# How is heat carried by photons?

Discussion in 'Physics & Math' started by Saint, Apr 27, 2020.

1. ### SaintValued Senior Member

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Can photon just disappear in the air? since it is mass less, it does not need to follow conservation of mass law.

3. ### Janus58Valued Senior Member

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It is "mass-less" in that that it has no "rest" mass. However, it still has energy and momentum, both of which are conserved. ( and "mass" is no longer, by itself, considered conserved, but it is the total mass-energy that is conserved.)
So for example, an electron and positron ( each with a rest mass) can join and produce two "mass-less" photons. It is just that the rest mass of the particles is converted to energy.
And under the right circumstances, two energetic enough photons can join to form an electron-positron pair.

5. ### SaintValued Senior Member

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Assume I am in a room which no light can escape from any gap.
I turn on the lamp, it is bright filled with light - many photons.
When I turn off the lamp, it is completely dark, where did the photons go?

7. ### Janus58Valued Senior Member

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Absorbed by the material of the walls, and converted into another form of energy. The walls would re-radiate that energy as photons again. These photons would be of lower frequency, and not in the visible range of the spectrum.

8. ### SaintValued Senior Member

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if all walls are made of mirror?

9. ### Janus58Valued Senior Member

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Mirrors are not 100% efficient. A standard mirror could be 90-95% efficient (5-10% of the light hitting it is absorbed and not reflected)
At 95%, after just 100 reflections the total light will have dropped to under 1% (if the initial light source was a 100w bulb, it would seem like the room was lit by a 1 w bulb.
If the room is 5 meters across, 100 reflections will occur in just 1/60,000,000 of a sec.
In another 1/60,000,000 of a second, the light in the room will have dropped to the equivalent of a 0.1 watt bulb.
A human's ability to notice a change in lighting is measured is thousands of a second, which is thousands of times longer than the time it takes for the light level to drop below the level that the eye can sense. So even though the light level is decaying over time and multiple reflections, it would still appear to blink out instantly to us.
Even if you went to the expense of getting really high quality specially designed mirrors of 99.9% efficiency, the light would still drop below eye sensitivity levels faster than your eyes could detect.

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It's a real shame that Saint continues to ask these questions, and then when given detailed valid answers, simply then decides to sneak off, like a thief in the night.......no thanks, no recognition at all. The fact that the detailed valid answers seem to invalidate the not so hidden agenda she approaches science with, says a lot about this thief in the night.

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

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I've never seen the word "Thankyou" posted by Saint. It's why I no longer answer his questions in his "Help with English" thread, and I'm rapidly losing interest in answering any of his other questions either.

wegs and exchemist like this.
12. ### zgmcRegistered Senior Member

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The thankless questions in this thread led to a cool link about black holes. Plus, the detailed explanations will help others with the same questions or just the OP. Thanks guys!

13. ### wegsMatter and Pixie DustValued Senior Member

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I stopped when he posted words on that thread (or it might have been another word thread) that are vulgar, “pretending” to not know their meaning.

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Probably because he was shamed into it?
In the clocks run slower when speeding thread.

15. ### Write4UValued Senior Member

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Oh well, who pays attention to details ?