THE ELECTRIC FORCE OF A CURRENT: WEBER AND THE SURFACE CHARGES OF RESISTIVE CONDUCTORS CARRYING STEADY CURRENTS

Abstract

Is there an interaction -some reciprocal force -between a current-carrying conductor and a stationary charge nearby? Beneath this simple question lie some remarkable misunderstandings, which are well illustrated by the fact that the answers to it commonly found in the scientific literature and also in many text books are incorrect. In case there is any uncertainty about the answer, all doubt will be eliminated by this book. It tackles the question in a brilliant and comprehensive manner, with numerous hints for relevant experiments and with impressive mathematical thoroughness. It is astonishing to learn that, as early as the middle of the 19th century, the German physicists Weber and Kirchhoff had derived and published the answer to this problem; however, their work was poorly received by the scientific community, and many rejected it as incorrect. The reasons behind this scientific setback, which are presented in detail in this book and supported with numerous quotations from the literature, represent a real treasure trove for readers interested in the history of science. It becomes clear that even in the exact science of physics people at times violate basic scientific principles, for instance by referring to the results of experiments which have never been carried out for the purpose under discussion. This book helps readers not only to develop a detailed knowledge of a seriously neglected aspect of the so-called simple electric circuit, but reminds us also that even eminent physicists can be mistaken, that mistakes maybe transferred from one text book generation to the next and that therefore persistent, watchful and critical reflection is required. A didactic comment is appropriate here. The traditional approach to teaching electric circuits based on current and potential difference is called into question by this book. When dealing with electric current one usually pictures drifting electrons, while for the terms “voltage” or “potential difference” one directly refers to the abstract notion of energy, with no opportunity for visualization. Experience shows that only few school students really understand what “voltage” and “potential difference” mean. The inevitable result of failure to understand such basic terms is that many students lose interest in physics. Those whose confidence in their understanding of science is still fragile, may attribute failure to grasp these basic concepts as due to their own lack of talent. Physics remains a popular and crucial subject, so the large numbers of students who each year study the subject implies that the search for less abstract and therefore more readily understood alternatives to traditional approaches is urgent. This book offers such an alternative. It shows that in respect to surface charges there is no fundamental difference between an electrostatic system and the flow of an electric current. It refers to recent curriculum developments concerning “voltage” and “potential difference” and presents a comprehensive survey of related scientific publications, that have appeared since the early papers by Weber and Kirchhoff. Why should we refer to drifting electrons when we teach electric current and yet not refer to drifting surface charges when teaching voltage or potential difference? The final objective of the curriculum when voltage is covered will certainly be to define it quantitatively in terms of energy. For didactic reasons, however ,it does not seem to be justifiable to omit a qualitative and more concrete preliminary stage, unless there is a lack of knowledge about the existence of surface charges. In the present market there are newly developed curriculum materials that cover basic electricity, to which the content of this book relates strongly. Comparison of the approach that this book proposes with more traditional approaches should dispel any doubts about the need for the methods that it describes. This book provides a crucial step along the path to a better understanding of electrical phenomenon especially the movement of electrons in electric circuits.