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I'm having a real tough time with this one, maybe I can get a little help.

A small helium neon laser emits red visible light with a power of 3.2 mW in a beam that has a diameter of 2.5mm. What is the intensity of the laser beam? Does this intensity obey the inverse square law?

Now I have for an answer an intensity of 0.652 W/m2 and that it does not obey the inverse square law (although this could be wrong).

For the intensity, I thought:

I = Power / ( 4 pi ( diameter / 2 ) ^ 2 )

but that gives me an intensity of only 0.163. And I thought that all light obeyed the inverse square law. I've done research for this on the net, but I can't find anything. A shove in the right direction would be appreciated.

Thanks!!!

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# Intensity of laser beam / Inverse square law

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