This book covers both the pre-quantum and post-quantum development of theoretical physics in a straightforward but fairly rigorous style. Unlike most modern physics courses which gloss over the basic physic subjects in preference to specialised topics like solid state physics, electronics, plasma physics, nanotechnology, cosmology, astrophysics and computer science, this book brings together the various branches of theoretical physics on one platform to give a panoramic view of the subject. The first four chapters of the book deal with the classical topics of Hamiltonian mechanics, theories of relativity, electromagnetic theory of radiation and thermodynamics. They are followed by chapters on atomic spectra and quantum mechanics, spectra of diatomic molecules, quantum theory of radiation, statistical mechanics, and nuclear and particle physics. Guided exercises form a unique feature of this book. The broad coverage of topics in theoretical physics makes this book an invaluable reference for senior undergraduate and postgraduate students of all branches of physics as well as research workers and physics teachers. The book will also serve for a foundation course for allied subjects such as astrophysics, geophysics, meteorology, laser physics and plasma physics.

**(June 1928 to November 2007), former chairman of the Department of Astronomy, Osmania University, and director of Nizamiah and Japal-Rangapur Observatories, spearheaded the growth of astrophysics in India. He was instrumental in laying the foundation in 1972 of the Astronomical Society of India, which he served in various capacities. Several of his students went on to become astronomers of the future. A recipient of the Andhra Pradesh Government's Best Teacher Award in 1984, Professor Abhyankar's theoretical work in stellar and planetary atmosphere and binary stars is internationally acclaimed. He has published more than 150 research papers and numerous popular articles. He is the author of two books on astrophysics—one on stars and galaxies and the other on solar physics, both published by Universities Press—as well as a scholarly and thought-provoking monograph on pre-Siddhantic astronomy in India. Professor Abhyankar passed away in November 2007 while working on this book.**

*K D Abhyankar***, after obtaining his PhD from the University of Pune, worked at research and teaching at the TIFR, Mumbai, HH Wills Physics Laboratory, Bristol, CCS University, Meerut, and HP University, Shimla, before moving to the University of Pune in 1984. He retired from the university in 2002, after which he worked as an Honorary Visiting Scientist at the National Centre for Radio Physics, TIFR, till recently. Professor Joshi has contributed several papers in journals and has also written for general readers—school children and college students. He has written six books, two of which are in Marathi and one in Hindi, and edited three others. Some of these books have been translated into Chinese, Persian and other languages.**

*A W Joshi***Chapter 1. Hamiltonian Mechanics**Introduction; System of n particles in Cartesian coordinates; Generalised quantities; Validity of Lagrangian and Hamiltonian equations in generalized coordinates; Principle of least action; Poisson brackets; Contact transformation; Hamilton-Jacobi equation; Some applications of Hamilton-Jacobi equations; The two-body problem; Virial theorem; Problems

**Chapter 2. Special and General Theories of Relativity**Background; Lorentz transformations; Generalised Lorentz transformations; Kinematic applications; Minkowski space; Relativistic mechanics; Elements of general theory of relativity; Gravitational lensing; Problems

**Chapter 3. Classical Theory of Radiation**Maxwell’s equations; Electromagnetic waves; Electromagnetic radiation by a molecule; Harmonic oscillator; Properties of transmitting medium; Relativistic transformation of electromagnetic fields; Electrodynamics of moving charges; Scattering of small particles; Appendix; Problems

**Chapter 4. Thermodynamics**Definitions; Equation of state; Changes in thermodynamic systems; First law of thermodynamics; Specific heats; Second law of thermodynamics; Absolute temperature; Entropy; The phase rule; Important thermodynamic functions; Theorem of radiation; Spectrum of thermal radiation; Problems

**Chapter 5. Atomic Spectra and Quantum Mechanics**Bohr’s theory of hydrogen atom; Sommerfeld’s modification of Bohr’s theory; Fundamentals of quantum mechanics; One-dimensional motion; Hydrogen and hydrogen-like atoms in quantum mechanics; Electron spin; Effect of spin in other atoms; Zeeman and Stark effects; Problems

**Chapter 6. Molecular Spectra**Introduction; Pure rotational bands; Vibration-rotation bands; Electronic bands; Multiplet structure of electronic states; Isotope effects; Strengths of bands and lines; Some typical examples of molecular spectra; Problems

**Chapter 7. Quantum Theory of Radiation**Quantization of pure radiation; Radiation and matter; First order approximation for transition; Computation of transition probabilities; Absorption, emission, and Einstein coefficients; Weisskopf.-Wigner picture; Problems

**Chapter 8. Statistical Mechanics**Kinetic theory of gases; Fundamentals of statistical mechanics; Expression for probability; Population functions; Equation of state for fermions; Some aspects of Bose gas; Classical non-degenerate state; Departure from thermodynamic equilibrium; Problems

**Chapter 9. Elements of Nuclear and Particle Physics**Discovery of the nucleus; Structure of the nucleus; Nuclear reactions and liquid-drop model of nucleus; Elements of particle physics; Applications in astrophysics; Problems Bibliography Index