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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Radiation energy density [closed]

Assuming that the sun is a spherical black body with a radius of $7\times 10^8m$. Calculate the sun's temperature and radiation energy density within it. The intensity of the sun's radiation at the ...
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Thermal radiation in a spherical object with a cavity in it

Consider this problem is related to the radiation of heat from an object. The object is a sphere with a cavity. It has an outer radius $R_o$, and the radius of the cavity is $R_i$. The emissivity of ...
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Absolute hot is unusual [closed]

According to the black body radiation theory wavelength of light decreases with increase in temperature whereas the frequency increases. The wavelength keeps decreasing till absolute hot where it ...
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Question. Why does the Trenberth et al Global Energy Flow chart divide the incoming solar flux of 1370 $\rm W/m^2$ by 4?

Why would you list the incoming solar radiation as 1/4 of its actual value? This would have the effect of reducing insolation to -40 deg C at the surface. It seems to me Trenberth is in error. The ...
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How to get spectral data of Sun?

I am doing project in blackbody radiation and i am about to analyse the spectral data of the incandescent lamp, hot metal, Sun and Sirius A. So i can find the displacement of the peak of curves using ...
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Calculating the sun's surface temperature based on measured powered on Earth's surface [closed]

I have a homework problem that states: At the surface of the earth, a 1-cm2 area oriented at right angles to the sun's rays receives about 0.13 J of radiant energy each second. Assume that the sun is ...
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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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Details of thermal radiation and Fraunhofer lines

I am a high school student in 11th grade and I am very confused in black body radiation , the way with which it is written in our textbooks is really confusing, I have a confusion,for e.g suppose we ...
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Wien's Displacement Law and reradiation of LWIR by $\rm CO_2$

Consider Wien's Displacement Law (if I understand correctly): λ = b / T Where, λ = Peak Wavelength b = 0.028977 mK (Wien's constant) T = Temperature According to this law $\rm CO_2$ molecules can only ...
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Thermoelectric Seebeck Crystalline Structure

Recently reading about Crystalline Structure in metals and other forms of doping. Being that thermal energy has so called phonons could it be that crystals in metal having an effect like that for ex. ...
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How to calculate range of radiation intensity from a blackbody spectrum

Lets suppose there is a spectrometer that measures cosmic background radiation, which has a blackbody spectrum. Suppose the spectrometer scans the blackbody radiation between wavelengths $\lambda _1$ ...
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Nocturnal freezing of water: Calculation of radiation through atmosphere?

I recently came across an article in Wikipedia, which claimed that medieval civilizations used to leave water out overnight in an insulated pot during clear and calm nights, which results in the ...
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A question on maximum emitted power (Wien's law)

I'm new to radiative topics and when I came across spectral emissivity, this approach for maximum emissive power confuses me. The book normalize the emissive power using $$\frac{E_{b \lambda}}{n^{3} T^...
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Will putting a fan behind a heater lower it’s heat output? [closed]

I have a small metal coil electric heater and I put a fan behind it to distribute the heat. As far as I can figure, if I cool off the heating elements then I lower the resistance. Will this lower the ...
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Is my understanding of thermal equilibrium of radiation correct?

In the description of a container with a hole as a blackbody, in Peter Atkins | Julio de Paula - Physical Chemistry, It's given that "the container with pin hole emits radiation that can be ...
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A question about thermal conductivity and heat transfer

Put a piece of cold pizza on top of a sheet of aluminum foil and then stick it in the oven to heat up. After about 10 minutes, the pizza should be nice and hot—the aluminum foil is the approximately ...
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Problems with the derivation of Planck's radiation law

I have tried to understand the derivation of Planck's radiation law, but there's a lot I don't quite understand. The derivation I've been reading is this one: https://edisciplinas.usp.br/pluginfile....
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Behaviour of gas present in space [closed]

Can we model the hydrogen gas present in space as an ideal gas? If so, can the cooling of space from the big bang obey the ideal gas law? And what would be the pressure of such a gas?
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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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Why are infrared images not great?

Why are infrared images not great? Simply googling infrared images, and looking at pictures of things like streets, people, animals, etc. . . I can't quite pin ...
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Comparative Efficiency of Thermal Radiation

Given two heatsinks identical to each other except in color, how can the differential efficiency of thermal radiation be determined? For example, if both heatsinks are aluminum, with one anodized as ...
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Clarification of why Rayleigh-Jeans law failed to explain blackbody radiation

I'm reading about why the Rayleigh-Jeans formula failed to explain blackbody radiation curves. The Rayleigh-Jeans formula: $$ E = kT\left(\frac{8\pi\nu^2}{c^3}\right) $$ I see explanations saying that ...
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What causes materials like Vantablack to have their high optical absorption properties?

As per the title of this post. From reading, I understand that blackbody radiation is a factor I should consider here, with light being absorbed and converted to heat etc. However, what I want to ...
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Why are good absorbers also good emitters?

I read that good absorbers are good emitters - hence a blackbody, that absorbs all kinds of radiation, also emits all kinds of radiation? I'm not able to get my head around this. What does it mean to ...
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Kirchhoff's law for glass and transparent crystals; how exactly do hot transparent materials produce so much visible thermal radiation?

Together, the current answers to Is the visible light spectrum from "red-hot glass" at least close to Blackbody Radiation? explain that while we can not necessarily call a heated sample of ...
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Why is it called a “black” body?

