From: Black, Heidi (BlackH@exchange.esuhsd.org)
Date: Tue Feb 12 2002 - 14:11:32 PST
Message-ID: <190CE0E37D38D311BFB9009027858A58021CF9AC@exchange.esuhsd.org> From: "Black, Heidi" <BlackH@exchange.esuhsd.org> Subject: lasers and the inverse-square law Date: Tue, 12 Feb 2002 14:11:32 -0800
OK, since no one else has taken this on I will give it a try...
lasers do spread out-nothing like a normal bulb, but the rays go off in
straight lines and in 2 dimensions which is what is required for the math of
inverse-square
one day while helping a student I looked at the text diagram from the
perpendicular, I finally saw that what we were talking about was similar
triangles, and that if the side doubled then the base had to double, and the
change on the base in one dimension was the same as the change on the
other, that resulted in area-which is squared!
because kids believe that the laser doesn't spread out, a fun lab is to have
the kids measure the size of the laser dot at multiple distances, use the
entire room---we did this to look for the "angle of divergence" through
grants and luck I have several lasers, one which was given to me because it
did not meet specs for angle of divergence, so it is nice to let the kids
know at least one group should get different results, trust your data....
put a box on the floor, tape a piece of paper on the side, shine the laser
at it and circle the dot at .5 meters, 1 meter, etc, (this is a great lab
for introducing the idea of sources of error!)---my son did a project
extrapolating this to the size the dot would be by the time it traveled to
the moon...
at least some of the diode lasers produce an oval shaped dot-I still prefer
the HeNe's
have fun!
Heidi
This archive was generated by hypermail 2.1.3 : Mon Aug 05 2002 - 09:21:40 PDT