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On 30 Sep 1999 10:29:58 -0400, Nieminen Juha wrote:
>Ron Parker <par### [at] fwi com> wrote:
> The speed of the photon must slow down at least somewhere so that
>the average speed could be less than c.
In the period of time between absorption and re-emission, the photon
doesn't exist. While it exists, its speed is exactly c. While it
doesn't, it doesn't have a speed but you can make a convincing argument
for assuming a value of zero. The time during which it doesn't exist
is small but nonzero, and it happens many many times while the photon
is traveling in a medium.
> If the photon is absorbed by a molecule, why does the photon leave the
>molecule in the exact same direction as it entered it?
This is something I don't know offhand. I suppose that the ability to do
that over a given frequency range is what makes it a transparent molecule
rather than an opaque one, however it comes by that ability. Something to
do with dielectric constants and such, but I changed majors before we got
into any of the heavy stuff.
It's also possible that it was an oversimplistic abstraction given to
first-year physics students. :)
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