Chapter 22

1. Chapter 22 Geometric Optics

2. Ray model of light • Most often, light travels in straight lines, or rays • Successfully explains reflection, refraction, and image formation by mirrors and lenses • Ray model doesn’t account for wave characteristics or relativity • Analysis of light using the ray model is known as geometric optics

3. Reflection • When light hits a surface, it can bounce off, be absorbed by, or travel through it • Reflection is when it bounces • If we see something that doesn’t produce its own light, it’s usually because light has reflected off it Transmitted Light Reflected Light Sunlight through Earth’s atmosphere Direct sunlight

4. Reflection • Incident ray—incoming ray of light • Reflected ray—outgoing ray of light • Normal line—line drawn perpendicular to the surface at the point where the light hits • Angle of incidence (i)—angle between the incident ray and the normal line • Angle of reflection (r)—angle between the reflected ray and the normal line • Law of Reflection--i = r

5. Reflection • Specular reflection—reflection off a flat (mirrored) surface • Parallel rays coming in are parallel rays going out • Mirrors, glass, some metal • Diffuse reflection—reflection off a rough surface • Light rays are scattered • Blackboard, paper, most surfaces

6. Refraction Snell’s Law: • Index of refraction (n) • How much a material bends light

7. Total Internal Reflection • Light is only partially refracted at a boundary • Sometimes, it’s not refracted at all • When n1 > n2 • Critical angle (c)—angle of incidence beyond which all light is reflected back into the medium

8. Gems

9. Primary Colors • How Pigments Add • Dyes • Colored objects • How light adds • Television sets • Monitors

10. Reflection • Images—the actual or apparent confluence of light rays • Real image—light rays actually converge • Image can be projected onto a screen • Virtual image—light rays seem to converge, but in reality do not • All images in a flat mirror are virtual

11. Reflection

12. Reflection • Image distance (di)—distance between the mirror and the image • Object distance (do)—distance between the mirror and the object • How tall does a mirror have to be in order for you to see your whole body?

13. Curved Mirrors • Scatter light in controlled ways • Can produce real or virtual images • Can magnify or minify • Can be analyzed analytically (equations) or graphically (drawing the rays) • Spherical are most common • Parabolic are most precise

14. Spherical Mirrors • Concave—inside of a sphere • Convex—outside of a sphere

15. Concave Mirrors • Principal axis—line drawn perpendicular to the center of the curved mirror • Through the center of curvature (C) if spherical • Focal point (F)—point through which all rays parallel to the axis are reflected • F is ½ as far away as C, C = 2F

16. Concave Mirrors • Spherical aberration—F is less defined as rays move farther away from axis • Scientists work only with small sections • Parabolic mirrors do not experience this aberration

17. Concave Mirrors • Ray tracing—graphically drawing rays of light to determine the position and size of an image • Objects represented as arrows, with the head being the top, bottom on the axis • Any two of three principal rays can be used, starting from the top of the object • Image drawn  from axis to intersection of rays

18. Concave Mirrors • Principal ray 1—parallel to principal axis • Reflected through F • Principal ray 2—through F • Reflected parallel to principal axis • Principal ray 3—through C • Reflected straight back through C • Any 2 will do, but a third will tell you how good your drawing is

19. Characteristics of images • Does it exist? • Real image—rays of light actually converge • Image distance is positive • Virtual image—rays of light don’t actually converge • Image distance is negative • Orientation • Right side up (+h) or upside down (-h) • Size • Magnified or minified