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From: sra@oddjob.UChicago.UUCP (Scott Anderson)
Newsgroups: net.physics
Subject: Re: Lightspeed
Message-ID: <528@oddjob.UChicago.UUCP>
Date: Sat, 10-Nov-84 03:18:43 EST
Article-I.D.: oddjob.528
Posted: Sat Nov 10 03:18:43 1984
Date-Received: Sun, 11-Nov-84 21:00:06 EST
References: <683@hou2h.UUCP>
Organization: U. Chicago: Astronomy & Astrophysics
Lines: 40

<<<<<<<

> Which reminds me of something else that has been bothering me since
> high school physics: if light does not propagate by 'disturbing' a
> medium, why does light travel at different speeds through different
> substances? (i.e., why does light refract through a lens or a prism
> and why do you get the illusion of a 'broken' pencil when you stick
> one in a glass of water?)

Light travels at slower speeds through material substances because it is
being absorbed and coherently reemitted.  This, in effect, slows it down.
The refraction occurs because, when passing between two substances, different
points on a wavefront will travel at different speeds, which 'bends' the
wavefront:

  >                        Air | Water (or other liquid refreshment)
      >                        |
          >                    |
              >                |
                  >            |
                      >        |
                          >    |
                              >|
                               | >
                               |   >
                               |     >
                               |       >
                               |         >
                               |           >
                               |             >
                               |               >

(Does this qualify as a doodle?)

Something in two different media, such as a pencil partially in water, will
have part of its image shifted by the refraction, and will therefore appear
'broken'.

 _,                                Scott   Anderson
 3~                                ...!ihnp4!oddjob