summarize this prelab, highlighting all the important equations and concepts:

2.1 Theory 2.1.1 Rays Light is a wave phenomenon. However, under certain circumstances, light (or another wave) can be treated approximately in terms of line segments that are called rays. Those cases where such a description is possible con- atitute the subject matter of geometrical optics. A ray may be thought of as a single line representing a narrow beam of light. A simple example will demonstrate the use of rays in predicting light behavior. Suppose a group of rays impinge on an object, as in Fig. 2.1. The object blocks some rays. leaving a shadow behind the object. In Weeks 6-8, you will study cases were the ray approximation is not valid. Qualitatively, the ray approximation is valid whenever the size of the object (such as the obstacle in Fig. 2.1) is large compared to the wavelength of light. Typical wavelengths of visible light are quite small (~ 5 x 10-7 m), so in everyday life the ray approximation is often satisfied