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Exam

Exam. The second exam in Physics 104 is on Thursday, March 24 from 5:45 - 7:00 PM . Rooms are same as Exam 1: Sections 303, 315, 316, 319, 320, 325(TAs Asgar, Geng, Yip) meet in B102 Van Vleck

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Exam

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  1. Exam • The second exam in Physics 104 is on Thursday, March 24 from 5:45 - 7:00 PM. • Rooms are same as Exam 1: • Sections 303, 315, 316, 319, 320, 325(TAs Asgar, Geng, Yip) meet in B102 Van Vleck • Sections 301, 304, 305, 306, 307, 309, 313, 314, 324(TAs Belknap, Hinojosa, Walker) meet in 3650 Humanities Sections 302, 310, 311, 312, 317, 318, 321, 322, 323 (TAs Dai, Hostetter, Ojalvo ) meet in B10 Ingraham • The exam will cover chapters 19-22. Physics 104, Spring 2011

  2. Lenses Refraction Through Lenses • Converging (Convex) • Diverging (Concave) • Image Position, Magnification and Type Physics 104, Spring 2011

  3. Images Formed by Refraction • Rays originate from the object point, O, and pass through the image point, I • When n2 > n1, • Real images are formed on the side opposite from the object Physics 104, Spring 2011

  4. Sign Conventions for Refraction Physics 104, Spring 2011

  5. Flat Refracting Surface • The image formed by a flat refracting surface is on the same side of the surface as the object • The image is virtual • The image forms between the object and the surface • The rays bend away from the normal since n1 > n2 Physics 104, Spring 2011

  6. Atmospheric Refraction The index of refraction depends on the density of the medium, and the density of a gas depends on the temperature. Thus, the index varies in the atmosphere. This results in interesting phenomena • Sunsets • Mirages Physics 104, Spring 2011

  7. Atmospheric Refraction and Sunsets • Light rays from the sun are bent as they pass into the atmosphere • It is a gradual bend because the light passes through layers of the atmosphere • Each layer has a slightly different index of refraction • The Sun is seen to be above the horizon even after it has fallen below it Physics 104, Spring 2011

  8. Atmospheric Refraction and Mirages • A mirage can be observed when the air above the ground is warmer than the air at higher elevations • The rays in path B are directed toward the ground and then bent by refraction • The observer sees both an upright and an inverted image Physics 104, Spring 2011

  9. Thin Lenses • A thin lens consists of a piece of glass or plastic, ground so that each of its two refracting surfaces is a segment of either a sphere or a plane • Lenses are commonly used to form images by refraction in optical instruments Physics 104, Spring 2011

  10. Thin Lens Shapes • These are examples of converging lenses • They have positive focal lengths • They are thickest in the middle Physics 104, Spring 2011

  11. More Thin Lens Shapes • These are examples of diverging lenses • They have negative focal lengths • They are thickest at the edges Physics 104, Spring 2011

  12. Converging Lens F All rays parallel to principal axis pass through focal point F n1 n1 n2>n1 axis Double Convex Physics 104, Spring 2011

  13. Converging Lens Principal Rays Image F P.A. Object F 1) Rays parallel to principal axis pass through focal point. 2) Rays through center of lens are not refracted. 3) Rays through F emerge parallel to principal axis. In this particular situation presented, image is real, inverted and enlarged Physics 104, Spring 2011

  14. Question Which way should you move object so image is real and diminished? • Closer to lens • Further from lens • Converging lens can’t create real diminished image. Physics 104, Spring 2011

  15. Ray tracing for a converging lens This could be used in a camera. Big object on small film This could be used as a projector. Small slide on big screen Thin lens equation: This is a magnifying glass Magnification: Physics 104, Spring 2011

  16. Diverging Lens Principal Rays Image F P.A. Object F 1)Rays parallel to principal axis appear to come from focal point. 2) Rays through center of lens are not refracted. 3) Rays toward F emerge parallel to principal axis. Image is virtual, upright andreduced. Physics 104, Spring 2011

  17. Question Which way should you move object so image is real? • Closer to lens • Further from lens • Diverging lens can’t create real image. Physics 104, Spring 2011

  18. Lens Equation Image p F axis Object f F q p= distance object is from lens (+ in front - behind) (+ behind - in front) q = distance image is from lens f = focal length of lens (+ converging - diverging) Physics 104, Spring 2011

  19. Multiple Lenses: Overview Imagefrom lens 1 becomes objectfor lens 2 2 1 f1 f2 Lens 1 creates a real, inverted and enlarged image of the object. Lens 2 creates a real, inverted and reduced image of the image from lens 1. The combination gives a real, upright, enlarged image of the object. Physics 104, Spring 2011

  20. Multiple Lenses: Lens 1 Imagefrom lens 1 becomes object for lens 2 p = 15 cm 2 1 f1 f2 f1 = 10 cm f2 = 5 cm q = 30 cm First find image from lens 1. Physics 104, Spring 2011

  21. Multiple Lenses: Lens 2 Imagefrom lens 1 becomes object for lens 2 2 p = 15 cm 1 L = 42 cm q = 8.6 cm f1 f2 f1 = 10 cm f2 = 5 cm q = 30 cm p=12 cm Now find image from lens 2. Notice that p could be negative for second lens! Physics 104, Spring 2011

  22. Multiple Lenses: Magnification Imagefrom lens 1 becomes object for lens 2 2 p = 15 cm 1 L = 42 cm q = 8.6 cm f1 f2 f1 = 10 cm f2 = 5 cm q = 30 cm p=12 cm Net magnification M = M1 M2 Physics 104, Spring 2011

  23. Combination of Thin Lenses Physics 104, Spring 2011

  24. Lens and Mirror Aberrations • One of the basic problems is the imperfect quality of the images • Largely the result of defects in shape and form • Two common types of aberrations exist • Spherical aberration • Chromatic aberration Physics 104, Spring 2011

  25. Spherical Aberration • Results from the focal points of light rays far from the principle axis are different from the focal points of rays passing near the axis • For a mirror, parabolic shapes can be used to correct for spherical aberration Physics 104, Spring 2011

  26. Chromatic Aberration • Different wavelengths of light refracted by by a lens focus at different points • Violet rays are refracted more than red rays • The focal length for red light is greater than the focal length for violet light • Chromatic aberration can be minimized by the use of a combination of converging and diverging lenses Physics 104, Spring 2011

  27. Preflight • A beacon in a lighthouse is to produce a parallel beam of light. The beacon consists of a bulb and a converging lens. Where should the bulb be placed? • Outside the focal point • At the focal point • Inside the focal point Physics 104, Spring 2011

  28. Preflight • A converging lens is placed in water. Its focal length: • Stays the same • Increases • Decreases Ratio of refractive indices has decreased. Therefore, less bending, which implies longer focal length. Physics 104, Spring 2011

  29. Preflight • A converging lens is used to project a real image onto a screen. A piece of black tape is then placed over the upper half of the lens. Which of the following is true? • Only the lower half of the object will show on the screen • Only the upper half of the object will show on the screen • The whole object will still show on the screen. Physics 104, Spring 2011

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