New trends in physics teaching, v.4; The ... - unesdoc - Unesco

New Trends in Physics Teaching IV
Sixth, whatever one’s approach, the generality of thermodynamics is probably better brought
out by a variety of examples of its uses, of as many kinds as possible, than by casting the argument
in abstract, generalized terms. But different examples needing different statistical calculations
would introduce difficult distractions, so that families of examples (such as two-state and allied
systems) with the same basic calculation for all offer advantages.
Seventh, the Boltzmann factor is the pivot around which applications turn, so that the sooner
one can get to it the better. But here Feynman illustrates that there is a choice to be made
between getting it in an ad hoc way, or getting it in a way that shows that it is a ratio of numbers
of microstates in a heat bath. In the Nuffield course we chose the latter, accepting the price in
terms of difficulty and length, for the reward in insight. In either case, given the Boltzmann
factor, a large number of interesting applications become immediately accessible.
Eighth, simplicity and economy are essential but difficult features to achieve. Every simplification
introduces detailed difficulties, often rather subtle ones which may remain hidden for a long
time. The Nuffield approach raises as many as any other. The really hard thing is to carve out an
economical approach which is coherent, taking in what one wants to include, and leaving out as
much else as possible. Often this requires a rather careful analysis of just what lies behind a superficially
simple argument.
Lastly, most approaches depend critically on how they solve the problem of having a statistical
approach without doing too much statistics. Feynman finds a way of doing no statistics; PSSC
finds a very simple case and builds everything on that; Gurney uses more statistics but invents a
quick way of avoiding purely technical mathematical problems, similarly used by Bent and
Nuffield physics. Reif uses computer simulation, as does Nuffield physics, to inspect the
behaviours of systems as opposed to analyzing and calculating them.
The whole paper has assumed that the decision to introduce thermodynamic ideas in a statistical,
or at least microscopic, way is right. It is clear that the decision creates considerable difficulties,
but they should be seen in the light of the problems students have in understanding an uninterpreted
macroscopic approach.
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