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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3answers
787 views

Why would different metals glow red at different temperatures?

According to everything I've been taught about incandescence and black-body radiation, and some quick Googling to confirm I'm not crazy, just about everything, regardless of composition, should start ...
5
votes
1answer
10k views

Planck's Law in terms of wavelength

I am drawing a blank when it comes to equation transformation. Wikipedia gives two equations for the spectral radiance of black body: First as a function of frequency $\nu$: $$I(\nu, T) = \frac{2 h ...
0
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0answers
38 views

Blackbody radiation: hohlraum

Laser beams with a power of 10^13 W are focused through two small holes (0.8mm diameter) of a hohlraum (cylinder), and radiation can escape through them. To find the equivalent temperature of BB ...
0
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1answer
18 views

Estimating fraction of radiant energy absorbed by a metal

I have a couple of texts on thermodynamics and radiant energy but am finding it difficult to figure out from these how energy absorption and reflection work. The area of interest is heating ferrous ...
0
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0answers
20 views

Concentrating Blackbody Radiation onto Another Blackbody

Although I know many arguments against concentrating blackbody radiation to create a spot hotter than the blackbody, I encountered this confusing counter-example. Consider a thin sphere blackbody of ...
1
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0answers
35 views

Radiation Problem Based on Stephan's Law [closed]

A spherical black body of radius r is kept inside another spherical black body of radius 2r. The inner body is maintained at a temperature T. Find out the temperature of the outer black body
1
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1answer
58 views

Temperature from gamma rays?

I was reading about gamma ray bursts and read something along the lines of 1 MeV gamma rays corresponding to a fireball above 2 billion degrees Celsius. How do scientists get temperature from that? ...
21
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6answers
639 views

Black Body Golf Balls

The surface of a golf ball has about 35% more surface area (than a similar sphere) due to its dimples. So my question is simple, given identical radius, ideal black body material, and temperature: ...
2
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1answer
111 views

Thermal gravitational radiation and its detection

To my poor knowledge on the topic, the gravitational waves that are most likely to be detected by LIGO or other experiments do not have thermal spectrum. But I'm not certain. I know that Hawking's ...
0
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0answers
29 views

View factor of two parallel coaxial *rectangular* plates

I've found a lot of tables and resources that list view factors (VF) for various geometrical configurations, but I couldn't find a single one that has the VF for two parallel coaxial rectangular ...
27
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8answers
3k views

What are the various physical mechanisms for energy transfer to the photon during blackbody emission?

By conservation of energy, the solid is left in a lower energy state following emission of a photon. Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium ...
7
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3answers
3k views

Why do moving particles emit thermal radiation?

While answering another question about heat in an atom, the discussion in the comments led to the question of how heat is related to thermal radiation picked up by infrared cameras. The answer is that ...
-1
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1answer
280 views

Dr. Pierre-Marie Robitaille: On the Validity of Kirchhoff's Law

Lately I've been researching about the black-body spectrum and the historical development of Planck's Law. I mainly wanted to understand a little bit more why many different objects (Stars, Hot ...
0
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0answers
52 views

Please help me with this doubt from thermodynamics

My textbook says that net rate of heat transfer due to radiation is $\epsilon \sigma A(T^4-T_o^4)$ but i couldn't understand it. Rate of emission is $\epsilon \sigma A T^4$ and rate of absorption is ...
3
votes
4answers
169 views

Why do dark objects emit more than lighter ones?

For the purposes of this question, "lighter" and "darker" refer to the absorptive qualities of the objects. Darker objects absorb more light, and therefore appear darker. I'm trying to understand the ...
0
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1answer
47 views

Proving that Planck's Law is dimensionally homogeneous [closed]

I would like to know whether it is possible to show that Planck's Law is dimensionally homogeneous, as well as the steps taken to prove it. $$B_\lambda(\lambda, T) =\frac{2 hc^2}{\lambda^5}\frac{1}{ ...
0
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0answers
12 views

Express Planck's Law for blackbody radiation in terms of frequency [duplicate]

I'm having trouble with substituting $\lambda$ with frequency. The problem: Show that $$u(f)=\frac{8\pi f^2}{c^3} * \frac{hf}{e^{hf/kT}-1}$$ Where I'm at: $$\frac{8 \pi f^2}{c^3} * ...
0
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0answers
38 views

On Rayleigh-Jeans black body distribution derivation

When trying to derive the Rayleigh-Jeans distribution function, all authors say that in k-space each solution of the electromagnetic wave functions(of waves inside a cubic black body) represents an ...
2
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1answer
75 views

Counting modes Rayleigh-Jeans

In the derivation of the Rayleigh-Jeans Law, we count the number of EM modes in a square cavity. After calculating the number of allowed modes due to boundary conditions, we multiply it by a factor of ...
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0answers
23 views

Radiation collapse to black hole

I want to find the temperature at which radiation in AdS will collapse to form a black hole. I have even found a reference that gives the answer but I cannot understand it: ...
0
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0answers
49 views

Does nature really follow the heat equation?

I think the heat equation says that the first derivative of temperature with respect to time in a stationary solid varies as the negative of the second derivative of temperature with respect to ...
3
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2answers
108 views

Why does black-body radiation work for *everything*?

Everything not at absolute zero gives off infrared radiation, we are taught. Now I assume that doesn't apply to dark matter, and in general only to atoms as we are familiar with. An atom by itself ...
0
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0answers
58 views

Heat Losses to furnaces

I am looking in to the thermal efficiency of a furnace vessel. I am wanting to get a full, or at least better, understanding on the calculations needed to look at the thermal efficiency. So I know ...
2
votes
4answers
119 views

Why does a black body radiate in all the frequency spectrum?

I understand why a black body absorbs every frequency(it is the definition of a black body!) but i do not understand why it also radiates at all frequency spectrum.
1
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1answer
51 views

Blackbody radiation

In the blackbody radiation experiment, the inside of the body is metal so its considered a conductor inside, shouldn't the electric field be zero, so we would be left with only magnetic field instead ...
7
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4answers
10k 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
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0answers
57 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
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2answers
139 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
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1answer
141 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. ...
1
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1answer
28 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
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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
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0answers
31 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
98 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
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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
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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
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1answer
21 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
106 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
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0answers
41 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
591 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
120 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
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0answers
52 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
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1answer
43 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
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2answers
60 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
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1answer
72 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
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1answer
107 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 ...
3
votes
1answer
74 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
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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
121 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
26 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
198 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. ...