"Some
time ago I received a call from a colleague. He was about to give a student
a zero for his answer to a physics question, while the student claimed a perfect
score. The instructor and the student agreed to an impartial arbiter, and I
was selected.
I read the examination question: "Show how it is possible to determine the height
of a tall building with the aid of a barometer."
The student had answered: "Take the barometer to the top of the building, attach
a long rope to it, lower it to the street, and then bring it up, measuring the
length of the rope. The length of the rope is the height of the building." The
student really had a strong case for full credit since he had really answered
the question completely and correctly! On the other hand, if full credit were
given, it could well contribute to a high grade in his physics course and certify
competence in physics, but the answer did not confirm this. I suggested that
the student have another try. I gave the student six minutes to answer the question
with the warning that the answer should show some knowledge of physics. At the
end of five minutes, he hadn't written anything. I asked if he wished to give
up, but he said he had many answers to this problem; he was just thinking of
the best one. I excused myself for interrupting him and asked him to please
go on. In the next minute, he dashed off his answer which read: "Take the barometer
to the top of the building and lean over the edge of the roof. Drop the barometer,
timing its fall with a stopwatch. Then, using the formula x=0.5*a*t^2,calculate
the height of the building."
At this point, I asked my colleague if he would give up. He conceded, and gave
the student almost full credit. While leaving my colleague's office, I recalled
that the student had said that he had other answers to the problem, so I asked
him what they were.
"Well," said the student, "there are many ways of getting the height of a tall
building with the aid of a barometer. For example, you could take the barometer
out on a sunny day and measure the height of the barometer, the length of its
shadow, and the length of the shadow of the building, and by the use of simple
proportion, determine the height of the building." "Fine," I said, "and others?"
"Yes," said the student, "there is a very basic measurement method you will
like. In this method, you take the barometer and begin to walk up the stairs.
As you climb the stairs, you mark off the length of the barometer along the
wall. You then count the number of marks, and his will give you the height of
the building in barometer units."
"A very direct method."
"Of course. If you want a more sophisticated method, you can tie the barometer
to the end of a string, swing it as a pendulum, and determine the value of g
[gravity] at the street level and at the top of the building. From the difference
between the two values of g, the height of the building, in principle, can be
calculated."
"On this same tack, you could take the barometer to the top of the building,
attach a long rope to it, lower it to just above the street, and then swing
it as a pendulum. You could then calculate the height of the building by the
period of the precession".
"Finally," he concluded, "there are many other ways of solving the problem."
"Probably the best," he said, "is to take the barometer to the basement and
knock on the superintendent's door. When the superintendent answers, you speak
to him as follows: 'Mr. Superintendent, here is a fine barometer. If you will
tell me the height of the building, I will give you this barometer."
At this point, I asked the student if he really did not know the conventional
answer to this question. He admitted that he did, but said that he was fed up
with high school and college instructors trying to teach him how to think.
The name of the student was Niels Bohr.
Ps. Niels Bohr got the Nobel Prize in Physics in 1922 ..... Ds.
Senast ändrad 15/1 2000 Johanna Nählinder