Re: NYS Physics Regents exam

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Most of the questions I missed were because I couldn't (didn't) look up
anything -- I didn't read the instruction carefully, but did get the
impression some data was available to the exmaninees.  (Yes, after
writing the below, I found the 2002 ed. Ref.  tables, which makes much of
this post "no longer  operative".)

I suppose I should have written only density, as mass / volume is
obviously not of interest.



Maybe I'm being "defensive" as I think preying upon the similarity of
corn oil to glycerol is a trick question -- since when is physics
instruction supposed to use trick questions.  Perhaps the students are
taught to the test, in which case it's not a trick question for them.  It
was obvious that the middle medium was denser, but I don't know the
density of glycerol.  Furthermore, glycerol (unless it has isomers) has a
fixed index, while corn oil does not.  Most CO grown in US is a GMO --
wonder what that's done to its index.  After finding the tables, I
plugged in its values and found a discrepancy of 0.02 in N or ~ 0.3  deg.
in angle.  Google didn't reveal the variation in index for corn oil.  The
Regents answer is fine as flint's index is rather variable.

Something I google found:

"OTHER NOTES: The index of refraction of pyrex is equal to that of
vegetable oil -- both are about 1.5. Also, regular glass and baby oil
have the same index of refraction.  It is also reported that cubic
zirconia and corn oil have the same index of refraction, but jewelers
report that different "kinds" of cubic zirconia have wildly different
refractive indices."

picayune  bc


"John S. Denker" wrote:

> 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.