Waves and Light

Abstract

The preceding chapters have illustrated the power of the atomic hypothesis. From the observations of Dalton and Gay-Lussac we were able to deduce the chemical composition of molecules and determine ratios of atomic masses. In the kinetic theory we modeled gas atoms and molecules as featureless hard spheres, which allowed us to interpret physical quantities such as temperature and pressure in terms of the more fundamental concepts of kinetic energy and momentum. Using values of the mean free path determined from measurements of the viscosity of gases, we could estimate Avogadro’s number and, consequently, the diameter and mass of single atoms. Later, the experiments of Faraday, Thomson, and Millikan proved conclusively that atoms have internal structure, i.e., they are themselves composed of smaller, more fundamental particles. We have identified one of these particles—the electron—and have found that it is removable, replaceable, and interchangeable. What other particles are contained in atoms? How are they assembled, and what holds them together?