Behaviour of photons in a 'sealed room'

  • #1

Main Question or Discussion Point

Hi could some one help me understand the relationship between photons and a sealed room to which no photons can escape. Say there is a light bulb in the room producing photons that are all the visible spectrum and the wall paper is made of beta carotine from carrots so some of the photons are absorbed and the orange ones are emitted.

Why is it when the light switch is turned off it all goes dark and does not give an orange light to the room as there are only orange photons in the room. Where do these orange photons go?

Im just starting on this so its probably a crazy question..!
 

Answers and Replies

  • #2
tiny-tim
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Welcome to PF!

Hi Neil! Welcome to PF! :smile:
Why is it when the light switch is turned off it all goes dark and does not give an orange light to the room as there are only orange photons in the room. Where do these orange photons go?
They do keep going when the light is switched off …

but every time they bounce off a wall, they run a risk of being absorbed :redface:

in say 0.1 seconds, for a standard-sized room, they bounce so many times that they're virtually all absorbed! :biggrin:
 
  • #3
Thanks. But say the wall is coated in something that will not absorb these orange wavelength photons. I thought that the idea was that materials only absorb certain wavelengths of photons and kind of chuck back photons that it cannot absorb - and this is what gives things their colour.

Is this not true? I had in mind some kind of 'vacuum flask' that would store light indefinetly because the photons were of a wavelength that could not be absorbed by the material.
 
  • #4
tiny-tim
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I had in mind some kind of 'vacuum flask' that would store light indefinetly because the photons were of a wavelength that could not be absorbed by the material.
Well, a perfect mirror should do that.

But I don't know how perfectly reflective a mirror can be.
 
  • #5
Oh ok like a fibre optic cable. so if you packed this mirror lined flask full of photons it would be like a light store for use at a later date as a torch. Not sure what maximum photon density you can get in a space is. Thanks.
 
  • #6
There's no limit to the number of photons that can occupy the same space (or if there is, it is not about to be achieved in currents labs), but even if you have 99.9999% reflection, light won't last a second in a hand-sized flask (and adding extra decimals is exponentially difficult).
 
  • #7
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Dr lots o watts is right.

But if you could somehow do it, the box would be getting filled with more and more yellow light. It would eventually get so much yellow light in it that it would destroy the lamp by burning it up.

If you could do it with an indestructible lamp, it would eventually get so bright inside with yellow light that you would be instantly killed by it the moment you opened the door.
 
  • #8
Dear NeilWallace I understand what you say but just read this - matter is condensed,passive,inertial or lazy :-) form of energy and light is energy.
Why don't you employ pair annihilation to get high frequency light.
 
  • #9
'pair annihilation..' I'd have to look into that as I dont understand it and figure its not something you can try at home.. :)

I think I understand the limitations of the light store in a flask idea without a 100% reflective surface it would not work and 100% reflective surfaces do not appear to exist.

I thought if you switched the light on in the flask for 10 minutes and had some sort of valve that limited the number of photons that could leave the flask to be the same rate of photon emission of the light bulb then theoretically you would have 10 minutes of light to light the room at a later date.

I think Ill stick to energy saving light bulbs.. :)
 
  • #10
Ha!Ha! :-)) Yeah! NeilVallace its really tough for performing Pair annihilation at home.I've to shell out billions of dollar and spend terawatts of energy just to get mere 1 kJ of energy from the experiment.The idea of power saving CFL is better. :-))
 

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