The differential equation describing the propagation of waves is presented and the technique of solving it for a given set of boundary conditions is established. Pressure in solids and liquids are shown to satisfy the wave equation. A formula giving the speed of sound in a gas as a function of temperature and of the specific heat of the gas is derived. The decibel scale for the measurement of sound loudness is defined. The wave nature of light is reviewed.
Index of refraction is defined.
The laws of reflection and refraction of light at a boundary between different media are established. The basic principles of geometrical optics are established. Formulae relating the radius of curvature of spherical lenses and mirrors to focal length, and relating image size and distance, object size and distance, and focal length are used to analyzed optical problems. The designs of the compound microscope and the telescope are explored. The interference and diffraction of light by a single slit or aperture are formulated.