All Questions
Tagged with thermal-radiation thermodynamics
669 questions
2
votes
4
answers
211
views
Does thermal energy include the energy of thermal radiation as part of its definition?
I can't get a simple answer to this simple question online, so I thought I'd ask here.
Thermal radiation is usually meant to be the energy associated with a given temperature of a material body. Now ...
- 8,776
0
votes
1
answer
140
views
Cooling of a solid vs hollow sphere
We have a solid and a hollow sphere made of same material, and of same dimensions.
We have to compare the temperatures of the sphere after a long time of cooling.
So initially I can safely say that ...
- 2,062
2
votes
1
answer
54
views
Why doesn't the accretion of ice, cause the ice to melt?
I was reading about the accretion of ice which describes the rate at which the ice layer above a lake thickens. It said that in order for the water just below the ice to solidify,heat had to be ...
- 23
1
vote
0
answers
76
views
Focusing blackbody light simulation
As an honest citizen, I do not intend to violate the laws of thermodynamics by concentrating the light emitted by a blackbody on a smaller area. However by playing with this wonderful 2d ray online ...
- 11
1
vote
1
answer
75
views
What fraction of heat is exchanged by thermal radiation (by ordinary objects)? [closed]
I understand that heat can be transferred by conduction, convection and thermal radiation.
So, lets say when I bring a cold glass of milk in a room at room temperature, then what fraction of heat is ...
- 1,306
3
votes
3
answers
344
views
Power emitted during thermal radiation
How does the power emitted during thermal radiation depend on time (if it does)? What are some sources refering to the particular relation between the power emitted during thermal radiation and time? ...
- 4,157
1
vote
1
answer
45
views
How is black-body radiation affected by recoil?
In a semi-relativistic framework, which accounts for the mass of an energetic photon ($=h\nu/c^2$), a black body cannot emit a photon whose relativistic mass is greater than its own. So the higher the ...
- 11
1
vote
1
answer
110
views
When a gas is in thermodynamic equilibrium, does it emit like a black-body? [duplicate]
Black-body radiation is said to be the thermal electromagnetic radiation within, or surrounding, a body in thermodynamic equilibrium with its environment or emitted by a black body. For the first case ...
- 221
7
votes
2
answers
2k
views
How a piece of metal put in the oven reaching a constant temperature of 3000 K fit the model of a hole in a cavity?
The common and practical model for a blackbody is a hole inside a cavity, and even stars can be made to fit into this model. My question is how to make anything else like a piece of metal at some ...
- 1,035
2
votes
1
answer
23
views
Doubt on the radiated heat of a black spheric shell
Consider a black spheric shell of radius $R$ manteined at temperature $T$ in an empty space. By Stephan-Boltzmann's Law we know that the power radiated is given by $\dot{Q} = 4\pi R^2 \sigma T^4$ but ...
- 402
3
votes
1
answer
50
views
Different radiation intensities from a black body
I am a high school student and was wondering about the radiation curve of a black body. Why do the emitted wavelengths from a black body have different intensities? What happens at the atomic level ...
- 647
3
votes
1
answer
130
views
Can an evaporating black hole emit protons with an energy beyond the GZK limit?
There are protons reaching the earth with energies that exceed what their interaction with the cosmic microwave background should allow, the so-called GZK limit.
Could an evaporating black hole emit ...
user353451
0
votes
0
answers
45
views
Temperature of copper block inside a metal container
I have one cylindrical metal container : ~20 cm in length; ~15 cm in diameter.
I have kept one small copper block inside this container. Copper block is thermally
insulated from all other components ...
- 1,034
1
vote
2
answers
72
views
Photoionization by black-body radiation
I am trying to solve the question:
"Show that if an atom is photoionized by black-body radiation with the
temperature $T^*$ such that $kT^*\ll I_H,$ the average kinetic energy acquired by an ...
- 63
1
vote
1
answer
233
views
Is the Drapers point inaccurate?
Is the Drapers point faulty since an oven glows visibly red without it actually reaching Drapers point? When the Drapers point blackbody radiation frequency is calculated by Wien's law it results ...
user348071
2
votes
2
answers
599
views
How does anodization increase emissivity?
In articles devoted to the study of the contribution of radiation to heat dissipation, it is often mentioned that an anodized heatsink has better emissivity compared to a bare heatsink.
Since the ...
- 23
2
votes
1
answer
37
views
Is there a relationship between the electrical power supplied to a material and the emitted wavelength?
I have a graphite bar that is used in a vacuum furnace that serves as a heating resistor and the heat is provided by radiation, so I would like to know by knowing the electrical input power (240kW), ...
