|
Rutherford story
Sir Ernest Rutherford, President of the Royal Academy,
and recipient of the Nobel Prize in Physics, related the following story:
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 this 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." (1885-1962) Danish Physicist;
Nobel Prize 1922; best known for proposing the first 'model' of the atom
with protons & neutrons, and various energy states of the surrounding
electrons - the familiar icon of the small nucleus circled by three
elliptical orbits ... but more significantly, an innovator in Quantum
Theory.
|
