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Questions tagged [thermal-radiation]

The temperature-dependent 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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1answer
46 views

Black body radiation net power emitted

I have a question related to a definition (intuitive understanding). It is stated that : The human body radiates energy as infrared light. The net power radiated is the difference between the ...
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1answer
37 views

How does an IR camera determine the temperature?

The IR cameras detect light in the IR where low temperature bodies (-20 - 40 deg) have their peaks of the black body radiance. How the detectors associate temperature to intensity measurement on a ...
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1answer
45 views

Solar Radiation [closed]

If I have two container whit the same shape and thickness and both are made with PE (Polyethylene). These two containers are exposed to the same amount of solar radiation, but one is black and the ...
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1answer
482 views

Arbitrary Planet Spectrum

During my revision for an astrophysics quiz, I have encountered a question where I don't know where to start because I feel like I am lacking some intuition. I would appreciate any feedback! ...
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If blackbody radiation at 6000K peaks in the optical, why aren't fluorescent bulbs at 6000K?

We know, via Wien's law, that a body at 6000K emits an electromagnetic wave at the peak wavelength in the visible spectrum. How come say the fluorescent tubes which also emit the EM waves that we can ...
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2answers
51 views

Planck's Constant, factor of 2

I'm just starting to look into the birth of Quantum mechanics, but I'm already a little confused by something. I've seen 2 different equations involving the Planck's constant so far: $hf = \mathrm{...
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2answers
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Heating a stock water tank

I am building an insulated cover to go around a plastic stock watering tank for the winter. I have no electricity in the pasture and don't want to axe ice in the tank all winter. I am building 3 sides ...
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1answer
179 views

Energy Density of Radiation

What actually does the term energy density u(v,T) denotes? Is it the energy density of cavity radiation or the radiation emitted by blackbody? Is it uniform? While we derive an expression of it , we ...
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Radiative Forcing

In a first approximation the radiative forcing $RF$ is related to the temperature change by the linear relation $$ \Delta T = \lambda \, RF $$ where $$ \lambda\approx 0.8 \, \frac{{\rm K}}{{\rm W}/{\...
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1answer
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Can emissivity value be 4?

We know I=p/A and I=uc which I is radiation density , P is total radiation power , A is surface area and u is energy density. By putting A in the other side we will have p=ucA since energy density is ...
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1answer
248 views

When/How does thermal radiation stop (if it stops) and conduction starts?

Consider two solid objects in the vacuum (of different materials, if you will) at different temperatures approaching each other until they make "perfect contact" through flat surfaces (no gaps or ...
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3answers
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Max. air temperature on Earth [duplicate]

Is there any max. temperature that air on Earth could reach, assuming that solar radiation is standard and the average temperature on Earth is 14.6 like today? I mean, is there any chance that the ...
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1answer
166 views

Wein's Displacement Law for Light Bulbs?

I know Wein's Law $\lambda_{max}=\frac{b}{T}$ works for ideal black bodies. I have some clear glass incandescent light bulbs which have Tungsten as a filament. Would Wein's Law of displacement be a ...
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1answer
41 views

Planck law near absolute zero

Is the Planck law of radiation valid even for $T$ near absolute zero? Why can we be sure that the mean photon number inside a black body is zero for $T\to 0$?
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1answer
135 views

In-Vacuum Cooling Via Blackbody Radiation

If thermal energy is lost via blackbody radiation, and it's relative to the temperature of the body and its surface area - could you effectively cool a large body by pumping all the thermal energy ...
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1answer
39 views

In which direction would a single atom go if it absorbed heat through radiation?

if a single atom with an absolute zero temperature was suspended in space, and it then received energy through radiation from a nearby object: if that atom was in a lattice, it would vibrate, but ...
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2answers
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Number of modes in cavity radiation

My question is that why do we consider an octant of sphere ( and calculate the volume of that shell to find the number of modes) but not another geometric object and its differential volume element?
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3answers
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How do fusion reactors deal with blackbody radiation?

