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

Hungary
explore rigid bodies and mechanical motion; mass; momentum (force); motion of centre of
mass; and energy and angular momentum.
Studies of the electron and the electromagnetic field in the third year open up the field of
energy extensively. The richness in form of the electromagnetic field makes it possible to handle
and transfer both energy and information with high efficiency. Students calculate the energy
density of a coil through which a current is flowing. Then they discuss the problem of energy
transfer from the source to the consumer. With the help of a special pair of wires (two narrow
plates), they discuss the propagation of energy and calculate the power density mathematically
as well as expressing it in terms of Poynting’s vector (5’): S = pi1 E B, where p, is the vacuum
permeability and E and B are the electric and magnetic fields.
As supplementary material, they discuss real situations as well; the wires have resistance and
then the direction of the Poynting vector is not parallel to the wire plates. In this case, the parallel
component characterizes the energy transported to the consumer and the perpendicular one gives
the energy dissipated in the wire as Joule heat.
It is in the fourth year that the features presented by the concept of energy are richest. The
introduction of the basic concepts of statistical physics and the application of simple probability
theory leads to a mathematical formulation of the concept of disorder and the second law of
thermodynamics. The connection between the direction of spontaneous processes in nature and
the minimum energy condition (valid in special cases) is also shown [ 15, 163.
The quantum states in an atom or a molecule can be modelled by standing waves on vibrating
strings. The wave behaviour of electrons can be demonstrated by electron diffraction, as in the
Nuffield Advanced Physics course [ 171. The low energy modes have the simplest patterns. The
eigenfunctions of a hydrogen atom, the formation of molecules (the delocalization of the
electrons) and the electronic states in a metal and a semiconductor are discussed. The interaction
of delocalized electrons leads to the development of the energy band structure as well as to the
understanding of the presence of free electrons and the high electrical conductivity of metals [ 181.
The treatment of nuclear physics is also based on the concept of energy. The binding energy
per nucleon depends on both Z and N and is a maximum for elements around iron in the periodic
table. Radioactive decay and the fusion of light nuclei show the tendency towards the energy
minimum. Consideration of the evolution of the universe leads us from a hot system through
hydrogen clouds to the formation of stars (building up nuclei with higher and higher atomic
numbers) and the emergence of the planets (offering a chance for life). The energy budget plays
a most important part in the appearance of life on Earth. And finally, at the end of the Grammar
School Physics course, the students discuss the energy supply problems of our society both now
and in the future.
On the school books and laboratory books
All four students’ books and the laboratory books have been published but have only been used
in some twenty-five to thirty schools. So we do not yet have such extensive practical experience
in grammar schools as teachers have in the primary schools. Looking through the books, we find
many good ideas about the way in which students may be encouraged to discover and understand
nature. They play, for example, simulation games with counters and dice in the first year while
studying the internal energy of a gas and the equipartition of energy. They make patterns and
structures with bearing balls and then they start to think about how the dependence of the interaction
energy of the particles depends on the distances of the first and second neighbours. In the
second year, a number of collision experiments are done by the students with pucks on an air
113