1202_LabManual.pdf

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If you need assistance, send an email to [email protected] . Include the room number and brief description of the problem. W ARM UP It is useful to have an organized problem-solving strategy such as the one outlined in the following questions. 1. Draw a fairly large sketch, showing a convex lens and a source of light with an easily identified top and bottom. Label the lens's focal points, and position the source so that an image will be created, which could be projected on a screen. 2. Determine the position of the image, by sketching the paths of rays from the top of the light source and the bottom of the light source. Indicate the position of the image in your sketch. Where should you position the screen in order to see the image? How many rays are needed to determine the position of the image? 3. Repeat the steps above with a lens of the same focal length, but with the light source farther away from the lens. Has the image moved closer to or farther from the lens? 15

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IMAGE POSITION – 1202Lab1Prob3 4. From your ray diagrams and geometry or trigonometry, write an equation that relates the distance between the lens and the image, the distance between the lens and the object, and the lens’s focal length. 5. Solve the equation in step 4 for distance of the object from the lens . What do you predict as a shape for a graph of the distance of the object from the lens vs. the distance of the image from the lens for a lens of fixed focal length? Sketch the shape of the graph you expect. Does the graph cross each axis ? If so, what are the values of the intercepts? 6. Solve the equation in step 4 for the distance of the object from the lens . What do you predict as a shape for a graph of the distance of the object from the lens vs. the distance of the image from the lens? What are the values of the intercepts where the graph crosses each axis? Draw a sketch of the graph shape you expect and indicate the expected values of the intercepts. P REDICTION Write out an expression that relates the distance of the image from the lens, the distance of the object from the lens, and the focal length of the lens. Use this expression to predict features of the graphs of the distance of the object from the lens vs. the distance of the image from the lens and (1/ the distance of the object from the lens ) vs. (1/ the distance of the image from the lens ). E XPLORATION Estimate the focal length of each convex lens by using a source of light that is far from the lens. Where should light from a very distant object be focused? Position the light source, convex lens and screen on the optical bench. Align the light source with the principal axis of the lens. Adjust their positions so that a focused image appears on the screen. Move the source slightly toward and away from the lens, each time adjusting the screen’s position to show a crisp image. Does the direction in which you have to move the screen match your responses to the warm-up questions?
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