Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

-2
votes
0answers
18 views

Heat transfer radiation

Consider a deep space probe constructed as 1m diameter polished aluminium sphere. If the solar energy received is 300W//m2, estimat/e the equilibrium temperature that probe reaches. For solar ...
52
votes
3answers
10k views

How does the Earth's center produce heat?

In my understanding, the center of the Earth is hot because of the weight of the its own matter being crushed in on itself because of gravity. We can use water to collect this heat from the Earth and ...
3
votes
2answers
44 views

Two questions about the standing waves in a black body

I am currently reading a derivation of Rayleigh-Jeans law for cavity radiation from Eisberg and Resnick 1 . The authors derive the law by considering a cavity with metallic walls. In the book, the ...
0
votes
1answer
46 views

Was Titan once warmed by a hot Saturn, & therefore much more Earth-like than it is today?

Is it possible that 4 billion years ago, Saturn was sufficiently hot to act as a second sun to Titan, so that conditions on Titan were then similar to those on Earth?
0
votes
1answer
31 views

Is a large open shiny metal bucket a good blackbody? [closed]

Would it being reflective be a good or bad thing towards it being a blackbody?
1
vote
1answer
45 views

Calculating radiative heat transfer between air and walls, what to use for the emissivity of air?

For example, say I have heated some air, I push it through a tunnel with cold black walls. Will the air radiate heat to the walls or will the walls radiate heat to the air? I understand that the ...
3
votes
1answer
33 views

Is there a blackbody spectrum of photons inside a solid?

My initial guess yes there is a blackbody spectrum of photons inside a solid. The process that emits thermal photons won't "know" that it is deep inside a solid and not near the surface, so the ...
32
votes
4answers
8k views

Why are solar panels kept tilted?

I have noticed that, in my country India, all the solar panels are tilted southward at an angle of ${45}^{\circ} .$ Even on buildings with inverted V-shaped roofs, solar panels are still oriented ...
0
votes
1answer
48 views

Energy radiated/emitted by an object in a black body environment?

What is the net energy radiated per unit time by a black body at temperature $T$ with emissivity $e$ and absorptivity $a$, if it’s placed in an environment of temperature $T_o$.Assume that $T$$\gt$$...
2
votes
0answers
63 views

Why does the emissitivity of metals increase (a lot) with temperature?

If we take a piece of metal (could be silver, nickel, platinum, copper, etc.) at room temperature, its emissivity is relatively low compared to that of a black body: about 0.05 vs 1.00. However if ...
2
votes
1answer
60 views

Simple heater (radiation) model for PID constants tuning

I've searched around a lot and maybe I just don't know what exactly to search (and even ask here) for, but I'd like to create a simple model/function of a heater dissipating heat to surrounding air, ...
0
votes
0answers
30 views

How much must the Sun's radiation be reduced to offset global warming?

About 70 % of earth is covered with clouds and the rate of atmospheric water vapor is increasing. Also the warming of the oceans will most probably cause more and deeper low pressures and increased ...
1
vote
2answers
51 views

What is the radiation density in a spherical oven? Does this pertain to the universe? [closed]

Imagine a spherical oven with radius R. The inside of the spherical wall is at temperature T (everywhere) and is assumed emit perfect black body radiation (everywhere). (1) What is the energy ...
0
votes
1answer
35 views

Why does a “cavity with a hole” model of a black body not absorb/emit radiation larger than the size of the hole/cavity?

This wikipedia article on the "cavity with a hole" model of a black body says: The hole is not quite a perfect black surface — in particular, if the wavelength of the incident radiation is longer ...
1
vote
1answer
37 views

Parabola black body heating

I'm having trouble figuring out why this following example of shenanigans wouldn't work. If you take a parabolic mirror (say from polished aluminium) with a magnification of M and construct it such ...
1
vote
0answers
40 views

Is the surface temperature of the sun constant?

