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Q & A: moving beam

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Most recent answer: 10/22/2007
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
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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