18 Ray Optics Slide 18-2

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Light rays travel in straight lines. The Ray Model of Light Light rays travel in straight lines. Light rays can cross. A light ray travels forever unless it interacts with matter. An object is a source of light rays. The eye sees by focusing a bundle of rays. Slide 18-9

Sources of Light Rays: Self-Luminous Objects A ray source A point source An extended source A parallel-ray source Slide 18-10

Seeing Objects Seeing a point or extended source Seeing an object by scattered light Seeing a ray source Slide 18-11

Shadows Slide 18-12

The Law of Reflection The incident ray and the reflected ray are both in the same plane, which is perpendicular to the surface, and The angle of reflection equals the angle of incidence: θr = θi . Slide 18-15

The Plane Mirror Slide 18-16

Refraction Slide 18-17

Snell’s Law of Refraction Slide 18-18

Slide 18-19

Total Internal Reflection Slide 18-21

Locating a Virtual Image Slide 18-22

Thin Lenses and Ray Tracing The focal point of a converging lens The focal point of a diverging lens Slide 18-23

Three Important Sets of Rays: Converging Lenses Slide 18-24

Ray Tracing: Real Images Slide 18-25

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Magnification of a Lens or Mirror Slide 18-29

Ray Tracing: Virtual Images Slide 18-30

Three Important Sets of Rays: Diverging Lenses Slide 18-31

Slide 18-32

Spherical Mirrors and Ray Tracing The focal point of a concave mirror The focal point of a convex mirror Slide 18-35

Three Sets of Special Rays for a Concave Mirror Slide 18-36

A Real Image Formed by a Concave Mirror Slide 18-37

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Three Sets of Special Rays for a Convex Mirror Slide 18-39

Ray Tracing for a Convex Mirror Slide 18-40

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The Thin-Lens Equation Slide 18-42

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Summary Slide 18-44

Reading Quiz When an object like a tree is illuminated by the sun, and you are looking toward the tree, light rays leave the object only from points at the top and base of the tree, but in every direction. from every point on the surface of the tree, but only toward your eyes. only from points at the top and base of the tree, but only toward your eyes from every point on the surface of the tree and in every direction. Answer: D Slide 18-5

Answer When an object like a tree is illuminated by the sun, and you are looking toward the tree, light rays leave the object only from points at the top and base of the tree, but in every direction. from every point on the surface of the tree, but only toward your eyes. only from points at the top and base of the tree, but only toward your eyes from every point on the surface of the tree and in every direction. Answer: D Slide 18-6

Reading Quiz A light ray can change direction when going from one material into another. This phenomenon is known as reflection. absorption. refraction. scattering. Answer: C Slide 18-7

Answer A light ray can change direction when going from one material into another. This phenomenon is known as reflection. absorption. refraction. scattering. Answer: C Slide 18-8

Example Problem If the aperture is very small, how far apart on the screen built into the left side of the box are the images of the point-like red and green light sources? Slide 18-13

Example Problem If the aperture is a circle 1 cm in diameter, what are the size and shape of the image of the green point-like light source? Do you need to know how far below the center of the aperture that source is? Slide 18-14

Example Problem What is the index of refraction of the plastic if a ray is refracted as in the figure? Slide 18-20

Checking Understanding Which of these ray diagrams is possibly correct? Answer: D Slide 18-27

Answer Which of these ray diagrams is possibly correct? D Slide 18-28 Answer: D Slide 18-28

Checking Understanding In this figure the image is produced by a lens. At which position A–E is the lens? Answer: D Slide 18-33

Answer In this figure the image is produced by a lens. At which position A–E is the lens? D Answer: D Slide 18-34