- 21
0
votes
1
answer
61
views
Does the radiation spectrum of bodies depend on it composition or not?
In the second edition of Quantum Physics by Robert Resnick and Robert Eisberg, they write
"Matter in a condensed state (i.e., solid or liquid) emits a continuous spectrum of radiation. The ...
2
votes
1
answer
142
views
Is a layer of gas with sufficiently large optical thickness really radiating as a black body?
Can a parcel of gas with large value of optical thickness really radiate like a black body?
I have in mind a simple (most likely oversimplified) model which yields
$$I_\nu = I_\nu(0) e^{-\tau\nu} + I_\...
- 1,391
0
votes
1
answer
72
views
Should heat conduction not always be accompanied by heat radiation?
Consider two solid elements exchanging heat due to the temperature gradient between them by heat conduction. Such problems are always modelled with one mechanism only. Example: The transient behaviour ...
- 3
-2
votes
1
answer
73
views
Are there any time irreversible processes on earth which aren't due to the sun?
The sun is very hot. The earth is cold. Energy always flows from hot to cold systems. Due to the temperature difference, useful energy can be imparted onto earth (i.e., blackbody radiation from the ...
- 11.8k
0
votes
0
answers
255
views
Planck's Black Body Radiation and Einstein's Quanta
Planck described blackbody radiation as quantized resonances in a cavity.
It was not until five years after Planck made his heuristic assumption of abstract elements of energy or of action that ...
- 10.8k
1
vote
1
answer
200
views
A function for the percentage of heat lost by an object immersed in a fluid due to conduction versus blackbody radiation
Is there a way to derive an equation for the amount of heat lost by an object immersed in a fluid due to blackbody radiation versus conduction using equations such as Planck's law, and the heat loss ...
1
vote
1
answer
87
views
$Q$ Transfer via Radiation Formula
According to the formula:
$$
\frac{\Delta Q}{\Delta t}=\sigma\epsilon A T^4
$$
What does $T$ refer to in a situation where I am modelling the power of radiation from air of temperature to surface of ...
- 113
1
vote
1
answer
614
views
What radiation spectra does neon glow at 2500 K?
A neon gas tube, when passed with high voltage electric current, will emit a characteristric spectrum of color.
This spectra lines are explained by the different combinatorial paths that electrons ...
- 627
3
votes
1
answer
53
views
Can low energy photons in equilibrium with a black body absorber create a high temperature in the absorber?
With enough flux can low energy photons warm a black body to any temperature?
eg a solar furnace can approach the surface temperature of the sun, but could it in theory go to any temperature? If all ...
- 49
9
votes
4
answers
2k
views
Why can Einstein coefficients be derived based on thermodynamically equilibrium relations when they are basically intrinsic?
Einstein coefficients for emission and absorption ($A_{21}$, $B_{12}$, $B_{21}$) are often derived from a consideration of thermodynamic equilibrium using Boltzmann statistics and comparison with ...
- 1,391
0
votes
2
answers
762
views
Spectral Irradiance of a Black Body
This website states that the spectral irradiance of a Black Body is
$$F(\lambda) = \frac{2 \color{red}{\pi} h c^2}{\lambda^5 (\exp (hc/k\lambda T)-1)}.$$
Other sources, however, state that it is
$$F(\...
- 2,740
2
votes
2
answers
121
views
Radiation of an object with a temperature gradient
Case 1: Suppose I have an infinite slab of thickness $D$ connected on one end to a heat bath at temperature $T_B.$ The other end of the slab is exposed to a vacuum, and is at temperature $T_E.$ The ...
- 2,740
0
votes
3
answers
108
views
Question on black body radiation
In black body radiation at thermal equilibrium, the absorptivity is equal to emissivity (to conserve energy). Is it fair to say that all of the photons falling on the body are absorbed and emitted? If ...
0
votes
0
answers
73
views
How can Kirchhoff's law of radiation be proven more rigorously and what does it really mean?
Kirchhoff's law of radiation states that emission factor equals absorbtion factor for any material body: $\epsilon = a$
I never understood this really: Lets say there a body which reflects totally any ...
- 1,391
1
vote
0
answers
80
views
Confusion with spectral density of the emitted power of blackbody radiation
I'm reading a book discussing electrons' velocity fluctuations, which would cause electronic noise when detecting signals.
Velocity fluctuations originate from thermal motion. Superimposed on the ...
- 11
1
vote
2
answers
182
views
If charged particles have Brownian motion, would this motion be associated with (or produce) heat or electricity?
If we have charged particles having Brownian motion, would this motion be associated with (or produce) heat or electricity? Would it produce electromagnetic radiation (and if it would produce it, what ...
