All Questions
57 questions
6
votes
2
answers
489
views
What is the purpose for the blackbody radiation graph to be graphed using the below parameters?
If you observe the above graph, for y axis, "intensity per wavelength" is used as the parameter. I am aware we use "per wavelength" because it is hard to measure and graph isolated ...
0
votes
2
answers
79
views
Regarding the absorption property of a blackbody
Consider a blackbody of surface area $S_b$ and at temperature $T_b$. It is placed inside an evacuated chamber (to neglect all the effects of convection), with walls of chamber at temperature $T_c$ and ...
- 393
1
vote
1
answer
50
views
Radiation power emmited by a material with two different temperatures [closed]
Let's consider a cylindrical sample of a solid material surrounded by air. From $0 \leq r \leq r_1$ the temperature of the material is $T_1$ and from $r_1 < r \leq R$, $T=T_0$ which is also the ...
- 33
0
votes
1
answer
100
views
Can a body be in thermal equilibrium at a different temperature from surroundings?
As per my knowledge bodies attain constant temperature (thermal equilibrium with surroundings) when they absorb and emit energy at equal rates.
Let us say temperature of surroundings is T1.
We have a ...
- 1
2
votes
0
answers
33
views
How did Kurlbaum and others measure the intensity of each wavelength to get blackbody radiation curve?
In 1900 Plank was faced with data that didn't agree with the Plank-Wien law. This data that plots different temperature curves - wavelength on the horizontal and intensity on the vertical (or rather ...
- 21
21
votes
6
answers
5k
views
How does fire heat air?
I understand that fire heats its surroundings via conduction, convection and radiation. I've read that conduction is nearly irrelevant to this process as air is a poor heat conductor. In descriptions ...
- 313
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
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
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
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
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
0
votes
1
answer
179
views
How was the black body intensity vs wavelength (or frequency) radiation curve historically produced?
I have read that Wilhelm Wien gave his formula to match the radiation curve of a black body as shown in the picture; which works well in high frequency region. Another formula by Rayleigh-Jeans is ...
1
vote
1
answer
205
views
Black body side of the Moon
A few closely related questions regrading the Moon thermodynamics:
The Moon is clearly not a black body, as it reflects a great deal of radiation incident on it. Still, it does absorb some radiation ...
- 65k
1
vote
1
answer
1k
views
Solar constant and Energy received by the Earth
I've been reading about black body radiation and I came across the topic of solar irradiance.
If we consider the sun to be a perfect blackbody, then the intensity of the solar radiation at a distance ...
- 1,853
0
votes
1
answer
665
views
Calculate the heat energy absorbed by an object without knowing its specific heat?
Say we know the mass of the object, the surface area, the temperature change, the time taken for the temperature to change and that all heat exchange happened through radiation
Can the stefan boltzman ...
1
vote
0
answers
115
views
It seems a stove top coil / burner element defies black body radiation
Most glow charts say that incipient red Heat is 1000 Fahrenheit or 540 Celsius , and bright orange is just shy of 2,000 Fahrenheit or 1093 celsius . But my fluke thermocouple rated at over 2,000 ...
9
votes
4
answers
3k
views
Can we feel heat in outer space? [duplicate]
Is there air outside of earth atmosphere? If not, could we feel heat coming from sun?
- 93
0
votes
1
answer
89
views
Entropy Change in Radiation and Convection
When a system loses it's internal thermal energy by emitting radiation or by convection what is change of the systems entropy mathematically?
I saw this question's answers for radiation only but still ...
user310884
1
vote
0
answers
38
views
Objects react different to different types of radiation
I am a bit confused about the different types of radiation and how objects react to it. In class, the professor showed us a cube with white, black and reflecting sides (the Leslie cube). Inside the ...
2
votes
1
answer
605
views
What truly is spectral blackbody emissive power?
I read that a blackbody at a temperature T, would emit thermal energy in the form of Electromagnetic waves. This thermal energy emitted per unit the area per unit time is called blackbody emissive ...
- 541
1
vote
1
answer
569
views
Thermal radiation vs emission spectra of gases
I am a high school student and I am very confused in absorption and emission spectrum of gases, for e,g take hydrogen at room temperature for simplicity, so that we can talk in terms of Bohr's model ...
- 470
1
vote
2
answers
110
views
What is black-body equivalent of UV part of solar spectrum?
If all non-UV light was filtered from sunlight, does this approximate a different type of black body radiation? Regular sunlight has a black-body temperature of 5777 K.
This is in relation to the ...
- 23
1
vote
2
answers
629
views
What is thermal radiation on a molecular level? [duplicate]
I’ve recently been scouring my Finnish high school level textbooks and online physics forums for an answer to the following question: ”How is thermal radiation created on a molecular level?” or ”What ...
- 51
1
vote
2
answers
168
views
What was the question to which Max Planck gave an explanation and how is it related to blackbody radiation?
Quoting from my text book - "several attempts were made to predict intensity as a function of temperature/wavelength". This line was preceded by the explanation for blackbody radiations and ...
- 185
4
votes
1
answer
1k
views
What does it mean when we say "a blackbody is in thermal equilibrium with it's surroundings"?
Quoting from my text book - "a blackbody is a perfect radiator of radiant energy. It is in thermal equilibrium with it's surroundings and radiated as much energy per unit area as it absorbs from ...
- 185
1
vote
1
answer
108
views
Understanding Kirchhoff's radiation law calculation from Weinberg's book
From second edition of Weinberg's Lectures on Quantum Mechanics,
Consider an enclosure whose walls are kept at a temperature $T$, and suppose that the energy per volume of radiation within this ...
