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OfflineSeussA
Error: divide byzero

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Tricky question
    #2375904 - 02/25/04 01:23 PM (13 years, 5 months ago)

A physics class is doing an experiment. A gamma ray, a photon of visible light, and an electron are all 'released' at the same time on one side of the classroom. The electron has a speed as close to the speed of light as possible. All three travel in the same direction, across the classroom. In what order do the three arrive at the opposite end of the classroom, and why?

Edit: Hint, they all arrive at different times.


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Edited by Seuss (02/25/04 03:31 PM)


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InvisibletrendalM
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Re: Tricky question [Re: Seuss]
    #2376505 - 02/25/04 05:09 PM (13 years, 5 months ago)

The gamma ray, then the visible light, then the electron.

Why?

Both the gamma ray and visible light are photons, which travel at light speed. However in an atmosphere the photons will be slowed down slightly as they are absorbed and re-emitted by atoms. The gamma ray photon has a much higher energy than the visible light photon, so it should "press" through the atmosphere slightly faster than the visible light photon. The electron arrives last of all because it cannot travel at the speed of light (it has mass) and also interacts with the intervening matter much more strongly than either of the photons (again, because it has mass).

Right?

My first thought was that the gamma ray and visible light would both arrive at the same time, but I guess the gamma ray has a better chance of moving through air at close to light-speed in a vacuum.


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OfflineSeussA
Error: divide byzero

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Re: Tricky question [Re: trendal]
    #2378330 - 02/26/04 08:12 AM (13 years, 5 months ago)

Very very close... and I would give you full credit for the answer. The electron will actually arrive second, followed by the visible light photon. As you indicated, visible light is slowed down due to refraction through the atmosphere. The gamma ray does indeed arrive first.

Source: Richard Fyneman's Lectures.


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InvisibletrendalM
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Re: Tricky question [Re: Seuss]
    #2378360 - 02/26/04 09:00 AM (13 years, 5 months ago)

Ahh, ok :smile:

I guess the electron would be able to squeeze through the atoms in the air without interacting too much with them...since the electron is negatively charged and the atoms are all in a stable state with electron shells surrounding them (which are also negatively charged, of course).

Faynman was a hip, hip cat :smile:


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