In preparing the book, the author has taken special care to present the topics in a coherent,simple and straightforward manner. SI units have been used throughout this book. Numericalproblems are solved in each chapter wherever necessary for the better understanding of thesubject. Exercises including problems have been given at the end of each chapter. This book is intended as a textbook for B.Sc and M.Sc Physics curriculum. It is also helpfulto the students of Chemistry, Materials Science and Engineering and those appearing forNational Eligibility Test (NET) and State Lecturer Eligibility Test (SLET).