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Re: NYS Physics Regents exam



Bernard Cleyet wrote:

I would
expect the same optical density for the first and last media.

0) Assuming that means index, not optical density, yes, the
first and last media have the same index. That is an
accurate conclusion that can be reached immediately,
without any detailed calculation.

1) Glycerol and corn oil have the same index; Regents exams
have been exploiting this coincidence for years:
http://www.sciencejoywagon.com/physicszone/review/04waves/92q43.html

2) The obvious temptation is to select answer #3. But that
would require ignoring what we know about Medium X, namely
that it has a higher index than glycerol.


This question can be answered quickly and confidently using
qualitative reasoning alone: Look up the four substances
involved and rank them according to index. Then check each
of the four selections to see which respect the orderings.

If you have time left over, you can use Snell's law to
confirm that the "best" answer is an absolutely fine answer
(as opposed to a best-of-evils) -- absolutely within the
range of the media in question.

======================

4) Summary:
-- Don't ignore Medium X.
-- Don't assume different media always have different indexes.