I was just wondering that during the suns mains sequence would it maintain a constant temperature at the surface and only cool once the hydrogen in its core runs out, or is it always slowly decreasing?...
0
votes
2answers
17 views

Relationship between Planck's law and absorbed frequencies

What is the relationship between the frequencies of radiation absorbed by a material and those emitted? I know that Planck's law tells us the spectral radiance, but how does this map to those ...
0
votes
1answer
44 views

Planck's Formula and Spectral Irradiance

this might seem like a really stupid question but I have spent around 2 hours to understand this but still I was not successful so I wanted to ask. I have to calculate and ploth a graph of spectral ...
1
vote
1answer
34 views

Why can we treat normal modes of black-body radiation as thermally independent?

In my professor's lecture notes about black-body radiation, a black body modeled by an opaque hollow box with a small hole is considered. After explaining why this is a sound model for a black-body, ...
1
vote
1answer
69 views

Where exactly does energy quantisation come in for light?

Planck quantised the energy of light in order to solve the black body radiation problem. However, I am confused as to exactly what he quantised. On one hand, I have seen that he quantised the energy ...
0
votes
0answers
34 views

Proving that universe is a blackbody

How can you theoretically explain why cosmic microwave background seems to be coming from a perfect blackbody given that the universe is no longer at thermal equilibrium?
2
votes
0answers
16 views

Does same material with different colour will ended up in same temperature if both of them receive same thermal radiation?

"Every good heat radiation absorbent is a good emitter." Suppose I have two identical material with different colour, placed in different room, receiving same and only thermal radiation. My ...
0
votes
2answers
29 views

Lasers to direct waste heat?

I've been thinking about ways to cloak ships in space, since they all are warmer than their background they can be seen in the IR spectrum (given a large enough telescope). So I was thinking, could ...
5
votes
3answers
2k views

Is Sun brighter than what we actually see?

I learned from that plasma can reflect radiations of frequency less than that of its own oscillations. If so, considering the plasma in Sun's atmosphere, it should also reflect solar radiations. That ...
0
votes
1answer
35 views

Heating due to sun's radiation [duplicate]

It is commonly said that heat received from sun is due to the infrared part of solar radiation. But from Wikipedia i found that most of the energy is received from visible light. Then why do we say ...
1
vote
0answers
27 views

Light Intensity vs Power for a Small Incandescent Lamp

Today I did a quick experiment where I measured the light intensity of a small incandescent bulb for a range of voltages (0 to 31V). I also measured the current. I expected to see the light ...
0
votes
0answers
21 views

Laser Detection Paint

Does there exist a paint which if a pulsed laser of ~1500-1600nm was fired at it it would emit visible light or IR Radation (3-5 micron)? I have seen up-converting inks and paints but I can't find ...
1
vote
1answer
61 views

How much did the universe expand since recombination time? [closed]

Assuming adiabatic expansion, and a temperature at recombination time of $2700^{\circ} C$, how much has the universe expanded if the temperature today is $2.7K$? My idea is to use $\frac{dQ}{dt}=A\...
0
votes
0answers
21 views

Emissivity not accounted for in Equilibrium Temperatures of Planets

I'm trying to understand how to calculate the Equilibrium Temperatures of Planets. This is the beginning of my working for it... However, whenever I look at external sources, (like this Princeton ...
0
votes
1answer
73 views

What is Kirchoff's thermal radiation law? [closed]

Is Kirchhoff's law true even if body is not thermal equilibrium with surrounding. And according to Kirchhoff's law absorptivity is equal to the emissivity of body.
1
vote
2answers
70 views

Violation of Stefan's law when shining a light on a black body

Suppose there is a black body in a dark room and the room temperature is constant. Now a ray a light is shone upon it. Since a black body absorbs all radiation that falls upon it, it must absorb more ...
1
vote
0answers
44 views

interference of blackbody radiation with medium

We know that radiation of blackbody is unpolarized. And also its phase are random. So I thought that electromagnetic waves from blackbody wouldn't be interfered. But what if there's a medium? For ...
4
votes
2answers
125 views

Do photons exist at all possible wavelengths? [duplicate]

My question refers to Photon flux spectrum diagrams. The diagram shows the number of photons at different wavelengths. My question is whether the graph is granular or continuous. Do photons exist at ...
22
votes
4answers
8k views

Why is the Sun approximated as a black body at ~ 5800 K?

