Modern Physics: for Scientists and Engineers
Book Preface
Modern Physics for Scientists and Engineers presents the ideas that have shaped modern physics and provides an introduction to current research in various fields of physics. Written as the text for a first course in modern physics following an introductory course in physics with calculus, the book is intended primarily for classes that are composed mainly of engineering students. The book begins with a brief and focused account of historical events leading to the formulation of modern quantum theory, and then ensuing chapters go deeper into the underlying physics.
The principal goal of this book is to help prepare engineering students for the upper division courses on devices they will later take and to provide physics majors and engineering students an up-to-date description of contemporary physics. The course in modern physics is the last course in physics most engineering students will ever take. For this reason, this book covers a few topics that ordinarily are taught at the junior/senior level. I include such topics in the book because they are relevant or interesting to engineering students and because these topics would ordinarily be unavailable to them. Topics such as Bloch’s theorem, semiconductor heterostructures, quantum wells and barriers, and a phenomenological description of semiconductor lasers help to give engineering students the physics background they need to benefit from the courses they will take later on semiconductor devices, and subjects like the Hartree-Fock theory, Bose-Einstein condensation, the relativistic Dirac equation, and particle physics help physics and engineering students appreciate the range and scope of contemporary physics.
The teaching of modern physics is made easier by computer applets available at the web site for the book. By making use of these applets, students learn to apply the ideas of modern physics to solve realistic problems rather than only the idealized problems appearing in other texts. The Hartree-Fock applet described in Chapter 5 on many-electron atoms comes up showing the periodic table. When a student clicks on a particular atom, the Hartree-Fock program working in the background calculates the atomic wave functions and displays them on the screen. The applet enables a student to appreciate the size of the atom and to calculate the strength of the interactions between the electrons. The ABINIT applet discussed in the chapters on semiconductors is sufficiently accurate to provide a realistic description of the band gaps of semiconductors. Using the applet, a student can change the scale of the unit cell in any one of the crystal directions and see how the band structure of the semiconductor changes.
A course in modern physics covers much that is new for the students causing them continually to adjust concepts that they have acquired earlier in their studies of classical physics. Each new idea is carefully introduced, and the book contains numerous examples that are worked out in detail. All derivations with any degree of complexity are relegated to the appendices. This practice enables the instructor to maintain the pace of the course and to keep the focus on the underlying physics. The appendices labeled by a single Roman letter appear in the back of the book, while appendices labeled by double Roman letters appear at the web site for the course. The goal of the extensive second set of appendices is to provide a broad background of resources for students and teachers without adding unduly to the length of the book. As can be seen from the table of contents, Modern Physics for Scientists and Engineers covers atomic and solid-state physics before covering relativity theory. When I was beginning to teach modern physics, I led off with the special theory of relativity as do most books, but I found that this approach had a number of disadvantages. Following the short treatment of relativity, there was invariably an uncertain juncture when I made the transition back to a nonrelativistic framework in order to introduce the ideas of wave mechanics. The students were asked to make this transition when they were just getting started in the course. Then, the important applications of relativity theory to particle and nuclear physics came at the end of the course whenwe had not used the relativistic formalism for some time. I found it to be better to develop nonrelativistic wave mechanics at the beginning of the course and “go relativistic” in the last four weeks. The course flows better that way. Personally, I find the ideas of Bohr, de Broglie, Schrödinger, and Heisenberg to be as compelling as the ideas of Einstein, but ordinarily they are not presented as well.
The introduction of this book begins with a review of the basic properties of particles and waves from the vantage point of classical physics. This descriptive material is intended to help students consolidate their understanding of classical physics. The second section of the introduction provides a brief overview of the important ideas of the new quantum theory. The introduction leads to the description in Chapter 1 of a few key experiments that enable us to characterize the possible ways in which radiation interacts with matter. In the context of these important experiments, the principles of wave mechanics are introduced for the first time in Chapters 2 and 3. Later chapters of the book deal with particular fields of modern physics. Chapter 6 includes a rather thorough account of the ideas and the technical developments that led to the ruby and helium-neon lasers and also a modern description of laser cooling and trapping of atoms. The treatment of condensed matter physics in Chapters 8 is followed by two chapters devoted to semiconductors that conclude with a phenomenological description of the semiconductor laser. Relativity and particle physics are then treated together. The chapters on relativity include a discussion of relativistic wave equations. I also give an intuitive discussion of how our view of scattering processes changes when we treat the force field of particles quantum mechanically. This discussion leads naturally to a qualitative description of Feynman diagrams and to particle physics.
