On Thu, Jun 23, 2011 at 9:31 AM, Michael Watterson wrote= : > On 23/06/2011 13:15, Yigit Turgut wrote: > > Intensity of light is reduced by inversely proportional to > > square of the distance. > not true with a laser. That would imply the spot doubles in diameter > with double distance. many don't > -- > > > The Inverse Square Law only applies to a point (or equivalent) source radiating energy in "all" directions - "all" directions meaning a spherical surface subtending an angle of 4pi steradians. Carey --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .