The temperature-dependant 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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68 views

Optimizing surface geometry for thermal radiation

I'm working on vacuum technology for a scientific project and one of the challenges is to optimize the cooling of 2500°C metals in vacuum. I'm wondering if it would be useful to design a grating on ...
4
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2answers
551 views

Do green stars exists?

I asked a university lecturer why we don't observe green stars, and he said the blackbody curve averages at that frequency such that the cones in our eyes don't recognise it. I have a hunch that ...
3
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2answers
217 views

Average surface temperature of Earth [duplicate]

I had a question in my school exam. Will the average surface temperature of the Earth be lower or higher, if there was no atmosphere? Now, the answer expected is "The avg temp will be lower, because ...
6
votes
2answers
785 views

How is a blackbody spectrum formed in the Sun?

Sunlight can be treated as BB radiation. Why is it a continuous spectrum while the sun contains only a few elements and the radiation from the jumps between atomic levels are discrete? How does the ...
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5answers
3k views

How does the concept of a “black body” make any sense?

In my introductory chemistry class, we are learning about the basics of quantum mechanics. We were introduced to the concept of emission and absorption spectra. Our textbook describes how electrons ...
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4answers
2k views

If a black body is a perfect absorber, why does it emit anything?

I'm trying to start understanding quantum mechanics, and the first thing I've come across that needs to be understood are black bodies. But I've hit a roadblock at the very first paragraphs. :( ...
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1answer
81 views

Prove Blackbody spectrum is independent of its composition [closed]

I got this question from a Text Book, I am not sure if StackExchange is the right place for debating answers, because I already have an answer but I am not sure about it: Consider two cavities of ...
0
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0answers
105 views

What kind of thing did Lummer and Wien use as a 'black body'?

When I was reading about the experiments on the black body, I was wondering what such a black body would look like. When I google for the black body used during these experiments by Wien and Lummer, I ...
4
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1answer
138 views

What does a hot, optically thin gas *look* like?

In another question I tried to answer what a sample of the Sun's photosphere or core would look like, if it could be brought into the lab. Here is a broader question - if I have a small inert ...
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2answers
1k views

Is frequency quantized in the black body spectrum?

I'm aware that there're some questions posted here with respect to this subject on this site, but I still want to make sure, is frequency quantized? Do very fine discontinuities exist in a continuous ...
10
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5answers
928 views

The strange thing about the maximum in Planck's law

I read that it makes a difference whether you calculate $\frac{dE(\lambda) }{d \lambda}=0$ or $\frac{dE(\omega)}{d \omega}=0$ in the sense that the maximum energy density with respect to the ...
4
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0answers
1k views

How do you estimate colour temperature based on the position of the sun in the sky?

I'd like to estimate the colour-temperature of sunlight (as applied in photography) based on the position of the sun in the sky for a mobile phone app I'm working on (app link from a more appropriate ...
136
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1answer
64k views

Why does NASA use gold foil on equipment and gold-coated visors?

I've read several websites about equipment covered with gold foil and astronaut helmet visors are coated with gold. However, their explanations are devoid of almost all physics content. Can someone ...
2
votes
1answer
232 views

What is thermal radiation? How does it move through space?

Assume that by some mysterious(at the lack of a better word) way I was able to make a bonfire on the moon and was able to sit next to it without a space suit. I will not be able to feel the heat form ...
0
votes
1answer
78 views

How does gas pressure increase the lifespan of Halogen tungsten lamps in the Halogen Cycle?

I am curious about this passage "Since quartz is very strong, the gas pressure can be higher,[5] which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and ...
2
votes
1answer
56 views

When I'm in a warm room how much of the warmth I feel is due to radiation from surfaces?

Say I'm in a room heated to 23C, once the temperature is in balance all the objects will also be 23C and radiating heat towards me. How much of the warmth I feel is due to this radiation, and how much ...
2
votes
1answer
139 views

Blackbody radiation in thermally inhomogeneous environment

The power radiated by the backbody is according to Stefan-Boltzmann law $$ P = \sigma \varepsilon A (T^4-T_{env}^{4} ).$$ Is the parameter $T_{env}$ supposed to be only the temperature in the near ...
0
votes
1answer
141 views

Does the color of clothes (especially underwar) define their perceived “warmth”?

