We’re rewarding the question askers & reputations are being recalculated! Read more.

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.

Filter by
Sorted by
Tagged with
1
vote
2answers
142 views

Why do hot objects tend to emit shorter wavelength? [closed]

So how do the temperature and wavelength related and why do hot objects tend to emit shorter wavelength?
0
votes
0answers
84 views

Difference between color and effective temperature

What is the difference between color temperature and effective temperature of a star? I have gone through the pages at wikipedia, but I still do not understand that. Can anyone please help?
19
votes
5answers
5k views

If perfect blackness violates the Uncertainty Principle, how isn't dark matter a violation?

In a recent tweet, Dr. Michio Kaku stated that perfect blackness would violate the Heisenberg Uncertainty Principle, i.e. every object must emit some radiation. I have two questions regarding this ...
1
vote
1answer
39 views

Missing link re: how does kelvin relate to temperature when talking about color temperature?

I am an electrician at a commercial electrical company. There is an in-house training program that posits the datum that when talking about the designations of color temperature for lights (for ...
2
votes
1answer
87 views

Thermal radiation from molten glass

Molten glass, on photos, appears to radiate light like a black body. However, as cold glass absorbs almost no visible light, I would guess the emissivity for visible light is very low. So I am ...
0
votes
0answers
19 views

How does brightness affect color? [duplicate]

How does brightness affect the color of light? For instance, the sun might be yellow because of the blue scattering when the light travels through the atmosphere - but if you look at it, it seems ...
0
votes
2answers
112 views

Why does the sun always have some whiteness? [duplicate]

So the atmosphere scatters light on its way to earth, making the color of our sky. For example, when the sky is blue on a clear, sunny day, the sunlight appears somewhat yellow because the blue light ...
0
votes
1answer
82 views

Empty container with pinhole - an assumption for a black body

I know that a black body is a hypothetical perfect absorber and radiator. It emits EM radiation with different intensities. But my doubt is, how can an empty container with a pinhole be considered a ...
3
votes
1answer
65 views

Physical Model for a Black Body

I am learning about black body radiation and it was stated in a textbook that The best model for a black body is a large cavity with a very small hole in it which absorbs all incident radiation. ...
5
votes
0answers
240 views

Is there a difference in the infrared absorption spectrum of a greenhouse gas when pure and when mixed with non-greenhouse gases?

According to the standard IPCC greenhouse climate change hypothesis a doubling of the preindustrial CO2 concentration of 285 ppm in the atmosphere - the current value is 405 ppm - would lead to an ...
0
votes
1answer
118 views

Intuitive understanding of the derivation of the Rayleigh-Jeans law

I know the Rayleigh-Jeans law and how the formula predicts UV catastrophe. Without getting into the exact derivation, I am trying to get some intuitive understanding of it by using some of the broad ...
0
votes
1answer
49 views

Local equilibrium of slow time varying thermal system

I'm trying to differentiate a thermal system in local equilibrium (and slow time varying) v/s a non-equilibrium system. For a thermal system which is slowly time varying, how does one define local ...
-1
votes
1answer
69 views

Does a black body in zero gravity emit EM radiation? [closed]

I have just recently thought of this query. However, I can find no evidence of any experiments ever being carried out on the effect of zero gravity on black body radiation.Perhaps someone here has ...
0
votes
1answer
22 views

Do materials approach black body behavior as temperature increases

I have emittance curves of a material (that cannot be shared) that show an increase in emittance values over a wide wavelength range. As the temperature increases, the value for emittance increases, ...
0
votes
1answer
19 views

How far can we track ionic based spaceships if antenna fails

Suppose we send an ionic based spaceship and all the antennas are broken on launch, suppose the spaceship destination is another solar system. Obviously we can track it with optical telescopes, but i ...
1
vote
1answer
92 views

Air gap in a radiant barrier insulation system: why?

It's generally accepted that a reflective surface, when used to insulate a system by reflecting radiant energy back to it, must have an air gap in front of it. Why exactly is this, and what determines ...
1
vote
0answers
118 views

Blackbody photon variance and number of modes [closed]

In an experiment to measure the photon statistics of thermal light, the radiation from a black- body source is filtered with an interference filter of bandwidth 0.1 nm centered at 500 nm, and allowed ...
2
votes
2answers
252 views

How to tie in black body radiation with quantum theory?