- 1,314
0
votes
1
answer
211
views
Line emission spectrum of gases and solids [duplicate]
when a gas like hydrogen is heated it shows discrete line in its emission spectrum but in case of solids we see a continuous spectrum why it is so???i have searched it on internet and some people says ...
- 31
0
votes
1
answer
213
views
Temperature rise due to thermal radiation? [closed]
Consider a cylindrical metal rod of a certain diameter and length and a rectangular plastic plate of certain dimensions. The rod is suspended in air above the plate at a certain distance from the ...
- 183
2
votes
1
answer
83
views
Drag force on mirror immersed in blackbody radiation
In Einstein's "On The Present Status of the Radiation Problem" he mentions a thought experiment where A mirror of mass $M$ and area $A$ that is perfectly reflective in the range of frequencies $\nu$ ...
- 649
0
votes
1
answer
219
views
What are all the types of radiation emitting from the Earth or an arbitrary mass in space?
I'm interested in what forces collectively act upon a body in space (obviously radially, so they usually cancel) due to pressures caused by emitted radiation (of any type, strength, "size"). Can you ...
- 293
1
vote
1
answer
704
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 ...
- 135
0
votes
1
answer
588
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$$...
- 126
1
vote
2
answers
374
views
How does the heat capacity of an object come into play in thermal radiation?
So say there's a cube in space acting as a blackbody.
Each side is 2 metres. Initial cube temperature is 400 Kelvin. Mass is 15 kg.
Say the heat capacity is 500 J/kgK. How would that affect thermal ...
- 31
0
votes
1
answer
53
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, ...
- 43
1
vote
1
answer
42
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 ...
- 607
4
votes
1
answer
3k
views
Do conventional ovens heat by thermal conduction or radiation?
I am curious which energy transfer mechanism dominates in a conventional oven, thermal conduction or thermal radiation?
A naive guess would be that early on, when the food is still cold, the heat ...
- 15.8k
2
votes
1
answer
230
views
Received heat by radiation from the surroundings
In Stefan's law, the radiated energy of a black body with a temperature of $T$ is
$q = \sigma T^4$
Where $\sigma$ is Stefan's constant.
However, if it is surrounded by a medium then the net radiated ...
- 77
4
votes
5
answers
4k
views
How hot would it get, if you put a greenhouse inside of a greenhouse inside of a greenhouse (like those Russian matryoshka dolls)?
I remember it being quite hot in the last green house I went inside, and I'm imagining how hot you can make it has something to do with the difference between the temperature inside and outside, ...
- 2,623
0
votes
1
answer
174
views
Are these statements about different emissivities correct?
I'd like to verify if my concluded statements regarding different emissivities are correct or not. And if not, why.
1
Two objects, one with an emissivity of 1 (object A) and one with a very low ...
- 471
3
votes
1
answer
256
views
Most efficient mechanism for heating air
I was read about small scale ion treatment which uses heats to high temperatures, would this be scalable and if so would there be any more efficient methods.
In summary, if you wanted to heat large ...
- 69
4
votes
3
answers
3k
views
Blackbody radiation Vs thermal radiation
I am having problems connecting the following 3 concepts:
Blackbody radiation and thermal radiation1.
Optically thin and optically thick mediums.
Local thermodynamic equilibrium (LTE) and ...
2
votes
1
answer
3k
views
Limitations of Newton's law of cooling?
My textbook states the following:
"One of the limitations of Newton's law of cooling is that this law holds true only if the temperature of the surroundings remains constant throughout the cooling ...
user106570
3
votes
2
answers
665
views
How does radiative cooling between the earth and space work?
On a chilly (but above freezing) temperatures on a clear night, you can freeze water outside because of radiative cooling.
By what mechanism do warm bodies on earth actually lose heat to space?
...
- 213
2
votes
2
answers
3k
views
Emissivity and Final Temperature of a Black and White object
Objects can be categorized as blackbodies (emissivity $\epsilon = 1$), grey bodies (emissivity $\epsilon < 1$) and white bodies (emissivity $\epsilon = 0$).
If we placed two objects (identical ...
- 93
2
votes
0
answers
969
views
Carnot Engine- Cold Reservoir is a black body [closed]
My question:
A satellite powered by a Carnot engine uses heat from a nuclear reactor at a fixed temperature T0. Heat is released into outer space via thermal radiation emitted by a set of fins at ...
- 21
2
votes
1
answer
16k
views
Highest temperature possible to achieve using magnifying glass and sunlight [duplicate]
Temperature of the surface of the sun is about 5750K. Can you heat an object to more than 6000K using magnifying glass and sunlight? According to second law heat cannot be transferred from colder to ...
- 345
1
vote
1
answer
82
views
Understanding view-/formfactor for radiation with a specific example
There is radiation coming from a point source (black body).
How much of the total emitted energy (from the point source) hits a spherical surface given by $\phi = 0 - \pi $ and $\theta = 0 - \pi/2 $?
...
1
vote
1
answer
100
views
Measured temperature (thermometre set to emissivity of 1) of smooth surface too high or to low?
We want to measure the temperature of a smooth flat surface with a thermometre based on absorption of thermal rays.
The emissivity setting of the thermometre is set to 1 (same as a black surface), ...
1
vote
1
answer
8k
views
Does tin foil keep heat out?
For example, if i were mailing a box of chocolates and lined the inside of the box with foil, then wrapped the chocolate in bubble wrap and placed it inside the foil lined box, would the box heat up ...
- 11
2
votes
1
answer
3k
views
How does heat travel?
How does heat travel? I have two competing thoughts here!!
Firstly some form of atomic/molecular process liberates a photon in the infrared region of the spectrum which is detected as heat by a ...
user58536