Joel Rauber's recent note which carried the following quotation from George
Spagna
"One 'problem with problem solving' is that students often develop strategies
for getting solutions which are'correct' without understanding anything at all
about the physics."
Reminded me of an incident about 25 years ago when I was teaching the second
semester of our algebra-based physics course during our summer school. We had
been studying light and specifically Snell's law. I had assigned a problem
which has variations in almost all physics texts.
"A coin is on the bottom of a pool 4 m deep. What is the apparent depth of the
coin, seen from above the water surface?"
I asked if anyone had gotten the problem. A student in the front row said that
he had it. I asked what he had for an answer, and he replied that the answer
was 3 m. I then asked him how he had obtained his answer, and the reply was
that he had divided the depth by the index of refraction of water (1.33 = 4/3
approximately). "What lead you to do that?" was my next question. "I looked in
the back of the book and saw that the answer was 3 m, so it was obvious that
we had to divide the depth by the index of refraction" was his reply.
"What if the answer was not given?" was my next comment. "How would have
gotten the answer?"
This led to a rather lengthy discussion and set the stage for examining the
problem in more detail and applying Snell's law. Some good came out of the
incident, but the student was initially puzzled as to why I wasn't happy with
his answer. Afterall, it was the correct answer was his thinking.
I'm sure you all have had similar experiences.
Roger
Roger A. Pruitt
Physics Department--Fort Hays State University
600 Park Street e-mail: phrp@fhsuvm.fhsu.edu
Hays, KS 67601 v-mail: 913-628-5357