by PhilipJ on 20 January 2006
I’m the TA for the undergrad thermodynamics course being offered this year, and they’ve just handed back their first problem set. The first problem (the so-called three-cylinders problem) is this:
Three identical cylinders are filled with unknown quantities of ideal gases. The cylinders are closed with identical frictionless pistons of mass M. Cylinders A and B are in thermal equilibrium with the room at 20 oC, and cylinder C is kept at a temperature of 80 oC. Is the pressure of Nitrogen gas in cylinder A greater than, less than, or equal to the pressure of the Hydrogen gas in cylinder B? Is the pressure of Hydrogen gas in cylinder C greater than, less than, or equal to the pressure of Hydrogen gas in cylinder B? Why?
Seems like a fairly straightforward problem, right? Well, based on the study below , of ~250 introductory physics students asked this problem, only 15% got the correct answer (which I’ll reveal to those who might be confused in the comments section after a few people post their thoughts!). Testing ~65 thermal physics students (who were physics majors), only 40% got the question entirely correct.
I had the pleasure of seeing Lillian McDermott (of the education physics research group at the University of Washington who did these studies) give a talk on these results, and its quite clear that the current methods used to try and teach physics concepts are inadequate. Do any of the other sciences have problems that stem from the very fundamentals? That only 40% of physics majors taking a class in thermodynamics got that answer correct is kinda scary [though my own class fared a little better, ~66% (N=25) had the correct answer].
 C. H. Kautz et al, Student understanding of the ideal gas law, Part I: A macroscopic perspective, American Journal of Physics 73 1055 (2005), the first of a pair of papers on the physics education of the ideal gas law.