Date: Sat, 28 May 2005 14:49:10 +0200

Author: Urs Lauterburg

Subject: Re: TIR Demo



My favorite, most basic and most transparent TIR-demo still is the one
where I would fill a long, tall but narrow aquarium about 2/3 with water
and some suspended Mastix particles to visualize a green laser beam. On the
bottom of the aquarium in the water there is a small rotatable mirror which
can be manually operated by a small knob from the outside. The laser is
leveled horizontally and aimed at the mirror resulting in a reflected beam
of a variable angle from 90 degree to almost a horizontal path. Now filling
the upper part of the aquarium with some smoke then covering the whole
thing with a lid, one can very nicely change the beam to go through all
stages of reflection. It will demonstrate very clearly when total
reflection takes place.

It's all there, happening right up in front of everybody with no detracting
superficially attractive artifacts or effects. This is exactly what I
think the purpose of our demos are and because it is really happening it
has a much greater and effective educational impact than just a picture or
even a video of the situation. This is our business (Well not really a
business).... but then again it does seem to be possible to sell knowledge
about nature to make money too.

Happy demoing physics !


Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

>A professor wants a demonstration of total internal reflection. The
>idea is to point a laser at an angle towards a notch in the top of a
>plastic cylinder. The laser light then spirals down around the
>cylinder. The cylinder should be big enough for a classroom to see
>it-about 30 cm tall, 20 cm diam.
>Are there any suggestions about how to build one, such as, type of
>plastic, minimum thickness of cylinder, any other consideration.

From Sat May 28 09:30:47 2005