Geometric Optics (Lecture I) Chapter 26 Geometric Optics (Lecture I) Dr. Jie Zou PHY 1161

Outline Reflection of light Refraction of light The law of reflection Specular and diffuse reflection Refraction of light Index of refraction Snell’s law Dr. Jie Zou PHY 1161

Rays and Wave Fronts Describe light in terms of “wave fronts” and “rays” Wave fronts: In the case of a water wave created by a rock dropped into a still pool of water, the wave fronts indicate the crests of water waves. Rays: The radial motion of the waves is indicated by the outward-pointing arrows, referred to as rays. Dr. Jie Zou PHY 1161

The Law of Reflection Reflection: Light changes its direction as being reflected onto a new path from for example a mirror or other shiny objects. Law of Reflection: r = i and the incident ray, the reflected ray, and the normal lie in the same plane. i = angle of incidence r = angle of reflection Dr. Jie Zou PHY 1161

Specular and Diffuse Reflection Specular reflection: the reflection of light from a smooth surface, in which all the reflected light propagates in a single direction. Diffuse reflection: If the surface is rough, the reflected light is sent out in a variety of directions. Dr. Jie Zou PHY 1161

The Refraction of Light Refraction: When a wave propagates from a medium in which its speed is v1 to another in which its speed is v2v1 , it will, in general, change its direction of motion. This phenomena is called refraction. Refraction is the bending of wave fronts and change in direction of propagation due to a change in speed. Dr. Jie Zou PHY 1161

Index of Refraction and Snell’s Law The speed of light in a given medium, v, is determined by the medium’s index of refraction, n. v = c/n For example: Diamond, n = 2.42; Flint glass, n=1.66; Water, n = 1.33; Air, n = 1.000293 (see Table 26-2) Snell’s Law: n1sin1 = n2sin2 Dr. Jie Zou PHY 1161

Example 26-4 A beam of light in air enters (a) water (n = 1.33) or (b) glass (n = 1.50) at an angle of 60.0° relative to the normal. Find the angle of refraction for each case. Dr. Jie Zou PHY 1161

Homework #11 Chapter 26, P. 941-942, Problems: #50, 51, 53, 54 (Physics, Walker, 4th edition). Dr. Jie Zou PHY 1161