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Unformatted text preview: Geometric Optics Prelab 1 Plexiglass 1.1 Plexiglass has an index of refraction n = 1 . 49 . What is the speed of light in plexiglass? The speed of light in a vacuum is c . The speed v of light in any other medium with index of refraction n is given by equation 30.2 in your textbook. 1.2 At what angle of incidence does one expect total internal reflection? The light is inside the plexiglass and is traveling towards the interface between plexiglass and air. The index of refraction of the plexiglass is n 1 = 1 . 49. The index of refraction of air is n 2 and is given in your textbook. Equation 30.5 in your textbook tells you that the critical angle c is given by sin c = n 2 n 1 Is your value for the critical angle c in degrees, and is it sensible? 2 The Lens Equation You have at your disposal a lens with focal length f = 150 mm. An object is placed at a distance s to the left of the lens. Where is the image plane s ? Is the image virtual or real? What is the magnification M ? You should read section 31.2 in your textbook before working on this problem. Write down the equations you use and lable the quantities which you calculate. (Be sure to distin- guish between the object distance s and the image distance s .) If you calculate a quantity, be careful to lable which variable it corresponds to. I will not give you credit for a handful of numbers scattered at random positions on a piece of paper. If you use a ruler to draw a ray diagram for each of the following cases, if your ray diagram is to scale, and if you use it to check whether your answers make sense, then I will give partial credit even in cases where you make an algebraic mistake. If you choose not to draw ray diagrams, then check your calculations carefully because in this case I will not give partial credit. Image Distance The lens equation is equation 31.5 in your textbook, 1 s + 1 s = 1 f 1 You know the focal length f of the lens. You are also given the position s of the object in each of the five cases. (This is the object distance .) You will need to solve for the position s of the image....
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