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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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 ...
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34 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}{ ...
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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} * ...
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26 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 ...
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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: ...
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45 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 ...
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76 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 ...
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19 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 ...
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4answers
99 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.
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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 ...
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93 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. ...
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143 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 ...
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21 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 ...
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26 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 ...
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2answers
76 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.
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16 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 ...
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1answer
27 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 ...
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1answer
20 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??
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43 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 ...
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28 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 ...
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42 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.
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1answer
34 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 ...
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3answers
93 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 ...
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1answer
102 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 ...
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2answers
37 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 ...
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64 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 ...
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1answer
57 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 ...
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83 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 ...
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1answer
20 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 ...
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37 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 ...
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1answer
55 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 ...
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1answer
61 views

light effects of electric current

In german high school textbooks and curriculua, the distinction of following main sorts of effects of electric current is usual: magnetic, heat, light and chemical. My question is, whether the glow ...
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326 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 ...
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1answer
37 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 ...
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26 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 ...
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1answer
56 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 ...
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1answer
86 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 ...
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1answer
49 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 ...
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94 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 ...
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1answer
40 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, ...
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1answer
78 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. ...
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34 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. ...
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3answers
284 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 ...
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74 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 ...
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2answers
104 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 ...
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1answer
29 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 ...
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65 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 ...
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1answer
65 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 ...
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1answer
60 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 ...
2
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2answers
215 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 ...