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Reflection and Refraction Chapter 29 Reflection • Reflection – some or all of a wave bounces back into the first medium when hitting a boundary of a second medium • When all the wave energy is reflected back instead of being transmitted, it is total reflection • If some energy is transmitted and some is reflected, the wave is partially reflected Reflection The Law of Reflection • Angle of Incidence – angle made by the incident ray and the normal • Angle of Reflection – angle made by the reflected ray and the normal • Law of Reflection – Angle of Incidence = Angle of Reflection The Law of Reflection Mirrors • Virtual Image – the point located behind a mirror where an object appears to originate • Your eye cannot tell the difference between an object and its virtual image • The image is as far behind a mirror as the object is in front of the mirror Convex Mirror • The virtual image is smaller and closer to the mirror than the object. Concave Mirror • The virtual image is larger and farther away than the object Diffuse Reflection • Diffuse Reflection – light incident on a rough surface is reflected in many directions • A surface’s roughness is dependent upon the wavelength of the wave incident upon that surface; the longer the wavelength, the smoother the surface will appear • To a piece of paper, light is reflecting diffusely Diffuse Reflection Reflection of Sound • An echo is reflected sound • Sound reflects from all surfaces of a room • Acoustics is the study of the way sound reflects off of objects in a room • Reverberations – Multiple reflections of sound within a room • The walls of concert halls are designed to make the reflection of sound diffuse Reflection of Sound Refraction • Refraction – the change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds • Wave Fronts – lines that represent the position of different crests • At each point along a wave front, the wave is moving perpendicular to the wave front • The direction of motion is best represented by a ray Refraction Refraction of Sound • Sound waves are refracted when parts of a wave front travel at different speeds • This happens in uneven winds or temperatures • Sound waves tend to bend away from warm ground, since it travels faster in warmer air • On a cold night, the speed of sound is slower near the ground than above, so we can hear over larger distances Refraction of Sound Refraction of Light • A pond or swimming pool may appear shallower than they actually are, a pencil in a glass of water will appear bent • All of these effects are caused by changes in the speed of light as it passes from one medium to another, or through varying temperatures and densities of the same medium – which changes the directions of light rays • Formula for the Index of Refraction (n) = (speed of light in vacuum)/(speed of light in material) Refraction of Light Atmospheric Refraction • On hot days there may be a layer of very hot air in contact with the ground, the light will travel faster through this air and will bend, creating a mirage • When you watch the sun set, you can still see the sun for several minutes after it has sunk below the horizon, because light is refracted by Earth’s atmosphere Atmospheric Refraction Total Internal Reflection • Critical Angle – the minimum angle of incidence for which a light ray is totally reflected within a medium • Total Internal Reflection – the 100% reflection of light that strikes the boundary between two media at an angle greater than the critical angle • Optical fibers utilize the concept of total internal reflection to feed light from one location to another, these cables are very useful for communications Total Internal Reflection Assignment • Read Chapter 29 (pg. 442-459) • Do Chapter 29 Assessment #28-41