The plasma of the ITER reactor is planned to be at 150 million K. Using the Stefan-Boltzmann law, setting the surface area as $1000\,\mathrm{m}^2$ (the plasma volume is $840\,\mathrm{m}^{3}$ so this ...
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2answers
256 views

Why is a perfect blackbody radiation completely unpolarized?

Given a collection of photons obeying the Planck distribution at some temperature $T$, is it possible to compute the average electric field they produce and argue that a perfect blackbody radiation is ...
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1answer
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Quantization and wave-particle dualism of light

I'm studying atomic spectras and got puzzled about light-quantization. I'll expose my effort to understand it so far. Blackbody radiation Around the year $1900$ Planck explained blackbody radiation ...
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2answers
242 views

Blackbody radiations

The energy absorbed per unit time by the body at an absolute temperature $T_1$ and kept at a surrounding of higher temperature $T_2$ is $$J=\epsilon\sigma A T_2^4.$$ What my question is that aren't ...
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2answers
355 views

Thermal equilibrium vs steady state

According to Kirchhoff's law, when two objects are in thermal equilibrium, both objects have the same temperature and each object emits as much energy as it absorbs. Also, the energy absorbed at each ...
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3answers
581 views

Stefan Boltzmann law and specific heat of a body

Consider a body (not blackbody) at temperature $T$ kept at surrounding of temperature $T_s$. Due to the temperature difference, heat will be lost from the body in the form of radiations from its ...
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1answer
176 views

Why have all stars roughly the same order of surface temperature?

Given that stars vary in volume over 10+ orders of magnitude, why are they roughly the same order of surface temperature (emitting much of their radiant energy in the visual range of the EM spectrum)? ...
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1answer
86 views

Mechanism for light generation

Is all observable light caused by electrons dropping to a lower discrete energy level while bound in an atom? If so, how can a continuum of frequencies be generated? Is the thermal radiation ...
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0answers
58 views

Why do black bodies or black colored bodies cool down faster than white ones? [duplicate]

Recently, I found an exercise in which a graph was shown with the variation of temperature of two painted cans as they received sunlight. One of the questions was "Which of these two bodies will ...
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1answer
400 views

How did Planck arrive at the idea that energy is quantized? [duplicate]

Max Planck, arguably the leading theoretical Physicist of his day, apparently used of experimental data to formulate his equation for black body radiation, which was a major step in the birth of ...
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3answers
255 views

What color are stars?

I know that the sun looks white to us because it emits a large variety of color, making it appear white to our eyes but does this mean that all stars emit a variety of light? If so, then how can we ...
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0answers
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What portion of the total power emitted by the Sun comes from photons?

We usually talk about luminosity, which is the total power from emitted photons. The other sources are neutrinos and the solar wind (which includes protons and other particles). I assume that most ...
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2answers
316 views

How can a neutron star radiate when it is neutral? [duplicate]

We know how to define the Temperature of a neutron star, as answered in this question. After watching the Sixty Symbols video about Forging Weapons from Neutron Stars, where the temperature and ...
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1answer
160 views

Does a neutrino gas emit blackbody radiation?

My understanding of the microscopic "mechanism" of blackbody radiation* in a gas is as follows: interactions between fluctuating charge distributions in particles of a gas create a microscopic random ...
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1answer
47 views

Degree of freedom and specific heat concept link with radiation

I was reading the black body radiation and there the total energy of the black body radiation is $E=\sigma T^4$ and so specific heat is $C_v = 4 \sigma T^3$ so it is proportional to $T^3$. I read ...
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3answers
129 views

How to calculate the Sun’s energy output? [closed]

What formula can be used to find the total energy being produced from the Sun in Joules per second? If I recall correctly, the energy is around $2.3012 {\cdot} {10}^{27}\,\frac{\mathrm{J}}{\mathrm{s}}...
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2answers
281 views

Can a black hole absorb photons whose wavelengths are greater than the BH horizon size?

