L10_thinlens3

L10_thinlens3 - Thin Lens Equation Name: Teammates:...

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Thin Lens Equation Name: Teammates: Introduction Consider a simple lens, light is refracted upon entering the lens, it travels in a straight line within the lens, and then is refracted again upon leaving the lens. Since the sides of the lens are not necessarily parallel, the light leaves the lens at a different angle from which it entered. Depending on the shape of the lens, the light is either focused or defocused. If we approximate both sides of a lens as spherical with radii of curvature r 1 and r 2 , then the focal length (d f ) of the lens when surrounded by air is given by the lens maker equation: f1 11 (n-1)( ) dr =+ 2 1 r where r 1 is positive if the center of the sphere is to the right of the lens and r 2 is positive if the center of the sphere is to the left, n is the index of refraction of the lens, This formula is extremely useful for creating a lens, it is not very useful for determining the focal length of a lens that has already been created. A more practical method for finding the focal length (d f ) of a lens is by using the thin lens equation Fig:1: Lab set up oi ddd += f 1 where d o is the distance the source (object) is away from the lens and d i is distance the image is behind the lens. This equation is applicable only for a thin lens approximation. Note that when d o is very large, d f is equal to d i . Procedure 1. Set up the optical bench as in Fig 1 using the d f = 200 mm focal length lens. 2. Set d o larger then 2d f and find the corresponding image by moving the screen until a focused sharp image is formed on the screen.
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This note was uploaded on 02/09/2011 for the course PHYS 1112L taught by Professor Adler during the Summer '10 term at Kennesaw.

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L10_thinlens3 - Thin Lens Equation Name: Teammates:...

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