense, that a=way we have a total power ...
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Is sun a black body? [duplicate]

My teacher told me that sun is a black body but after reading at various sites whre they say that sun is not a black body but has black body radiations because it cannot absorb all radiations.
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Planck theory of discrete energy of photons and electromagnetic spectrum

Planck said that "energy of photon is quantized. That means energy of a photon cannot be any random value but a certain values only". If this is true how electromagnetic spectrum is continuous. For ...
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Black body radiation and line spectra

Firstly, Blackbody radiation and line spectra are both a phenomenon of energy emitted(EM), but why is the blackbody radiation spectrum continuous while line spectra is not continuous? Secondly, ...
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Why are solar panels kept tilted?

I have noticed that, in my country India, most of the solar panels are tilted southward at an angle of ${45}^{\circ} .$ Even on buildings with inverted V-shaped roofs, solar panels are still oriented ...
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239 views

Feynman Lectures Vol I 41-2: why can $\omega$ replace $\omega_{0}$ in deriving Rayleigh’s law?

NB: I understand that the model presented here is the "failing" classical model. I'm just trying to understand the formal reasoning of the model. In The Feynman Lectures on Physics Vol. I Ch. 41-2 ...
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128 views

Is it possible to extrapolate a black body radiation graph of the visible spectrum of a light bulb into the infrared and uv spectrum?

If the colour spectrum graph in the visible spectrum is plotted, is it possible to use a specific equation to extrapolate the curve? What if it's a light bulb that isn't a black body (CFL, LED)? Would ...
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2answers
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Could a foggy double-paned window be amplifying UV rays?

Ever since my living room double-pane window got foggy, I've noticed that I feel very uncomfortable/sick when it is a very sunny day (similar to the way I feel when I've been out for too long in the ...
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Why doesn't hot charcoal glow blue?

I was learning about black body radiation and the explanations given by Max Planck and Albert Einstein when a thought crossed my mind. When we heat an iron piece, its color changes gradually from ...
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The equilibrium era and energy density

In Weinberg's 'Cosmology', at page 109, he presents an era "of equilibrium" when "the temperature and density were sufficiently high so that radiation and matter were in thermal equilibrium. Then, ...
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1answer
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What is the average energy of visible light photons, of what we perceive to be white light? (i.e. visible spectrum of 5500K radiation)

Visible light is anything between 1.65eV and 3.10eV, so the answer is somewhere between these values. Naively we could average this to 2.375 eV, but that would not be actual average of full spectrum ...
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Blackbody flux model (Xspec: bbodyrad)

Above is the model I fit my data too in Xspec. Xspec is a piece of software where you can model spectra from observations with their set models. It handles things like absorption, reddening, etc. to ...
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2answers
467 views

Modeling a wine cooler heat loss to ambient

I'm trying to model the steady state heat loss to ambient, in W, for a wine cooler similar to the following: For the modeling, I will need the following variables/constants: $T_a$ [K]: Ambient ...
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1answer
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Inconsistency in two equations for Planck law given by professor

I know there are a variety of questions about this topic but I have been searching the internet for a long time and couldn't find a proper answer. The question is simple: I saw the following formula ...
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Can radiators cool down using only back body radiation?

If you could produce a very thin tube, say less than the thickness of a human hair, designed to carry a hot liquid inside, the diameter is small so that the liquid would have a high surface area to ...
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What processes permit (presumed) emission by, but prohibit absorption of, IR photons by non-greenhouse gas molecules?

It is said that because of bond-structures / possible vibrational states, non-greenhouse-gases / homonuclear diatomics cannot absorb IR. Presumably there is no question that all gases, being matter, ...
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1answer
155 views

Black body radiation curve

See images about black-body radiation. How does Planck's quantum theory explain the low intensity of radiation for high frequencies? I.e why does the black body curve become lower at the high ...
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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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Frequency and wavelength of thermal radiation [duplicate]

Why for a given temperature these forms of Wien's law implies a different maximal wavelength?
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238 views

How long does a black hole last after it becomes white hot?

According to Stephen Hawking's theory of black holes, once a sufficient mass has been lost through evaporation, the escape velocity $3 \times 10^8$ meters per second so light is able to escape from ...
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Principle of a pyrometer

How does a pyrometer work? Especially how do I ensure that the temperature of a single spot is measured (where the laser points at)? Here is a scheme of the structure but I guess it's not really ...
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2answers
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Is it possible for a radiant heat transfer to create higher temperature in the sink compared to the source?

Assume we concentrate the rays of the sun onto an object (in the vacuum of space) that has very low emissivity - The energy coming in is higher than the amount being emitted as radiation - hence it ...
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How much additional mass does the Earth gain each day from solar radiation?

According to this answer, energy has some (minimal) mass associated with it. Therefore, when lots of energy hits the earth (such as solar radiation in a 24 hour period) shouldn't the earth gain some ...
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179 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 $\ R_1=...
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Why do thermal cameras work at infrared radiation and not at visible one?

From the Wien's law I have computed the Spectral Irradiance of a black body at 1000°C. From different thermal cameras manufacturers web sites, a lot of Thermal Cameras work in the range 6-14 $\mu m$....
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Do initially heat(radiation) shield has temperature between the high temperature end and low temperature end?

Suppose two constant temperature (T1) and( T2 ) (T1>T2) large plane surfaces are there , in order to reduce heat loss we provide a heat shield in between them , i know at steady state there exists a ...