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Author Topic: In a mirrored room would light bounce back and fiurth continuously?  (Read 274 times)

Offline thedoc

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Chris Carson asked the Naked Scientists:































































   Consider a room lined with mirrors with no windows and the lights off. You stand in the middle of the room. It's dark. You turn on the lights, the room lights up, then turn them off. Why does it go dark again? Why doesn't the light from the lights just infinitely bounce around the room, keeping the room lit by the infinite reflection of the lights?































































































































What do you think?
« Last Edit: 15/11/2016 15:24:34 by _system »


 

Offline RD

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... Why doesn't the light from the lights just infinitely bounce around the room, keeping the room lit by the infinite reflection of the lights?

Mirrors are not 100% reflective : some of the light-energy is lost to heat during each reflection.

The light would reverberate in the mirrored room for a short period , ~1/100,000th of a second , so not humanly noticeable.
« Last Edit: 13/10/2016 13:24:06 by RD »
 

Offline Bored chemist

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Offline evan_au

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If you take a glass mirror, and look through the edge, you can't see through to the other side.

Light is almost totally absorbed after passing through 1m of glass.
- The glass is (say) 5mm thick.
- So after 200 reflections, it would have passed through the glass 200 times and been absorbed
- If the room is 5m wide, light would have traveled about 1km before being absorbed
- In this example, absorption will take 1/300,000 second.
- Of course, if you use an astronomical mirror, and put the reflective coating on the outside of the glass, it might last for 10,000 reflections, but that is still faster than human reaction time.

But there is another absorber: the observer. If you are in the room, you are definitely opaque, and you will absorb any light that hits you after 1 reflection, plus any that hits you after multiple reflections and/or scattering.

So the light will be absorbed very quickly.
 

Offline syhprum

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only in a gas discharge laser with very high grade mirrors are there sufficient reflections to have a useful effect.
 

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