Most chapters of the book have fewer than forty pages, making it possible for an instructor to cover the main topics in each chapter during one week. To give me some flexibility in presenting the material, I usually choose three or four chapters that I will not cover except for making a few qualitative remarks and then choose another four chapters that I will expect my students to know in only a qualitative way. My selection of the subjects I cover more extensively depends upon the interests of the particular class. Typically, the students might be expected to be able to work problems for the first three chapters and the first section of Chapter 4, for Chapter 7 on Bose-Einstein and Fermi-Dirac statistics, for Chapter 8 on condensed matter physics, for Chapter 11 and the first two sections of Chapter 12 on relativity theory, and the first five sections of Chapter 13 on particle physics. The students might also be asked qualitative quiz questions for Chapters 5, 6, 9, 10, and last two sections of Chapter 12. Suitable quiz questions and problems can be found at the end of each chapter. In my own classes, I give typically six quizzes and two tests during the course of the semester. The practice of giving frequent quizzes keeps students up on the reading and makes them better prepared for our discussions in class. Also, as a practical matter, our physics courses are always competing with the engineering program for the study time of our students. Only by requiring in some concrete way that students keep up with our courses can we expect a continuous investment of effort on their part.
Keeping in mind the interests ofmy engineering students, I have given a rather complete account,of the recent events surrounding the development of lasers and the production of Bose-Einsteincondensation, while providing more focused accounts of older subjects. Some modern subjects such as semiconductor lasers and the quark model are easier to treat pedagogically rather than historically. The history of particle physics, in particular, can appear chaotic to an elementary student.
I feel strongly that any class in physics should reach out to the broad majority of students, but that the class also should allow students the opportunity to follow their interests beyond the level of the general course. The introduction and the first three chapters of the book provide an introduction to quantum mechanics at an elementary level. These introductory chapters are followed by chapters describing the various fields of contemporary physics: atomic, statistical, and condensed matter physics, relativity theory, and particle and nuclear physics. The introductory chapters of the book are accessible to a broad range of modern physics students, and the chapters on the fields of modern physics each begin at the same level of difficulty as the introductory chapters. However, the chapters on the fields of modern physics gradually become more difficult as the range of the subjects covered increases. Also, the topical chapters treat a few subjects which are above the level of the general course. The teacher can ensure that the course is at the proper level of difficulty by omitting difficult sections and guiding the students through longer chapters that are included in their entirety.
This book, which covers the entire range of topics in contemporary physics, was made possible by the active participation of many physicists who are at the forefront of research in their field of physics. For Bose-Einstein condensation I would like to thank Eric Cornell, one of the recipients of the Nobel Prize in 2001, for reading my description of the work of his group and sending me several important suggestions. In the field of condensed matter physics, I would like to thank John Wilkins, who has served as Chair of the division of condensed matter physics of the American Physics Society, for reading early versions of my chapters on the electronic structure of solids and semiconductor lasers and managing to keep me on track. I am also thankful to Mike Santos and Michael Morrison at the University of Oklahoma, John Davies of University of Glasgow, Massimiliano Galeazzi at University of Miami, and Wael Karain of Birzeit University for reading my four chapters on condensed matter physics and sending me many valuable suggestions, and to Jim Davenport, Dick Watson, and Vic Emory for their hospitality in the condensed matter theory group of Brookhaven National Laboratory during the summer when I wrote the first draft of my solid state chapters. I appreciate the willingness of Shi Yu Wu and Peter France of the University of Louisville for allowing me to attend their classes on condensed matter physics.
In the area of atomic physics, I would like to thank Charlotte Froese Fisher of the National Institute of Standards and Technology for providing me with a version of the Hartree-Fock program she has developed and also providing the original version of the Hartree-Fock applet, which Simon Rochester and I developed further so that it could be used in conjunction with this book. I would like to thank Ingvar Lindgren, my coauthor of the book, Atomic Many-Body Theory, and Sten Salomonson of Göteborg University for many insightful discussions, and Andy Weiss of the National Institute of Standards and Technology and Ghassan Andoni of Birzeit University for reading an early draft of my chapters on atomic physics and giving me several helpful comments
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