Does white underwear keep you warm more or less than similar pieces of black color? IMHO, white color would more "reflect" back the existing temperature of the human body. However, black would ...
5
votes
1answer
330 views

How does temperature in a solid sphere change with time when moving through a gas?

I'm interested in the following problem: There is a solid sphere with radius $r$ and mass $m$ at temperature $T_{s0}$. It is moving at velocity $v_s$ through a gas of temperature $T_g$. How does the ...
3
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0answers
79 views

Chemical Potential and Blackbody Radiation

What is the physical significance of the fact that the chemical potential of the photons in a box of volume V is zero ?
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6answers
3k views

Is a suit that hides a soldier's heat signature fundamentally possible?

I recently played "Crysis", a game where the protagonist wears a suit that allows the player to hide both himself and his heat signature. Then I watched Iron Man 3, where a kid suggests that Tony ...
3
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0answers
139 views

black body simulation

black body radiation is typically understood from Planck's argument of light resonance in a box, from which the density of states is computed. Now, suppose I want to simulate a black body ...
0
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4answers
244 views

What happens when I place an object of certain temperature in space ? Does it loose its entire heat energy?

Can i obtain absolute zero temperature this way? And let's assume there is no cosmic microwave background and also assume that there is a way to shield the object from any heat source, such as the ...
2
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2answers
1k views

What is the real interpretation of Planck's constant and what are its origins?

In the physics texts I have read and from other online information, I gather that Planck's constant is the quantum of action or that it is a constant specifying the ratio of the energy of a particle ...
10
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2answers
494 views

Where did the energy released due to gravitational binding energy of the Earth go?

The gravitational binding energy of the Earth is $2×10^{32} J $, so the same amount of energy must have been released during the Earth's history. According to this and this, the current internal ...
5
votes
4answers
226 views

Light Polarizer and the Second Law of Thermodynamics

I have stumped myself with a thought experiment of my own devising. Suppose I take a beam of wholly depolarised, but otherwise plane wave light. Its von Neumann entropy per photon is $\log(2)$ nats ...
2
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3answers
7k views

Realistic calculation of heat loss for pipe

Good day everyone, I am new on this site and I hope to find here help, since I am not going anywhere with the literature I have found. I try to calculate realistically the heat loss of a hot, ...
6
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1answer
707 views

Thermal AdS and the Hawking Page phase transition

I have some difficulty understanding the concept of pure thermal radiation, as described in Hawking and Page's paper on the Hawking-Page phase transition. The four-dimensional thermal AdS solution ...
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3answers
4k views

Cooling a satellite

Satellites are isolated systems, the only way for it to transfer body heat to outer space is thermal radiation. There are solar panels, so there is continuous energy flow to inner system. No airflow ...
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4answers
157 views

Best way to heat something in aluminum foil? [closed]

Let's say we have a wet piece of paper, wrapped in aluminum foil, that we need to heat up in the fastest and most energy efficient way possible (no flamethrower). What would that be? Details ...
1
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5answers
865 views

Why do the high frequency waves have the most number of modes?

While reading the Wikipedia page of Ultraviolet Catastrophe, I came across how Rayleigh and Jeans applied the equipartition theorem. They told that each mode must have same energy. Now as the number ...
0
votes
1answer
80 views

How does the density of states for black-body radiation change with geometry?

If I have a hollow conducting cylinder with another conducting cylinder inside it (as with a coaxial cable), would the density of states of the photons/radiation between the two cylinders be any ...
29
votes
3answers
1k views

The Pioneer anomaly finally explained?

Pioneer 10 & 11 are robotic space probes launched by the NASA in the early 1970's. After leaving our solar system, an unusual deceleration of both spacecrafts has been measured to be approximately ...
6
votes
1answer
447 views

Bunsen Burners and the Sun

Why do Bunsen burners burn blue in the center? What element is being burned? Why does the sun glow yellow, and not blue-a Bunsen burner is much cooler and yet it burns blue. Is it because the ...
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1answer
500 views

Calculating the Sun's emitted power in a wavelength range?

