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Yes, even though i can consider myself knowing general stuff about cosmology and astronomy there is something i don't quite get.
If you are in a closed room where there is no glass for light to pass or no windows and there is a lamp at the wall. When you switch it on it produces photons right? The thing we call light. When you switch it off everything goes black again. If those particles can't go anywhere because light has nowhere else to go or pass through why does room seem dark after i switch it off?
I believe there is something i don't quite know to understand this because it bugs my mind for a few days lol. Answers from physics majors are appreciated.
 
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17006 Posts
A bit of an aside, but have you tried the people over at reddit.com/r/askscience ?
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Aren't they just absorbed by the walls as heat ?
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On May 01 2012 14:20 Empyrean wrote:
A bit of an aside, but have you tried the people over at reddit.com/r/askscience ?
No i didn't try that, i don't quite understand how reddit works too but will check it out thanks.
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On May 01 2012 14:22 Bengui wrote:
Aren't they just absorbed by the walls as heat ?
Would anything change if the walls are isolated?
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They're absorbed by the walls and converted into kinetic energy in the constituent particles, i.e. the temperature rises. Sometimes they're reemited at equal energies (mirrors) or lower energies (infrared etc).
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Pretty sure the light turns into heat.
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As a high school AP Chem student I probably am not qualified to answer this, but I believe that the photons are absorbed by the atoms of the room, exciting the electrons in the atoms and therefore being converted to heat.
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Thank you for the answers guys.
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On May 01 2012 14:27 Aelfric wrote:Show nested quote +On May 01 2012 14:22 Bengui wrote:
Aren't they just absorbed by the walls as heat ? Would anything change if the walls are isolated?
No, when the photons are absorbed by the walls it does not matter whether the walls are connected to anything. The energy can also be absorbed by any atoms or molecules floating between the walls as kinetic energy (movement/heat).
The isolation of the walls would just mean that the energy would remain in the box, if I've understood what you mean by isolation correctly.
The one exception I can think of to absorption would be if every surface in the room, including the room-facing facets of the light source, is a perfect mirror and the room is a total vacuum. In that case, I believe the photons would reflect off the surfaces forever.*
*Barring any quantum/other weirdness
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Theoretically speaking, if you make a room out of perfect mirrors, then the room would stay lit forever. Of course, it would be difficult to observe this effect, since cameras / eyeballs /etc. are not perfect mirrors. Also, it's probably impossible to build a perfect mirror (although we can get really close if the wavelength is restricted).
Edit: whoops, -_-Quails beat me to it.
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They loose energy or it is transferred to atoms that the photon hits creating thermal energy or otherly known as heat. They do not disappear in your thought experiment, just they change form so to speak! Hope this helps.....was it a homework question do i dare gander to ask?
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On May 01 2012 15:00 Jastermarrel wrote:
They loose energy or it is transferred to atoms that the photon hits creating thermal energy or otherly known as heat. They do not disappear in your thought experiment, just they change form so to speak! Hope this helps.....was it a homework question do i dare gander to ask?
No, it wasn't a homework question. It seems like an easy question but i wonder how i couldn't realise it could turn into heat lol.
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Anything that can emit radiation can also absorb radiation. Thus, whatever lightbulb/diode/whatever will absorb almost all of the radiation incident upon it. When you compare the distance that EM radiation covers in 1/30th of a second to the volume it can travel (assuming the mirrors reflect 100% of the radiation incident upon them, which would be very convenient), you'll find that you'd need an incredibly big room to even notice the dimming. It should I believe follow an exponential decay function. So you would need walls that don't absorb any radiation, a method of observation that didn't absorb radiation, and the method of radiation generation would also have to have no radiation absorbing capabilities. IF you find all 3 of those impossibilities, then this will work.
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Yeah.....although light thought of as photons have behavior that resemble particles, they're not necessarily 'hard' particles like you think per se. As radiation/waves light will be absorbed.
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On May 01 2012 14:52 -_-Quails wrote:Show nested quote +On May 01 2012 14:27 Aelfric wrote:On May 01 2012 14:22 Bengui wrote:
Aren't they just absorbed by the walls as heat ? Would anything change if the walls are isolated? No, when the photons are absorbed by the walls it does not matter whether the walls are connected to anything. The energy can also be absorbed by any atoms or molecules floating between the walls as kinetic energy (movement/heat). The isolation of the walls would just mean that the energy would remain in the box, if I've understood what you mean by isolation correctly. The one exception I can think of to absorption would be if every surface in the room, including the room-facing facets of the light source, is a perfect mirror and the room is a total vacuum. In that case, I believe the photons would reflect off the surfaces forever.* *Barring any quantum/other weirdness
Thanks for these, educated me as well.
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Additionally, consider that the energy absorbed by the walls would probably be re-emitted at a wavelength near the peak of its black body spectrum (that energy which would not be thermally conducted elsewhere, at least). At room temperature,this wavelength is nowhere near the visible spectrum.
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On May 01 2012 23:07 Ryalnos wrote:
Additionally, consider that the energy absorbed by the walls would probably be re-emitted at a wavelength near the peak of its black body spectrum (that energy which would not be thermally conducted elsewhere, at least). At room temperature,this wavelength is nowhere near the visible spectrum.
We need better eyes.
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