Human Retina. Sharp Spot: Fovea Blind Spot: Optic Nerve

Transcription

1 I am Watching YOU!!

2 Human Retina Sharp Spot: Fovea Blind Spot: Optic Nerve

3 Human Vision

4 Optical Antennae: Rods & Cones Rods: Intensity Cones: Color

5

6 Energy of Light 6 10 ev 10 ev 4 1 2eV 40eV KeV MeV Energy to ionize atom or molecule: eV

7 Light:Visible Spectram nm & THz Increasing Energy

8 Where does light actually come from? Light comes from the acceleration of charges.

9 Accelerating Charges

10 Oscillating Charges Radio & Microwave Frequency of EM wave is the same as the frequency of oscillation.

11 How is Infrared Light made? Light comes from the acceleration of charges.

12 Thermal Excitation: f ~ T Incandescence Color shifts to shorter wavelengths (higher frequency) as an object is heated. increasing temperature

13 How is Visible Light made? Light comes from the acceleration of charges.

14 Light is emitted when an electron in an atom jumps between energy levels either by excitation or collisions.

15 Atoms are EM Tuning Forks They are tuned to particular frequencies of light energy.

16 Atomic Emission of Light Each chemical element produces its own unique set of spectral lines when it burns

17 Hydrogen Spectra

18 Light Emission via Atomic Excitations

19 Incandescent Light Bulb Full Spectrum of Light All frequencies excited!

20 Light:Visible Spectram nm & THz Increasing Energy

21 ROYGBIV

22 If you pass white light through a prism, it separates into its component colors. long wavelengths R.O.Y. G. B.I.V spectrum short wavelengths

23 Visible Sun: The Photosphere Atomic Excitations: nm at a few thousand Kelvin.

24 Intensity of Visible Sunlight

25 Additive Primary Colors Red, Green, Blue

26 Mixing Colored Light RGB Color Theory

27 RGB Color Theory

28 Additive Complementary Colors Yellow, Cyan, Magenta The color you have to add to get Red + Green = Yellow Blue + Green = Cyan Red + Blue = Magenta Red + Blue + Green = White white light. White light red light =?? White light yellow light =??

29 Why is the Sky Blue?

30 Why is the Sky Blue? Air Molecules absorb and re-radiate blue in all directions This is called scattering. So everywhere you look in the sky you see blue.

31 Why are Clouds White? A large collection of atoms and molecules vibrate in all frequencies. All the frequencies (colors) added together make white light.

32 Why are Sunsets Red?

33 Why are Sunsets Red? By the time the light reaches your eye, all the blue and most of the green have been scattered out. White light minus green and blue is red light.

34 Why is the Ocean Cyan? White light minus cyan is red. Ocean water absorbs red.

35 Why are some materials colored?

36 Why are some materials colored? Colored materials absorb certain colors that resonate with their electron energy levels and reject & reflect those that do not.

37 Look at me with your filters! What do you see?

38 Mixing Colored Pigments Subtractive Colors Pigments subtract colors from white light.

39 Mixing Colored Pigments Subtractive Colors Pigments subtract colors from white light. Yellow + Cyan = Green Cyan + Magenta = Purple Yellow + Magenta = Red Yellow + Cyan + Magenta = Black

40 Subtractive Primary Colors Yellow, Cyan, Magenta Printing with Pigments Yellow + Cyan = Green Cyan + Magenta = Purple Yellow + Magenta = Red Yellow + Cyan + Magenta = Black

41 Mixing Colored Light RGB Color Theory

42 Thin Film Interference When reflecting off of different surfaces and traveling through different thickness, different frequencies take different times to travel and can undergoes a phase shift in wavelength. When the waves rejoin, they interfere destructively canceling out different frequencies of light.

43 Light Rays

44 We can consider light waves to be RAYS because if the object it interacts with are several times larger than the wavelength of light, it acts like it travels in straight lines and acts like a ray.

45 Light Rays: Ignore Diffraction and Interference of waves! Diffraction depends on SLIT WIDTH: the smaller the width, relative to wavelength, the more bending and diffraction. We will assume that λ<<d, where d is the diameter of the opening. This approximation is good for the study of mirrors, lenses, prisms, etc.

46 Transparency Selective Absorption Glass resonates strongly with UV and infrared, absorbing those frequencies while transmitting visible frequencies.

47 The heating effect of a medium such as glass or the Earth s atmosphere that is transparent to short wavelengths but opaque to longer wavelengths: Short get in, longer are trapped!

48 Why are most materials Opaque? (Opaque Can t see through) They absorb light without re-emitting it. Vibrations given by the light to their atoms and molecules are turned into random kinetic energy they become slightly warmer.

49 Opacity: Mirrors Free electrons in opaque reflective surfaces can vibrate, absorb & re-emit at any frequency.

50 Why does a mirror reflect light? Mirrors are metallic (conductors) and have free electrons. These free electrons can absorb and re-emit a continuous spectrum of EM frequencies and so more of the incident light is reflected back and not absorbed by the material. Why does polishing a mirror make it more reflective?

51 Law of Reflection

52 A virtual image is formed when light rays do not pass through the image point but only appear to diverge from that point. Virtual Images can not be displayed onto screens. Real and Virtual Images A real image is formed when light rays pass through and diverge from the image point. Real images can be displayed on screens

53 Mirror Object & Virtual Image Virtual Image: An image that cannot be projected onto a surface. A virtual image only appears like light rays came from the location of the image, they are not really there. Mirrors make Virtual Images.

54 Does a mirror produce an image that is reversed right-left or front-back?

55 Mirror Object & Virtual Image If the candle is ½ a meter in front of the mirror, how far behind the mirror is the image located?

