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Author Topic: Speed of Light  (Read 15192 times)

Offline Ylide

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Re: Speed of Light
« Reply #25 on: 26/02/2004 04:28:01 »
yea, that sounds right...I knew it was some metal vapor, but I couldn't recall which.  



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Offline C-guy

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Re: Speed of Light
« Reply #26 on: 10/03/2004 02:18:09 »
quote:
Either way, no matter what the medium, you're still not going to, as gpan put it, catch up with a photon.

I disagree. Certain radioactive materials emit particles going faster than the speed of light in water or air. This is what causes the Cerenkov effect.


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Offline chris

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Re: Speed of Light
« Reply #27 on: 10/03/2004 04:08:11 »
Hi C-guy.

Can you please explain what the cerenkov effect is ?

Chris

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Offline C-guy

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Re: Speed of Light
« Reply #28 on: 11/03/2004 03:01:59 »
This is the best site I could find in ten minutes.

http://nova.nuc.umr.edu/~ans/cerenkov.html [nofollow]

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Offline qpan

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Re: Speed of Light
« Reply #29 on: 12/03/2004 01:58:55 »
quote:
Originally posted by C-guy

quote:
Either way, no matter what the medium, you're still not going to, as gpan put it, catch up with a photon.

I disagree. Certain radioactive materials emit particles going faster than the speed of light in water or air. This is what causes the Cerenkov effect.


Moving at the speed of light.



In a vacuum, nothing can catch up with a photon (as even if you were travelling faster than the speed of light relative to a point, relative to you the speed of light in a vacuum would remain constant- time itself would instead, warp).
Would anything actually be able to catch up with a photon in another medium though?


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Offline tweener

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Re: Speed of Light
« Reply #30 on: 12/03/2004 17:43:12 »
Good question.  I don't understand the quantum mechanical explanation of why the speed of light in a material is slower than that in a vacuum.  If the beta particles in a nuclear reactor are emitted with a speed greater than that of light in water (but slower than in a vacuum), they might be able to catch a photon in the water.  Maybe.

After reading the link about Cherenkov radiation, I still don't understand how the beta particles interact with the water molecules.  The rotational energy of a water molecule causes radiation at 22 Ghz 30somthing GHz and a few other lines a little higher.  These frequencies are substantially below infrared and would not cause "blue" light.  I'm not saying it doesn't happen, I just don't understand the process.  A few minutes with Google would probably help a lot, but I'm too lazy.

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Offline Ylide

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Re: Speed of Light
« Reply #31 on: 13/03/2004 08:40:00 »
John:  A beta particle is basically a high energy electron.  When it collides with a water molecule, it will impart some energy to it.  This can cause an electron in one of the atoms in the water molecule to jump an energy level or two.  When it drops back down to its normal level, it will emit light of a certain energy.  Without doing the calculations, I'm guessing that energy corresponds to the frequency of blue light.  Find me the average energy of a beta particle and I'll do the calculations and settle the matter.

I'm guessing that any medium that would slow light to below 'c' would slow any other particle's travel speed as well.  If the photon is faster than 'c' in that medium, it would be just as hard to catch.  



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Re: Speed of Light
« Reply #31 on: 13/03/2004 08:40:00 »

 

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