Waves and Light

Abstract

The preceding chapters have illustrated the power of the atomic hypothesis. From the observations of Dalton and Gay–Lussac you saw how to deduce the chemical composition of molecules and determine ratios of atomic masses. You also saw that by modeling gas atoms and molecules as featureless hard spheres, you could develop a kinetic theory of gases that allowed you to interpret physical quantities such as temperature and pressure in terms of the more fundamental concepts of kinetic energy and momentum. Also you saw how the kinetic theory can be used to connect the concept of mean free path to measured values of the viscosity of gases to obtain an estimate of Avogadro’s number and, consequently, the size and mass of single atoms. Later, the experiments of Faraday, Thomson, and Millikan proved that atoms have internal structure, i.e., they are themselves composed of smaller, more fundamental particles. One of these particles is the electron, and it is removable, replaceable, and inter-changeable. What other particles are contained in atoms? How are they assembled, and what holds them together?