56 How long does a mirror have to be to see your entire image in?

57 Mirror Reflection Convex & Concave Which is convex? A or B?

58 Focal Length Shown by Parallel Rays

59 Refraction: Bending of Light Transmitted through Materials

60 Refraction: Bending of Light Transmitted through Materials

61 Light Bends because it Slows Down.

62 Atoms are Optical Tuning Forks If the frequency of incident light resonates with the electron energy levels in the atom, then the atoms absorb and re-emit the light, and that takes time.

63 Atoms are Optical Tuning Forks Light slows down as it travels through glass because it takes time to be absorbed and re-emitted.

64 Light refracts toward the normal when it slows down (air to water) and refract away from the normal when it speeds up (water to air)

65 Principle of Least Time

66 Index of Refraction n = c v n 1 Vacuum: 1 Water: 1.33 Glass: 1.46 Diamond: 2.4

67 Apparent Depth 25

68 Total Internal Reflection

69 If you pass white light through a prism, it separates into its component colors. long wavelengths R.O.Y. G. B.I.V short wavelengths

70 How much it bends depends on WAVELENGTH. long wavelengths R.O.Y. G. B.I.V short wavelengths

71 Atoms are Optical Tuning Forks The glass is more tuned to higher frequencies and so the Blue takes more time to be absorbed and re-emitted. It takes longer to interact so it travels slower through the glass. Therefore it bends more.

72 Dispersion Shorter wavelengths bend more through the glass.

73 The speed and wavelength change but the FREQUENCY does NOT. Fr Frequency depends on the oscillating source! long wavelengths R.O.Y. G. B.I.V short wavelengths

74 How are Rainbows Formed? Different Colors bend different amounts!

75 More Rainbow facts an observer is in a position to see only a single color from any one droplet of water. your rainbow is slightly different from the rainbow seen by others your rainbow moves with you disk within the bow is brighter because of overlapping of multiple refractions (which don t occur outside the disk)

76 Rainbows Dispersion & Internal Reflection

77 Lenses Bringing Light into Focus Converging Lens Diverging Lens

78 Lenses A lens nicely bends the straight-line paths of light.

79 Lenses A converging lens can project an image.

80 Focal Point Every lens has a focal point the distance away from the lens that rays come into focus. The focal point depends on the shape and thickness of the lens.

81 Real Images

82 Virtual Images

83 Lenses Image formation is a consequence of light traveling in straight lines The first camera the pinhole camera illustrates this fact.

84 Pin Hole Camera Camera Lens Why aren t images produced on the wall without a lens or hole?

85 Accomodation

86 Vision Defects

87 Nearsighted

88 Far-Sighted

89 If the object light interacts with is about the size or smaller than the wavelength of light, it acts like a wave and exhibits diffraction and the Ray model no longer holds.

90 Diffraction depends on SLIT WIDTH: the smaller the width, relative to wavelength, the more bending and diffraction.

91 Another Way to Bend Waves

92

93 Double Slit is VERY IMPORTANT because it is evidence of waves. Only waves interfere like this.

94 Double Slit

95 Double Slit for Electrons shows Wave Interference

96 Dispersion: Diffraction Gratings Waves can be bent by diffraction. Light can be dispersed by diffraction. The greater the wavelength, the greater the angle. How does this compare to dispersion with a prism?

97 Dispersion: Diffraction Gratings How does this compare to dispersion with a prism? Longer wavelength light is bent more with a grating. Shorter wavelength light is bent more with a prism.

98 Polarization The EM fields are aligned in specific directions.

99 Polarization of Light Plane Polarized Circular Polarized Polarization upon Reflection

100 Circularly Polarized EM Wave

101 Elliptically Polarized EM Wave

102 Two crossed polarizers cut all light. But add a third polarizer in between and Light shines through! How is this so? Light is in a Superposition of Polarization States! This is a Quantum Effect.

103 Electromagnetic Spectrum Increasing Energy

104 How is UV made?

105 X-Ray Production By High Voltage Discharge

106 X-Ray Production By High Voltage Discharge

107 Accelerating Charges Synchrotron Radiation X-Ray and Radio

108

109 How can we SEE Black Holes? We see the X Rays produced by matter falling into them.

110 X Ray Imaging when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film. When X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film.

111 Gamma Ray Production by Nuclear Decay when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film P U + He+ γ

112 Gamma Ray Production Matter-antimatter annihilation

113 Gamma Ray Burst

114 Ionizing Radiation: UV, Xray & Gamma Energy to ionize atom or molecule: eV

115 Ionizing Radiation: UV, Xray & Gamma

116 Light can Kill

117 Biological Effects of Ionizing Radiation

118 Atomic Thermal Blast IR, VISIBLE, UV

119 EM Radiation Hazards: Are Low Frequencies Dangerous?

120 Sunlight Gives Life! The Greenhouse Effect

121 Cosmic EM Radiation The Atmosphere

122 Visible Sun: The Photosphere Atomic Excitations: nm at a few thousand Kelvin.

123 Radio Image of the Sun Synchrotron Radiation: 10.7 cm 2800MHz

124 Infrared Sun More than half the Sun s power is radiated in IR.

125 UV Sun

126 X-Ray Sun Bremsstrahlung Radiation (braking, in German)

127 Gamma Ray Sun Bremsstrahlung Radiation (braking, in German)

128 Multiwavelength Solar Flare

129

130 Where are the black dots?

131 Are the bricks crooked?

132 Keep staring at the black dot in the center. After a while the gray haze around it will appear to shrink.

133 Which arrow is longer?

134 Which inner box is larger?