Re: Hearing Light?

["Robert W. Harris" <rwharris@CATH-MEM.ORG>]

Bringing the black membrane of a stethoscope very close to a 7.5 W
incandescent bulb produced a quite distinct hum in the stethoscope, which
surprised me.  Moving the stethoscope away, or shielding it with a piece of
paper proved that the hum was due to the flickering of the bulb.

I'll have to buy a jar of pickles.

I wonder if the stethoscope is a better "matching transformer" than the tube
you were using???

Br. Robert W. Harris
Catholic Memorial High School
rwharris@cath-mem.org
http://www.cmphysics.org
-----Original Message-----
From: Michael Edmiston <edmiston@BLUFFTON.EDU>
To: PHYS-L@lists.nau.edu <PHYS-L@lists.nau.edu>
Date: Tuesday, August 15, 2000 1:09 PM
Subject: Hearing Light?


> The recent issue of "The Physics Teacher" has an article titled "Hearing
> Light."  (Phys. Teach, September 2000, page 356.)
>
> We are unable to reproduce an experiment described in this article and we
> wonder if anyone else has tried it.  The experiment uses a half-blackened
> pickle jar to receive the light of an incandescent light bulb.  A small
hole
> in the lid serves as a place for one to place his ear, and the claim is
that
> the heating/cooling of the air in the jar (as the bulb's light output
> fluctuates due to 60-cycle AC current) can be heard as a 120-hertz tone.
>
> Robert Suter, a professor at Bluffton College, first saw this and asked if
I
> believed it.  I did not believe it, so Bob and I tried several experiments,
> and we have not been able to detect the claimed effect.  Here is what we
> tried.
>
> We first tried the experiment as suggested, and heard nothing.  Past
> experience told us that incandescent light output does not fluctuate much
> because the filament cannot cool down very much using 60-Hz AC.  We
> monitored a 60-watt light bulb with an amplified phototransistor and showed
> this is true... the light output does follow a 120-Hz sine curve, but the
> amplitude of the fluctuations is not very significant... nothing like the
> 120-Hz light fluctuations from a florescent tube.  Therefore, any thermal
> detector would have to be pretty sensitive, and we doubt the pickle jar is
> sufficiently sensitive, and perhaps cannot heat/cool fast enough.
>
> To see if a larger effect would produce an audible tone in the pickle jar,
> we made a chopper so we could expose the jar to incandescent light that
> fluctuated from completely off to completely on.  Our phototransistor
proved
> our chopper was very effective.  Again, we could hear nothing at the pickle
> jar.  The 60-watt bulb was only a couple inches from the jar, with the
> chopper between.  We even put a piece of rubber tubing from the lid to our
> ear (like a stethoscope).  If the end of the tube was held near the
chopper,
> we could easily hear the 100-120-Hz tone that the chopper created in the
> air.  But when the tube was held to the hole in the pickle-jar lid, we
heard
> nothing.
>
> Has anyone else tried this?  Has anyone else heard anything?
>
>
> Michael D. Edmiston, Ph.D.              Phone/voice-mail:
419-358-3270
> Professor of Chemistry & Physics        FAX:
419-358-3323
> Chairman, Science Department            E-Mail
edmiston@bluffton.edu
> Bluffton College
> 280 West College Avenue
> Bluffton, OH 45817