Re: SR examination question

["John S. Denker" <jsd@MONMOUTH.COM>]

At 09:09 PM 5/18/01 -0500, Rick Tarara wrote:

> In my mind the original question is a simple 'moving clocks run slow'
> question and aimed at introductory students where the instruction and the
> text on SR goes little beyond:
>
> 1)  Moving clocks run slow
> 2)  Moving masses increase
> 3)  Moving length contract along the direction of motion

But whatever happened to the rest of the physics?

 4)  Moving clocks are offset in proportion to how far away
     they are located.

> Of course this is not the first (or last) time a topic that started out as
> a discussion for a H.S. or College intro course has turned into a
> free-for-all at the theoretical dissertation level.  ;-)

I thought a dissertation was supposed to be original scholarly
research.  ISTM there is no time in the last 95+ years when "discovering"
the non-invariance of simultaneity at a distance would meet this standard.


We can discuss three levels of sophistication:
 a) How sophisticated is the questioner?
 b) How sophisticated are the answers given here?
 c) How sophisticated are the students, the intended test-takers?

a) It seems to me that the questioner would do well at the 2nd grade level,
having mastered the notion that the second-hand goes around once per
minute.  At the college introductory physics level, the questioner would
not do so well, having overlooked the issue of simultaneity at a distance.

b) The answers that have been posted here do not require anything more than
 -- physics: knowing that simultaneity-at-a-distance is an issue,
 -- physics: being able to draw a spacetime diagram, and
 -- English: realizing that clauses beginning with "when" express a timing
condition.

c) I would hope that any student who expects to do well on the IB test
would be able to handle things at this level.


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

There is some good that can come of this.

At 11:30 PM 5/18/01 -0700, Michael Bowen wrote:

> In the "real world", students will naturally encounter poorly or
> incompletely stated problems;

Quite so.  In the real world, one should request clarification, to find out
what the real problem is.

> However, examinations are not the appropriate venue for this training
> to occur

I agree.

OTOH, in preparation for such a test, students should be warned that goofy
questions are not particularly uncommon.  These questions become a test of
character (how well do you handle adversity and frustration) rather than a
test of physics skill.

Here are some suggestions for dealing with ambiguous questions within the
artificial world of multiple-choice tests:
 -- Look at the choices being offered.  If the question is ambiguous, but
only one of the plausible answers is offered, go for it.
 -- Similarly, know how the test is graded.  Know how strict is the
penalty for guessing.  If only two of the offered choices are consistent
with the question, usually it is to your advantage to pick one of them at
random.
 -- Don't waste time on goofy questions.  Take your best shot, and move
on.  Better yet, before moving on, put a mark in the question-book or on
the answer-sheet to indicate that it is questionable.  If you have time
left at the end, come back and fuss with the questionable items.

At 02:28 PM 5/17/01 +0200, Mark Sylvester wrote:
> Am I missing something, or is it that ambiguous questions are
> common in this area?

Indeed!  I find ambiguous and/or just-plain-wrong questions to be very
common in this area.

In particular, there seems to be a tradition of using _paradoxes_ to teach
relativity.  IMHO this is the opposite of good pedagogy.

By analogy:  I could come up with a dozen really tricky paradoxes in
elementary Newtonian mechanics -- but they would only serve to confuse
students, not enlighten them.

Teachers should not tell students "look how tricky and complicated this
subject is."  The message should be "if you think about this in the right
way, it all works out fine."  Paradoxes usually come from stating the
question in unclear or deceptive terms.  When people are trained to express
things properly, it becomes nearly impossible even to state a paradox.  To
relate this to the current example:  If students are accustomed to speaking
and thinking in terms of Jane-when and Peter-when, they will know instantly
that the question is broken at the point where it says "When ...."