So i know a black body is a perfect absorber and perfect emitter.. doesnt have to be black, but why is the term "black" used. In my textbook, it says that "at lower temperatures a ...
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Fraunhofer lines during an eclipse

I know that Fraunhofer lines are certain wavelengths in the Sun's spectrum that are 'missing' because of absorption at the chromosphere. In other words, they are 'dark'. But my book clearly states ...
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Why does an increase in temperature lead to an increase in dipole oscillation?

As far as I know, heat radiation is caused by the electromagnetic waves produced by the permanent or induced dipoles of the heated material. The higher the heat, the higher the frequency of ...
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Comparing Wein's formula with Rayleigh-Jeans' formula for energy density of blackbody radiation

In our Higher Secondary textbook, it is clearly stated that Wein provided with the formula of Blackbody radiation based on the thermodynamics' law below $$ E_{\lambda} d\lambda = 8 \pi hc\lambda^{-5}e^...
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Is radiation emitted in a particular direction by a body?

If a body is transferring heat by the mode of radiation, then will it emit it at direction perpendicular to its surface only, or will it be emitted in all the directions. Hope my question is clear.
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Are there black body-like thermal emissions of gravitational waves?

According to the answer to this previous question: Yes, all of the fields in quantum electrodynamics are excited in blackbody radiation, not just the electromagnetic field. But, (as I understand) ...
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Why $C_p$ is zero for photon gas?

For photon gas, We know that $$U=u(T)V, \ \ p =\frac{u(T)}{3}$$ As $$G=U+pV-TS=uV+\frac{u}{3}V-\frac{4u}{3}V=0$$ $$dG=-SdT+Vdp=0$$ $$\Rightarrow s=\frac{dp}{dT}\not=0$$ $$dp=0\Rightarrow dT=0$$ which ...
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Black body radiation and why do we see different colors?

I am high school student and I am really confused about how black body radiation or radiation from any general body works? Suppose we are observing the color of any body is green, does it mean that it ...
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Eye contact via the moon [closed]

Consider two lovers $L_1, L_2$ in different cities looking - as lovers do - at the moon at night. They do not have line of sight with each other, but maybe they can take comfort in the fact, that they ...
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What exactly is the physical setup of the Rayleigh-Jean's law derivation?

I've looked at multiple derivations online and they all seem to start by considering a perfectly reflective metallic box. I am under the impression that if you first add some material, such as a piece ...
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Black body radiation and second law

I'm struggling on finding what's wrong with my model of the following system which seems to break the second law: Imagine two punctual perfect black bodies at two temperature $T1 $ and $T2$. Each ...
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Percentage of light radiated by a black body in certain wavelengths [closed]

I want to calculate the % of light radiated by a blackbody of a certain temperature (arbitrarily 9000K) in certain wavelength boundaries, arbitrarily say 1nm - 100nm. Is there a formula that gives you ...
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Why do all black bodies at the same temperature exhibit the same emission spectrum?

I’m reading Eisberg & Resnick Quantum Physics, and there’s a part in the introduction that’s confusing to me. They say, “independent of the details of their composition, it is found that all black ...
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Why doesn't a Planck type derivation work for Hawking radiation?

In Planck derivation of black body radiation. Planck hypothesized $E=h\nu$ and got the correct black body radiation spectral function. What is confusing me is why doesn't similar arguments work for ...
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Discrepancy of $4π/c$ for radiated intensity in a blackbody radiation

Plancks radiation law is sometimes given as $B(\nu, T)=\frac{8π h \nu^{3}}{c^{3}} \frac{1}{e^{\frac{h \nu}{k_{\mathrm{B}} T}}-1}$ as is shown in the plot But Wikipedia says: ...the spectral radiance ...
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Is there an analogue of Hawking radiation for other massive bodies?

Without resorting to formal GR, it is possible to derive the structure of the Hawking temperature formula through simple dimensional analysis after assuming an ansatz of $$T \sim R^a\hbar^bk_B^cc^d,\...
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What is a thermal source and its spectral-thermal modes?

I know what a thermal state is. But I am wondering how we can determine that a source is thermal or not? E.g. is the light coming out from an LED, thermal? On the other hand, what are spectral-thermal ...
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Solar radiation = Shortwave radiation?

this is a super-basic question but I am new to all this and a bit confused. I want to understand the process of radiation and other things like evaporation on the temperature of the Earth's surface. ...
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How do neutron stars emit black body radiation?

If my understanding is correct, black body radiation is emitted by a substance due to the substances coupling with the electric field. The negatively charged electrons in atoms for example can couple ...
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Blackbody radiation- time evolution of blackbody radiation [closed]

Blackbody-Stefan Boltzmann equation describes to energy released per unit time per unit area of body. I want to know the time dependent behavior of black body when it keeps out side to emit energy via ...
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What exactly is Planck's constant? how did they calculate it?

What exactly is Planck's constant? I'm a pharmacy student and I've googled this question but couldn't find an answer I'd understand. It would be so great if somebody could tell me how we calculated ...
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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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Where do Photons in Hot “Box” Come From?

I've read through some related questions, like here, but these don't quite answer my question. Say I have an oven at room temperature, and I raise the temperature to 400 K. During this process, the ...
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If the moon became a black hole, how much lower would the temperature be on Earth's surface?

I read that if the Sun became a black hole the Earth would become colder, but the effect would be negligible because the mass of the hole is still there so there would still be tides. But, how much ...
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Planck`s law for an interval of wavelengths

Planck's law for spectral radiance of a black body for a wavelength: $$P=\frac{2hc^2}{\lambda^5}\frac{1}{e^{hc/\lambda k_bT}-1}$$ If I want to know the spectral radiance for an interval of wavelengths,...

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