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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21 views

What is the physical meaning of source function in Radiative transfer? [on hold]

What is the importance of source function?What does that actually mean? I know that it's a ratio of emission coefficient to absorption coefficient. But I am not able to understand its physical meaning....
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0answers
27 views

How to calculate temperature of the universe from cosmic microwave background radiation? [closed]

Two scientists detected the cosmic microwave background radiation at a frequency of 160 GHz. What is the temperature of the universe? So I used the following two equations. peak wavelength x ...
4
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1answer
57 views

An ideal black - body at room temperature is thrown into a furnace. It is observed that? [on hold]

An ideal black - body at room temperature is thrown into a furnace. It is observed that? (A) initially it is the darkest body and at later times the brightest. (B) it is the darkest body at all ...
3
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1answer
35 views

Moving heat problem: instant toast?

Toast-making usually takes a couple minutes using something like a conventional toaster oven to brown the surface of a piece of bread, making toast. However, this duration may be inconvenient. What ...
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1answer
27 views

Trouble in deriving the Rayleigh-Jeans formula from the steps shown on HyperPhysics site

Hi I am very new to this aspect of physics and I am having trouble with the derivation of the Rayleigh-Jeans from the steps shown at the hyperphysics web site. I have emailed Dr. Rod Nave who is ...
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1answer
41 views

How does radiative cooling between the earth and space work?

On a chilly (but above freezing) temperatures on a clear night, you can freeze water outside because of radiative cooling. By what mechanism do warm bodies on earth actually lose heat to space? ...
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1answer
27 views

Heat loss by radiation reference

In our lab practice, we measured the rate of heat loss of a copper plate in atmospheric pressure and the rate of heat loss of the same plate in high vacuum ($\sim 10^5 torr$). So all I could find for ...
1
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1answer
35 views

understanding thermal radiation in a conductor, gas and insulator

Context: I was in my bliss of ignorance and happiness when I was taught that quantum mechanics was about nice discrete values of energies. Now I am introduced the idea of Fermi Energy in a block of ...
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3answers
645 views

Cooling down to absolute zero by radiation

Consider a system consisting of a gas, it is put in a container which is permits transmission of all kinds of electromagnetic waves. If this system is isolated and put in a perfect vacuum, and left ...
3
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1answer
31 views

Reaching equilibrium in a blackbody and light-matter interaction

Suppose we have a metallic cavity maintained at a fixed temperature. Suppose we start with any distribution of radiation that is not in equilibrium with the container. Gradually, when the equilibrium ...
2
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3answers
97 views

How do Black Bodies Absorb and Emit Radiation? [duplicate]

I have learnt how the gases of elements are able to absorb only certain wavelengths of EM radiation corresponding to the energy transitions between energy levels of orbitals. Furthermore, these ...
2
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2answers
46 views

Radiative Cooling of metal object

We have this experiment where a metal bar is heated and then we have to make a model for the cooling that occurs. We get numbers for how long it takes the metal bar to cool from 200 to 100 degrees ...
1
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1answer
47 views

Why do High Pressure Gases produce a Continuous Spectrum?

I am aware that low pressure/density gases produce an emission spectrum as there are specific energy transitions that the electrons can make, emitting certain frequencies of EM waves. However high ...
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1answer
21 views

Radiation-Glossy Black vs Matte White

Well, studying the chapter Heat I know that a matte black body radiates heat more than a glossy white one but can anyone give me an answer about what happens when its a glossy black body and a dull ...
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0answers
58 views

Is the visible light spectrum from “red-hot glass” at least close to Blackbody Radiation?

In this really nice answer @RobJeffries explains the difference between the ideas of Thermal Radiation and Blackbody Radiation in the context of a source which may be in thermal equilibrium, but who's ...
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0answers
38 views

Finding the exponent of $\lambda$ in Wien's displacement law

I am reading this paper on a short history of the $T^4$ radiation law. In particular, on page 5, By assuming that the wavelength of radiation emitted by a molecule was a function only of its ...
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0answers
54 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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2answers
33 views

Diminishing solar temperature and its effects on earth

This is a hypothetical question; considering both the earth and the sun as black bodies. If the temperature of the sun decreased N times, what would be the effect on the radiation intensity received ...
3
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1answer
83 views

If an object has a temperature, does it have to radiate?

I'm reading through a powerpoint presentation about Hawking Radiation (HR). They are explaining all of the reasons that built up to the postulate of HR, and one of the reasons is that if there is a ...
3
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1answer
61 views

Radiative equilibrium of a relativistic black body

A black body in empty space in the CMB rest frame should (discounting starlight) come to an equilibrium temperature of around 2.7 K. However, if the body is moving relative to the CMB frame, one side ...
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2answers
84 views

Is it possible to produce higher temperature than the light source with passive device only?

Suppose the light source is a black body with average temperature 2000K, and I want to use it to heat another black body to 2500K, via passive devices only. Here passive device means lens, mirror, ...
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0answers
15 views

Black body with radial radiation emission/absorbtion

Is there any model using some kind of material that can approach a spherical black body in a reduced scale?
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2answers
29 views

Power absorbed by an object inside a perfect blackbody cavity

Suppose you were inside a thick spherical shell of inner radius $R$, which was a perfect black body at some temperature T. What would be the power a sphere of radius $r$ would absorb located inside ...
0
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1answer
32 views

Is thermal transfer in a vacuum proportional to temperature difference?

