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Offline CZARCAR

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?what is radiant heat?
« on: 29/01/2011 11:05:53 »
the side of a hot woodstove "radiates". Is this similar to a flashlight shining outwards from the side of the stove?= the radiant heat projects horizontally, unaffected by gravity except for when it hits air molecules,dust,etc?   thanx


 

Offline Geezer

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?what is radiant heat?
« Reply #1 on: 30/01/2011 08:23:28 »
Pretty much. It's electromagnetic radiation at frequencies below the visible spectrum, sometimes referred to as infrared radiation, or, if you prefer, a stove is spewing out energy in the form of lots of photons that humans can only see with the benefit of infrared detectors. If you look at a stove through a night vision scope, it will appear to be white hot.
 

Offline CZARCAR

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?what is radiant heat?
« Reply #2 on: 01/02/2011 10:25:22 »
So the stove inside a glass enclosure insulated by a vacuumn between 2 layers of glass? or a vaumn is ineffective insulation against radiant heat?
 

Offline Geezer

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?what is radiant heat?
« Reply #3 on: 01/02/2011 20:25:50 »
So the stove inside a glass enclosure insulated by a vacuumn between 2 layers of glass? or a vaumn is ineffective insulation against radiant heat?

It doesn't seem to stop it from travelling from the Sun to the Earth.
 

Offline CZARCAR

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?what is radiant heat?
« Reply #4 on: 16/02/2011 15:07:27 »
black radiates heat better as well as absorbs better? seems contradictory?
 

Offline Joe L. Ogan

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?what is radiant heat?
« Reply #5 on: 16/02/2011 19:05:52 »
black radiates heat better as well as absorbs better? seems contradictory?
Is that really true?  Why?  Thanks for comments.  Joe L. Ogan
 

Offline Bored chemist

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?what is radiant heat?
« Reply #6 on: 16/02/2011 19:42:54 »
It's true. It has to be or you could break the laws of energy conservation.
 

Offline Joe L. Ogan

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?what is radiant heat?
« Reply #7 on: 16/02/2011 20:20:42 »
What if the surrounding area is very hot?  Thanks for comments.  Joe L. Ogan
 

Offline Joe L. Ogan

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?what is radiant heat?
« Reply #8 on: 16/02/2011 21:11:15 »
Isn't the real reason that White is sort of neutral in the process?  It does not absorb as much radiant heat so it does not have as much to radiate?  In other words, it isn't that black radiates heat better than white but it has a lot more of it to work with?  Thanks for comments.  Joe L. Ogan
 

Offline Bored chemist

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?what is radiant heat?
« Reply #9 on: 17/02/2011 20:44:29 »
It's a bit more general than that ( I was going to say "it's a grey area" but I'd sooner leave the awful puns to other people)

http://en.wikipedia.org/wiki/Kirchhoff's_law_of_thermal_radiation

 

Offline bardman

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?what is radiant heat?
« Reply #10 on: 18/02/2011 05:05:13 »
Exactly, black objects absorb light in the visible spectrum. This why they are black, they reflect no light. They do not necessarily absorb light in the infrared range better, though some might. The light it absorbs energizes the object and thus it gives off heat. Were it hot enough, it would also give off light in the infrared range through a process called blackbody radiation. All objects radiate a spectrum of light based on their temperature. The suns spectrum peaks in the visible range, which is why we have the sunlight we can see.
 

Offline Joe L. Ogan

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?what is radiant heat?
« Reply #11 on: 10/03/2011 18:33:54 »
I am intrigued by the fact that Radiant heat from the sun travels at the speed of light.  Where does it all go to?  If it does not strike an object, it just keeps travelling.  Does it stop at the edge of space or does it just gradually dissipate?
Thanks for comments.  Joe L. Ogan
 

Offline burning

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?what is radiant heat?
« Reply #12 on: 10/03/2011 19:33:01 »
I am intrigued by the fact that Radiant heat from the sun travels at the speed of light.  Where does it all go to?  If it does not strike an object, it just keeps travelling.  Does it stop at the edge of space or does it just gradually dissipate?
Thanks for comments.  Joe L. Ogan

Well radiant heat is energy transfer by electromagnetic radiation.  It pretty much by definition has to travel at the speed of light.

