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Re: moving wall laser demo



There was an article in The Physics Teacher between 10 and 15 years ago, as
I recall. It was an interferometer-type of thing. A glass slide was used
as a beam-splitter. One branch was reflected off a mirror on the wall then
to a photocell. The other branch went directly to the photocell which was
wired as the input to an amplifier. Minute changes in distance (leaning on
the wall) changed the path difference which caused a varying intensity,
which caused varying voltage, which caused the sound. That is my
recollection. The title was something like "listening to the wall groan".
Is there a searchable index for TPT?

Br. Robert W. Harris
Catholic Memorial High School
rwharris@cath-mem.org
http://www.cath-mem.org/physics/contents.htm

-----Original Message-----
From: kyle forinash <kforinas@IUS.EDU>
To: PHYS-L@lists.nau.edu <PHYS-L@lists.nau.edu>
Date: Tuesday, June 27, 2000 6:56 PM
Subject: moving wall laser demo


Can anyone give me a reference to a demonstration I saw a few years back?

It was something along the lines of gluing a tiny mirror to a wall,
shining a laser off the mirror, collecting the laser light with a
sensor of some kind and turning the beam into sound (or some kind of
display). If I recall correctly the idea was to somehow have the
sensor set-up sensitive enough that you could 'hear' the wall move if
you pushed on it with your hand. I don't recall exactly how the beam
detector or setup was sensitive enough to the wall's location to be
able to detect its very slight motion.

Any hints or a reference would be appreciated. Thanks in advance.

kyle
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kyle forinash 812-941-2390
kforinas@ius.edu
Natural Science Division
Indiana University Southeast
New Albany, IN 47150
http://Physics.ius.edu/
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