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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Nature of blackbody oscillators

I know that thermally excited materials "act as atomic oscillators" which can oscillate in a continuous range of frequencies, producing light in said frequencies. But in my searches, the nature of the ...
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Does the iron melt? Radiative-heat transfer

A molten metal (iron type A) is in vacuum (no air) at a constant temperature ($T_m$) equal to 1500 C (equal to its melting temperature) with emissivity $\epsilon_m$. At a distance of 10 cm there is a ...
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Derivative of Planck's law [on hold]

I am trying to get the derivative of Planck's law: $$B\lambda(\lambda,T) = \frac{2\pi hc^2}{\lambda^5} \frac{1}{e^{hc/\lambda k_BT}-1} .$$ I can't seem to the answer as below: $\frac{dB\lambda}{d\...
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If I stood next to a piece of metal heated to a million degrees, but in a perfect vacuum, would I feel hot?

A friend of mine told me that if you were to stand beside plate of metal that is millions of degrees hot, inside a 100% vacuum, you would not feel its heat. Is this true? I understand the reasoning ...
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How hot can the surface of a planet be?

I just read this article https://edition.cnn.com/2018/07/02/world/newborn-planet-image-study/index.html and noticed that the astronomers estimates the surface temperature of the planet to 1000 °C. ...
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Waves in Box are Black Bodies?

From what I understood, a Blackbody is a perfect absorber, and hence also a perfect emitter since it is in thermal equilibrium. One example of a blackbody is a box with interior walls painted in black....
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Would a metallic sphere, filled with water, “survive” in lava? [closed]

Imagine a metallic (steel) sphere, that somehow is filled with water and sealed. Then the sphere is thrown into lava. What would happen then? Would the water inside the sphere turn into steam and ...
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How does the photon energy formula $E=h\nu$ mean the quantum nature of energy?

The frequency v can be less than 1. So the energy is starting from zero, and is continuous. The black body radiation is also continuous spectrum given an arbitrary temperature T.
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Deriving intensity of light as a function of frequency

Page 4 of the textbook Quantum Field Theory and the Standard Model by Schwartz says the following: The incompatibility of observations with the classical prediction led Planck to postulate that the ...
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Do metallic meshes work in practice as thermal radiation shields?

The other day I was thinking about the wire mesh cover used in microwaves to keep the microwave radiation inside cooking your food. The idea is that the spacing of the mesh is much smaller than the ...
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Does water vapour also emit radiation when rising into the air before condensing?

There are topics on how water vapour absorbs radiation ("How does carbon dioxide or water vapour absorb thermal infra red radiation from the sun?"), but what I am looking for is can water vapour also ...
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How many photons are emitted by a lightning strike?

As the title suggests, I'm curious to know, approximately how many photons are emitted in a single lightning strike?
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Deriving Planck's Constant from Wien's Displacement Law

So I'm reading an introductory book on Quantum Theory (David Park, 3rd ed.) and I am having trouble with the following question: "According to Wien's displacement law, the wavelength $\lambda_m$ at ...
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Effect of anodisation dye colour on absorptivity-to-emissivity ratio of aluminium

Anodised aluminium is a common material used in space, and it is commonly dyed black as this gives it an absorptivity-to-emissivity (a/e) ratio close to unity. This page says black anodic films have ...
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Can we concentrate the “cold of the sky” with a parabolic dish to cool things down during the day?

It's well known that we can focus sunlight with a parabolic dish to collect heat. But if we look at the thermal images of the sky we can see that the clear blue sky is quite cool. So by turning the ...
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How does a gas lamp mantle work? Is it just black body radiation?

Old gas lighting often involved a thing called a "mantle" which was a cloth mesh coated with thorium dioxide. The gas flame heated the mantle and the mantle gave off the indoor lighting that people ...
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Have some publications on solar radiation pressure force applied Lambert's Cosine Law incorrectly?

I'm trying to calculate the solar radiation pressure force on a near-earth satellite. Several authoritative sources (books, journal papers) give the force on a partly specular, partly diffusive ...
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Earth's Effective Area

Let's suppose the Earth is a black body. Usually, when determining its energy balance, the following approximation is taken into consideration: $$ \pi R_{Earth} ^2 I_{Sun} = \sigma T_{Earth} ^4 4\pi ...
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Method to solve solar heat transfer equation

Solar radiation heat transfer between two surfaces is a fairly common problem for solar physics. The equations vary; but usually include the solar energy flux and thermal radiation from a surface ...
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Confusion on Kirchhoff law of thermal radiation

Reading through the "Radiative Processes in Astrophysics", I came to the part where he discusses blackbody radiation, and among others, states that the specific intensity is a universal function of ...
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probability of emission vs absorption in thermal radiation

I am trying to make sense of the thermal radiation emitted by a gas. The radiative transfer equation is $$\frac{dI}{dx} = \epsilon - \kappa I,$$ where I is the intensity, $\epsilon$ is the ...
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Radiation emitted from a real melted piece of steel [1800C] VS emissivity

In a lot of questions I read that a good approximation of the radiation emitted from a hot piece of steel is the black body radiation. Than I search for the value of the emissivity of molted metal ...
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Emissions from a Blackbody and the UV Catastrophe

Recently I found myself becoming confused over a topic that I thought I had previously understood. In a theoretical blackbody which reaches thermal equilibrium the energy absorb is equal to the ...
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Hawking Radiation and negative energy [duplicate]

Why is it that only the particle with negative energy is absorbed into the black hole on the event horizon during Hawking Radiation? What discriminates between the particle or antiparticle?
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Will thermal radiation of hot humid outdoor air cause a person indoor to feel warmer than if it were cool or dry outside?

The hypothesis is this: Water molecules, due to their asymmetry and electric dipole are particularly susceptible to radiation at specific frequencies. That suggests that excited water molecules will ...
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Why we expect a black hole to have an emissivity of 1? [duplicate]

Just wondering: why we expect a black hole to have an emissivity of 1? Can anyone give some ideas?
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Could the plume from an exploded nuclear reactor corrode helicopter blades?

I was recently watching the new TV series Chernobyl and was curious if something that occurred was even physically possible. In the show, the physicist instructs the pilots of a helicopter not to fly ...
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Why do compressed liquids heat up when allowed to expand unlike gases?

This is an experimental observation on a chromatographic column. I am trying to reconcile two observations, one with gases and one with liquids. Assume a narrow tube packed with very small 2-3 micron ...
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How does the Earth's center produce heat?

In my understanding, the center of the Earth is hot because of the weight of the its own matter being crushed in on itself because of gravity. We can use water to collect this heat from the Earth and ...
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Two questions about the standing waves in a black body

I am currently reading a derivation of Rayleigh-Jeans law for cavity radiation from Eisberg and Resnick 1 . The authors derive the law by considering a cavity with metallic walls. In the book, the ...
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Was Titan once warmed by a hot Saturn, & therefore much more Earth-like than it is today?

Is it possible that 4 billion years ago, Saturn was sufficiently hot to act as a second sun to Titan, so that conditions on Titan were then similar to those on Earth?
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Calculating radiative heat transfer between air and walls, what to use for the emissivity of air?

For example, say I have heated some air, I push it through a tunnel with cold black walls. Will the air radiate heat to the walls or will the walls radiate heat to the air? I understand that the ...
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Is there a blackbody spectrum of photons inside a solid?

My initial guess yes there is a blackbody spectrum of photons inside a solid. The process that emits thermal photons won't "know" that it is deep inside a solid and not near the surface, so the ...
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Why are solar panels kept tilted?

I have noticed that, in my country India, all 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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Energy radiated/emitted by an object in a black body environment?

What is the net energy radiated per unit time by a black body at temperature $T$ with emissivity $e$ and absorptivity $a$, if it’s placed in an environment of temperature $T_o$.Assume that $T$$\gt$$...
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Why does the emissitivity of metals increase (a lot) with temperature?

If we take a piece of metal (could be silver, nickel, platinum, copper, etc.) at room temperature, its emissivity is relatively low compared to that of a black body: about 0.05 vs 1.00. However if ...
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Simple heater (radiation) model for PID constants tuning

I've searched around a lot and maybe I just don't know what exactly to search (and even ask here) for, but I'd like to create a simple model/function of a heater dissipating heat to surrounding air, ...
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How much must the Sun's radiation be reduced to offset global warming?

About 70 % of earth is covered with clouds and the rate of atmospheric water vapor is increasing. Also the warming of the oceans will most probably cause more and deeper low pressures and increased ...
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What is the radiation density in a spherical oven? Does this pertain to the universe? [closed]

Imagine a spherical oven with radius R. The inside of the spherical wall is at temperature T (everywhere) and is assumed emit perfect black body radiation (everywhere). (1) What is the energy ...
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Why does a “cavity with a hole” model of a black body not absorb/emit radiation larger than the size of the hole/cavity?

This wikipedia article on the "cavity with a hole" model of a black body says: The hole is not quite a perfect black surface — in particular, if the wavelength of the incident radiation is longer ...
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Parabola black body heating

I'm having trouble figuring out why this following example of shenanigans wouldn't work. If you take a parabolic mirror (say from polished aluminium) with a magnification of M and construct it such ...
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Is the surface temperature of the sun constant?

I was just wondering that during the suns mains sequence would it maintain a constant temperature at the surface and only cool once the hydrogen in its core runs out, or is it always slowly decreasing?...
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Relationship between Planck's law and absorbed frequencies

What is the relationship between the frequencies of radiation absorbed by a material and those emitted? I know that Planck's law tells us the spectral radiance, but how does this map to those ...
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Planck's Formula and Spectral Irradiance

this might seem like a really stupid question but I have spent around 2 hours to understand this but still I was not successful so I wanted to ask. I have to calculate and ploth a graph of spectral ...
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Why can we treat normal modes of black-body radiation as thermally independent?

In my professor's lecture notes about black-body radiation, a black body modeled by an opaque hollow box with a small hole is considered. After explaining why this is a sound model for a black-body, ...
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Where exactly does energy quantisation come in for light?

Planck quantised the energy of light in order to solve the black body radiation problem. However, I am confused as to exactly what he quantised. On one hand, I have seen that he quantised the energy ...
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Proving that universe is a blackbody

How can you theoretically explain why cosmic microwave background seems to be coming from a perfect blackbody given that the universe is no longer at thermal equilibrium?
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Does same material with different colour will ended up in same temperature if both of them receive same thermal radiation?

"Every good heat radiation absorbent is a good emitter." Suppose I have two identical material with different colour, placed in different room, receiving same and only thermal radiation. My ...
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Lasers to direct waste heat?

I've been thinking about ways to cloak ships in space, since they all are warmer than their background they can be seen in the IR spectrum (given a large enough telescope). So I was thinking, could ...
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Is Sun brighter than what we actually see?

I learned from that plasma can reflect radiations of frequency less than that of its own oscillations. If so, considering the plasma in Sun's atmosphere, it should also reflect solar radiations. That ...