Elements Of Electricity

ELEMENTS OF ELECTRICITY BY ANTHONY ZELENY, PH. D. Professor of Physics, University of Minnesota SECOND EDITION FIFTH IMPRESSION McGRAW-HILL BOOK COMPANY, INC. NEW YORK AND LONDON 1935, BY THE McGRAW-HiLL BOOK COMPANY, PREFACE TO THE SECOND EDITION The treatment of the electromotive force impressed by a moving magnetic, field on a stationary conductor has been changed from that given in the first edition to one requiring the introduction of one more basic phenomenon which, however, is shown to be a consequence of relative motion. This treatment makes clear the distinction between the conservative and the non conservative electric fields and thereby also clarifies the picturing of electromagnetic pulses. The action of the thermocouple is treated at length and unusual clarity is believed to have, been attained by representing diagrammatically the magnitudes of the contributing Thomson and Peltier effects. The chapter on Alternating Currents has been enlarged, and capacitive circuits are now treated as fully as the inductive. The reciprocal relationship between electric and magnetic fields is fully developed. Practically every article is improved in some manner, the more modern topics arc brought to date, and three appendixes are added. The author wishes to acknowledge his indebtedness to those who pointed out errors in the first edition and suggested changes. They contributed much toward the making of a significant improvement in the text. ANTHONY ZELENY. MINNEAPOLIS, MINN , April, 1935 PREFACE TO THE FIRST EDITION This text is the outgrowth of many years of teaching the subject of electricity to engineering, pre-medical, and arts students in the first course of college physics. The ever-increasing need in all fields for a better understanding of electricity and the continual encroachment of new subjects on the time of the student require that much be taught in the least possible time. The first course, being the only one in electricity for the great majority of the students, must be sufficiently comprehensive and contain enough practical information to meet, as far as possible, the needs common to all the groups. It must give the clearest possible picture of the interrelations between the various phenomena by explaining them in terms of the most basic facts and concepts. The student then acquires a foundation which enables him to formulate the quantitative relation ships and to obtain, thereby, a training in analytical thinking and an ability to read intelligently the ordinary literature of the subject. In attempting to meet these requirements, and in the hope of improving the exposition of the subject, the author has departed considerably from the usual method of presentation. All the major phenomena are explained in terms of physical concepts which are reducible to two basic phenomena. This explanation is made possible by taking the point of view that electric fields have inertia, interpenetrates freely, and are inseparable from their elemental charges. Superposed fields are then construed to exist as independent fields even though they neutralize one another's action on electric charges. It follows that an uncharged body is surrounded by both a negative electric field, which is the resultant of the superposed elemental fields of all its electrons, and an equal opposite positive field due to the fields of all its protons. It also follows that when electrons are in motion within or with a conductor, each electron is surrounded by a magnetic field which is inseparably associated with the moving elemental electric field. A magnetic field is therefore regarded as an aspect of a moving electric field...