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.

learn more… | top users | synonyms (2)

7
votes
4answers
11k views

What causes hot things to glow, and at what temperature?

I have an electric stove, and when I turn it on and turn off the lights, I notice the stove glowing. However, as I turn down the temperature, it eventually goes away completely. Is there a cut-off ...
1
vote
0answers
58 views

At the lambda point, why does specific heat capacity tend to infinity?

The specific heat capacity is the energy required to raise the temperature of unity mass by 1K, if at the lambda point all the bosons occupy the lowest quantum state, shouldn’t the specific heat ...
1
vote
2answers
144 views

Can kinetic energy in atoms result in emission of all types of EM radiation?

I already know the fact that when solid objects heat up, they emit thermal energy which is also known as infrared radiation. However, if the atoms in that solid were to begin gaining more or less ...
0
votes
1answer
159 views

How is it possible that Thermosphere can maintain so much heat? [closed]

Thermosphere is the Layer of Atmosphere in approx 100-1000 km altitude. Particles in thermosphere are typically at 1400 K temperature. But the sun activity can raise the temperature up to 2300 K. It'...
1
vote
1answer
30 views

Qualitative difference between bremsstrahlung and thermal bremsstrahlung

Hopefully this is an easy question. I hear the terms bremsstrahlung and thermal bremsstrahlung being used. However, I, incorrectly, thought that they were used interchangeably. So, what is te ...
2
votes
1answer
2k 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?
0
votes
0answers
32 views

Why does vertical polarizer absorb the vertically polarized waves?

They explain that vertical wires serve as the secondary transmitter: the waves induce since oscillations of electrons in the wire effectively absorbing the wave. Ok, let's believe that wave is ...
3
votes
2answers
108 views

Is sun a black body? [duplicate]

My teacher told me that sun is a black body but after reading at various sites whre they say that sun is not a black body but has black body radiations because it cannot absorb all radiations.
0
votes
0answers
17 views

Is black hole a black body? [duplicate]

I have studied in my physics class today that black body is one which absorbs radiation of all wavelength incident on it , Its absorptance is unity , reflectance and transmittance is zero . I wonder ...
1
vote
1answer
30 views

Do all thermal radiators have the same surface brightness?

Imagine I heat a piece of metal to 1000K. It will be red hot and will emit black body radiation corresponding to this temperature. But what about the brightness? Assuming the bulk is opaque, does it ...
0
votes
1answer
23 views

Blackbody radiation

Radiation in the blackbody is reflected from the walls because it's absorbed and quickly remitted by the atoms on the wall, why don't they just absorb it but reflect it totally??
3
votes
3answers
111 views

Why doesn't power generated by thermal radiation violate Carnot's theorem?

It seems to me that you could use thermal radiation to drive an engine that does not require a cold reservoir. Carnot's theorem states that the only way to convert heat into work is with a temperature ...
0
votes
0answers
44 views

Why does an optical pyrometer read low in the open?

An optical pyrometer relies on the fact that the brightness of heat radiation from a body depends on its temperature. I have come across the fact that an optical pyrometer invariably reads low when ...
3
votes
2answers
598 views

Hawking Radiation: how does a particle ever cross the event horizon?

The heuristic argument for Hawking Radiation is, that a virtual pair-production happens just at the event horizon. One particle goes into the black hole, while the other can be observed as radiation. ...
4
votes
1answer
130 views

Why don't I see green flames more often?

I was just thinking today that I usually see red flame, and have seen plenty of blue flame, but not green. My naive presumption for coloration of flames would suggest that I would see more green, so ...
0
votes
0answers
56 views

Can anyone explain Wien's distribution law

I searched the internet for this but could find only the equation associated with the law. I want to know what this law states, what are its significance and why is it called as "distribution" law.
1
vote
1answer
45 views

How does a gas emit radiation with temperature when it's particles motion are linear?

Particles in gas move faster with temperature in a linear motion (root mean velocity equation?) right? It explains increase in pressure and effusion proportional to temperature. Solids emit radiation ...
0
votes
2answers
75 views

Is the equilibrium temperature of a black body higher than other objects?

