Chapter 11.pdf

RefractionFigure 11.30 The spoon appears tobe broken because light rays changedirection as they move from air intowater and from water into air.Although light travels in straight lines, it bends when it passes fromone medium into another, such as from air into water. A medium(plural: media) is a material that is being used or is undergoing aprocess. The bending of light rays as they pass between two differentmedia is called refraction. Refraction causes some very interestingvisual effects. For example, the handle of the spoon in Figure 11.30appears to be broken at the level of the top of the water. When lightfrom the spoon passes from the water into the air, the light rays arebent. Refraction is more than just an optical curiosity. It is used indesigning and building camera lenses, eyeglasses, and telescopes.Refraction is due to changes in the speed of light. For example, aslight moves from air into water, its speed decreases. Different mediaslow down light by different amounts. The more that light slows down,the more the light is refracted.You may have stood beside a pool or lake and seen something on thebottom that you wanted to pick up. Yet, when you dove in, the objectwas not where it appeared to be. This is because the light rays changeddirection at the surface of water as they passed between the water andthe air. Figure 11.31 shows light rays moving from water into air andrefracting as they leave the water. When we view the refracted lightrays, we assume they have travelled in a straight line. If you trace thelight rays that reach the eyes back in a straight line, you will find thatthey do not lead to the chest. Instead, the light from the chest in deepwater appears to be coming from shallower water.During ReadingPurpose of anIllustrationState the topic and purpose for theillustrations on these and thefollowing pages in this section. Findwords in the caption that also occurin the text. Write a statement abouthow the illustration helps you tounderstand a concept or idea.water surfaceimage of chestactual chestFigure 11.31 The underwater chest appears to be higher than it really is.The Speed of LightIn the vacuum of space, where there are very few particles, light travelsat almost 300 million m/s or 3.0 × 10 8 m/s. Moving at this speed, lightcould travel seven times around the Earth in one second. However, justlike a student trying to move from class to class when the hallways arefull, it is impossible for light to move at top speed when particles get inthe way.436 UNIT D Light and Geometric Optics