Apparently spectral solar radiation is approximated by a black body at 5800 K. The spectral black body distribution (Planck distribution) is shown below (from Incropera, Fundamentals of Heat and Mass ...
0
votes
0answers
35 views

How come we can treat space as a blackbody?

I thought that the condition to be a black body was that an object had to absorb all incident radiation without reflecting any. My understanding is, electrons in atoms absorb the incoming radiation. ...
0
votes
0answers
11 views

How to add protective enclosure around exposed thermal camera

First off, let me state that I'm not entirely sure this is the right forum for this question. This was the only section I found multiple questions pertaining to thermal imaging, however, so I thought ...
0
votes
1answer
25 views

Thermal radiations

everything having temperature above 0 k emits radiation. But those radiations depend upon temperature of the body and not on nature of the body. Why thermal radiations are not material dependent?
0
votes
0answers
37 views

How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
-1
votes
1answer
24 views

How many degrees Celsius/Fahrenheit can be reached in 1 square meter area using magnifying glasses?

The magnifying glasses are each 10 meters in diameter, their collected light is concentrated via mirrors into a 1 square meter spot. Is it possible to get a temperature higher than 2000 degrees ...
1
vote
0answers
52 views

Heat transfer on Mars

SCENARIO: I have been tasked with finding the heat transfer across a composite wall on Mars. On the left of the wall there is air maintained at Earth atmospheric conditions and room temperature (101 ...
0
votes
0answers
39 views

Black hole absorbing photons?

If a black hole has a radius that is not that much smaller than the wavelength of light emitted by the sun, and is at the same temperature, shouldn't it be able to absorb photons as well as emit them? ...
0
votes
1answer
46 views

How many $\text{watt}$ are required to obtain $500°$$\text{C}$? [closed]

I am using two $1000$ $\text{watt}$ heating elements in a cylindrical chamber of volume $7500$ $\text{cm}^3$ with a limited opening at two sides. The cylinder has a radius of $6$ $\text{inch}$. How ...
3
votes
1answer
38 views

Is thermal coupling to a too cold thermal background impossible?

In (Krauss & Starkman 1999) the authors critique (Dyson 1979), and in one section argues that in the very far future cooling will become impossible because thermal contact with the cosmic ...
1
vote
1answer
45 views

Emissivity and absorptivity relation question

This question is related to another discussion here about emissivity of bodies. What interested me is to verify what extend the wavelength between emissivity and absorption is conserved at thermal ...
0
votes
2answers
88 views

What is the reason for the emission of electromagnetic waves from the sun? [duplicate]

What is the reason for the emission of electromagnetic waves from the sun and why curve its in about the visible light is maximum?
2
votes
2answers
71 views

How much change in Earth's orbital distance to change average temperature by 1°C?

How much closer/farther would the Earth need to be to/from the Sun to effect a $1 \sideset{^{\circ}}{}{\mathrm{C}}$ increase/decrease in average temperature?
0
votes
0answers
41 views

What actually causes blackbody radiation? [duplicate]

I've spent a fair bit of time reading up on answers detailing exactly how blackbody radiation is created but I have seen two different explanations for how it is created. The Kinetic Energy (KE) of ...
0
votes
2answers
33 views

Why do we take the derivative of the number of modes with respect to frequency (Rayleigh-Jeans)

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/rayj.html We arrive at this result: $$N(\nu)=\frac{4}{3}\frac{\pi L^3\nu^3}{c^3}.$$ So now we have a function representing the number of ...
2
votes
2answers
91 views

Questions on derivation of Rayleigh-Jeans equation

So it starts by assuming a cube cavity with length $L$ that acts approximately as a black body. [note: the cube length is $a$ but I'm using $L$ instead] Standing waves are formed inside the cavity, ...
2
votes
3answers
121 views

Why is methane considered an important greenhouse gas?

Methane’s absorption bands are centered at 3.2 and 7.2 microns -- far off the peak of the Planck spectrum for a 290 K blackbody near 16 microns. Moreover, its absorption bands overlap with the water ...