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16.1 – Light Fundamentals Visible light is part of a very broad range of frequencies called

16.1 – Light Fundamentals Visible light is part of a very broad range of frequencies called The Electromagnetic Spectrum. Visible light ranges from 700 nm to 400 nm

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16.1 – Light Fundamentals Visible light is part of a very broad range of frequencies called

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  1. 16.1 – Light Fundamentals Visible light is part of a very broad range of frequencies called The Electromagnetic Spectrum. Visible light ranges from 700 nm to 400 nm ROYGBIV Radio – microwaves – infrared – visible – ultraviolet – x rays – Gamma rays. Longer wavelength Shorter Wavelength Lower freq, Lower energy (E=h.f) Higher Freq, High Energy

  2. Speed of light, c = 3x108 m/s C = λ.f E/M radiation follows the inverse-square law Roemer - determined in 1670 - Careful measurement of period of Io. 14 sec longer period when earth moving away, 14 sec faster than towards. By 1676 figured it took 22 min to cross earth’s diameter. Came up with 220,000,000m/s, ~ 3/4 present value. By 1926 measuring time between 2 mtns, at 2.997996x108 m/s.

  3. Transparent- Materials light passes thru undistorted Translucent- light passes thru distorted Opaque- Light cannot pass thru *White light is made up of all wavelengths of visible light: ROYGBIV -It can be separated by a prism or by Filters. Primary colors of light: RED GREEN BLUE Primary pigment colors: CYAN MAGENTA YELLOW -pigments absorb colors of light Ex1) Magenta: Reflects ______,______ absorbs _______ Cyan: Reflects _____,______ absorbs ______ Yellow: Reflects ______,______ absorbs ______ Red paint: Reflects _______ absorbs ______,______ Complimentary colors – add together to form white light. Ex2) Comp. to magenta is ______ Comp. to red is ______ Comp. to yellow is ______ Ch16 HW#1 1-11

  4. Lab16.1 – Light Intensity - due tomorrow - go over Ch16 HW#1 at beginning of period

  5. Chapter 16, HW#1 1. What is the frequency of yellow light if the wavelength is 556nm? 2. What is the wavelength of red light if its frequency is 4.28 x 1014 Hz? 3. Convert 700nm, the wavelength of red light, to meters 4. The sun is 1.5x1011 m from Earth. How long does it take for the sun’s light to reach us? 5. The distance to the moon can be found with the help of mirrors left on the moon by astronauts. A pulse of light is sent to the moon and returns to Earth in 2.562s. Using the defined speed of light, calculate the distance from Earth to the moon.

  6. Chapter 16, HW#1 1. What is the frequency of yellow light if the wavelength is 556nm? 2. What is the wavelength of red light if its frequency is 4.28 x 1014 Hz? 3. Convert 700nm, the wavelength of red light, to meters. 700nm = 0.000000700m = 7x10-7m 4. The sun is 1.5x1011 m from Earth. How long does it take for the sun’s light to reach us? 5. The distance to the moon can be found with the help of mirrors left on the moon by astronauts. A pulse of light is sent to the moon and returns to Earth in 2.562s. Using the defined speed of light, calculate the distance from Earth to the moon. d = v.t = (3x108m/s)(2.562sec)=

  7. 6. The intensity of light at a distance of one meter from a 100 W light bulb is 140 lux. (What the lux you ask? Well it’s the amount of luminous flux per square meter, of course! Since that doesn’t probably make any sense to you, don’t worry about the units. Just answer this question:) What would be the intensity at a distance of 2 meters? 7. A red apple is red because it absorbs what primary color(s) of light, and reflects what primary color(s) of light? 8. My school colors were cyan and magenta. If you are looking at the magenta color on the school building, what color(s) are being absorbed? What color(s) are being reflected? How about with the cyan color – what’s absorbed and what’s reflected?

