1. Light and the Electromagnetic Spectrum

2. Light as Energy There is much evidence in our world that light is a form of energy.

3. Electromagnetic Spectrum Electromagnetic waves include visible light and several other types of waves. Arranged in order, they form the electromagnetic spectrum. Electromagnetic waves include visible light and several other types of waves. Arranged in order, they form the electromagnetic spectrum.

4. Electromagnetic Spectrum Waves with shorter wavelengths have higher frequencies and greater energies. Radio waves are the least energetic; gamma waves are the most energetic. Waves with shorter wavelengths have higher frequencies and greater energies. Radio waves are the least energetic; gamma waves are the most energetic.

5. Radio Waves used in TV and radio transmissions used in communications microwaves used in TV and radio transmissions used in communications microwaves

6. Infrared Waves produced by the thermal motion of atoms all matter emits infrared waves have many commercial uses produced by the thermal motion of atoms all matter emits infrared waves have many commercial uses

7. Visible Light Waves narrow band 3.9 × 10 14 to 7.7 × 10 14 Hz λ = 770 nm to 390 nm deep red to deep violet a continuous spectrum narrow band 3.9 × 10 14 to 7.7 × 10 14 Hz λ = 770 nm to 390 nm deep red to deep violet a continuous spectrum

8. Ultraviolet Waves greater energy and higher frequency than visible light three levels greater energy and higher frequency than visible light three levels

9. X-rays produced when high- energy electrons strike atoms and suddenly decelerate penetrate solid matter medical and industrial diagnostics produced when high- energy electrons strike atoms and suddenly decelerate penetrate solid matter medical and industrial diagnostics

10. Gamma Rays produced by high-energy changes in subatomic particles stopped only by very thick or dense materials high doses can cause damage to living things produced by high-energy changes in subatomic particles stopped only by very thick or dense materials high doses can cause damage to living things

11. Sources and Propagation of Light

12. Incandescent sources are objects that are heated until they glow. The frequency and color of the light are related to the object’s temperature. Incandescent sources are objects that are heated until they glow. The frequency and color of the light are related to the object’s temperature. Incandescent

13. consist of a sealed glass tube containing a gas and fitted with electrodes current flowing through the tube generates visible light type of gas determines color of light consist of a sealed glass tube containing a gas and fitted with electrodes current flowing through the tube generates visible light type of gas determines color of light Gas-Discharge

14. Fluorescent lights emit UV which strikes phosphors on the inside of the glass tube. Phosphors glow when struck by high-energy EM radiation. Fluorescent lights emit UV which strikes phosphors on the inside of the glass tube. Phosphors glow when struck by high-energy EM radiation. Gas-Discharge

15. light at a single frequency single, energetic EM wave extremely intense many practical uses, but not suitable for area lighting light at a single frequency single, energetic EM wave extremely intense many practical uses, but not suitable for area lighting Lasers

16. light-emitting diodes solid-state electronic component that emits monochromatic light when a small potential difference is established across it light-emitting diodes solid-state electronic component that emits monochromatic light when a small potential difference is established across it LED’s

17. wide variety of applications have become practical for illumination use low power and are very efficient wide variety of applications have become practical for illumination use low power and are very efficient LED’s

18. generate light with minimal heat through chemical reactions chemiluminescent bioluminescence— produced by living things very efficient generate light with minimal heat through chemical reactions chemiluminescent bioluminescence— produced by living things very efficient Cold Light

19. Many have tried to calculate the speed of light. Galileo Ole Rømer Armand Fizeau Léon Foucault Albert Michelson Many have tried to calculate the speed of light. Galileo Ole Rømer Armand Fizeau Léon Foucault Albert Michelson The Speed of Light

20. The currently accepted value for the speed of light is exactly 299,792,458 m/s. We usually round this to 3.00 × 10 8 m/s. This is the speed of light in a vacuum (c). The currently accepted value for the speed of light is exactly 299,792,458 m/s. We usually round this to 3.00 × 10 8 m/s. This is the speed of light in a vacuum (c). The Speed of Light

21. Light travels outward in concentric spherical waves. Light waves travel at equal speeds through a uniform medium. plane waves wave fronts Light travels outward in concentric spherical waves. Light waves travel at equal speeds through a uniform medium. plane waves wave fronts Light Waves

22. Huygens’s principle postulates how light waves propagate. wavelets envelope Huygens’s principle postulates how light waves propagate. wavelets envelope Light Waves

23. Mathematical Description Light Waves The magnitude of the electric field strength (E) and the magnitude of the magnetic field vector (B) both act as sine waves. E = E max sin ωt B = B max sin ωt The electric field and the magnetic field are in phase. E = E max sin ωt B = B max sin ωt The electric field and the magnetic field are in phase.