There isn't an edge of space, and the light will indeed keep going until it runs into something.  If by dissipate you mean that the energy disappears somehow, that doesn't happen.  But the energy gets spread out over a greater and greater area the further away from the sun you get (the well known inverse square law).  Space is big and empty enough that the radiant heat transfer from all the stars in the universe outside of our solar system is pretty much negligible, at least in terms of helping keep Earth at a survivable temperature.
 

Offline techmind

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?what is radiant heat?
« Reply #13 on: 21/03/2011 00:06:04 »
So the stove inside a glass enclosure insulated by a vacuumn between 2 layers of glass? or a vaumn is ineffective insulation against radiant heat?

Conceptually, yes. The vacuum is no insulation against radiant heat.
In practice, common glass though transparent to visible light, tends to absorb a lot of IR. You might be able to use very thin mica windows, or Calcium-Fluoride (or something) if you wanted to do the experiment for real...
 

Offline yor_on

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?what is radiant heat?
« Reply #14 on: 23/03/2011 02:47:13 »
I am intrigued by the fact that Radiant heat from the sun travels at the speed of light.  Where does it all go to?  If it does not strike an object, it just keeps travelling.  Does it stop at the edge of space or does it just gradually dissipate?
Thanks for comments.  Joe L. Ogan

Well radiant heat is energy transfer by electromagnetic radiation.  It pretty much by definition has to travel at the speed of light.

There isn't an edge of space, and the light will indeed keep going until it runs into something.  If by dissipate you mean that the energy disappears somehow, that doesn't happen.  But the energy gets spread out over a greater and greater area the further away from the sun you get (the well known inverse square law).  Space is big and empty enough that the radiant heat transfer from all the stars in the universe outside of our solar system is pretty much negligible, at least in terms of helping keep Earth at a survivable temperature.

But what about the expansion?

If I think of light as waves propagating, will the expansion stretch it? And how far can you stretch a wave before it becomes a straight line? Even if I assume that the wave is infinitely bent so there always will be just a slight 'bendedness' left :) Isn't the universe said to be infinitely large?

So who will 'win'?
Ahem :)
 

Offline Geezer

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?what is radiant heat?
« Reply #15 on: 23/03/2011 19:11:28 »
I am intrigued by the fact that Radiant heat from the sun travels at the speed of light.  Where does it all go to?  If it does not strike an object, it just keeps travelling.  Does it stop at the edge of space or does it just gradually dissipate?
Thanks for comments.  Joe L. Ogan

Well radiant heat is energy transfer by electromagnetic radiation.  It pretty much by definition has to travel at the speed of light.

There isn't an edge of space, and the light will indeed keep going until it runs into something.  If by dissipate you mean that the energy disappears somehow, that doesn't happen.  But the energy gets spread out over a greater and greater area the further away from the sun you get (the well known inverse square law).  Space is big and empty enough that the radiant heat transfer from all the stars in the universe outside of our solar system is pretty much negligible, at least in terms of helping keep Earth at a survivable temperature.

But what about the expansion?

If I think of light as waves propagating, will the expansion stretch it? And how far can you stretch a wave before it becomes a straight line? Even if I assume that the wave is infinitely bent so there always will be just a slight 'bendedness' left :) Isn't the universe said to be infinitely large?

So who will 'win'?
Ahem :)


I think in this case it's best to think of photons that travel until they encounter matter, which could take a very long time.
 

Offline CZARCAR

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?what is radiant heat?
« Reply #16 on: 23/03/2011 21:58:56 »
whoa!
I am intrigued by the fact that Radiant heat from the sun travels at the speed of light.  Where does it all go to?  If it does not strike an object, it just keeps travelling.  Does it stop at the edge of space or does it just gradually dissipate?
Thanks for comments.  Joe L. Ogan

Well radiant heat is energy transfer by electromagnetic radiation.  It pretty much by definition has to travel at the speed of light.

There isn't an edge of space, and the light will indeed keep going until it runs into something.  If by dissipate you mean that the energy disappears somehow, that doesn't happen.  But the energy gets spread out over a greater and greater area the further away from the sun you get (the well known inverse square law).  Space is big and empty enough that the radiant heat transfer from all the stars in the universe outside of our solar system is pretty much negligible, at least in terms of helping keep Earth at a survivable temperature.

But what about the expansion?

If I think of light as waves propagating, will the expansion stretch it? And how far can you stretch a wave before it becomes a straight line? Even if I assume that the wave is infinitely bent so there always will be just a slight 'bendedness' left :) Isn't the universe said to be infinitely large?

So who will 'win'?
Ahem :)


I think in this case it's best to think of photons that travel until they encounter matter, which could take a very long time.
radiant heat off the side of the stove hits air molecules . radiant from sun will intercept other waves?  then what?
« Last Edit: 23/03/2011 22:01:37 by CZARCAR »
 

Offline Geezer

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?what is radiant heat?
« Reply #17 on: 23/03/2011 23:28:22 »
Photons emitted by the Sun don't intercept anything, because there is nothing to intercept. Space is a vacuum. (There are actually some molecules floating around in space, but not very many.)
« Last Edit: 23/03/2011 23:34:59 by Geezer »
 

Offline CZARCAR

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?what is radiant heat?
« Reply #18 on: 23/03/2011 23:53:03 »
Photons emitted by the Sun don't intercept anything, because there is nothing to intercept. Space is a vacuum. (There are actually some molecules floating around in space, but not very many.)
so what happens if 2 photon waves collide headon?
 

Offline Geezer

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« Reply #19 on: 24/03/2011 03:25:20 »
Photons emitted by the Sun don't intercept anything, because there is nothing to intercept. Space is a vacuum. (There are actually some molecules floating around in space, but not very many.)
so what happens if 2 photon waves collide headon?

Nothing.
 

Offline imatfaal

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?what is radiant heat?
« Reply #20 on: 24/03/2011 14:08:33 »
Photons emitted by the Sun don't intercept anything, because there is nothing to intercept. Space is a vacuum. (There are actually some molecules floating around in space, but not very many.)
so what happens if 2 photon waves collide headon?

Nothing.

Can you not get some forms of scattering interaction via virtual particle pair interactions in QED?  Classical there is no bouncing billard-ball scattering, but I think there are possibilities in non-classical theory
 

Offline Geezer

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?what is radiant heat?
« Reply #21 on: 24/03/2011 19:24:42 »


Can you not get some forms of scattering interaction via virtual particle pair interactions in QED?  Classical there is no bouncing billard-ball scattering, but I think there are possibilities in non-classical theory


I'm not sure  :D. I suppose the possibilities are annihilation or combination.

Annihilation seems unlikely as it would mean the photons' energies would no longer exist. Combination would seem unlikely as it would require the formation of a new photon with an energy that was the sum of the energies, and therefore, at a higher frequency.

Mind you, if the combination thing works, it will be a great source of useful energy. We would be able to convert infrared radiation into UV light and use it to power photocells.

(I expect JP to trash my answer  ;D)
 

Offline yor_on

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?what is radiant heat?
« Reply #22 on: 25/03/2011 00:06:08 »
How would they do it Imatfaal?

Do you mean that assuming that they are inside Planck time that would be noticeable?
It was a new one to me :)
 

Offline imatfaal

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« Reply #23 on: 25/03/2011 12:38:06 »
I think photons can scatter by exchange of virtual particles (a pair of charged/anti-charged fermions).  QED scattering with exchange of electron positrons has been well theorised and i think observed in high powered electron/proton colliders, both particles emit a photon before collision which then scatter off each other by exchange of virtual elctron/positron.  QCD research is also looking at it because when the fermion pair mentioned above is a quark/anti-quark then very precise reactions can be determined. - but that's about the limit that I can type without recourse to references.  I will expound later
 

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?what is radiant heat?
« Reply #23 on: 25/03/2011 12:38:06 »

 

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