Some Questions Have Many Answers:
Niels Bohr on Learning

Ernest Rutherford

Several years ago, SCI added the story that follows below to its online library. Unfortunately, the source of the story was not captured and is now lost. A biographical sketch of Bohr states: "In 1911, Niels Bohr earned his PhD in Denmark with a dissertation on the electron theory of metals. Right afterwards, he went to England to study with J.J. Thomson, who had discovered the electron in 1897. Most physicists in the early years of the twentieth century were engrossed by the electron, such a new and fascinating discovery. Few concerned themselves much with the work of Max Planck or Albert Einstein. Thomson wasn't that interested in these new ideas, but Bohr had an open mind. Bohr soon went to visit Ernest Rutherford (a former student of Thomson's) in another part of England, where Rutherford had made a brand-new discovery about the atom." In November of 2008, SCI received the note immediately below regarding the authenticity of the story attributed to Rutherford.

Ernest Rutherford

A colleague just pointed me to the rather amusing story about how Rutherford was involved in Bohr's early education in physics -- you know, the barometer story that you publish on your site.

I find it highly amusing that a site that claims to teach people to search for the truth publishes a story that is so obviously a hoax.

Niels Bohr was born in 1885 and got his doctorate at University of Copenhagen at age 26 in 1911. His entire university (college) carreer up to that point was in Copenhagen. It seems reasonable to assume he started college some time in 1903-05. Possibly as early as 1900, but I find it hard to believe it was any earlier than this.

Rutherford was appointed chair of physics in Montreal, Canada in 1898.

Here he did the work that earned him the nobel prize in chemistry 1908. In 1907 he took the chair of physics at Manchester University.

It seems a tad unlikely that Rutherford would ask a common student to travel the atlantic (or even to England) for a rather silly physics problem -- also it seems unlikely that Bohr in the later part of his studies should be given such a problem at all, so the 1907-1911 period is highly unlikely.

The story claims that Rutherford "received a call" from a colleague. The first transatlantic phone call was made in 1927, so that makes it quite impossible for a Copenhagen professor to have called Rutherford while the latter was in Canada. I do not know if telephony was possible between Copenhagen and Manchester in 1907-1911. I do however know that it wasn't easy. Long distance calls at that time required special booths. It seems immensely more reasonable that Bohr's professor would contact a local physicist.

It's still a funny story. But come on: Give up the claim that it has anything to do with Bohr or Rutherford. It doesn't.

Peter B. Juul / from Denmark / 27 November, 2008


***

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 state of the surrounding electrons -- the familiar icon of the small nucleus circled by three elliptical orbits ... but more significantly, an innovator in Quantum Theory.