Suppose we place a black body and an object of lower emissivity, both of the same shape, into an evacuated glass contained, and we place that container in sun light. After time, if both reach thermal ...
0
votes
1answer
79 views

Blackbody or characteristic emission of radiation

I am trying to understand what determines to what degree energy from a "hot" object is emitted as characteristic radiation or blackbody radiation. For example in a gas discharge lamp, a considerable ...
2
votes
1answer
123 views

Partition Function and BlackBody Radiation

I'll start with a few definitions: $$\beta \equiv \frac{1}{k_bT}$$ Where T is the temperature of a system. And the partition function: $$Z \equiv \sum_{j}e^{-\beta \epsilon_j}=\int D(\epsilon)d\...
3
votes
1answer
75 views

Maximum Temperature?

I have been reading a lot about wavelengths of light and Planck's law and such. Curious as to whether a minimum wavelength of $h$ (Planck's Constant) indicates that there is in some way an absolute ...
0
votes
1answer
51 views

What would happen to the Earth's atmosphere if all the solar radiation was in the extreme ultraviolet?

According to this, our Earth's atmosphere is completely opaque to radiation with wavelengths less than 100 nm as this radiation has enough energy to ionize the air. Since the surface temperature of ...
0
votes
2answers
142 views

Confusion with Blackbody Radiation

A blackbody is a theoretical object that perfectly absorbs all the light that falls on it. From what I understand this is an ideal situation and does not actually exist in reality. Certain objects are ...
0
votes
1answer
28 views

How can I apply Planck's law to calculate the photon energy density of a warm room?

I am trying to calculate the rate at which photons of any particular frequency will pass through a volume in a room illuminated by black body radiation only. I've found a couple of starting points ...
3
votes
2answers
219 views

Temperature of a falling meteor

I am reading "What if?" article https://what-if.xkcd.com/20/ and I'm interested in it's scientific background. Mr. Munroe writes: As it [the meteor] falls, it compresses the air in front of it. ...
11
votes
3answers
20k views

Why do lightbulbs continue to glow after the light is turned off?

I've noticed that whenever I turn the lamp off in my room at night, the lightbulb seems to continue to glow for a minute or so after that. It's not bright though; the only way I even notice it is if ...
0
votes
0answers
92 views

Can thermal states of light be monochromatic?

As one can read from the quantum optics textbooks each mode of light of a certain frequency, spatial configuration and polarization can be considered as a quantum harmonic oscillator. One can imagine ...
0
votes
1answer
62 views

Entangled systems and heat

Suppose I have two extended bodies that are entangled to each other. Are the thermal properties of the objects affected in some way by entanglement? For example, Imagine that one of the entangled ...
13
votes
3answers
377 views

What does a blackbody sound like?

Update: According to this wikipedia article, blackbody radiation is just thermal noise (Johnson–Nyquist noise); if that's what I'm looking for, what does it sound like? If a blackbody has a ...
9
votes
6answers
37k views

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 ...
0
votes
1answer
41 views

Trouble understanding the derivation of Black Body Radiation modes

I am looking at this: http://physics.ucsc.edu/~drip/5D/photons/photons.pdf Counting the Modes in the Box and I understand everything up to the point when it talks about spherical shell in m-space. I ...
3
votes
6answers
685 views

Extracting heat energy without a heat engine

Is it possible to extract the molecular kinetic energy from a system directly (without the use of a heat engine / temperature gradient) and convert that to another form of energy, such as electricity, ...
0
votes
0answers
31 views

Continuous vs. Line Spectra

A hot solid or liquid produces a continuous emission spectrum while a hot rarefied gas produces a discrete emission spectrum. (And a hot dense gas produces a continuous spectrum with absorption lines?)...
1
vote
1answer
63 views

How to use Planck's law of Black Body radiation?

