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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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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8 views

Infrared Camera spectral filtering with an uncooled camera? [on hold]

I have been doing experiments with thermal cameras and stumbled upon CO2 detection. Having ordered a filter I was full of joy and immediately tried it out - nothing happened. So I talked to the ...
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2answers
24 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 ...
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1answer
394 views

Calculating new temperature of an object when air temperature changes

I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time. Basically I get periodic readings from an air temperature sensor in a ...
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2answers
80 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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343 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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Blackbody: In what factor should we change a temperature for the wave length to change by a factor of 2.5 [closed]

Here is the question: In what factor should a bodies' temperature change for its wavelength to change in a factor of 2.5? Here is what I tried: $T1 × \lambda_1 = T2 ×\lambda_2 = 2.5 \lambda_1 T2 $ ...
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Why does the Stefan-Boltzmann law work for power absorbed?

The setup is as follows: There is a body of emissivity $e$ and surface temperature $T$ whose surroundings have a temperature $T_s$ and may be assumed to be a black body. The body radiates at a ...
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12 views

Why Free-Free emission is regarded as Thermal emission?

I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we ...
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290 views

Thermal radiation of a nitrogen sphere

Let's imagine a : sphere of 100% pure nitrogen (N2), (edit: 1 m diameter) with a constant volume (edit: using a kind of "magic forcefield") (edit : at 1 bar) in the void far from any light source ...
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1answer
76 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 ...
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53 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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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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48 views

Can the energy released from a black hole be calculated at the time of birth?

this might be a stupid question but when a black hole is formed it releases a lot of energy our satellites just catch the gamma rays and X rays released by the black hole. can we estimate the amount ...
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12 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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1answer
387 views

Conservation of energy when focusing black body radiation on another black body

This question about whether or not it is possible to focus black-body radiation to make something hotter than the radiation's source was answered mostly negative: the second law of thermodynamics ...
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2answers
23 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 ...
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1answer
181 views

Work done in adiabatic reversible process

I was solving a problem on turbine.the steam works on turbine adiabatic reversibly .Is change in enthalpy or is it change in internal energy which equal this work?
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30 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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29 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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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 ...
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0answers
31 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 ...
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1answer
36 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
25 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 ...
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417 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
19 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 ...
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48 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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The temperature of photon and its energy

Do photons have temperature? If not, does it mean that photon lose energy while travelling through space? As the planets farther away from the sun are comparatively cooler than the one that are ...
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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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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 ...
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6answers
329 views

Is nature quantized?

I was reading Planck's postulate the other day on Wikipedia and couldn't help but noticing the sentence: "...is the postulate that the energy of oscillators in a black body is quantized..." ...
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2answers
155 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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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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79 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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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 ...
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Is it possible to focus the radiation from a black body to make something hotter than that black body?

My previous question wasn't specific enough. I'll try to be more specific. Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative ...
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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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140 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
39 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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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?
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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 ...
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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 ...
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36 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
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 ...
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17 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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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
54 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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630 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: ...
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1answer
108 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 ...