Five experiments and 19 activities are presented in this Unit 5 handbook. The experiments are related to electrolysis, charge-to-mass ratio, elementary charge determination, photoelectric effects, and spectroscopic analyses. The activities are concerned with Dalton's theory, water electrolysis, periodic tables, single-electron plating, cloud chambers, accelerators, counters, spectrographs, Einstein's work, cathode rays, x-rays, ionization, differences in atomic models, Rutherford atom, and de Broglie waves. A reprinted chemi-crostic and a specially designed cigar box atom are also incorporated in the activities. Moreover, three film loops are introduced in terms of production of sodium electrolysis, Thomson's atomic model, and Rutherford scattering. Demonstrations, construction projects, and self-directed instructions are stressed in the activities. The four chapters in the handbook are designed to correspond to the text, with complete instructions in each experiment. Some experiments and activities are suggested for assignment, and the remaining are used at student discretion. Illustrations are provided for explanation purposes. The work of Harvard Project Physics has been financially supported by: the Carnegie Corporation of New York, the Ford Foundation, the National Science Foundation, the Alfred P. Sloan Foundation, the United States Office of Education, and Harvard University. (CC)