Heat transfer by infrared radiation (the very basics)

  • #26
Reposted for clarity;

Drakkith, you said,

“Remember that thermal energy is the energy an object has that is stored in the random vibrations and other motions of its composite particles.”

For energy to be stored in the particles of an object is something I can begin to get my head around [I think] but for it to be stored in the vibrations of these particles is something that puzzles me. Particles are concrete things, yes? They are objects, yes? But a vibration is something that a thing does, it is not a concrete thing itself, no? A vibration is more abstract, no? This is similar to my puzzlement over particles, eg, an electron, having negative charge; does it have negative charge? Or is it negative charge?

“…the Sun serves as the main source of heat here on the Earth's surface, but plenty of heat still comes from inside the Earth.”

And that energy that’s inside the Earth didn’t come from the Sun? Where did that come from?

“No, both radiation and convection are involved (and conduction too I'm sure). There is no 'starting point'. The radiator heats the room via all three methods.”

But if we go back to when the radiator was first installed one of the three types of thermal energy transfer must have taken place first, no? We install the system and switch it on. The boiler heats the water. The hot water in the radiator heats the surface of the radiator and the surface then radiates heat energy into the air in the room, no?

“Of course (re sunbathers using foil to reflect the sunlight onto their faces).”

So they get the direct sunlight [IR radiation] from the Sun on their face and then they add to this by getting the sunlight that would otherwise hit their chest/shoulder area? Would it be significant? Or negligible?

“It reflects the IR radiation from their bodies back onto their bodies, where it is absorbed.”

So they miss out on the heat that is being reflected [due to wearing the foil blanket] but this is negligible in comparison with the heat that they would lose if the heat leaving their bodies was not reflected back into their bodies? Why don’t we see more aluminium foil clothing around in the winter? Does it have to be directly next to the skin?

“The Sun, by being at nearly 6,000 kelvin, emits strongly in the visible light region of the spectrum, but it also emits some amount of every frequency up to that point too (and a little bit beyond the visible range). This includes radio waves, microwaves, IR radiation, and a small amount of UV radiation.”

But not x-rays nor gamma rays? Also, I’ve been looking at images of the EM spectrum and most have 10^3 m next to radio waves re their wavelength. I assumed that they were therefore all around that length (a km or so) but have since read that they range from as short as 1mm to as long as a km or so; is that correct? And is 6000K equal to 5,726.85C?

“144 nanometers”

I am finding the discovery of these very small (and very large) measurements / quantities a profound experience. Nanometres, picometres, femtoseconds etc; does this mean that a metre (and a second) can be divided ad infinitum? Take a millimetre. A nanometre is one millionth of a mm, yes? So the mm can be divided into (at least) a million parts. Can we keep dividing it without end?

And a femtosecond is 10^-15 seconds, one quadrillionth of a second. That is profound. A second consisting of a thousand trillion parts / instances / units. So, a thousand trillion events (at least) can occur during one second? Can we divide the second ad infinitum also?

“It's not about what's possible, it's about what's probable.”

Very thought-provoking quote. At the risk of sounding pedantic, does this really mean it’s about what is highly probable (if something is possible it is probable (even if it has an extremely low probability), no? Also, determining what is possible is a vast task, yes?
 
  • #27
jbriggs444
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Shot gunning questions is a poor use of these forums. Doing so without proper use of quote tags is bad form. Just now I highlighted a portion of your message, clicked on "+ Quote" in the pop-up that appeared and then clicked "Insert Quotes" in the message panel down here where I am typing. Easy.

I am finding the discovery of these very small (and very large) measurements / quantities a profound experience. Nanometres, picometres, femtoseconds etc; does this mean that a metre (and a second) can be divided ad infinitum? Take a millimetre. A nanometre is one millionth of a mm, yes? So the mm can be divided into (at least) a million parts. Can we keep dividing it without end?

And a femtosecond is 10^-15 seconds, one quadrillionth of a second. That is profound. A second consisting of a thousand trillion parts / instances / units. So, a thousand trillion events (at least) can occur during one second? Can we divide the second ad infinitum also?
Our units can be divided ad infinitum. No matter how small the unit, we can divide that unit into 1000 pieces and come up with a new unit. The mathematical field of study called "real analysis" goes into that sort of thing in some depth.

The fact that we can define a unit does not ensure that it is meaningful. Units smaller than the resolution of our instruments are of little use. Quantum mechanics imposes difficulties on our abilities to measure the very small or the very brief.
 
  • #28
Drakkith
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For energy to be stored in the particles of an object is something I can begin to get my head around [I think] but for it to be stored in the vibrations of these particles is something that puzzles me. Particles are concrete things, yes? They are objects, yes? But a vibration is something that a thing does, it is not a concrete thing itself, no? A vibration is more abstract, no? This is similar to my puzzlement over particles, eg, an electron, having negative charge; does it have negative charge? Or is it negative charge?
Energy isn't stored 'in' the particles themselves, but in their motion and relative positions. Vibration is a motion and a collection of particles vibrating back and forth (kind of like a spring with two balls on the end that move back and forth) have energy due to this back and for motion. Opposite charges also have potential energy when they are separated. If allowed to, they will accelerate towards each other, turning this potential energy into kinetic energy.

And that energy that’s inside the Earth didn’t come from the Sun? Where did that come from?
Most of it is left over energy from the formation of the Earth. When the gas and dust of the early solar nebula collapsed to form the Earth it was heated to thousands of degrees, which is why the Earth was initially molten. Over the past 4.5 billion years or so the Earth has lost some of that energy, which is why the crust has cooled down and solidified. But there's still plenty of energy left, as most of the inside of the Earth is still extremely hot.

But if we go back to when the radiator was first installed one of the three types of thermal energy transfer must have taken place first, no? We install the system and switch it on. The boiler heats the water. The hot water in the radiator heats the surface of the radiator and the surface then radiates heat energy into the air in the room, no?
The point is that none of the three ways of transferring heat is more fundamental than the others, no matter how you set up your heating system.

So they get the direct sunlight [IR radiation] from the Sun on their face and then they add to this by getting the sunlight that would otherwise hit their chest/shoulder area? Would it be significant? Or negligible?
Yes, that's pretty much it. The light that hits the reflector would have hit somewhere else (perhaps somewhere else on their body or the ground) but is instead reflected onto their face. The result can be significant if the reflector is a good reflector of UV.

So they miss out on the heat that is being reflected [due to wearing the foil blanket] but this is negligible in comparison with the heat that they would lose if the heat leaving their bodies was not reflected back into their bodies? Why don’t we see more aluminium foil clothing around in the winter? Does it have to be directly next to the skin?
It has to face the person's body, yes. They would miss out on the incoming IR radiation from the surroundings, but most of the time the surroundings are at a much lower temperature than the person's body, so they would lose heat to the surroundings. The blanket keeps this from happening by reflecting that IR back onto them.

But not x-rays nor gamma rays? Also, I’ve been looking at images of the EM spectrum and most have 10^3 m next to radio waves re their wavelength. I assumed that they were therefore all around that length (a km or so) but have since read that they range from as short as 1mm to as long as a km or so; is that correct? And is 6000K equal to 5,726.85C?
The Sun doesn't emit much X-ray or gamma radiation by virtue of its temperature. However, the Sun isn't just a hot, static object. It's a ball of hot plasma and there are many different things going on near the surface that emit other types of radiation other than blackbody radiation.

I am finding the discovery of these very small (and very large) measurements / quantities a profound experience. Nanometres, picometres, femtoseconds etc; does this mean that a metre (and a second) can be divided ad infinitum? Take a millimetre. A nanometre is one millionth of a mm, yes? So the mm can be divided into (at least) a million parts. Can we keep dividing it without end?
You can indeed.

Very thought-provoking quote. At the risk of sounding pedantic, does this really mean it’s about what is highly probable (if something is possible it is probable (even if it has an extremely low probability), no? Also, determining what is possible is a vast task, yes?
Yes and yes.
 
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  • #29
From bbcbitesize (re infrared radiation);

"Because no particles are involved, radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth."

Q. I’ve heard physicists talk about ‘the vacuum of space’ not really being a vacuum, ie, it’s not the empty space we once thought it to be, rather it’s actually a ‘bubbling brew of virtual particles popping in and out of existence at every moment’; would heat transfer by infrared radiation be possible in an actual vacuum (an actual empty space), or rather across an actual vacuum (in an actual vacuum there would be nothing to transfer the heat from and to, yes?) ?
I'm guessing that you heard that heat can't be transferred across a vacuum, but then you thought, "Well how does the Sun heat the Earth across the vacuum in between?", and then you thought "Hey! I heard physicists talk about how vacuum isn't really vacuum but has virtual particles pop and an out of existence. Maybe that's how the heat of the Sun gets across the vacuum of space to the Earth!" That's all totally wrong. Heat is the transfer of kinetic energy from some molecules to other molecules, through collisions between molecules, and that obviously can't happen without molecules in between. Obviously, no heat can be transferred across the vacuum of space. It is electromagnetic waves from the Sun that interact with the Earth that increase the temperature of the Earth. You use phrases like "infrared radiation", and most people here are assuming that you are referring to infrared light which is part of the electromagnetic spectrum, but from the context, I strongly suspect that you are using the phrase "infrared radiation" to mean "heat", because you are not really clear what heat is or what infrared light is. You're not puzzled as to how we can still see the Sun despite the vacuum in between Earth and the Sun. Yet you are puzzled as to how we can feel the heat of the Sun despite the vacuum between the Earth and Sun. There is no heat being transferred from the Sun to the Earth. There are electromagnetic waves that travel from the Sun to the Earth. Heat and temperature have to do with the kinetic energy and collective motion of atoms and molecules. Infrared light is part of the electromagnetic spectrum, in the same way visible light is part of the electromagnetic spectrum. Infrared light has a longer wavelength than visible light.
 
  • #30
Drakkith
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Obviously, no heat can be transferred across the vacuum of space.
Obviously nothing, heat can certainly be transferred through a vacuum by radiation.

There is no heat being transferred from the Sun to the Earth.
Of course there is. Heat transfer via radiation is one of the three modes of heat transfer, the other two being conduction and convection.
 
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  • #31
davenn, you said,

“The big bang didn't have a point origin, as in an explosion and expanding out - there's been many threads on PF on the currently understood understanding of this .. try some searching - Drakkith and phinds are 2 common contributors.”

Thanks. I’m currently studying this, and will check out Drakkith and phinds’ contributions.

“You don't need to go any further back than the solar nebula to find the source of the internal heat in any of the planets.”

With respect, I disagree. If I’ve understood you correctly the solar nebula only goes back to around 4.6 billion years ago so, even if we accept that the Big Bang is complex and often misunderstood, the solar nebula itself had a source of heat, and that in turn had a source, all the way back to the conditions of the Big Bang (whatever they might be); so the ultimate source of the internal heat in any of the planets is not the solar nebula.
 
  • #32
davenn
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With respect, I disagree. If I’ve understood you correctly the solar nebula only goes back to around 4.6 billion years ago so, even if we accept that the Big Bang is complex and often misunderstood, the solar nebula itself had a source of heat, and that in turn had a source, all the way back to the conditions of the Big Bang (whatever they might be); so the ultimate source of the internal heat in any of the planets is not the solar nebula.
That is incorrect

As I said, for the internal heat of the planets and the starting nuclear reactions in the core of the sun.... the solar nebula is the direct source
The gas and dust etc that made up the solar nebula was quite cool before it condensed and heated up under the influence of gravity

You are trying to make it more complex than it is or it needs to be


Dave
 
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