Chapter 44
Geometrical Optics
Opticsis the branch of physics concerned with the study of light. It may be divided into three main areas:
- Geometrical opticsis the study of mirrors, lenses, and the images formed by these devices. Geometrical
optics generally ignores the wave nature of light. - Physical opticsstudies phenomena related to the wave nature of light: interference, diffraction, polar-
ization, and so on. - Photometryis the study of the brightness of light.
We’ll begin our study of optics in this chapter with geometrical optics, studying mirrors first, then lenses.
44.1 Law of Reflection......................................
We begin with the simplest of the laws of optics, thelaw of reflection. The law of reflection states that when
a light ray strikes a reflective surface (e.g. a mirror), it will reflect off of that surface at an angle equal to its
incident angle:
iDr (44.1)Hereiis theangle of incidence, andris theangle of reflection. In optics, all angles are by convention
measured with respect to thenormal(perpendicular) to the surface.