Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Hearing Light?



At 12:08 PM 8/15/00 -0400, you wrote:
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.

I have been amused by the thread that was spun from this article, and it
reminded me of something that I heard as a youngster: that bees should not
be able to fly.

I had no difficulty replicating the sooted pickle jar (// half liter) and
at least 6 other people (of varying ages) were also able to hear the "hum"
without being told what they were to listen for. Then I tried another jar
of the same size but with a separate thin piece of plastic, sprayed with
flat black paint, and I could still hear the hum but VERY faintly.

Next I tried a merichino cherry jar that was somewhat smaller, sooted in
the original way, and this sounded louder to me, so I figure that larger
jars will not work as well.

In all instances, shielding the jar from the light makes it easy to tell
what changes in case one has to contend with tinitus problems.

It seems to me that the nascent carbon does the best either because of its
structure or because it is adhering to the rigid glass, compared with the
plastic material. It made no difference whether I used the sooted glass
while it was still very hot or after it had cooled.

Clearly the purpose of the article was to call attention to the sensitivity
of the human ear and not to SERIOUSLY suggest one was listening to "light."
But it does provide a very stable 120Hz reference and can provoke
interesting classroom discussion. In fact, the record of disagreement on
this issue so far should make it all the more interesting to the student.

Tom Ford