H S Hans was formerly UGC Emeritus Fellow in the Department of physics, Panjab University, Chandigarh, where he had been Professor and Head since 1967. He obtained his M Sc from Banaras Hindu University and his Ph D from Aligarh Muslim University in experimental nuclear physics, an area which he pursued abroad in Swarthmore, Texas, A and M, Agronne National Laboratory, Rochester University (USA) and Birmungam University (UK). A cyclotron laboratory at Panjab University is an outcome of his efforts. Professor Hans has published a large number of research papers in international and national journals of repute. He has been UGC National Lecturer and National Fellow. He has been, for many years, the coordinator of ULP (COSIP) of his department, which inspired a number of authors to develop a series of textbooks of which this book is the first attempt. He has also authored a book on Nuclear Physics (2001) for postgraduate students.

S P Puri, ex UGC Emeritus Fellow, was Professor and Chairman, Department of Physics, Panjab University, Chandigarh. He received his M Sc from Panjab University and Ph D from Aligarh Muslim University, Aligarh. He did his postdoctoral research at Bartol Research Foundation, Swarthmore PA (USA). He later joined University of Alabama (USA) as Visiting Assistant Professor of Physics and also visited University of Uppsala, Sweden. He was one of the earliest in the country to establish the studies of Nuclear Gamma-Ray Resonance (Mossbauer Effect) in Roorkee in 1963. His other special fields of interest include Crystal and Molecular Field Theories. He has authored a number of books including Special Theory of Relativity (1972); Fundamentals of Vibrations and Waves (1989); Classical Electrodynamics (1990) and compiled Collected Scientific Papers of Prof PS Gill (1971). Being deeply involved in pedagogy and with a view to promoting the learning processes, he has developed solutions manuals of all of his textbooks.