Day 67: Inverse Square Law
This is in response to a question from physics teacher @writehandrule on Twitter:
— Bryan (@writehandrule) December 21, 2011
I have found some success using the gravitation simulation from The Physics Classroom website and the accompanying activity that helps students “derive” the inverse square relationship.
Upon further pondering, I wondered if introducing the invervse square law for light first (a more concrete inverse-square law, in my opinion) would be more effective. So I rigged together this little demo involving a grid of dots drawn on an overhead projector.
In the video, fellow physics teacher Mr. Longhurst, stands 1 meter in front of the projector. You can count 64 “light beams” (8 dots x 8 dots) on the mini-whiteboard he’s holding. Then he moves to stand 2 meters from the projector; now there are 16 light beams on the WB (4×4). Finally he moves 4 meters away, and there are 4 light beams on the board (2×2).
If you’d rather an activity for small groups, you might be able to pull it off very cheaply with just diffraction grating “rainbow” glasses and a red laser pointer. (The rainbow glasses produce a grid of light beams rather than just a line of beams like a regular diffraction gratings.)