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PHY2049 Summer 2011

PHY2049 Summer 2011. The following clicker numbers are no longer going to be counted. They have not been registered. 420441 461211 462681 497478 625833 Exam 2 (Ch. 28-33 ) is scheduled for Monday July 11 during class times. Images. Chapter 34

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PHY2049 Summer 2011

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  1. PHY2049 Summer 2011 • The following clicker numbers are no longer going to be counted. They have not been registered. 420441 461211 462681 497478 625833 • Exam 2 (Ch. 28-33) is scheduled for Monday July 11 during class times.

  2. Images Chapter 34 One of the most important uses of the basic laws governing light is the production of images. Images are critical to a variety of fields and industries ranging from entertainment, security, and medicine In this chapter we define and classify images, and then classify several basic ways in which they can be produced. 34-

  3. A clear sheet of polaroid is placed on top of a similar sheet so that their polarizing axes make an angle of 30◦ with each other. The ratio of the intensity of emerging light to incident unpolarized light is: A. 1/4 B. 1/3 C. 1/2 D. 3 /4 E. 3 /8

  4. Two Types of Images real image lens object object mirror virtual image Image: a reproduction derived from light Real Image: light rays actually pass through image, really exists in space (or on a screen for example) whether you are looking or not Virtual Image: no light rays actually pass through image. Only appear to be coming from image. Image only exists when rays are traced back to perceived location of source 34-

  5. A Common Mirage Fig. 34-1 Light travels faster through warm air  warmer air has smaller index of refraction than colder air  refraction of light near hot surfaces For observer in car, light appears to be coming from the road top ahead, but is really coming from sky. 34-

  6. Plane Mirrors, Point Object Fig. 34-3 Plane Mirror: Fig. 34-2 Plane mirror is a flat reflecting surface. Identical triangles 34- Since I is a virtual image i < 0

  7. Plane Mirrors, Extended Object Fig. 34-5 Fig. 34-4 Each point source of light in the extended object is mapped to a point in the image 34-

  8. Plane Mirrors, Mirror Maze Fig. 34-6 Your eye traces incoming rays straight back, and cannot know that the rays may have actually been reflected many times 1 7 8 2 2 4 3 6 5 9 1 3 4 5 6 7 8 9 34-

  9. Spherical Mirrors, Making a Spherical Mirror Fig. 34-7 plane Plane mirror  Concave Mirror 1. Center of Curvature C: in front at infinity  in front but closer 2. Field of view wide  smaller 3. Image i=p  |i|>p 4. Image height image height = object height  image height > object height concave Plane mirror  Convex Mirror 1. Center of Curvature C: in front at infinity  behind mirror and closer 2. Field of view wide  larger 3. Image i=p  |i|<p 4. Image height image height = object height  image height < object height convex 34-

  10. Spherical Mirrors, Focal Points of Spherical Mirrors Spherical Mirror: Fig. 34-8 convex concave r > 0 for concave (real focal point) r < 0 for convex (virtual focal point) 34-

  11. Images from Spherical Mirrors Fig. 34-9 Spherical Mirror: Lateral Magnification: Lateral Magnification: Start with rays leaving a point on object, where they intersect, or appear to intersect marks the corresponding point on the image. Real images form on the side where the object is located (side to which light is going). Virtual images form on the opposite side. 34-

  12. Locating Images by Drawing Rays Fig. 34-10 • A ray parallel to central axis reflects through F • A ray that reflects from mirror after passing through F, emerges parallel to central axis • A ray that reflects from mirror after passing through C, returns along itself • A ray that reflects from mirror after passing through c is reflected symmetrically about the central axis 34-

  13. Proof of the magnification equation Similar triangles (are angles same) Fig. 34-10 34-

  14. Spherical Refracting Surfaces Fig. 34-11 Spherical Refracting Surface: Real images form on the side of a refracting surface that is opposite the object (side to which light is going). Virtual images form on the same side as the object. When object faces a convex refracting surface r is positive. When it faces a concave surface, r is negative. CAUTION: Reverse of of mirror sign convention! 34-

  15. Thin Lenses Fig. 34-13 Thin Lens: Thin Lens in air: Converging lens Diverging lens Lens only can function if the index of the lens is different than that of its surrounding medium 34-

  16. Images from Thin Lenses Fig. 34-14 Real images form on the side of a lens that is opposite the object (side to which light is going). Virtual images form on the same side as the object. 34-

  17. Locating Images of Extended Objects by Drawing Rays Fig. 34-15 • A ray initially parallel to central axis will pass through F2 • A ray that initially passes through F1, will emerge parallel to central axis • A ray that initially is directed toward the center of the lens will emerge from the lens with no change in its direction (the two sides of the lens at the center are almost parallel) 34-

  18. Two Lens System p2 i1 i2 O I2 p1 I1 O2 Lens 1 Lens 2 • Let p1 be the distance of object O from Lens 1. Use equation and/or principle rays to determine the distance to the image of Lens 1, i1. • Ignore Lens 1, and use I1 as the object O2. If O2 is located beyond Lens 2, then use a negative object distance p1. Determine i2 using the equation and/or principle rays to locate the final image I2. 34-

  19. A football field is about 100 meters long. The time for light to travel this distance is about: A. 0.33x10-6 s B. 0.33 ms C. 33 min D. 3 hr E. 3 yr

  20. Optical Instruments, Simple Magnifying Lens Fig. 34-17 Simple Magnifier: Can make an object appear larger (greater angular magnification) by simply bringing it closer to your eye. However, the eye cannot focus on objects closer that the near point pn~25 cmBIG & BLURRY IMAGE A simple magnifying lens allows the object to be placed close by making a large virtual image that is far away. Object at F1 34-

  21. Fig. 34-18 Optical Instruments, Compound Microscope O close to F1 I close toF1’ Mag. Lens 34-

  22. Optical Instruments, Refracting Telescope Fig. 34-19 I close toF2and F1’ Mag. Lens 34-

  23. Three Proofs, The Spherical Mirror Formula Fig. 34-20 34-

  24. Three Proofs, The Refracting Surface Formula Fig. 34-21 34-

  25. Three Proofs, The Thin Lens Formulas Fig. 34-22 34-

  26. The time for a radar signal to travel to the Moon and back, a one-way distance of about 3.8 × 108 m, is: A. 1.3 s B. 2.5 s C. 8 s D. 8min E. 1 × 106 s Radio waves of wavelength 3 cm have a frequency of: A. 1MHz B. 9MHz C. 100MHz D. 10, 000MHz E. 900MHz The light intensity 10m from a point source is 1000W/m2. The intensity 100m from the same source is: A. 1000W/m2 B. 100W/m2 C. 10W/m2 D. 1W/m2 E. 0.1W/m2

  27. Light of uniform intensity shines perpendicularly on a totally absorbing surface, fully illuminating the surface. If the area of the surface is decreased: A. the radiation pressure increases and the radiation force increases B. the radiation pressure increases and the radiation force decreases C. the radiation pressure stays the same and the radiation force increases D. the radiation pressure stays the same and the radiation force decreases E. the radiation pressure decreases and the radiation force decreases

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