I would have thought that heat dissipation was proportional to temperature difference, especially in a vacuum. Is this true?
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2answers
37 views

Black Body radiation (intensity in certain distance)

i need some help with this task: I have a black body radiator which is spherical and it has radius $r=0.56m$. It radiates with intensity $1.5\frac{kW}{m^2}$. I would like to know the intensity in ...
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2answers
87 views

How is Planck's radiation law related to $E=h\nu$

How did Planck conclude $E=h\nu$ from his radiation law?
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2answers
55 views

Emissivity and Final Temperature of a Black and White object

Objects can be categorized as blackbodies (emissivity $\epsilon = 1$), grey bodies (emissivity $\epsilon < 1$) and white bodies (emissivity $\epsilon = 0$). If we placed two objects (identical ...
2
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0answers
53 views

Carnot Engine- Cold Reservoir is a black body [closed]

My question: A satellite powered by a Carnot engine uses heat from a nuclear reactor at a fixed temperature T0. Heat is released into outer space via thermal radiation emitted by a set of fins at ...
2
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1answer
43 views

Characteristic room-temperature photon energy - is this nomogram wrong?

Reading this recent ars technica article on the James Webb telescope, something kept bothering me about the nomogram - shown below. The credit says it is from The Opensource Handbook of Nanoscience ...
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1answer
31 views

Synthetic Photometry - Calculating a colour index

I have a theoretical black body spectrum, described by plancks law. I also ave the bandpass sensitivity function for various filters. I would like to calculate a colour index from this information, so ...
4
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1answer
423 views

Why 8–15 µm is considered “thermal infrared” if typical room temperature kT is 48 µm?

According to Wikipedia: Long-wavelength infrared (8–15 µm, 20–37 THz, 83–155 meV): The "thermal imaging" region, in which sensors can obtain a completely passive image of objects only slightly ...
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1answer
23 views

When thermal IR gets reflected from an object, does it change its wavelength (frequency)

I'm working with thermal infrared (IR) cameras to detect human thermal radiation. I notice I can easily distinguish non-human objects throughout the camera's field of view, though all are at same room ...
0
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1answer
61 views

Planck's law - energy, frequency and temperature dependancy

Unlike radio waves, thermal radiations are emitted at a broad range of frequencies. So, at a given temperature, an object might be emitting a lot of frequencies. Is that correct? So ehen Planck's ...
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26 views

Isothermal expansion of a cavity containing electromagnetic waves?

The cavity is perfectly reflecting , and simulates a black body . Is it that during an isothermal expansion of a cavity containing electromagnetic waves the internal energy density is constant and ...
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0answers
15 views

Physics 3 recommended book with solutions [duplicate]

I'm new to this forum and wanted to ask for a recommendation for a book which has these subjects with problems and solutions:(if this is not a valid question please tell me) -Intro to Waves -Fourier ...
4
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2answers
161 views

Why aren't the hottest stars mostly invisible due to radiating mostly in ultra-violet? [duplicate]

The hottest stars have surface temperatures in the range of 40,000K. Wolfram Alpha says that such a star acting as a black body should radiate almost no energy in the visible spectrum. Why then do ...
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0answers
12 views

In non-metallic solids w/ just atoms or ions (no molecules), are bonds (vibrations) and electronic transitions the sole cause of blackbody radiation?

Since there wouldn't be a conduction band filled with any electrons in a non-metallic solid made of just atoms or ions (no molecules), it's hard to imagine any other type of movement and dipole moment ...
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1answer
91 views

Help me solve a heat conduction/emission transfer problem. Mathematica has failed me

My problem: A thin-walled tube (length $L$, diameter $D$ and wall thickness $t \ll D$) is in a vacuum. It is held on one end (at $x=0$) by a heat source at constant temperature $T(0)=T_0$. The only ...
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3answers
36 views

Black Body Spectrum Plot

I'm Having trouble replicating the Black Body model for sun shown on this plot To my understanding I should only use Planck's formula: $$I(\lambda) = \frac{2\pi hc^2}{\lambda^5}\dfrac{1}{exp\left(\...
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2answers
82 views

Is Moon too hot?

I find it puzzling that Moon's maximum "daily" equatorial temperature is almost 400K. Earth's theoretical black body temperature would be 279K at 1AU, and Moon is the same distance from Sun, yet its ...
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0answers
34 views

How to integrate to find the view factor of two parallel disks of different radii? [closed]

You have two parallel coaxial disks of different radii. I have tables that give me the value as $$F_{ij} = \tfrac{1}{2} [S - \sqrt{S^2 - 4(r_j/r_i)^2}]$$ where $$S = 1 + \frac{1 + R_j^2}{R_i^2}$$ ...
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2answers
152 views

Is this conceptualization of blackbody radiation logical/correct?

From what I understand, a blackbody is a body which does not emit radiation as a result of atomic excitation/relaxation but rather solely due to the kinetic energy of its particles due to interactions ...
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1answer
30 views

In solids, is it phonons, or is it the oscillations of electrons in bands, that emit most of the blackbody radiation?

In solids (most any object we see), which tends to emit most of the blackbody radiation: phonons (atomic, or molecular dipole, lattice vibrations) or oscillating electrons in their energy bands?
0
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1answer
59 views

Why do metals have low emissivity values in general?

Is there any specific physical explanation behind this? I know from reading about emissivity that it depends upon surface roughness. So does metal with rough surface gets higher/lower emissivity?
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0answers
39 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 ...
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1answer
21 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 ...
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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 ...
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0answers
36 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
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1answer
63 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? ...
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0answers
31 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 ...