I am wondering whether a black hole can absorb photons whose wavelengths are greater than the horizon size of the black hole. I have seen different contradicting opinions on the answer. For instance ...
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1answer
162 views

Radiation cooling in space [closed]

Would the droplet cooling system from Mass Effect be actually possible in our universe? I'm interested in expanding the space industry and promote manufacturing in space. One of the biggest problems ...
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0answers
50 views

How does a microbolometer array resolve temperature?

I'm told that handheld thermal sensors measure black body radiation with a bolometer array. I don't understand how ones goes from IR photon counts to temperature. Is the camera somehow spectrally ...
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3answers
4k views

Emissitivity of copper - Why are copper heatsinks all shiny?

This wikipedia article states that emissivity of polished copper is 0.04, and emissivity of oxidized copper is 0.87 - more than 20x of the polished copper. So my question is - why are all copper ...
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1answer
48 views

Can radiant heat (as felt near lava) be measured as a temperature?

An opaque object that is subject to radiant heat may show an increase in temperature. Like a reporter near a Hawaiian lava flow. That reporter then referred to the radiant heat as "up to some amount ...
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1answer
77 views

Temperature rising of solar collector

I would like to calculate the heating of a polyethylene solar collector as a result of the sun's radiation. the collectors are uncovered collectors. Suppose I have a certain intensity $I$ of solar ...
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1answer
238 views

Blackbody radiation of a tungsten lamp

What is the source of the humps in the blackbody radiation of a tungsten halogen lamp?
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Does the black-body radiation formula (Stefan-Boltzmann) change if the photon turns out to be massive?

The black-body radiation formula, the Stefan–Boltzmann law, is derived treating photons as massless. Questions: What would the Stefan–Boltzmann law look like if derived assuming that photons have ...
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1answer
126 views

Why does a solar oven need a transparent lid?

The Premise: Imagine a solar collecting oven and how it works. Like the one below. We know it works by the greenhouse effect, letting light through, reflecting light from other areas as well with its ...
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1answer
351 views

Redshift of matter-radiation equality from $T^4$

I am trying to solve the following problem. Argue on dimensional grounds that the energy density of blackbody radiation at temperature T should scale as $T^4$. Use this to find the redshift of ...
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1answer
115 views

What was Planck's motivation for the frequency dependence in $E=nh\nu$?

Many accounts of the history of quantum physics explain how Planck resorted to quantizing energy in an "act of desperation" while attempting to solve blackbody radiation, only to discover by surprise ...
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1answer
335 views

How Planck's quantum theory of energy solved the ultraviolet catastrophe? [duplicate]

Hello I am a high school student and I am stucked at a concept in chemistry . I have studied black body radiation and Planck's quantum theory which is written in very short description but I have to ...
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4answers
348 views

Why doesn't the moon appear yellow?

The sky is blue (I'm told) because nitrogen in the atmosphere scatters short blue wave lengths of light from the sunlight, which is also why the sun appears somewhat yellowish rather than white, as it ...
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1answer
83 views

Finding amplitude of Fourier coefficient

I'm dealing with a confusing problem related to radiative transfer in atmospheres. In this problem, the solar flux on a planet it being modeled by $$S(t)=S_0+\sum_{n=1}^{\infty}S_n\,e^{in\omega t} \, ,...
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2answers
425 views

Thermal Radiation of human body

I've read that all bodies emit electromagnetic radiation of all wavelengths. Does this mean that humans emit gamma rays too (excluding the radiation from radionuclides present in humans)?
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1answer
47 views

Does a spaceship heat up if frictional force acts on it?

I was doing a homework question: The answer that I have pasted in the box is the given answer. I understand that the total energy of the spaceship decreases as it experiences friction, and as a ...
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0answers
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Why gravitational waves are not part of thermal phenomena?

Electromagnetic waves are part of thermal phenomena in the form of thermal radiations. But why gravitational waves do not show up as a thermal phenomenon, for example, why gravitational waves do not (...