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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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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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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Physics of the convection oven

I don't understand how convection ovens can cook food faster than radiant heat ovens. Guides to convection ovens claim that they cook food 25-30% faster than radiant heat ovens, but do not really ...
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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 ...
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How to add markers to IR photographs

I'm using an IR camera to identify thermal patterns. The thermal images are similar to this [LINK] image. I'd like to add markers to the area being measured to determine dimensions and normalize the ...
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The entropy given by stefan Boltzmann's law looks remarkably similar to the volume of the sphere; $S(T)=\frac{4}{3}\sigma T^3$

If I am not mistaken the entropy for a blackbody per unit area is given by: $$S(T)=\frac{4}{3}\sigma T^3.$$ The volume of a sphere is given by: $$ V(r) =\frac{4}{3}\pi r^3. $$ Is this coincidental? I ...
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Quantifying how much would Jupiter heat up if you accelerate Jupiter out of orbit around the sun using fusion candles? [closed]

So, I responded to a post of someone saying that you could turn Jupiter into a spaceship using fusion candles. I mentioned that doing so would dramatically heat up the planet, especially if you were ...
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Is cooling by infrared absorbing rectenna possible?

We know that every hot objects emits IR radiation. We also know that plasmonic rectenna can absorb and convert IR radiation to electricity. Question: what will happen if we put an hot object inside a ...
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Is spectral radiancy same of a blackbody radiation for area element $dA$ imagined in different orientation?

Spectral emissive power $e$ is defined as the power emitted through per unit area per unit frequency. And spectral radiancy $f$ (frequency, $T$) is the energy falling perpendicular to a unit area per ...
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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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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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How can both of these versions of Wien's displacement law be correct? [duplicate]

I'm reading Bohren's "Fundamentals of Atmospheric Radiation" and I'm finding one of the points in the first chapter troubling. The author introduces Planck's distribution, both in terms of $\...
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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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Aren't all objects luminous in a sense?

In my physics class, I learned about "nonluminous objects" - these are objects which don't produce their own light. But, don't all objects emit light by black body radiation? So are all ...
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Why does Quantum Harmonic Oscillator treatment to Blackbody Radiation result in Ultraviolet Catastrophe?

Planck, in his treatment to solve Blackbody Radiation, considered that the Electromagnetic Waves inside the Cavity of the Blackbody are Standing Waves due to Oscillating charges on the wall of the ...
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Deriving Wien's approximation

Without Planck's law from where and how could one empirically get this. Could it be got from power is proportional to fourth power of temperature.
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Planck's assumptions for Treatment of Blackbody Radiation

Planck, in his treatment to solve Blackbody Radiation, considered that the Electromagnetic Waves inside the Cavity of the Blackbodyare Standing Waves due to oscillating charges on the wall of the ...
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What would provide greater thermal insulation, a single 1.5 inch thick wool sweater, or 5 thin 0.3inch sweaters layered over each other?

So in this hypothetical,its winter time and your wearing lets say a shirt and a jacket, but inbetween the shirt and jacket you have the option of a sweater. But which layout would result in greater ...
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Equilibrium in blackbody radiation

I was reading this post and I think I am still confused. A blackbody $radiator$ is not in equilibrium, by definition, since it is radiating. If so, why does the blackbody spectrum accurately describe ...
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Emissivity of a perfect reflecting body

So from thermal classes, we kept saying reflectance + emissivity = 1, and thus for a perfect reflecting body, there's zero emissivity. But what about a reflecting body that is heated internally? Say ...
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Wien's constant different value using spectral energy density of frequency variation [duplicate]

I was trying to find the value of Wien's constant using the spectral energy density from frequency $\nu$ to $\nu+d\nu$ (Planck's distribution). When I solve it, I end up with the equation $$x\,e^x=3(e^...
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Planck's Law notation

I have just picked up the book Elementary Quantum Mechanics by Peter Fong, and on the first page he writes Planck's law as $$u(\nu)d\nu=\frac{8\pi h \nu^3}{c^3}\frac{1}{e^{h\nu/kT}-1}d\nu$$ where $u(\...
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I’m studying black body radiation and I can’t understand how it produced due to the vibrations of atoms

So,in my physics school book it’s written that atoms don’t radiate as long as they are stable ”in the ground state” I can’t understand how I mean isn’t all the bodies radiate as long as they have a ...
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What makes a lightbulb glow?

I am self-studying electricity and magnetism, and I am confused about a point. I have learnt that the drift speed of an electron is extremely small. However, according to Drude's model, the electron ...
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Deriving black body law from fluctuation-dissipation theorem?

Is it possible to prove the Blackbody radiation law using the fluctuation-dissipation theorem? Has it been done, or is there some reason why it wouldn't work? I would appreciate if you could point me ...
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How does thermal wavelength work exactly?

In many sources it is stated that the thermal wavelenth indicates the rough size of the atom. It is then stated that this wavelenght is the de-Broglie wavelength of a particle with a momentum with the ...
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Does radiant heat energy increase the temperature of any gases it passes through?

I am in an HVAC/R technician certification class, and the instructor taught us that radiant heat energy only increases the temperature of solid objects, and the temperature of gases are not affected ...
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Building orientation - how come both summer and winter solstice used for a facade?

