1. Copyright © 2010 McGraw-Hill Ryerson Ltd. What is refraction and how can it be used? Topic4.5 (Pages 332-43) Today we will be... Having a short quiz on mirror ray diagrams. Learning about refraction. Today we will be... Having a short quiz on mirror ray diagrams. Learning about refraction (Topic 4.5).

2. Copyright © 2010 McGraw-Hill Ryerson Ltd. Refraction is the bending of light when it crosses a boundary between two substances. Refraction is the change in the direction of light when it travels from one substance into another. A medium is the substance or material through which light is travelling. The plural of medium is media. Through what medium or media is light travelling in the image on the left? In the spoon photo, the two media are air and water.

3. Copyright © 2010 McGraw-Hill Ryerson Ltd. ACTIVITY 4.17 - The Reappearing Coin How can the coin pictured below, at the bottom of a cup of water, be seen, even though it is not in the person’s “line of sight”?

4. Copyright © 2010 McGraw-Hill Ryerson Ltd. Refraction is the bending of light when it crosses a boundary between two substances. The images below show how light is refracted when it moves from air into water. New terms related to refraction include refracted ray (the ray after crossing a boundary between media) and angle of refraction (the angle between the refracted ray and the normal).

5. Refraction is the bending of light when it crosses a boundary between two substances. The incident ray, the refracted ray, and the normal all lie on the same plane. The incident ray and the refracted ray are on opposite sides of the line that separates the two media. Light bends towards the normal when the speed of light in the second medium is less than the speed of light in the first medium. Light bends away from the normal when the speed of light in the second medium is greater.

6. COPY THIS DOWN! What Causes Refraction Light refracts because it travels at different speeds in different media. When light enters a medium that causes it to slow down, it bends toward the normal. When light enters a medium that causes it to speed up, it bends away from the normal.

7. Copyright © 2010 McGraw-Hill Ryerson Ltd. ACTIVITY 4.15: Interpret a Model to Describe Refraction The car in the diagram represents a light ray. Other parts of the diagrams represent 2 different media and the normal. Assume the media being represented are air and water. 1.Make a new sketch of the figure below to translate each of the two diagrams into a ray diagram. Use labels to identify the ray, the media, the normal, the angle of incidence, and the angle of refraction in each diagram. 2.Write a caption for each diagram that explains how the light ray refracts. Start the first caption like this: “When the speed of a light ray slows down...”. Start the second caption like this: “When the speed of a light ray increases...”.

8. ACTIVITY 4.15: Interpret a Model to Describe Refraction 2. (a) WHEN THE SPEED OF A LIGHT RAY SLOWS DOWN... The light ray bends toward the normal. 2.(b) WHEN THE SPEED OF A LIGHT RAY INCREASES... The light ray bends away from the normal.

9. Copyright © 2010 McGraw-Hill Ryerson Ltd. Refraction is used in communications and other technologies. When the angle of incidence of the light entering the water is very small, nearly all of the light enters the water and refracts. As the angle of incidence gets larger, more of the light reflects and less refracts. most refractingmost reflecting

10. Copyright © 2010 McGraw-Hill Ryerson Ltd. Refraction is used in communications and other technologies. Some of the light hitting the surface of a body of water reflects, and some refracts.

11. Copyright © 2010 McGraw-Hill Ryerson Ltd. Total Internal Reflection Total internal reflection: a condition in which no light can escape from a medium because the angle of incidence is larger than the critical angle (i where R = 90°). In images C and D, the angle of incidence is so large that the ray of light never leaves the water. The critical angle is reached in C. In images A and B, as the angle of incidence increases, less light is reflected.