About the Book: The purpose of this book is to motivate the students to organize their thoughts and prepare them for solving problems in the vital areas of Modern Physics and Solid State Physics. Each chapter begins with a quick review of the basic concepts of the topics and also, a brief discussion of the equations and formulate that are to be used for solving the problems. Examples and illustrations are provided then and there to expedite the learning process and the working knowledge. About 700 problems have been treated in total; three hundred problems have been worked out providing the required details. Answers for the other four hundred problems have been provided at the end of the book. This book will cater the needs of GATE aspirants and postgraduates in Physical Sciences and certain branches of Engineering aiming for teaching posts in colleges and universities through written tests conducted by U.G.C. The inner feeling of the author is that this book will serve the purpose of students doing their course work in Science and Engineering. About the Author: Dr. S.O. Pillai, after serving for sixteen years as a senior lecturer in Alagappa Chettiar College of Engineering and Technology, Karaikudi, joined College of Engineering in 1976 as Assistant Professor through Tamil Nadu State Service Commission. In 1978, his services were transferred to Anna University on his option. Publication of forty research papers on the basis of his independent experimental work in the fields of Materials Science and Ultrasonic about a dozen articles on different topics of current interest in leading dailies and the students `feedback on his all-round accomplishments during his career, spanning over forty years, fetched him `Dr. Radhakrishnnan Best Teacher Award` for the year 1990. Recognizing his gem as a regular blood donor for over a period of 20 years and for having completed thirty-eight years of unblemished service as on 31-06-1998, Anna University honored him with a citation and an award.