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Light, Reflection, and Refraction

Light, Reflection, and Refraction. Chapters 14 and 15 OPTICS. Electromagnetic Waves. Magnetic field wave perpendicular to an electric field wave All objects emit EMWs.  Temp EMW Electromagnetic spectrum Range of all frequencies of light

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Light, Reflection, and Refraction

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  1. Light, Reflection, and Refraction Chapters 14 and 15 OPTICS

  2. Electromagnetic Waves • Magnetic field wave perpendicular to an electric field wave • All objects emit EMWs. •  Temp EMW • Electromagnetic spectrum • Range of all frequencies of light • Visible light is a very small portion of that entire spectrum.

  3. c • Speed of Light - 3.00 x 108m/s. • = (wavelength) x (frequency) • c = ƒ

  4. Example • AM Radio waves • 5.4 x 105 Hz • 1.7 x 106 Hz •  = ?

  5. Visible Light • Part of the EMS humans can see • Red - 750nm (x10-9m) • Purple - 380nm • Bees, Birds – UV • Snakes – IR

  6. Reflection • Light waves usually travel in straight paths • Change in substance changes direction • Opaque - does not permit light • some light reflected • some light absorbed as heat

  7. Reflection • Texture affects reflection • Diffuse reflection (rough) • reflects light in many different directions, • Specular reflection (smooth) • reflects light in only one direction • Smooth – variations in surface 

  8. Mirrors • Light striking a mirror reflects at the same angle that it struck the mirror

  9. Flat Mirrors • p = q • p- objects distance to the mirror • q - distance from the mirror to the image • Virtual image • Does not exist • Made by our eyes

  10. Ray Diagrams • Used to predict the location of the image of an object

  11. Concave Spherical Mirrors • Reflective surface is on the interior of a curved surface • C – center of curvature • R – Radius (distance to C) • f – Focal Point (1/2 R) • Principal axis • any line that passes through C • usually oriented with an object

  12. Mirror Equations • 1/object distance + 1/image distance = 1/focal length 1/p + 1/q = 1/f • Magnification (M) = Image height/object height (h / h) - (q / p) • M = h / h = - (q / p)

  13. Sign of Magnification

  14. Concave Spherical Mirror Rules • A ray traveling through C will reflect back through C • A ray traveling through (f) will reflect parallel to the PA • A ray traveling to the intersection of the PA and the mirror will reflect at the same angle below the PA. • A ray traveling parallel to PA will reflect through the focal point

  15. Ray Diagrams • Draw three rays • The image forms at the point of intersection • Example • f = 10.0cm • p = 30.0cm • h = 3.00cm

  16. Convex Spherical Mirrors • Reflective surface is on the outside of the curve. • The points f and C are located behind the mirror • negative

  17. Rules • A ray parallel to the PA will reflect directly away from f. • A ray towards f will reflect parallel to the PA • A ray towards C will reflect directly away from C. • A ray to the intersection of PA and mirror will reflect at the same angle below the OA. • Trace the 3 diverging lines back through the mirror to reveal the location of the image which is always virtual

  18. Example • f = -8.00cm • p= 10.0cm • h = 3cm

  19. Parabolic Mirrors • Rays that hit spherical mirrors far away from the OA often reflect though other points causing fuzzy images, spherical aberration. • Telescopes use parabolic mirrors as they ALWAYS focus the rays to a single point.

  20. Refraction • Substances that are transparent or translucent allow light to pass though them. • Changes direction of light • Due to the differences in speed of light

  21. Analogy • A good analogy for refracting light is a lawnmower traveling from the sidewalk onto mud

  22. Index of Refraction (n) • The ratio of the speed of light in a vacuum to the speed of light in a medium •  n -  c

  23. Snell’s Law • ni(sini) = nr(sinr) • r = sin-1{(ni/ nr)(sini)} • Example • i = 30.0⁰ • ni = 1.00 • nr = 1.52

  24. i = 30.0⁰ • ni = 1.00 • nr = 1.52

  25. Total Internal Reflection • If the angle of incidence of a ray is greater than a certain critical angle the ray will reflect rather than reflect • This principal is responsible for the properties of fiber optic cables. • Remember the lawn mower analogy…

  26. Critical Angle • sin Θc = nr / ni • As long as nr < ni • What is the critical angle for light traveling from Diamond to Air?

  27. nr = 1.000 ni = 2.419

  28. Thin Lenses • Converging • Diverging • f- curve of lens & index of refraction

  29. Converging Lens Diagram • Ray parallel to PA, refracts through far focal point • Ray through center of lens, continues straight line • Ray through near focal point, refracts through lens, continues parallel to PA • Treat lens as though it were a flat plane.

  30. Diverging Lens Diagram • Because the rays that enter a diverging lens do not intersect a virtual image is formed by tracing back the refracted rays. • Ray 1 - parallel to PA, refracts away from near f, trace back to near f. • Ray 2 - ray toward far f, refracts parallel to PA, trace back parallel to PA • Ray 3 - ray through center, continues straight, trace back toward object

  31. Sign Conventions for Lens

  32. Converging Lens Example • p = 30.0cm • f = 10.cm

  33. Diverging Lens Example • p = 12.5cm • f = -10.0cm

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