Table of contents

This special section of European Journal of Physics brings together a series of articles dedicated to examples of environmental physics. Physics is above all an underpinning science and one that plays a crucial role in understanding the environment and the major issues that confront the world today. The social and political problems of global warming, ozone depletion, the spread and consequences of pollution, and the development and exploitation of energy sources all require an understanding of the basic underlying physics. Similarly, our ability to model and thence predict our weather and climate requires knowledge of many disparate physical processes. Environmental physics, as its name implies, is the application of the principles of physics to problems in the natural and man-made environment. It plays a pivotal role in exploring, monitoring and, above all, understanding the world we live in, and humanity's effect on it, both on local and global scales [1].

In the 1980s, with the discovery of the ozone hole and increasing interest in the observation and effects of `acid rain', the topic of `environmental' or `green chemistry' was developed and adopted by many universities' chemistry departments as a core part of their undergraduate teaching programme. Physics departments were initially slower to appreciate the growing interest in, and need for, training in environmental studies. However, today most physics departments provide at least one undergraduate course in which the environmental applications of physics are explored. Several successful environmental physics undergraduate degrees are now offered worldwide, together with Masters and postgraduate options. Environmental issues have now also become an integral part of school science programmes, encouraging a new generation of students to appreciate (and study) physics. However, the teaching of environmental physics should not be simply an extension of a physics class with examples of physical laws and principles given an environmental slant; instead it should be taught with the intention of describing the environmental problem/issue and using physics to demonstrate how it may be investigated and/or quantified.

European Journal of Physics has published many articles in recent years demonstrating the application of physics to environmental issues. However, in this special section we wish to demonstrate something of the diversity of topics while giving the reader examples of how to teach the subject. In the first article, Egbert Boeker, Rienk van Grondelle and Piet Blankert (the first two being authors of the text book Environmental Physics [2]) describe how they have developed the teaching of environmental physics to undergraduates. Piet Blankert and Jan Mulder then detail some laboratory experiments that they have used to demonstrate the role of key physical principles in the environment. They have established a website that lecturers and teachers might use to construct their own experiments. Johan Bohman, Bertil Dynefors and Sharon Kühlmann-Berenzon have taken physics out of the classroom and for several years run a successful field campaign requiring their students to develop their own experimental programme. Ross Reynolds explains how our understanding of the environment has been revolutionized by the use of satellite technology which now may be directly accessed from any PC. Finally, as an example of how physics is being used to explain our weather, John Mason and I discuss the physics underlying a thunderstorm, an example of the diversity of physics necessary to explain any natural phenomenon.

In reading these papers it is hoped that the reader will gain an appreciation of how physics is essential to studying our planet and ensuring its future development. Only by training the next generation of students in physics will we be able to meet the challenge of how humanity's increasing impact on the delicate environmental/ecological balance of the Earth may be tempered and controlled. It is the responsibility of those teaching physics to the current and future generations of students to ensure that its importance to the development of environmental research is as great as in the more `traditional' physics research topics of nuclear and particle physics, cosmology and astronomy. European Journal of Physics will therefore welcome further examples of how physics is being taught in an environmental context. It is hoped that these five papers will act as a stimulus and catalyst for further papers from the physics community.

References

[1] Mason N and Hughes P 1998 An Introduction to Environmental Physics (London: Taylor and Francis) [2] Boeker E and van Grondelle R 1999 Environmental Physics 2nd edn (New York: Wiley)

Environmental physics is understood as the physics connected with analysing and mitigating environmental problems. It draws on most sub-disciplines of physics and provides a way of making physics relevant. In this paper the motivation of teaching environmental physics is discussed and examples of course content and supporting student work are given, based on work in the authors' department.

In the framework of teaching environmental physics at the Free University of Amsterdam (VUA) six experiments in environmental physics have been developed. The experiments are incorporated in the student laboratories for physics majors. Therefore, first an overview is given of the set-up and methodology of the student laboratories in general. Next, the experiments are described. They are available on the web for anybody to copy including a typical 'example experiment' to test the equipment and experimental procedure. As an example an experiment on laser Doppler anemometry is described.

With 15 years of experience of teaching environmental physics, we still need to develop our curriculum. In this paper we present our findings from teaching environmental physics in close association with mathematical statistics in an applied field measurement campaign. Here not only environmental physics is taught, but also the concept of experimental planning, design, implementation, and evaluation of a field measurement campaign. The field measurement gives the students the opportunity to follow the whole process starting from experimental planning, including formulating the questions to answer, through design of the experiment, sample collection, analysis, and evaluation, together with the writing of a final report. All possible aspects of the problem that the students are working on can be carefully investigated, but the emphasis has been on understanding the whole process of carrying out a field campaign. This holistic view gives the students more interest in and better motivation for exploring the subject. This course gave the students insight into the field of interdisciplinary environmental research, promoted their creativity, and also gave the teachers a feeling of satisfaction.

