Textbook in PDF format In this book is presented an introduction to classical electrodynamics, with emphasis on the oscillatory aspects of the electromagnetic field - that is, on vibrations, waves, radiation, and the interaction of waves with matter. The content is designed primarily for the use of second or third year students of physics and engineering who have had a semester of mechanics and a semester of electricity and magnetism. The aim throughout has been to provide a mathematically unsophisticated treatment of the subject, but one that stresses modern applications of the principles involved. The book is an outgrowth of a one-semester course taught by us during the past five years at the Massachusetts Institute of Technology. And although, traditionally, it has been a course for sophomores in the Department of Physics, it has been well attended by students from other departments in the Schools Qf Science and Engineering. During our involvement in the course we have not used a prescribed text; instead we distributed notes which were revised and extended each year. This book is the culmination of four successive editions which have been exposed to the scrutiny of some 2000 students. There are eight chapters. In the first chapter, the reader is introduced to the physics of oscillators. Mechanical oscillations are often more easily visualized than electrical ones, and for that reason examples from mechanical systems are freely used. But the stress is on electrical systems and on the motion of charged particles in particular. For example, to give the student as much exposure as possible, we prepared (Appendix 3) a Fortran computer code that allows him to watch the motion of an electron subjected simultaneously to a de magnetic field and a crossed RF electric field. Nonlinear and coupled oscillations are also included in this chapter. Chapter 2 deals with waves; for the sake of simplicity only the scalar wave equation is discussed at this stage, and examples are drawn from waves on strings, sound waves in pipes, etc. Fourier analysis of periodic disturbances and analysis of wave packets are introduced at the end of the chapter. After a brief review of Maxwell's equations, Chapter 3 is taken up with the propagation of electromagnetic waves in vacuum. Wave polarization, linear and angular momentum associated with a wave, and radiation pressure are discussed. The whole of Chapter 4 is devoted to the classical problem of radiation from accelerated charges. The radiation field is calculated by the method of J. J. Thomson. This approach is physically very revealing and for that reason is preferred, in an introductory text such as this one, to the formal mathematical techniques used in more advanced books. The latter part of the chapter is taken up with applications: to antennas, to bremsstrahlung, to cyclotron radiation. A section on black-body radiation is also included. Guided waves and resonant cavities are discussed in Chapter 5. Traditionally, these subjects were limited in their usefulness to radio and microwave frequencies. Today, lasers and integrated optics make this subject relevant also to optical wavelengths, a fact which we tried to bring out in the text. Chapter 6 is devoted to a discussion of the interaction of electromagnetic waves with matter — dielectrics, metals, and plasmas. On the microscopic level the subject is developed along the lines of the classical electron theory of Lorentz. On the macroscopic level, Maxwell's field equations are formulated in terms of "physical" quantities, namely E, В, P, and M. The traditional use of D and H is purposely avoided in this book since at this level of a student's experience these quantities tend to confuse. Chapter 7 deals with boundary value problems: reflection and refraction at dielectric and metal surfaces. This is followed by a discussion of Thomson and Rayleigh scattering and the problem of radiation reaction. The chapter ends with an account of stimulated emission and of the free electron laser. A nonquantum mechanical approach to this problem is adopted. Chapter 8 deals with interference and diffraction. Here we revert to scalar waves and the approximate theories of Huygens, Fresnel, and Kirchhoff. This is forced upon us by the extreme mathematical difficulties encountered in a rigorous electromagnetic treatment of this subject. Short Appendices on the addition of periodic vibrations and on the use of complex numbers are included. The book ends with some 70 problems for home assignment. M. K. S. units are used throughout. The book contains more material than can be covered in one semester. The individual instructor must pick his own balance between the topics and examples to be covered. Furthermore, the material presented lends itself to a wide range of lecture demonstrations which can be both instructive and fun, for the students as well as the lecturer, but that further limits the available time. We have made no attempt to prejudge those chapters or sections which might be appropriate for a one semester course as there are many variables to be considered in such a selection. The oscillator The wave The electromagnetic field Sources of radiation Guided waves Interaction of waves with matter Reflection, refraction, and scattering Interference and diffraction Appendix 1 A little mathematics on superposition of periodic motions Appendix 2 A little mathematics on complex quantities Appendix 3 Electron subjected to an rf electric field orthogonal to a steady magnetic field Problems Units and dimensions Some constants Acknowledgments Index