From: Peter Geschke (pgeschke7@home.com)
Date: Thu Jul 26 2001 - 10:31:47 PDT
Date: Thu, 26 Jul 2001 10:31:47 -0700 Subject: UV doesn't penetrate glass? From: Peter Geschke <pgeschke7@home.com> Message-ID: <B785A213.4ED%pgeschke7@home.com>
Hey everybody,
My brain is on summer vacation and I can't seem to resolve this conflicting
issues here in my sunburned mind. Can you help explain my dilemma? The
following is an email from a student and my non-definitive answer. Never
mind why our district is teaching with Conceptual Physical Science with 8th
graders - that's another issue altogether!
-- Peter Geschke
Chemistry Teacher
Mission San Jose HS
41717 Palm Avenue
Fremont, CA 94539
work 510-657-3600 x 3528
pgeschke7@home.com
> Hello Mr. Geschke,
>
> This is Andrew, a student of your's from last year. I have a small
> question: is it possible to become sun-tanned or burnt through a window?
> I used to be
> pretty sure it was not, I think I learned from 8th grade science that UV
> rays cannot penetrate glass, but now I'm not so sure - advertisements
> state that
> tinted windows block more UV rays than untinted ones and many sunglasses
> are not able to competely block UV. Can someone be tanned or burnt
> through glass?
>
> Thank you, this has been bugging me for a while.
>
>
>
> Andrew
>
Not that small of a question, I don't think...
UV rays certainly seem to penetrate glass. There is ample evidence of
this...for example, some furniture in your house is probably somewhat faded
due to the UV coming in through windows...I'm almost certain you can be
sunburned inside a car with the windows closed...sunglasses are almost
certainly plastic lenses, though, so we can't consider that.
But, I looked in Conceptual Physical Science, the book you used in 8th
grade...and I found this question and answer:
"Q: Why is glass transparent to visible light but opaque to ultraviolet and
infrared? A: The natural frequency of vibration for electrons in glass is
the same as the frequency of ultraviolet light, so resonance in the glass
occurs when ultraviolet rays shine on it. The energetic vibrations of
electrons generate heat instead of wave re-emission, so the glass is opaque
at higher frequencies. In the range of visible light, the forced vibrations
of electrons in the glass are at smaller amplitudes - vibrations are more
subtle, re-emission of light rather than the generation of heat occurs, and
the glass is transparent. Lower-frequency infrared causes whole molecules,
rather than electrons, to resonate, and again heat is generated and the
glass is opaque."
Conceptual Physical Science: Hewitt, Suchocki, Hewitt, (c) 1994, p. 280
So, what this all boils down to is "I don't get it"....and when "I don't get
it", I sometimes turn to a maillist set up for science teachers through the
Exploratorium Teacher Institute...I'll post this there, and we'll see if we
can get further clarification.
Mr. G
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