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Light, Mirrors, and Color

Light, Mirrors, and Color. E. B. Electromagnetic Radiation (i.e., light). --. waves of oscillating electric (E) & magnetic (B) fields. --. source is vibrating electric charges. R O Y G B V. electromagnetic spectrum. IR. UV. visible. X-rays. microwaves. radio waves. cosmic rays.

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Light, Mirrors, and Color

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  1. Light, Mirrors, and Color

  2. E B Electromagnetic Radiation (i.e., light) -- waves of oscillating electric (E) & magnetic (B) fields -- source is vibrating electric charges

  3. ROYGBV electromagnetic spectrum IR UV visible X-rays microwaves radio waves cosmic rays gamma rays large l small l Most of the energy the Earth receives from the Sun is in the form of visible light. low f high f low energy high energy

  4. Earth Sun 3 mos. later… * The Speed of Light Ole Roemer (1676) observes eclipse of one of Jupiter’s moons, Io, which has a period of 42.5 hours. Jupiter w/orbitingIo * Io was late. Roemer figured it was the light that was late in reaching Earth. He estimated light’s speed to be ~2/3 of accepted value today.

  5. Albert Michelson (1879) -- first to get an accurate value for speed of light speed of light in vacuum (and air) is constant c = 3.00 x 108 m/s c = f l

  6. Find wavelength of a B-104 (FM 104.1) radio wave. = 104.1 x 106 Hz f = 104.1 MHz Find wavelength of a WGN (AM 720) radio wave. = 720 x 103 Hz f = 720 kHz

  7. light year: distance light travels in one year (~100 x 109 stars) MILKY WAY GALAXY Earth (T = 200 x 106 yrs.) 3,000 ly 16,000 ly 30,000 ly 100,000 ly

  8. r = 1 m r = 2 m r = 3 m Behavior of Light Brightness is proportional to the inverse of the distance from the source

  9. Light-Material Interaction transparent: most light rays travel through material and remain parallel e.g., glass, water translucent: some light rays travel through material, but material scatters them e.g., frosted glass opaque: essentially no light travels through material; all light is reflected e.g.,

  10. normal: to surface Qi Qr SURFACE Reflection Qr: angle of reflection Qi: angle of incidence incident ray reflected ray relative to normal Qr and Qi are measured… Qr = Qi Law of Reflection:

  11. Types of Reflection specular diffuse Compared to light l, surface irregularities are… …SMALL …LARGE visible light + mirror visible light + clothing radio waves + like…everything.

  12. mirrored outer surface Spherical Mirrors convex mirror: R f C F P.A. (front of mirror) (behind mirror) P.A. = principal axis C = center of curvature F = focal point f = focal length R = radius of curvature = 2f

  13. mirrored inner surface concave mirror: R f C F P.A. (front of mirror) (behind mirror)

  14. Mirror Ray Diagrams Rules: through F parallel to P.A. through C real image: rays actually intersect; can project it on a screen virtual image: rays appear to intersect, but don’t; cannot project it on a screen

  15. F C f C F f SMALLER; UPRIGHT; VIRTUAL INVERTED; REAL

  16. C C F F f f NO IMAGE LARGER; UPRIGHT; VIRTUAL

  17. f = focal length CONCAVE,+ R = radius of curvature CONVEX,– Mirror Equation and Magnification p = object dist. always on LEFT; always + q = image dist. LEFT,+,REAL; RIGHT,–,VIRTUAL h = object height always UPRIGHT; always + h’ = image height UPRIGHT,+; INVERTED,–

  18. Concave mirror has radius 55 cm. Object is 84 cm from mirror, is 24 cm tall. Find focal length, image distance, and magnification. Describe image. R = +55 cm p = 84 cm q = ? M = ? h = 24 cm

  19. +27.5 cm C F Concave mirror has radius 55 cm. Object is 84 cm from mirror, is 24 cm tall. Find focal length, image distance, and magnification. Describe image. +84 cm h = +24 cm q = +41 cm M = –0.49 (h’ = –11.7 cm) SMALLER: INVERTED; REAL +55 cm

  20. Concave mirror has focal length 36.0 cm. Object has height 18.0 cm, is 8.00 cm from mirror. Describe image. f = +36.0 cm h = 18.0 cm p = 8.00 cm

  21. Concave mirror has focal length 36.0 cm. Object has height 18.0 cm, is 8.00 cm from mirror. Describe image. LARGER; UPRIGHT; VIRTUAL h = 18.0 cm F +8.00 cm q = –10.3 cm M = 1.29 +36.0 cm h’ = 23.2 cm

  22. C F f Concave mirror has focal length 30 cm. Object of height 10 cm is at mirror’s focal point. Describe image. .

  23. Convex mirror has radius 64.0 cm. Object has height 24.0 cm, is 30.0 cm from mirror. Describe image.

  24. F C q (–) Convex mirror has radius 64.0 cm. Object has height 24.0 cm, is 30.0 cm from mirror. Describe image. h = +24 cm h’ (+) p = +30 cm f = –32 cm q = –15.5 cm SMALLER; UPRIGHT; VIRTUAL; on the right M = 0.517 h’ = 12.4 cm

  25. C Parabolic Mirrors Drawback of spherical mirrors: rays // to, and far from, P.A. are NOT reflected through F -- resulting blurring = spherical aberration -- remedied using parabolic mirrors

  26. flashlight radio telescope satellite dish headlight Examples of Parabolic Mirrors

  27. Color WHITE White light contains all visible ls. ROYGBV Objects that “are”… White all none visible ls, and absorb reflect Colored some some Black no all

  28. B Cyan Magenta G R Yellow Primary colors of light (NOT pigments): W red, green, blue R + G + B = W Light is additive. Two colors of light are complimentary if, when added, they produce white light. W = B + Y (Y = G + R) W = R + C (C = B + G) W = G + M (M = B + R)

  29. B Y G Pigments are subtractive. blue pigment (incident W light) ROYGBV yellow pigment ROYGBV blue pigment + yellow pigment ROYGBV

  30. unpolarized light polarizing filter polarized light (blocks ) Polarization Normally, light is unpolarized; E and B fields are vibrating randomly i.e., polarized light: orderly vibrations (half as bright)

  31. Sun JENNY glare: horizontally-polarized light reflected off horizontal surfaces unpolarized horizontally polarized (glare) -- horiz. surface acts as a polarizer -- sunglasses are vertically polarized

  32. c = f l c = 3.00 x 108 m/s

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