  8. 6. The intensity of light at a distance of one meter from a 100 W light bulb is 140 lux. (What the lux you ask? Well it’s the amount of luminous flux per square meter, of course! Since that doesn’t probably make any sense to you, don’t worry about the units. Just answer this question:) What would be the intensity at a distance of 2 meters? Inverse square law: double distance = 4X less light = 35 lux 7. A red apple is red because it absorbs what primary color(s) of light, and reflects what primary color(s) of light? Red absorbs blue, green, reflects red. 8. My school colors were cyan and magenta. If you are looking at the magenta color on the school building, what color(s) are being absorbed? green What color(s) are being reflected? blue,red How about with the cyan color – what’s absorbed red and what’s reflected? blue,green

  9. 9. If you have yellow, cyan, and magenta paints, which two would you mix to make a blue pigment? 10. You put a piece of red cellophane over one flashlight and a piece of green cellophane over another flashlight. You shine the light beams on a white wall. What color will you see where the two flashlight beams overlap? 11. You now put both the red and green cellophane pieces over one flashlight. If you shine the flashlight beam on a white wall, what color will you see?

  10. 9. If you have yellow, cyan, and magenta paints, which two would you mix to make a blue pigment? Mix cyan and magenta 10. You put a piece of red cellophane over one flashlight and a piece of green cellophane over another flashlight. You shine the light beams on a white wall. What color will you see where the two flashlight beams overlap? 11. You now put both the red and green cellophane pieces over one flashlight. If you shine the flashlight beam on a white wall, what color will you see?

  11. 9. If you have yellow, cyan, and magenta paints, which two would you mix to make a blue pigment? Mix cyan and magenta 10. You put a piece of red cellophane over one flashlight and a piece of green cellophane over another flashlight. You shine the light beams on a white wall. What color will you see where the two flashlight beams overlap? red + green = yellow 11. You now put both the red and green cellophane pieces over one flashlight. If you shine the flashlight beam on a white wall, what color will you see?

  12. 9. If you have yellow, cyan, and magenta paints, which two would you mix to make a blue pigment? Mix cyan and magenta 10. You put a piece of red cellophane over one flashlight and a piece of green cellophane over another flashlight. You shine the light beams on a white wall. What color will you see where the two flashlight beams overlap? red + green = yellow 11. You now put both the red and green cellophane pieces over one flashlight. If you shine the flashlight beam on a white wall, what color will you see? red doesn’t allow blue or green green doesn’t allow blue or red = nothing gets thru: black

  13. Ch16.2 – Reflection, Diffraction, Polarization Reflection:

  14. Ch16.2 – Reflection, Diffraction, Polarization Reflection: Θi Θr Law of Reflection: Angle of Incidence = Angle of Reflection Θi = Θr Ex1) A light ray strikes a mirror at a 53˚ angle to the normal. A. What is the angle of reflection? B. What angle does the incident ray make with the reflected ray?

  15. Ch16.2 – Reflection, Diffraction, Polarization Reflection: Θi Θr Law of Reflection: Angle of Incidence = Angle of Reflection Θi = Θr Ex1) A light ray strikes a mirror at a 53˚ angle to the normal. A. What is the angle of reflection? 53˚ B. What angle does the incident ray make with the reflected ray? 106˚ What colors of light reflect off a mirror? What colors of light reflect off a sheet of white paper?

  16. Polarization of Light Most light sources produce unpolarized, or incoherent light.

  17. Polarization of Light Most light sources produce unpolarized, or incoherent light. A polarizing filter will cut out all light rays that don’t line up with the filter’s orientation.

  18. Polarization of Light Most light sources produce unpolarized, or incoherent light. A polarizing filter will cut out all light rays that don’t line up with the filter’s orientation. If a 2nd filter is added, that is parallel to the first, light still gets thru both.

  19. Polarization of Light Most light sources produce unpolarized, or incoherent light. A polarizing filter will cut out all light rays that don’t line up with the filter’s orientation. If a 2nd filter is added, that is parallel to the first, light still gets thru both. If a 2nd filter is added that is perpendicular to the 1st, no light gets thru both.

  20. Polarization of Light Most light sources produce unpolarized, or incoherent light. A polarizing filter will cut out all light rays that don’t line up with the filter’s orientation. If a 2nd filter is added, that is parallel to the first, light still gets thru both. If a 2nd filter is added that is perpendicular to the 1st, no light gets thru both.

  21. Diffraction – bending of light around barriers AM Radio Waves can bend over mountains

  22. Diffraction – bending of light around barriers Light waves can bend when passing thru small openings. Double slit interference – proved light is a wave.

