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Re: Speed of Light With a Microwave



Cherie,

I noticed the same thing and briefly contemplated writing a letter to TPT;
I'm sure someone has. The thing I also noticed is that you can read the
ruler in the picture and it clearly shows a distance that is about half of
that used in the article to get the speed of light. (Weren't we just
talking about the sinister effects of "knowing the right answer"?)
However, I think the situation is further complicated by the fact that one
should not necessarily expect the standing wave pattern to be oriented
horizontally. If it isn't, then the distances between melted spots on the
surface of the marshmallow will not bear any simple relationship at all to
the wavelength.

TPT often suffers from its loose policy of peer review. I think there are
some benefits to keeping the publication process simple, especially given
the low levels of editorial support that AAPT is likely providing.
Nevertheless, it is a shame when things like this make it to press and,
possibly, into the curricular bag of tricks of credulous readers.

John

On Fri, 16 May 1997, Cherie Lehman wrote:

In the most recent _Physics Teacher_, there appeared a one-page article
which described how one could use a pan of marshmallows in a microwave oven
to determine the speed of light. The method involves measuring the
distances between hotspots or more-cooked places on the top of the layer of
marshmallows. It is asserted that this distance is the wavelength of the
microwaves. I am having trouble understanding why this is so. It seems
reasonable that a standing wave may be set up inside the microwave. It also
seems reasonable that the hot spots would correspond to the anti-nodal
points. What I don't get is why the distance between the anti-nodes should
be a wavelength. One-half wavelength makes more sense to me as the distance
between consecutive antinodes. Help me, someone, please.

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