- 2,878
-1
votes
1
answer
165
views
What is the maximum temperature gradient between two points? [closed]
What is the maximum temperature gradient between two points?
If the environment material affect the solution, you can assume that the environment is vacuum.
For example, can we change the temperature ...
- 135
0
votes
1
answer
139
views
How does the density of the air affect our perception of temperature?
The classic experiment where you have someone put one hand in a bowl of hot water and the other in a bowl of cold for a while then move their hands to a warm bowl is a classic demonstration that our ...
- 22.8k
1
vote
0
answers
49
views
Radiation Graphs and their meaning
I am looking a two graphs, the first one is radiation vs $\frac{1}{x^2}$ (Inverse Square Law) and the second one is radiation vs $T^4$(Stefan-Boltzmann Law).
The equations of my inverse square graph ...
- 123
1
vote
0
answers
69
views
Thermalization of two gases at different temperatures [closed]
Consider a box with partitions $A$ and $B$ each filled with a (possibly different) gas at temperature $T_A$ and $T_B$, and is separated by an adiabatic barrier. Each partition is in thermal ...
- 111
2
votes
2
answers
331
views
What physical property defines how fast a material loses thermal energy? [closed]
I was thinking about the following - let's say, I want to heat a 100 ml of vegetable oil in a 30 cm stainless steel pan (which weighs 1 kg) to 220°C. How should I proceed to reach the desired ...
- 121
2
votes
2
answers
106
views
Will a black hole disappear?
Reading The brief history of time by Stephen Hawking and the chapter 7 BLACK HOLES AIN’T SO BLACK has below.
Does it mean if his theory is correct, a black hall can disappear on its own?
Because ...
- 169
1
vote
1
answer
264
views
How the Stefan's law will change if the body isn't a black body?
The Stefan's law for black body radiation where energy varies with the forth power of the temperature but what will happen if the body isn't black body? Would it be still forth power of temperature ...
1
vote
1
answer
80
views
Is passive cooling below ambient temperature using a spacecraft radiator possible?
Consider the following set-up: a spacecraft radiator is placed inside a vacuum chamber with transparent walls, on the surface of the Earth. The radiator acts as a heatsink touching one of the walls of ...
- 159
0
votes
1
answer
149
views
How does Kirchoff's law of Thermal radiation explain that to cool below ambient temperature have to radiate through atmospheric transparency window?
Kirchhoff's law of thermal radiation is "a body emits radiation at a given temperature and frequency exactly as well as it absorbs the same radiation." Is this law valid only at thermal ...
7
votes
1
answer
887
views
Could the solar shield on the James Webb telescope have been pitch black or does it need to be highly reflective?
When I look at pictures of the sun shield on the James Webb Space telescope (JWST), I see something that looks highly reflective (and hence must have a very low emissivity). My intuition tells me that ...
- 1,599
8
votes
6
answers
4k
views
Why do dark objects absorb visible light but only emit infrared radiation?
What is it about the molecular structure of dark coloured objects that means they absorb most of the visible light that falls on them, but radiate infrared?
Naively I would think that if a molecule ...
- 523
3
votes
2
answers
682
views
What is the meaning of a thermal equilibrium between matter and radiation?
I understand that the thermal equilibrium between two bodies means that the two bodies attain the Same temperature. Therefore,there is no flow of a thermal energy between them. However, I don't know ...
- 1,035
2
votes
3
answers
440
views
Why is the black body radiation independent of composition and incident radiation?
There have been questions similar to this, but most of them do not explain the mechanism responsible for the phenomena but instead explain through contradiction of second law of thermodynamics, for ...
- 659
0
votes
1
answer
63
views
Doubt regarding rate of loss of heat due to radiation
My doubt is with regards to radiation emitted by a body and how we define the rate of loss/gain of heat due to the same.
For my question, let us consider a body of: * surface area A
...
-1
votes
1
answer
131
views
Application Of Kirchoff's Law In A Desert [closed]
Homework Statement::
Sand is rough and black so it is a good absorber and radiator of heat depending on temperature.
During the day, sand's radiation of the sun's energy superheats the air and causes ...
- 229
3
votes
3
answers
430
views
Why using a sum instead of an integral solves the Ultraviolet catastrophe?
Im reading about how using a sum instead of an integral when deriving the Rayleigh-Jeans law (in the equipartion part) solves the ultraviolet catastrophe. basically doing the following replacement:
$$\...
- 97
0
votes
1
answer
443
views
Building a house that is warm in winter and cool in summer [closed]
The Northern house architecture is strikingly different from that used in the South (I am not taking extreme cases, thinking more of Northern or Germany versus Mediterranean:
Thick layers of thermal ...
- 65k