Chapter 10 Lesson 6, "Bending Light"
Materials:
Objective:
Anticipatory Set:* Show the students several pictures and ask what they see in the pictures. Refraction 1, Refraction 2, Refraction 3, Refraction 4, Refraction 5, Note that all the pictures show an object appearing to be bent as it is placed in water. Remind students of the discussion in lesson 4 of the speed of light. Light travels the fastest through empty space and as it hits the atmosphere it begins bumping into things that slow the light down. As the light slows the photons are bent. the further the thicker the substance the more they are bent. Here is how it works. In lesson 5 we talked about the rays that were being reflected. Today we are going to talk about the rays that penetrate the surface. When these rays move from a thinner substance to a thicker substance the photons slow down and this causes a turning in the ray of light.
Teacher Input:* Show the students this Venn diagram and tell them they need to draw one in there notes and through the discussion today they should fill it up with characteristics of each a concave lens and a convex lens.
First of all a lens is a curve piece of clear material that refracts light waves like we just seen with the water. The way the lens is shaped makes a big difference on how the light is bent. Lenses are used in eyeglasses, cameras, magnifying glasses, microscopes, lasers and telescopes. A concave lens will be thinner in the middle than the edges which causes light rays to spread out. This creates a shaper image and can help people who are nearsighted. A convex lens curves outward which causes the light rays to bend inward. A convex lens will magnify an image if held close to the object and will turn an image upside down if held far away from the eye. It can also be used to concentrate light and energy of a large area into a single point and start a fire.
So how can these two types of lens be used to help vision problems? Here is how the normal eye works. If a person is near sighted the image focus before the nerves on the back of the eye. If a person is farsighted the image comes into focus after the back of your eye where the nerve receptors are. Both of these make an image blurry. To fix a nearsighted eye a doctor finds the right lens to separated the light rays just a little so that they come into focus at a later point. For a far sighted person the lens used is convex so that the light rays come into focus sooner and if the glasses are perfect the image will come into focus right were your nerve receptors are. These receptors cover the entire back of your eye except for the small area where your optical nerve enters the eye. Each of your eyes has a blind spot but because you have two eyes you have two separate blind spots and one eye normally covers for another. If you want to find your blind spot open this picture and then cover your left eye. Move concentrate on the "t" as you do move toward the screen and you will notice the big black dot disappear.
Guided Practice:* Review this venn diagram with the students and have them move the characteristics to the right part of the Venn diagram. Then have the students answer the questions on page 304 as a group.
Independent Practice:* Students will completed the worksheet, "Sound and Light: Terms Review." Students will read lesson 6 in their books
Check for Understanding:* Students will take the quiz for lesson 10-06 "Bending Light"
Duration:
30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).
Alaska Content Standards Addressed in this lesson:
