# How does light carry heat

Discussion in 'Physics & Math' started by Magical Realist, Mar 3, 2017.

1. ### Magical RealistValued Senior Member

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More specifically, what in the nature of massless photons allows them to carry the heat of one mass of incandescent moving atoms to another mass? Are the photons vibrating? Is this what the lightwave is? Why does the heat in light not cool off in its transmission thru space?

3. ### James RJust this guy, you know?Staff Member

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Photons carry energy. A hot object emits photons of various energies, which propagate outwards from the object. When they hit another object, the photons can be absorbed, giving up their energy to the second object. This causes the atoms/molecules etc. to giggle around, rotate, vibrate etc., with the result that the second object heats up.

The light wave picture is similar. All waves transfer energy from place to place - e.g. a water wave brings in energy from the ocean and dumps it on the beach. Light waves are the same. When a light wave hits an object, it can cause electrical charges in the object to move around. Those charges, in turn, tend to transfer their energy to other particles, atoms, molecules etc, as described in the paragraph above.

Photons don't "cool off" in transit because they are not interacting with anything as they travel. There's no way for them to lose energy.

There are only three ways to transfer heat from one object to another: conduction (contact), convection (due to a physical flow of substance from one place to another) and radiation. If none of those methods is available, heat transfer cannot occur.

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5. ### Magical RealistValued Senior Member

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What kind of energy? Can we measure it? Isn't a photon energy already? What is physically different about a photon with more energy from one with less energy? Is this same energy correlated to brightness?

Last edited: Mar 3, 2017

7. ### DaveC426913Valued Senior Member

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Yes. Different tools will detect different frequencies: radio antennae, retinae, photographic film, etc.
Photons are the carriers of electromagnetic energy.
Its wavelength/frequency.
High freq / short wavelength = high energy. (X-rays, cosmic rays)
Low freq / long wavelength = low energy (radio waves)
No. Brightness (or intensity) at a given frequency would be determined by number of photons per unit area.

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8. ### Q-reeusValued Senior Member

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Just out of interest, what kind of basic theory did you learn before becoming iirc a bona fide US navy radar technician?

9. ### Magical RealistValued Senior Member

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What does radar have to do with how photons carry heat?

10. ### Magical RealistValued Senior Member

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So you're saying the heat energy carried by photons is the same as electromagnetic energy?

So the wavelength of the photon determines the amount of heat it carries?

11. ### DaveC426913Valued Senior Member

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I'm certain they would have drilled into any radar tech not to stand in front of the emitter. It would cook them.

Photons don't "carry" heat; their energy can be converted to forms that are experienced as heat.
Since higher frequency photons have more energy per unit, a given intensity of EMR will transfer more energy to a target, which may manifest as more heat.
Heat is not a simple subject. For example, if the object is an insulator or reflector, the heat conversion may be poor, even if there is plenty of energy.

Last edited: Mar 4, 2017
12. ### Magical RealistValued Senior Member

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[rey-dahr]
Spell Syllables
See more synonyms on Thesaurus.com
noun
1.
Electronics. a device for determining the presence and location of an object by measuring the time for the echo of a radio wave to return from it and the direction from which it returns.

Doesn't explain how heat is transmitted by photons.

So it's frequency of the photon now not it's wavelength?

Won't more photons per unit area produce more heat?

Last edited: Mar 4, 2017
13. ### DaveC426913Valued Senior Member

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er...

f = 1/w
w=1/f
They're two sides of the same coin.

Heat is not transmitted by photons; energy is transmitted by photons.
Energy can be converted to what we experience as heat.

Ultimately, yes. Because more photons per unit area means more energy per unit area, which can be experienced as heat.

14. ### RandwolfIgnorance killed the catValued Senior Member

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MR, does radar transmit heat? If so, how?

15. ### Magical RealistValued Senior Member

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That's my question. Refer to the OP.

16. ### Magical RealistValued Senior Member

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So this energy isn't heat but turns into heat when it hits matter? How can that happen?

17. ### RandwolfIgnorance killed the catValued Senior Member

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I read the OP - "How does light carry heat?" Do you know the answer to my question? Here it is again: "does radar transmit heat? If so, how?" If you have no clue just say so. I merely thought you had some level of training in this area, no?

18. ### DaveC426913Valued Senior Member

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Heat is a measurement of the movement of a collection of atoms.
Photons are absorbed by the atoms, giving them a kick, which makes them move. Lots of atoms with lots of kinetic energy is what we call heat.

19. ### Magical RealistValued Senior Member

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Radar is made of photons. I'm being told they carry energy but not heat. So according to the posters here, radar doesn't transmit heat.

20. ### Magical RealistValued Senior Member

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How do massless particles give them a "kick"?

21. ### DaveC426913Valued Senior Member

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Because they are energy.
A photon is a quantized unit of energy. When an atom absorbs it, it can manifest in other forms such as kinetic energy.

22. ### DaveC426913Valued Senior Member

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There is some glossing over happening here. This is a whole college course. We're giving you what we can in paragraph form.

"Transmitting heat" is a simplistic description. To go into it in detail requires understanding the intermediate stages of energy conversion.

Radar transmits energy. Energy can be converted to heat.

23. ### Magical RealistValued Senior Member

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Doesn't it require mass to exert a force on the atoms? Or maybe energy and mass are the same thing?