Meteorology is a challenging physical science that is ever more important in the modern day world. Weather satellites have been a component in many aspects of both meteorological operations and research—and provide an interesting means of teaching some physical science. They can be used to enliven the basic theory of orbits, to illustrate the environmental 'utility' of sensing both solar and terrestrial radiation (including some radiation laws), to exemplify the theoretical and practical spatial resolution of optical systems, and to illuminate the nature and role of physical processes within the atmosphere. In addition, their data form a very important basis for monitoring global change through time and space averaging of various radiative fluxes.

The salient facts concerning the dynamical, physical and electrical properties of a thunderstorm, and of the detailed structure and associated electric field-changes of lightning flashes, are marshalled to deduce the criteria for a satisfactory quantitative theory of charge generation and separation leading to the growth of electric fields strong enough to initiate and to sustain lightning activity.

A quantitative theory is presented of how charges are generated and separated when supercooled cloud droplets make grazing contact with the undersides of hail pellets (graupel) polarized initially by the Earth's fine-weather electric field. The rebounding droplets acquire a positive charge and are carried by the convective updraught towards the top of the cloud, while the hail pellets carrying a net negative charge fall towards cloud base. This creates a vertical dipole field which increases the polarizing charges on the hail pellets and so accelerates the rates of charge generation and separation, and so reinforces the vertical electrical field, which grows exponentially until insulation of the air breaks down and triggers a lightning flash.

It is demonstrated that a thunderstorm cell, 2 km in diameter, producing small hail falling at 30 mm h⁻¹ can produce vertical electric fields of ∼5000 V cm⁻¹ in about 10 min involving the separation of ∼50 C of charge, enough to initiate a lightning flash which, on average, neutralizes about 20 C. As long as the hail persists, it continues to generate and separate sufficient charge to produce a succession of lightning flashes at about 30 s intervals. More frequent discharges at say 10 s intervals would require high rates of hail production in larger cells but are more likely to be produced by large multi-cellular storms sustained by strong convective currents for perhaps several hours.

The Doppler effect is a phenomenon which relates the frequency of the harmonic waves generated by a moving source with the frequency measured by an observer moving with a different velocity from that of the source. The classical Doppler effect has usually been taught by using a diagram of moving spheres (surfaces with constant phase) centred at the source. This method permits an easy and graphical interpretation of the physics involved for the case in which the source moves with a constant velocity and the observer is at rest, or the reciprocal problem (the source is at rest and the observer moves). Nevertheless it is more difficult to demonstrate, by this method, the relation of the frequencies for a moving source and observer. We present an easy treatment where the Doppler formulae are obtained in a simple way. Different particular cases will be discussed by using this treatment.

We study the propagation of electromagnetic waves in a chiral fluid, where the molecules are described by a simplified version of the Kuhn coupled oscillator model. The eigenmodes of Maxwell's equations are circularly polarized waves. The application of a static magnetic field further leads to a magnetochiral term in the index of refraction of the fluid, which is independent of the wave polarization. A similar result holds when absorption is taken into account. Interference experiments and photochemical reactions have recently demonstrated the existence of the magnetochiral term. The comparison with Faraday rotation in an achiral fluid emphasizes the different symmetry properties of the two effects.

The vector decomposition theorem of Helmholtz leads to a form of the Coulomb gauge in which the potentials are expressed in a form that is totally instantaneous. The scalar potential is expressed in terms of the instantaneous charge density, the vector potential in terms of the instantaneous magnetic field.

The place and size of physics within academic teaching in Romania have obviously changed, and reform of the academic training system is underway. This paper reports on a didactical experiment conducted at the University of Craiova, one of the most representative higher education institutions in Romania, testing the efficiency of some evaluation methods applied to the teaching process of physics. This process functions under the actual conditions in which the academic teaching takes place.

This paper presents a résumé of the history of piezoelectricity during the 19th and 20th centuries. By examining the experiments, concepts and theories presented in Lord Kelvin's scientific communications and those of his contemporaries, this paper aims to show that he played an important role in the development of piezoelectricity. Kelvin's contribution was that he produced the measurement instrumentation that led to the discovery of piezoelectricity and laid some of the essential theoretical groundwork that led to the important applications of piezoelectricity in the 20th century.

Spatial filtering is a well-known process used in coherent optical imaging to modify the image of a partially transparent object (input). A simple method for predicting the effect of a spatial filter inserted in the Fourier plane of the input is set out. The principle of the method rests on general properties of Fraunhofer diffraction and applies to any kind of optical arrangement; it provides, nevertheless, a quantitative treatment of the problem. The phase-contrast method illustrates the simplicity of the method, an example of dark-ground filtering shows its efficiency in laying out numerical calculations.

A flaw is pointed out in the justification given by Charitat and Graner (2003 Eur. J. Phys.24 267) for the use of the Biot–Savart law in the calculation of the magnetic field due to a straight current-carrying wire of finite length.

This letter points out that various parameters that are used in electronic technology are related to one another in ways that involve the fine-structure constant.