I'm having trouble understanding the physical basis for the UV catastrophe in blackbody radiation graphs. Is the source of the drop off past UV because the electrons in a blackbody substance can't ...
0
votes
1answer
58 views

Is placing a fire safe inside a larger fire safe helpful?

If I put a small fire safe (say, one rated for 1 hour at 1700°F) inside a larger, equivalently-rated fire safe, to what degree is the fire/heat protection improved?
2
votes
1answer
100 views

Inferring Properties of Stars from Masses and Radii

I have two questions related to inferring properties of stars from their masses and radii. What properties of a star's spectrum could we deduce? In particular, do all stars emit like black bodies? ...
1
vote
1answer
115 views

Why isn't the emissive power of a black body 1?

My text book has a question which says that the emissive power of a black body isn't one but the answer states that the absorptive power is 1, considering that $$e=a \tag{Kirchoff's law}$$ and a ...
0
votes
1answer
83 views

What is the difference between Wien's Displacement Law for peak frequency vs peak wavelength?

While doing research for a high school report I came across the fact that WDL actually has two forms, one for peak frequency and one for peak wavelength, and that these two forms are not the same and ...
0
votes
1answer
143 views

Calculating rate of heat loss through conduction and radiation

I'm trying to calculate the rate at which a hollow cylinder with a heating element inside will lose heat, specifically through both conduction and radiation. I realize that the total heat loss per ...
2
votes
1answer
159 views

Questions on derivation of the Rayleigh-Jeans law

I'm following this derivation of the Rayleigh-Jeans law: https://thecuriousastronomer.wordpress.com/2013/10/28/derivation-of-the-rayleigh-jeans-law-part1/ There are a few points that I don't quite ...
8
votes
2answers
954 views

Can we see emission lines in stars?

I read that stars show both absorption and emission lines. While how we see absorption lines is clear to me, I don't understand how (and when) we see the emission lines. Based on what I read in ...
2
votes
1answer
248 views

Difference between emission spectrum and black body spectrum

Why is an emission spectrum dependent on the chemical composition of the body's material, but the black body spectrum is independent of the material and only based on the body's temperature? Aren't ...
1
vote
1answer
29 views

Does there exist a notion that generalizes a black body to include other emission processes than electromagnetic ones?

A black body by definition is a perfect absorber for all incident electromagnetic radiation. It isotropically emits electromagnetic radiation whose spectral distribution only depends on the ...
1
vote
2answers
73 views

Black body/Sun radiation - λmax

The Sun's effective temperature is 5778K. Using Wien's law we can calculate the wavelength λmax in which we observe the maximum amount of radiation received from the black body. After doing the ...
0
votes
1answer
50 views

Has there been a quantifed estimate of the thermal impact of human activity? Not to include “greenhouse gasses” [closed]

In 1984 I read a prediction by the biological scientist and Nobel Laureate Konrad Lorenz that heat produced by human activity would necessarily increase Earth's average atmospheric temperature. His ...
1
vote
1answer
71 views

Planck Blackbody Radiation: Is this an error in the textbook?

the textbook I am reading describes two forms of equations of Blackbody Radiation. $$d\rho(\nu, T) = d\rho_\nu(T)d\nu = \frac{8\pi h}{c^3}\ \frac{\nu^3d\nu}{e^{h\nu/k_BT}-1}\ . $$ Substituting $ c = \...
1
vote
1answer
48 views

Planck blackbody radiation

I am reading a chapter about blackbody radiation in my physics textbook, and I encountered the following equation: $$d\rho(\nu, T)=\rho_\nu(T)d\nu=\frac{8\pi k_BT}{c^3}\nu^2d\nu$$ which is a classical ...
1
vote
0answers
21 views

How does temperature correspond to number of particles produced?

I'm looking to calculate the number of particles per unit time produced by a Schwarzschild black hole through Hawking radiation. I know that the temperature of the black hole goes as $\kappa/2\pi$, ...
0
votes
2answers
102 views

Electromagnetic radiation from sun and human body

What is the difference between infrared radiation produced in sun and thermal radiation, in infra red range, by human body in terms of its energy or are they the same?
5
votes
1answer
87 views

Is there an equivalent of black body radiation for other particles?

