Date: Sun, 05 May 2002 16:17:24 -0700 (PDT)
Author: William Beaty
Subject: ultrasound demos?
Hey, is anyone using those little ultrasonic foggers for physics demos?
The price is down to $24 on one website.
Mist for lasers? Boring!
These underwater ultrasound beams are fairly parallel. The fogger can
make splotches on a submerged "liquid crystal postcard". Fill a tank with
slightly warm water so the "postcard" starts to turn red. It will become
sensitive to thermal changes. I found that you can use an ultrasonic
fogger to write your initials on the submerged postcard from over 20cm
Since this forms a thermal "camera film" which displays the acoustic
energy distribution, there are many untested possibilities: focus the beam
with a lens made of wax, ice, etc. Split and combine two beams and
observe interference stripes? Cast shadows of complicated objects (can
you make an 'x-ray' of a dead fish?)
I've occasionally noticed visible underwater standing wave nodes. If the
Fogger is aimed upwards and is a few inches from a submerged horizontal
metal plate, and if the water has some misty bubbles (from the hot water
tap), then a row of parallel bubble-filled "disks" will form in the region
between the fogger and the plate. I've seen photos of this demonstration
performed in air using styrofoam beads, but the water version requires no
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William J. Beaty SCIENCE HOBBYIST website
EE/programmer/sci-exhibits science projects, tesla, weird science
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