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Lecture 22

Lecture 22. Dispersion and Prisms Total internal Reflection Flat mirrors Convex and Concave. Fig. 22-24, p.741. Total Internal Reflection. Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refraction

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Lecture 22

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  1. Lecture 22 • Dispersion and Prisms • Total internal Reflection • Flat mirrors • Convex and Concave

  2. Fig. 22-24, p.741

  3. Total Internal Reflection • Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refraction • Ray 5 shows internal reflectionDemo

  4. Critical Angle • A particular angle of incidence will result in an angle of refraction of 90° • This angle of incidence is called the critical angle

  5. Critical Angle, cont • For angles of incidence greater than the critical angle, the beam is entirely reflected at the boundary • This ray obeys the Law of Reflection at the boundary • Total internal reflection occurs only when light attempts to move from a medium of higher index of refraction to a medium of lower index of refraction

  6. Fiber Optics • An application of internal reflection • Plastic or glass rods are used to “pipe” light from one place to another • Applications include • medical use of fiber optic cables for diagnosis and correction of medical problems • Telecommunications

  7. Fig. 22-26a, p.743

  8. Fig. 22-26b, p.743

  9. Fig. 22-26c, p.743

  10. Fig. 22-29, p.744

  11. p.744a

  12. p.744b

  13. Fig. P22-2, p.747

  14. Fig. P22-18, p.748

  15. Notation for Mirrors and Lenses • The object distance is the distance from the object to the mirror or lens • Denoted by p • The image distance is the distance from the image to the mirror or lens • Images are formed at the point where rays actually intersect or appear to originate • Denoted by q • The lateral magnification of the mirror or lens is the ratio of the image height to the object height • Denoted by M

  16. Types of Images for Mirrors and Lenses • A real image is one in which light actually passes through the image point • Real images can be displayed on screens • A virtualimage is one in which the light does not pass through the image point • The light appears to diverge from that point • Virtual images cannot be displayed on screens

  17. More About Images • To find where an image is formed, it is always necessary to follow at least two rays of light as they reflect from the mirror

  18. Flat Mirror • Simplest possible mirror • Properties of the image can be determined by geometry • One ray starts at P, follows path PQ and reflects back on itself • A second ray follows path PR and reflects according to the Law of Reflection

  19. Fig. 23-4, p.756

  20. Properties of the Image Formed by a Flat Mirror • The image is as far behind the mirror as the object is in front • q = p • The image is unmagnified • The image height is the same as the object height • h’ = h and M = 1 • The image is virtual • The image is upright • It has the same orientation as the object • There is an apparent left-right reversal in the image

  21. Application – Day and Night Settings on Auto Mirrors • With the daytime setting, the bright beam of reflected light is directed into the driver’s eyes • With the nighttime setting, the dim beam of reflected light is directed into the driver’s eyes, while the bright beam goes elsewhere

  22. B = Bright D = Dark Fig. 23-5a, p.756

  23. Fig. 23-5b, p.756

  24. Spherical Mirrors • A spherical mirror has the shape of a segment of a sphere • A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve • A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

  25. Concave Mirror, Notation • The mirror has a radius of curvature of R • Its center of curvature is the point C • Point V is the center of the spherical segment • A line drawn from C to V is called the principle axis of the mirror

  26. Spherical Aberration • Rays are generally assumed to make small angles with the mirror • When the rays make large angles, they may converge to points other than the image point • This results in a blurred image • This effect is called spherical aberration

  27. Image Formed by a Concave Mirror • Geometry can be used to determine the magnification of the image • h’ is negative when the image is inverted with respect to the object

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