So all objects composed of matter emit black body radiation, which is photons of various frequencies. Is there an equivalent of black body radiation for other processes? Is there gluon black body ...
4
votes
1answer
47 views

Colour Temperature and the thermal temperature [duplicate]

I understand that Colour Temperature correlates with the object's thermal temperature, such as a red-hot piece of iron being ~360c and the incandescent bulb filament is about 2500c. Why are sources ...
-1
votes
1answer
58 views

How to obtain the luminosity of a blackbody disk? [closed]

How do I get the luminosity of blackbody disk (negligible thickness) with temperature $T$ and radius $r$? Also how can one obtain the flux density if the object is at a distance $d$ and an ...
2
votes
2answers
105 views

What determines the timescale for fluctuations in the electromagnetic field from a light source?

Let's say you place an electric field meter some distance from a light bulb. As a function of time the output of the meter would be $\mathbf{E}(t)$. I would guess that the electric field will be some ...
2
votes
2answers
1k views

What is the difference between reflection and emission?

What is the difference between a body that simply reflects the light that falls upon it and a body that absorbs and emits it (like a black body in thermal equilibrium)? How can one experimentally ...
12
votes
3answers
1k views

Humans have an average energy budget of $100$ Watts, but the power radiated from the body is $1000$ Watts?

On average a human consumes around $2000$ kilocalories per day. This converts to roughly $2000000$ calories / $86400$ seconds or around $100$ joules / second giving roughly $100$ watts. But if you ...
2
votes
2answers
103 views

Why a metallic mirror temperature cannot be read by a thermal camera?

When I look at a first surface mirror with a thermal camera I don't see the temperature of the mirror but the temperature of the reflected objects. It is like if a polished metallic surface don't lose ...
1
vote
0answers
46 views

Does a high-velocity ion being neutralized by an electron emit Brehmsstrahlung radiation?

I'm curious about a point of the physics of Polywell electrostatic confinement fusion devices. One of the key claims made in the design is that by confining some "low temperature" electrons to a ...
0
votes
2answers
148 views

Does the Earth emit heat?

I'm reading my first book on physics "Seven brief lessons on physics" by Carlo Rovelli, and in his chapter on "Probability, time and heat of black holes", he mentions that Stephen Hawking showed that ...
0
votes
1answer
265 views

Can a cold surface emit heat radiation?

If I place a hot body behind a cold glass, it would transmit the hot bodys radiation and thus pass heat radiation. Could the glass surface still be considered cold in terms of contact temperature, ...
0
votes
1answer
106 views

What does blackbody radiation look like for negative-temperature systems?

Using the thermodynamic definition of temperature, $$\frac{1}{T}=\frac{\partial S}{\partial U}\bigg|_{V,N}$$ negative temperatures are possible, in systems where the entropy decreases when energy is ...
4
votes
3answers
104 views

Why does a heated body emit light?

I'm having my first lectures on Quantum Physiscs. We just discussed the black body and thermal radiation. However, why does a heated body emit light? How it is that a rise in temperature produce a ...
46
votes
4answers
12k views

Why don't we use infrared light to heat food?

Why don't we use infrared (IR) or even the far IR just to heat food in a microwave oven instead of, of course, the conventional 2.45 GHz microwaves? Don't people call IR heat waves?
2
votes
0answers
36 views

Shortest path to understanding black body radiation

I'm a mathematician studying quantum mechanics. I noticed I lack some statistical physics prerequisites. However, because I am in a rush, I'd like to learn just as much of it as I need to understand ...
9
votes
2answers
2k views

Why does classical physics imply every mode of vibration should have the same thermal energy?

I've just started reading about photo electric effect here, and my high school level understanding goes something like this : 1) By 1900 we had Maxwell equations and treated light as a wave. 2) But ...
0
votes
2answers
2k views

What is Planck's quantum theory of radiation?

In Planck's quantum theory of radiation we get to know light travels not continuously but discontinuously in the form of small packets of energy called quantum..... Does it means in short means that ...
0
votes
2answers
115 views

Why do I need energy quantization to explain the blackbody spectrum? [duplicate]

I don't understand why the postulate of "Energy Quantization" is needed to explain the black body energy spectrum. I think it suffices to say that Energy is proportional to frequency. That statement ...