I am planning to build a shed atop my terrace. I was analyzing the sun path to determine the overhang length, facade height etc, but got stuck with a conflict as below. The summer sun's location peaks ...
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Is Thermal radiation emitted by a blackbody some photons

If a blackbody absorbs all radiation and emits some due to it's heat, then is the thermal radiation actually some photons that are not in the visible region? Can there be a blackbody that emits ...
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Why does wien's law only apply to blackbodies?

thinking about it the sun is just made of atoms , if it absorbs or not it's different ? i don't exactly know how to word it; just why only things that absorbs all radiations are valid in wien's law
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Is it possible to explain the Ultraviolet Catastrophe as a manifestation of the Riemann-Lebesgue Lemma?

Is it possible to explain the Ultraviolet Catastrophe as a manifestation of the Riemann-Lebesgue Lemma? I don't fully understand any of both topics, but reading about the Ultraviolet Catastrophe on ...
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Long temporal coherence sunlight

What is the reason that sunlight have short temporal coherence? I know everybody says that coherence length is inversely proportional to bandwidth. Does it mean that if sunlight passes through a very ...
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Will stainless steel heat up faster than a cordierite-based surface in a gas oven?

Background: As some may know, pizza stones, used to accumulate heat before the pizza dough is put into the oven, are often made of cordierite. If it's well heated it should provide the underside of ...
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Gas to solid heating?

I am doing a study on the phenomenon of pyrolysis. This is purely a study of the underlying physics. Generally, in practice, pyrolysis feedstock is heated conductively but we are examining the energy ...
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Why while deriving Rayleigh Jeans law in this book, an EM wave is divided into its components along the three axes & how is the math formed?

An EM wave making arbitrary alpha, beta and gamma angle with x,y and z axes respectively is divided into its components along the three axes? What does it even mean? If the components along the three ...
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Comparing the variance of the position of particles of a sample of matter with the sample's temperature

As the title suggests i have attempted comparing the variance of the position of particles of a sample of matter with the sample's temperature. Now firstly we need to clarify the basics: method for ...
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Absorption spectra Oxygen vs temperature

Whilst recently commissioning a spectroscopic Tunable diode laser "Oxygen Analyser" on a waste-to-energy plant, I wondered how the Analyser (which fires a narrow wavelength laser across the ...
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How to create a function modelling Earth's temperature due to heat radiation over time (if it wasn't receiving heat) [closed]

I am trying to model the Earth's temperature cooling if the sun disappeared, by plotting Earth's temperature over time. I know that the Stefan Boltzmann law ensures that Earth would not cool at a ...
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1 answer
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Why does cooling down thermal imaging cameras increase sensitivity?

A lot of high-sensitivity thermal cameras and sensors are (cryogenically) cooled down to low temperatures to achieve these high sensitivities. For example. the Stinger missile, and the James Webb ...
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Is energy rule violated here? [closed]

We know that for an EM radiation , energy is given by : $$E = \frac{hc}{\lambda}$$ . Where $h$ is Planck's constant , $c = 300000000$m/s and $\lambda$ is wavelength of the radiation. Clearly, energy ...
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Why solar flux concentrators can achive only $\rm 1500°C$ of temperature if Sun temperature is $\rm 5500°C$?

Why solar flux concentrators can achive only $\rm 1500°C$ of temperature if sun temperature is $\rm 5500°C$ ? If it is possible to concentrate a flux from a parabolic mirror of area $\rm 400\ m^2$ to ...
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A black dome around a space probe [closed]

The given problem states that As a result of heating by a nuclear energy source of strength I inside a probe ,its surface temperature is T .The probe is now enclosed within a thin thermal protective ...
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Emissive power of a blackbody

I have a doubt in this question from iit jee 2000. Here, the plot is of spectral intensity vs. Wavelength graph of 3 blackbodies. And the answer is: T1>T2>T3 and the justification is given by ...
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Question regarding Prevost theory of heat exchange

According to Prevost theory of heat exchange if the temperature of a body is higher than the surroundings, emission>absorption.For example the body at a particular temperature is at equilibrium and ...
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Absorption vs emission not in thermodynamic equilibrium

I have read that good absorbers are good emitters. The argument goes that at thermodynamic equilibrium, the amount of radiation a body emits must be the same as it absorbs, otherwise the body will ...
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A question regarding absorptivity and emissivity of black body

A perfectly black body absorbs all incident radiation on it at any temperature and emits all radiations at any temperature,and thus at equilibrium absorption=emission.Say the black body is kept in a ...
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Value of radiated power from a black radiator at the peak of the spectrum [closed]

What is the value of the radiated power in the wavelength range of $\Delta\lambda = 100 nm$ from a black radiator of surface area $2.00 m^2$ at temperature $45^\circ$ at the peak of the spectrum?
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Why doesn't a laser emit black body radiation?

While deriving A and B coefficients we use Planck's law of blackbody radiation, but the spectrum obtained from the laser is not that of a blackbody because we get a very small band of light as output. ...
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Is the Rayleigh Jean Formula an approximation of a poisson distribution?

I'm a senior physics major planning to pursue a PhD. I'm finally taking my Thermo/Stat Mech course and I realized that the Poisson distribution looks similar to the curve of the Rayleigh-Jean Formula ...
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Is Planck temperature really the highest temperature?

Actually I was learning about Wien's displacement law. It states that $$\lambda T=2.898×10^{-3} mK$$ This is actually a part of Planck's law where the Planck's constant originated. Now Planck's ...
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