On the wikipedia page for Black Body radiation, it states that: where $I(\nu,T)$ is the energy per unit time (or the power) radiated per unit area of emitting surface in the normal direction per ...
1
vote
1answer
99 views

Black Body radiation and Uv, x and gamma rays [closed]

Is the reason why UV, x-rays and gamma rays are non-existent on the blackbody radiation spectrum is because instead of the atoms present in the walls of the blackbody absorbing the energy, the energy ...
1
vote
1answer
162 views

Modes inside a cavity and black body radiation

Consider a perfect conductor that encloses a spatial volume such as a parallelepiped or cylinder. If we solve Maxwell's equations inside that volume, seeking solutions that depends on time with a ...
1
vote
1answer
45 views

Method used to prove emissive power, $E \propto T^4$

Stefan's Law states that emissive power($E$) of a black body is proportional to $T^4$. But how did Stefan arrive at the conclusion? I mean, it is not possible currently to get a perfectly black body, ...
0
votes
1answer
99 views

Blackbody radiation and thermal equilibrium?

I'm new to blackbody radiation and I have been struggling with the following question: The dominant wavelength of light from the sun is 510nm. Estimate the equilibrium temperature of the earth. ...
10
votes
2answers
298 views

Would a rocky planet orbiting so close to a very hot star eventually vaporize?

I was thinking about the physics behind a hypothetical scenario where a planet the size and the mass of the Earth is orbiting so close to a very hot star and what the long-term fate of such a planet ...
1
vote
2answers
61 views

Direction of thermal radiation

Take an object that radiates thermal radiation. In which direction does the thermal radiation go? I would think it equally distributed through all directions, but I can't seem to find it mentioned. ...
2
votes
3answers
496 views

Non-ideal black body's thermal radiation?

Planck's law neatly describes the thermal radiation of an ideal black body in thermal equilibrium. So the question is, what about things that are not black bodies? Like an object with a mirror finish?...
1
vote
3answers
110 views

why do coiled wire create so much heat?

I am wondering how coiled wire creates so much heat when a current is passed through it. Is it just a larger surface area of heated substance is available or are interacting forces at work eg ...
3
votes
2answers
768 views

How to interpret Stefan-Boltzmann's law?

The Stefan-Boltzmann equation states $e=\sigma T^4$, but how do we interpret this? Is this completely wrong: A body of size $s^2$ generates the radiation/temperature $T^4$ for a given size and a ...
0
votes
2answers
121 views

Will the Sun ever get 100x powerful? If so, when?

I was doing a theoretical research regarding life on Titan. The temperature of Titan is so low, and it needed more sunlight, as a result, the Sun would require to get hotter. My question is, when will ...
1
vote
1answer
43 views

AM1.5 Spectral Irradiance unit conversion

I have the AM 1.5 spectrum http://rredc.nrel.gov/solar/spectra/am1.5/ Which gives spectral irradience in units of $\frac{W}{m^2 nm}$ vs wavelength in $nm$. For my purposes I need this spectrum in ...
2
votes
1answer
81 views

Einstein's 1905 “Concerning an Heuristic…emission and transformation of light”

I'm currently attempting to read Einstein's annus mirabilis papers, starting with his introduction of the quantization of light in the paper: "Concerning an Heuristic Points of View Toward the ...
0
votes
2answers
93 views

What is a simple calculation to figure out how many watts needed to maintain a hot piece of tungsten?

The specific heat of tungsten is $.13 (\text{kJ /(kg K)})$. 1 cubic cm of tungsten is .0193 kg And the melting point of stainless steel is $1900 \deg \text{K}$ conservatively (giving it plenty of ...
0
votes
1answer
81 views

What physical process is the source of blackbody radiation? [duplicate]

Blackbody radiation is the radiation given off an object solely as a result of its absolute temperature. The (continuous) spectrum is given solely by the temperature. How can this be? Why should a ...
3
votes
2answers
493 views

Frequency and Wavelength peak for Wien's displaement law of a blackbody [duplicate]

This is a question relating to Wien's displacement law for the Planck function. As we all know frequency and wavelength are related to the speed of light by: $$\nu\lambda=c$$ However, why is it ...