  23. Diffraction – bending of light around barriers Light waves can bend when passing thru small openings. Double slit interference – proved light is a wave. Less Bright Dark Bright Dark Brightest Dark Bright Dark Less Bright Ch16 HW#2

  24. Lab17.1 Reflection - due tomorrow - Ch16 HW#2 due at beginning of period

  25. Ch16 HW#2 12. Light coming from the sun is coherent or incoherent? What does this mean? 13. When 2 polarizing filters are placed so that they both are aligned vertically, will light pass thru? 14. Polarizing filters are placed perpendicular to each other, will light pass thru? 15. Incident ray strikes a plane mirror at 25˚ to the normal. What is the angle of reflection?

  26. Ch16 HW#2 12. Light coming from the sun is coherent or incoherent? What does this mean? Incoherent. It propagates outward as transverse waves in every plane, and at many wavelengths. 13. When 2 polarizing filters are placed so that they both are aligned vertically, will light pass thru? 14. Polarizing filters are placed perpendicular to each other, will light pass thru? 15. Incident ray strikes a plane mirror at 25˚ to the normal. What is the angle of reflection?

  27. Ch16 HW#2 12. Light coming from the sun is coherent or incoherent? What does this mean? Incoherent. It propagates outward as transverse waves in every plane, and at many wavelengths. 13. When 2 polarizing filters are placed so that they both are aligned vertically, will light pass thru? Yes 14. Polarizing filters are placed perpendicular to each other, will light pass thru? No 15. Incident ray strikes a plane mirror at 25˚ to the normal. What is the angle of reflection? Θi=25˚

  28. Ch16 HW#2 12. Light coming from the sun is coherent or incoherent? What does this mean? Incoherent. It propagates outward as transverse waves in every plane, and at many wavelengths. 13. When 2 polarizing filters are placed so that they both are aligned vertically, will light pass thru? Yes 14. Polarizing filters are placed perpendicular to each other, will light pass thru? No 15. Incident ray strikes a plane mirror at 25˚ to the normal. What is the angle of reflection? Θi=25˚Θr=25˚

  29. Ch16 HW#2 16. An incident ray strikes a mirror at an angle of 50˚ to the mirror surface. What is the angle of incidence and angle of reflection? 50˚

  30. Ch16 HW#2 16. An incident ray strikes a mirror at an angle of 50˚ to the mirror surface. What is the angle of incidence and angle of reflection? 40˚ 40˚ 50˚

  31. Ch17.2 – Refraction Light bends as it passes from one medium to another. - the more optically dense a material, the more it bends light. - when passing from a less dense medium to a more dense medium light bends towards the normal. - when passing from a more dense to less dense medium light bends away from normal Index of refraction - a measure (n = 1.0) of how much a material bends light. Air ΘiFor this chapter: Air: 1.0 water: 1.33 glass: 1.53 diamond: 2.42 (table pg397 Glass or internet) (n = 1.53) Air (n = 1.0)

  32. Ch17.2 – Refraction Light bends as it passes from one medium to another. - the more optically dense a material, the more it bends light. - when passing from a less dense medium to a more dense medium light bends towards the normal. - when passing from a more dense to less dense medium light bends away from normal (n = 1.0) Air ΘiΘreflection Glass Θrefraction (n = 1.53) Θ Air (n = 1.0) Θ

  33. Snell’s Law ni×sinΘi = nr×sinΘr Ex1) A light ray passes thru air at an angle of 30˚ to an unknown transparent material at an angle of 19˚. What's the index of refraction ff the unknown material? 30 n = 1 nr = ? 19 Ex2) Light passes from air at an angle of 45˚ to diamond which has an index of refraction of 2.42. What angle does it pass thru the diamond at? 45 ni= 1 nr = 2.42 Θ

  34. Snell’s Law ni×sinΘi = nr×sinΘr Ex1) A light ray passes thru air at an angle of 30˚ to an unknown transparent material at an angle of 19˚. What's the index of refraction ff the unknown material? AIR UNKNOWN (1.0)×sin30 = nr×sin19 nr = 1.53 30 n = 1 nr = ? 19 Ex2) Light passes from air at an angle of 45˚ to diamond which has an index of refraction of 2.42. What angle does it pass thru the diamond at? (1.0)×sin45˚ = (2.42)×sinΘr Θr = 17˚ 45 ni= 1 nr = 2.42 Θ

  35. ni×sinΘi = nr×sinΘr Ex3) A light ray passes from water (n = 1.33) at an angle of 40˚ into glass (n = 1.53). What angle does it pass thru the glass? 40˚ ni = 1.33 nr = 1.53 Θ

  36. ni×sinΘi = nr×sinΘr Ex3) A light ray passes from water (n = 1.33) at an angle of 40˚ into glass (n = 1.53). What angle does it pass thru the glass? AIR UNKNOWN (1.33)×sin40 = 1.53×sinΘ nr = 34˚ 40˚ ni = 1.33 nr = 1.53 Θ

  37. Index and the Speed of Light speed of light in a vacuum (c = 3 x 108 m/s) index of refraction in that material speed of light in that material Ex4) Find the speed of light in water.

  38. Index and the Speed of Light speed of light in a vacuum (c = 3 x 108 m/s) index of refraction in that material speed of light in that material Ex4) Find the speed of light in water. Ch17 HW#1 1 – 6

  39. Lab17.2 Refraction - due tomorrow - Ch17 HW#1 due at beginning of period

  40. Ch17 HW#1 1 – 6 1. Light in air is incident on a piece of glass (n = 1.52) at an angle of 45˚. Find the angle of refraction. 2. A ray of light passes from air into water (n = 1.33) at an angle of 30˚. Find the angle of refraction. 45˚ ni = 1.0 nr = 1.52 Θ 30˚ ni = 1.0 nr = 1.33 Θ

  41. Ch17 HW#1 1 – 6 1. Light in air is incident on a piece of glass (n = 1.52) at an angle of 45˚. Find the angle of refraction. 2. A ray of light passes from air into water (n = 1.33) at an angle of 30˚. Find the angle of refraction. 45˚ ni = 1.0 nr = 1.52 Θ 30˚ ni = 1.0 nr = 1.33 Θ

  42. 3. A ray of light is incident on a diamond (n = 2.42) at an angle of 45˚. Find the angle of refraction. (Compare to #1) 4. A block of unknown material is submerged in water. Light in the water is incident on the block at an angle of 31˚. The angle of refraction is 27˚. Find the index of refraction of the block. 45˚ ni = 1.0 nr = 2.42 Θ 30˚ ni = 1.33 nr = ? 27˚

  43. 3. A ray of light is incident on a diamond (n = 2.42) at an angle of 45˚. Find the angle of refraction. (Compare to #1) 4. A block of unknown material is submerged in water. Light in the water is incident on the block at an angle of 31˚. The angle of refraction is 27˚. Find the index of refraction of the block. 45˚ ni = 1.0 nr = 2.42 Θ 30˚ ni = 1.33 nr = ? 27˚

  44. 3. A ray of light is incident on a diamond (n = 2.42) at an angle of 45˚. Find the angle of refraction. (Compare to #1) 4. A block of unknown material is submerged in water. Light in the water is incident on the block at an angle of 31˚. The angle of refraction is 27˚. Find the index of refraction of the block. 45˚ ni = 1.0 nr = 2.42 Θ 30˚ ni = 1.33 nr = ? 27˚

  45. 5. What is the speed of light in: a. ethanol (n = 1.36) b. quartz (n = 1.54) 6. What is the index of refraction of a plastic where the speed of light is 2 x 108 m/s.

  46. 5. What is the speed of light in: a. ethanol (n = 1.36) b. quartz (n = 1.54) 6. What is the index of refraction of a plastic where the speed of light is 2 x 108 m/s.

  47. Ch17.3 – Applications of Light Total Internal Reflection - Occurs when light passes from more dense to a less dense medium. (Light rays bend away from normal) Air, n = 1 Water, n = 1.33 Critical Angle - angle where Θr = 90˚

  48. Ex1) Find the critical angle for diamond into air. Air, n = 1 Diamond, n = 2.42 Ex2) Find the critical angle for glass into air. Air, n = 1 Glass, n = 2.42

  49. Ex1) Find the critical angle for diamond into air. Air, n = 1 Diamond, n = 2.42 Ex2) Find the critical angle for glass into air. Air, n = 1 Glass, n = 1.52

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