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Q & A: moving beam

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Most recent answer: 10/22/2007
Q:
If I aim a flashlight at the heavens and turn it on for one second, have I now created a lightbeam 300,000 km long, travelling at 300,000 km/sec?

Itís my understanding that, in the front of the beam, there will be action taking place - an electric field will be creating a magnetic field which will in turn be creating another electric field - on and on and on. If this is true, then what about the trailing end of the beam - would these fields be disappearing from the back of the beam? Otherwise, it seems the beam would not be 300,000 km. long - but would constantly be growing.
- Jeff (age 60)
Sacramento, CA US
A:
You're basically right. However, the wave nature of light does imply that the beam will gradually smear out, sideways at first.

Mike W.

(published on 10/22/2007)

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