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Feb.23,2012
Looking through old files (in a futile attempt to purge) I came across this classic physics exam question:
Show how it’s possible to determine the height of a tall building with the aid of a barometer.
As the story goes, one student answered this way:
“Take the barometer to the top of the building and attach a long piece rope to it. Lower the barometer until it hits the sidewalk, then pull it up and measure the length of the rope, which will give you the height of the building.”
What? The teacher expected a different answer, using the standard equation involving the difference in pressure at the top and bottom of the building.
When challenged to come up with “the right answer,” the student gave several. Among them:
1. 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. Using simple proportion, determine the height of the building.
2. 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.
And so on.
My favorite remains this one: 
“Take the barometer to the basement and knock on the superintendent’s door. When the superintendent answers, say: ‘Mr. Superintendent, if you will tell me the height of this building, I will give you this barometer.’”
How would you grade this student? In a future blog, I’ll tell you how I handled a similar physics classroom situation.
** Legend has it that the student was Niels Bohr (1885-1962, Nobel Prize in physics, 1922), but then a legend can say anything and get away with it.
Tags : bohr, physics class
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I ran into a similar situation, in real life. As an undergraduate, I took a test involving Rutherford scattering. I came up with an unexpected solution which nonetheless gave the right answer. I was severely marked down for it.
Later, in grad school, I was tasked with grading exams. One bright fellow — only one — came up with the same calculation I had used. So I gave him the points I should have gotten.
Called “thinking outside the box”, which the prof should praise or from which, at least, learn.
That doesn’t surprise me at all, Ellen. Neither does your generosity later.
My thoughts exactly, Liz.
I think the student’s answers will provide a more accurate height than that found by measuring barometric pressure. And I like Ellen’s “pay it forward” kindness!!!
Reading The Emperor of All Maladies. Surely a cautionary tale, and inspiration, to “thinking outside the box”.
I’d think that would be a tough read, Liz.