experiment12.pdf - Experiment 12 Phys2212K Georgia State...

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Experiment 12 Phys2212K Georgia State University 1 Index of Refraction and Total Internal Reflection Name: Group Members: Date: TA’s Name: Materials: Ray box, two different transparent blocks, two letter size white pages, pencil, protractor, two nails, and graph paper. Objectives: 1. Understanding image formation due to refraction. 2. Finding the index of refraction of a transparent material. 3. Observing total internal reflection and experimentally finding critical angle. Part 1: Introduction and Predictions Take a look at the transparent cube in which you find a vertical strip on one of its sides. If you look through the opposite side of the cube as shown in the side view below, you see the strip (image of the strip) appear to be closer to you than the actual strip (object) because the light coming from the strip is refracted as it exits the cube to get to your eye. We will use the method of parallax as you used in the tutorial to locate the image and compare the location of the image with the location of the object. Vertical strip observer Light scattering off of the strip (the object) first travels through the block (medium 1) and then travels through the air (medium 2) to get to your eye. 1. What is the index of refraction of air? 2. Is the index of refraction in medium 1 (block) larger or smaller than medium 2 (air)? 3. Do you think the image appears to be closer to you or farther away than the object?
Experiment 12 Phys2212K Georgia State University 2 4. Do you think the image is real or virtual? Why? 5. Do you think that the image is formed because light is being reflected or because light is being refracted? 6. Let’s test our answers by constructing a ray diagram below (viewed from above looking down at the block on the table). The diagram shows rays of light leaving the vertical strip in three directions. These rays travel through the cube. Predict what happens to the rays when they pass from the cube into the air. Draw the path of the three rays after they pass from the cube to air, that is, show the path of each ray starting at the arrow head in the drawing and going in some direction in the air. We have drawn the normal (perpendicular line) at each of point that our rays arrive at the surface. Use reasoning from Snell’s law to decide the direction for each ray, that is, if the ray moves to a region of smaller index of refraction, does the angle increase, decrease or stay the same.

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