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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Temperature of thermally isolated space region

If we thermally isolate a region in space, say using a hypothetical material of $0$ conductivity, and measure the region's temperature, will it be 2.7K?
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530 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 ...
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318 views

Radiative cooling time for a black body

Okay, so this is confusing me a bit. How can I calculate the time it takes to cool a perfect black body from an initial temperature $T$ down to equilibrium temperature (say, 3 K for space)? I know ...
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2answers
1k views

Planck's distribution and Bose-Einstein distribution?

If the application of the Bose-Einstein distribution is in blackbody radiation, then what is Planck's distribution? Are they same? How did Planck know that he should use a Bose-Einstein distribution ...
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1answer
312 views

What is “number degrees of freedom for frequency ν”. Frequency is 1D right?

The book QM Demystified states this about black body radiation spectrum: An attempt to explain these results using classical theory was codified in the Rayleigh-Jeans formula, which is an ...
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335 views

Does coffee with cream cool slower than black coffee?

At Modernist Cuisine, Nathan Myhrvold states that "Coffee with cream cools about 20% slower than black coffee". He then gives three reasons, two of them related to radiation and the third one to the ...
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605 views

How to derive Stefan constant from Planck's Blackbody radiation?

How to derive Stefan constant from Planck's Blackbody radiation? Consider the following expression relating to blackbody radiation: $$\phi(\lambda) d\lambda= E({\lambda}) \, ...
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3k views

All objects radiate energy, but we cannot see all objects in the dark. Why?

We claim that all objects radiate energy by virtue of their temperature and yet we cannot see all objects in the dark. Why not?
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2answers
81 views

Energy loss of Earth

How does the Earth lose the energy that it gains from the sun's radiation if it is surrounded by - and in contact with - nothing?
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2k views

Why is spectrum obtained by sunlight, said to be continuous?

My sir spoke about atomic spectra today. Sir said that, unlike the spectrum obtained by analyzing the sunlight, the spectra of atoms are not continuous. I got a doubt here, i,e even the sunlight ...
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1answer
153 views

Continous spectrum of black body radiation [duplicate]

I am wondering why black body emission spectrum is continous. Assuming only quantum effects that is electrones falling to less energetic orbitals it should be discrete. Is the continous part emerging ...
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1answer
354 views

Wien's Displacement Law for real bodies

It is known that for perfect blackbodies, $$\lambda T= c$$ where $\lambda= \text{peak wavelength}$ $T= \text{Absolute temperature}$ $c= \text{Wien's constant}$ ...
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1answer
520 views

Why do dark objects radiate thermal electromagnetic energy faster than light objects?

Kirchhoff's law of thermal radiation says that: For a body of any arbitrary material, emitting and absorbing thermal electromagnetic radiation at every wavelength in thermodynamic equilibrium, ...
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2answers
848 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 ...
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1answer
342 views

Filament in a lightbulb, thermal radiation

I'm trying the following: The filament inside a 100 W lightbulb has an absorption coefficient of 0.25, and while operating, it is at a temperature of 2,573 K. What's the size of the surface of the ...
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1answer
640 views

How does heat energy travel in space?

How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us?
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1k views

Is there a heat transfer equation that takes conduction, convection, radiation and dT/dt into account?

I see equations that take 2 or 3 of the listed parameters into account but I haven't been able to find one that is that complete. I'm seeking to solve this equation using matlab for a simulation ...
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2answers
284 views

Why the cavity radiation has the form of standing waves?

I'm reading about the cavity radiation in the context of blackbody theory. I'm asking myself: WHY do we describe this radiation by the use of standing waves? Why can't they be not-standing, maybe ...
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114 views

How do I map color to temperature?

Following up to Do burning red coals and red-hot iron have the same temperature? and Are Colors Emitted at Specific Temperatures?, how do I determine the temperature of the object by the color of the ...
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1answer
2k views

Wien's displacement law in frequency domain [duplicate]

When I tried to derive the Wien's displacement law I used Planck's law for blackbody radiation: $I_\nu = \frac{8 \pi \nu^2}{c^3} \frac{h \nu}{e^{h\nu/k_bT}-1}$ Asking for maximum: $\frac{dI_\nu}{d ...
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56 views

What state is fire? Solid, Liquid or Gas or Plasma? [duplicate]

What state is fire? Solid, Liquid or Gas or Plasma? I was just roaming around when this question popped out of my mind. In what state is FIRE?
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Is “dark clothes for winter, light for summer” relevant?

We are told to wear light clothes in summer as they are better at reflecting sunshine and keeping us cool. And dark clothes absorb sunshine and keep us warm. But is it really relavent? If I buy ...
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1answer
71 views

Definition of isotropy of radiation and its consequences

I have encountered different notions of isotropy of radiation and I would like to know if they are the same and what the exact definition of isotropy is, if one exists. Let's take black body ...
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162 views

Quantum mechanics: How do the atoms in an electronic circuit enter a smaller orbit on the filament of an incandescent light bulb?

Bear in mind that this is not a homework question, and I have put together some stuff to work on from below: http://www.doublexscience.org/how-fluorescent-lights-work-quantum-mechanics-in-the-home/ ...
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1answer
163 views

What's the relationship between the energy density of a black-body and its radiant exitance?

Through a bit calculation we can derive that in a cavity, the energy density $$u(f,T)=\overline{E(f)}\times G(f)=\frac{8\pi h}{c^3}\frac{f^3}{e^{h\nu /kT}-1}$$ If we take the integral over all ...
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1answer
97 views

Intensifying a light source using black body concept

Is it possible to intensify light by initially passing it through an apparatus like a perfectly black body and then through a colloidal solution? What kind of material can be used inside the ...
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1answer
331 views

Why is there a space between the flame and the nozzle on the space shuttle?

Why is there some space between the flame and the nozzle on the space shuttle? (see above picture)
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2answers
483 views

Showing Wien's Displacement Law from Wien's Law

Does anyone know how I would show that $\lambda * T$ is constant, using only Wien's Law? That $\rho(\lambda,T) = 1/\lambda^5*f(\lambda T)$ I differentiated, but all I could get was $\lambda T = ...
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1answer
261 views

Spectral Distribution Function Related to Energy Density

I'm a little confused as to why the Energy Density of a black body is related, in particular by $4/C$, to the spectral distribution function. One is per area, while the other is per volume, I'm lost. ...
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1answer
235 views

What is the net radiative balance between two blackbodies with different temperature?

Context In trying to understand a crop productivity model, I want to figure out how to derive the equation for the net exchange of longwave radiation between two adjacent blackbodies (soil and ...
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1answer
545 views

Do burning red coals and red-hot iron have the same temperature?

It would seem that Planck's law implies that objects of similar radiation spectra have the same temperature if the objects are "similarly close" to being black bodies. Am I right to infer that ...
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2answers
210 views

Black bodies, energy per unit volume

While reading about black bodies, I found that the average energy per mode per unit volume is $KT$ classically, but I don't understand why this is per unit volume. The linear oscillators are ...
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2answers
379 views

Does the Cosmic Microwave Background obey $\sigma T^4$?

The fact that the CMB has a temperature of 2.7 degrees Kelvin is well publicized, but I have a harder time finding a measure of the wattage per unit area. The Wikipedia article on the CMB is totally ...
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2answers
365 views

Polar ice caps and thermal radiation

I was reading an article on global warming and it said that the polar ice caps, because they are white, reflect a lot of the sun's radiation. The article also has a picture of some houses in England ...
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1answer
299 views

Do bifacial solar panels operate at lower temperature than normal solar panels?

Bifacial solar panels have a glass backplane instead of the usual aluminum and are designed to absorb and convert to electricity light incident on either face. Many manufacturers claim that their ...
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0answers
53 views

Nuclear Weapon Effects: Cloud Rise [closed]

I am interested in modeling the rise of a nuclear cloud to stabilization height post detonation. I am interested in any ideas you may have on the approach. I have collected some research on the topic ...
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0answers
55 views

Can we make any substance that will produce ions at low temprature

I am talking about thermal ionization, Is to possible to make any material or is there any element that can be ionized at let say 20 degree centigrade Temperature? I am a computer engineer and into ...
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8k views

2 ways to generate electromagnetic wave

According to Maxwell's equations, accelerating charges emit electromagnetic radiation. According to Quantum physics, heating causes electromagnetic radiation too. These 2 radiations, are they ...
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Which color of an umbrella is more effective against sunlight?

It's usually said that black umbrellas are best against sun, since black absorbs most of the radiation . The common umbrellas in market(atleast in India) are painted black outside and silvery inside. ...
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2answers
485 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 ...
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1answer
256 views

Study of Black-body Radiation

Why did scientists study black body radiations from something as complicated as a hollow container rather than the radiation from something simple like a thin solid cylinder?
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1answer
4k views

Kirchhoff law of thermal radiation

Kirchhoff's law of thermal radiation states that for thermal equilibrium for a particular surface the monochromatic emissivity $\epsilon_{\lambda}$ equals the monochromatic absorptivity ...
128
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1answer
57k 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 ...
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1answer
529 views

Measuring temperature at a distance

http://www.youtube.com/watch?v=gKYrXHZwtPw In this video it is explained that Land Skin Temperature (LST) are measured by NASA's Aqua and Terra satellites. It seems it works by collecting the ...
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1answer
263 views

On the atomic level, how is incandescent light structured?

I want to know from the smallest possible originating structures how the light I see generated from heat is made by atoms themselves.
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1answer
330 views

Can't understand a thing about emissivity concept

I can't understand something about emissivity. Emissivity is defined as the ratio of the radiant energy of an object, to radiant energy of blackbody at a temperature $T$. So, The vegetation has ...
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2answers
506 views

Planck's Law-Where does it come from?

It seems that Planck's constant was made from fitting a curve for blackbody radiation, is it just experimental-further more his assumption that energy comes in quanta seems to have been a guess. Why ...
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3answers
290 views

Can visible light be emitted from a non-thermal source?

I was reading about thermal and non-thermal radiation and I was wondering if visible light can be emitted from a non-thermal source?
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1answer
213 views

Blackbody radiation force (link), what are the fundamental forces behind it?

Here is a link to an article from phys.org describing what the scientists (M. Sonnleitner at the University of Innsbruck and Innsbruck Medical University in Austria, M. Ritsch-Marte at Innsbruck ...
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956 views

Cooling down a container in outer space

If I have two containers filled with very hot water(~210F) with one in outer space and one on earth, which one has a higher rate of cooling initially? Imagine the containers are single wall metal ...