Is there an equation that describes the Sun's emitted power on the surface [in $\frac{W}{m^2}$] over a selected wavelength range (from $\lambda_1$ to $\lambda_2$) ? I am guessing this can be ...
6
votes
2answers
273 views

Why doesn't diamond glow when hot?

In an answer to this SE question, the respondent explains that heating a perfect diamond will not cause it to glow with thermal blackbody radiation. I don't quite follow his explanation. I think it ...
2
votes
3answers
789 views

What are thermal energy distributions?

I am trying to understand the photoelectric-effect deeply. My teacher used the Planck's law and integrated it to deduce the Stefan-Boltzmann law. He somehow showed some quantum-physical ...
0
votes
2answers
113 views

Could airport security devices detect differences between printed and written documents?

If airport security scanners of any kind (xray, thermal, whatever else they use) looked at two items: A printed paper textbook The same printed paper textbook into which we have inserted a regular ...
6
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2answers
582 views

How exactly does applying the Equipartition Theorem to radiation leads to UV catastrophe?

I'm reading a book by George Gamow, "Thirty years that shook Physics" and have trouble understanding his way of describing the UV catastrophe. In a first part he points out that applying the ...
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1answer
213 views

How does heat travel?

How does heat travel? I have two competing thoughts here!! Firstly some form of atomic/molecular process liberates a photon in the infrared region of the spectrum which is detected as heat by a ...
0
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1answer
252 views

Is the physics of $j = \rho v$ questionable? What are the consequences? [closed]

In electrodynamics you have the quantity $\mathbf{j}$, which represents density of current per surface area. It is often said that $\mathbf{j} = \rho\mathbf{v}$, for geometric reasons. When I make ...
1
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0answers
21 views

How to understand/derive Eq 5.5 in Geiner's Quantum Mechanics - An Introduction?

Geiner's Quantum Mechanics - An Introduction has an unnumbered equation above Eq. 6 in section 2.4 discussing density -- not sure if it is energy density -- of radiation: ... $$dE/dV = E/V =a ...
3
votes
1answer
127 views

Blackbody and standing waves

I'm reading articles about black body radiation and why classical mechanics fails to explain it. My question is: Why do EM waves have to be standing wave in a cavity?
2
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2answers
1k views

Does coffee cool faster than tap water?

A friend of mine, based on casual observation, believes that coffee will cool faster than ordinary hot tap water. Being curious about this I have tried to investigate it myself, but I'm not well ...
5
votes
2answers
911 views

Is a black body sphere inside a black body shell hotter than the shell?

I am missing something very basic here. Let us assume the shell is at a fixed temperature T by a power generator. The sphere inside will radiate the same power it absorbs. The power radiated by the ...
1
vote
1answer
254 views

Plancks law of blackbody radiation

I am going to plot this curve with wave length: $$ I(f)df = \frac{2 \pi h}{ c^{2} } \cdot f^{3} \cdot \frac{1}{ e^{ \frac{h f}{kT}-1 } } df $$ converting: $$ I( \lambda )d \lambda = \frac{2 ...
2
votes
1answer
120 views

How can Wien's Displacement Law be 'changed' to a version for frequency?

Wien's Displacement Law stated that for a blackbody emitting radiation, $$\lambda_{max}=\dfrac{1}{T}$$ where $T$ is the temperature of the body and $\lambda_{max}$ is the maximum wavelength of ...
0
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2answers
242 views

Does quantum mechanics contradict macroscopic determinism?

I am wondering whether it is true to ask whether determinism is still completely viable at macroscopic scales given that the constituent particles behave according to QM when the dimensions get small ...
8
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2answers
342 views

radiation thermodynamics paradox

This question is concerned with a thermodynamic paradox for radiating bodies and radiation in a cavity of a specific shape. Consider two nested shells that are axisymmetric ellipsoids with the same ...
0
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1answer
47 views

Index of refraction appearing in the radiative transfer equation

In this publication the Radiative Transfer Equation (RTE) (eq. (7)) contains the following emission term: $$n_i^2\kappa_{d,i}L_{b,i}(\mathbf{r})$$ where $n_i$ is the refractive index of component ...