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Questions tagged [thermal-radiation]

The temperature-dependent emission of electromagnetic waves. Combine this tag with the [thermodynamics] tag for a macroscopic view or the [quantum-mechanics] tag for a microscopic explanation.

When to Use this Tag

can be used to discuss the spectrum of electromagnetic radiation as a function of the temperature of a body. Depending on the size of the body and your specific interests, you can combine it with any of , and/or , and others.

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Why are good absorbers also good emitters?

I read that good absorbers are good emitters - hence a blackbody, that absorbs all kinds of radiation, also emits all kinds of radiation? I'm not able to get my head around this. What does it mean to absorb all kinds of radiation? Radiation of all…
stoic-santiago
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Ionizing radiation in thermal radiation

According to the black-body radiation equation, the spectrum extends to infinitely high frequency (although its intensity gets small quickly towards high frequency). (1) How do you roughly estimate the ionizing radiation power in common high power…
jw_
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Do burning red coals and red-hot iron have the same temperature?

It would seem that Planck's law implies that objects of similar radiation spectra have the same temperature if the objects are "similarly close" to being black bodies. Am I right to infer that burning red coals and red-hot iron have approximately…
sds
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What is the difference between thermal and infrared imaging?

Is there any sort of difference between thermal radiation and infrared radiation at least when detected by a camera? What are the differences between the two?
Sean
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I don't understand black body radiation graphs

Let's look at the above graph. This black body graph is for the temperature of 5000K. Each temperature has a different black body graph? How am I supposed to read this graph? Do I start from the left, the right, or the peak? As wavelength is…
silenceislife
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Planck's Law-Where does it come from?

It seems that Planck's constant was made from fitting a curve for blackbody radiation, is it just experimental-further more his assumption that energy comes in quanta seems to have been a guess. Why would energy come in quanta? Wikipedia says that…
user24082
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Bunsen Burners and the Sun

Why do Bunsen burners burn blue in the center? What element is being burned? Why does the sun glow yellow, and not blue-a Bunsen burner is much cooler and yet it burns blue. Is it because the relative size, or are they two different phenomena?…
user24082
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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 absorbs only specific frequencies, and this gives…
JDługosz
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Radiation pressure on a Dyson sphere

To find the outward pressure from the sun's light on an enveloping spherical shell (Dyson sphere), one can simply divide the insolation by $c^2$. Using the entire system, we can specify the power of the sun in watts, $W$, leading to a pressure of…
Alan Rominger
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Why is there emissivity + reflectivity + transmittance = 1?

Foillowing this question, I understand that $emissivity + reflectivity + transmittance = 1$ Where does this relationship comes from? What are the physical phenomena explaining this relationship?
Manu H
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A few question about the black body radiation

This is my understanding of the black body radiation: a black body is heated. The energy from the heat causes the electrons in the body to oscillate, so they will emit electromagnetic waves. If we plot the intensity of radiation against the emitted…
kave33
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Does a box with a hole which acts very close to black body an efficient way to create infrared radiation?

Actually I've got few questions. I've seen an experiment in which a box with hole drilled in it, when viewed from Infrared camera, shows the radiation emitting from it. Q1: So, is a Black Body an efficient way to convert visible spectra light to…
Eyy boss
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Is the Unruh radiation isotropic?

The Unruh effect is the prediction that what appears to be a Minkowski vacuum to an inertial observer, would appear to be a thermal bath of particles to an observer accelerating uniformly in the same spacetime. My question is: does the accelerating…
contrariwise
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Does thermal radiation intensity really depend on object's surface colour?

I am not a physicist, but I am trying to maintain the level of my intuition and basic knowledge in physics. Recently I tried to look at thermal radiation and black-body radiation. After I looked through Wikipedia articles, my intuitive…
Alexey
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Continous spectrum of black body radiation

I am wondering why black body emission spectrum is continous. Assuming only quantum effects that is electrones falling to less energetic orbitals it should be discrete. Is the continous part emerging classically from oscilating charges?…
user35001
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