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[Phys-L] Re: Ambiguous Question

Mike your points are well taken and I agree. Student thought processes and interpretations are
quite different than our own. This is easily seen if you give written exams rather than multiple
choice tests. Next semester I have to give up written questions due to course load, but I will
miss seeing how students approach questions that I think are very clearly written. Students make
the most amazing connections.

Just now, for example, I was just covering mass-energy equivalence. I was disucssing how the Sun
is losing its mass every second as energy is sent from it out into space. Then, since I use a
sclassroom response sytem, I asked them the following question, written by the author of our
textbook,

In which one of the following situations does a cup of coffee have the greatest mass?
A. when its temperature is 60 F sitting on a table at sea level
B. when its temperature is 95 F sitting on a table at sea level
C when its temperature is 95 F sitting on a table in a mountain cabin
D. when its temperature is 60 F sitting on a table in a mountain cabin

After the majority of students selected choice A, I asked if anyone would be willing to explain
this answer. One student explained that since the coffee was cold and had already lost its energy,
like the Sun losing its energy, that it had to be the most massive.

I then discussed the types of energy involved in the situation and asked them to try again.
This time, the class was evenly split between choices B and C. I asked someone if they would
explain why they chose choice B. A student indicated that since the coffee was closest to the
Earth, it had more energy. because as you go up into the mountains your weight is less.

I agree it is good for people to learn how to put things in context and
infer what is meant when the meaning is not explicitly clear.
Therefore, I do not quibble that this goes on, that we might hope
students would be better at it, and we might wonder if there are ways to
help students learn to do this.

However... And I think this is a _big_ however... Is a general exam the
proper place to do this? If the goal of the exam is to see if students
understand center-of-mass material, do we want to compromise our
discernment of who understands and who does not understand by throwing
in the requirement of figuring out exactly what the professor had in
mind? That seems pretty dumb to me.

It has the added "feature" of making the students angry. Is that what
we want?... To turn physics students away, grumbling, "physicists are
impossible; they expect you to read their minds."

It has another added "feature" of not modeling clarity. Don't we want
to train science students to write unambiguously. Do we accept
lab-notebooks that requires the reader to infer things. (I don't.)

And while we're talking about reading peoples' minds... Could those of
you who are mentioning the idea that students should learn to infer
things please make it explicit what you think should be done in this
case. Are you suggesting that the students who interpreted the 3-m walk
as relative to the dock, and answered the dog ends up 17 m from the
dock... Should get less than total credit?

While you ponder that, let me note that the professor was not intending
to require that students infer this. He admits it would have been
better if he had said 3 m relative to the boat since that is what he
wanted. He admits he will make this more clear in the future. Thus,
when he now says the students should have figured it out, I would say he
is just covering his mistake and he is stupidly alienating the students
who answered 17 m by not giving them credit.

Would you please relieve me from reading your minds by telling me
whether the prof should or should not give credit to the students who
viewed the 3-m walk as 3 m relative to the dock.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu



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