24. Mathematical Description Light Waves James Clerk Maxwell related electricity, magnetism, and light.

25. Reflection and Mirrors

26. Light can be regarded as a group of rays. Light travels in reasonably straight lines. Reflection: light waves change direction Light can be regarded as a group of rays. Light travels in reasonably straight lines. Reflection: light waves change direction Ray Optics

27. Diffuse reflection: light waves reflect in random directions Regular or specular reflection: light waves reflect predictably Diffuse reflection: light waves reflect in random directions Regular or specular reflection: light waves reflect predictably Ray Optics

28. normal = perpendicular angle of incidence (θ i ) angle of reflection (θ r ) normal = perpendicular angle of incidence (θ i ) angle of reflection (θ r ) Ray Optics

29. Law of Reflection Ray Optics The incoming ray, the normal, and the reflected ray all lie in the same plane. The angle of incidence equals the angle of reflection.

30. Albedo Visible-light albedo is a ratio of the reflected light to the incident light. All light is reflected: albedo = 1.00 All light is absorbed: albedo = 0.00 Visible-light albedo is a ratio of the reflected light to the incident light. All light is reflected: albedo = 1.00 All light is absorbed: albedo = 0.00

31. Albedo geometric albedo: sun is directly behind the observer relative to the observed object bond albedo: no regard to the position of the sun geometric albedo: sun is directly behind the observer relative to the observed object bond albedo: no regard to the position of the sun

32. Plane Mirrors The image we “see” in a mirror is called a virtual image. In a plane mirror, it appears that the left and right sides are reversed. The image we “see” in a mirror is called a virtual image. In a plane mirror, it appears that the left and right sides are reversed.

33. Plane Mirrors By using multiple plane mirrors at various angles, we can see multiple images 90° → 3 images 60° → 5 images 45° → 7 images By using multiple plane mirrors at various angles, we can see multiple images 90° → 3 images 60° → 5 images 45° → 7 images

34. Plane Mirrors The number of images (n) for a given angle θ is determined by this formula: n = - 1 360° θ θ

35. concave mirrors convex mirrors Spherical concave mirrors produce spherical aberration. not an issue with parabolic mirrors concave mirrors convex mirrors Spherical concave mirrors produce spherical aberration. not an issue with parabolic mirrors Curved Mirrors

36. principal focus or focal point (F) distance from F to mirror is the focal length (f) radius of the mirror (R) is important for spherical concave mirrors principal focus or focal point (F) distance from F to mirror is the focal length (f) radius of the mirror (R) is important for spherical concave mirrors Concave Mirrors

37. center of a spherical mirror (C) is the center of the spherical surface line through F and C intersects mirror at its vertex (V); called the principal or optical axis center of a spherical mirror (C) is the center of the spherical surface line through F and C intersects mirror at its vertex (V); called the principal or optical axis Concave Mirrors

38. On a spherical concave mirror, the focus (F) is midway between V and C. Concave Mirrors f = 2 2 R R

39. Concave Mirrors

40. object distance (d O ) is the distance of the object from the mirror image distance (d I ) is the distance of the image from the mirror object distance (d O ) is the distance of the object from the mirror image distance (d I ) is the distance of the image from the mirror Concave Mirrors

41. There are six possible cases with the object located on the optical axis. A real image is one which can be focused on a screen. “in front of” the mirror There are six possible cases with the object located on the optical axis. A real image is one which can be focused on a screen. “in front of” the mirror Concave Mirrors

42. Case 2 (d O > R) Concave Mirrors

43. Case 4 (f < d O < R) Concave Mirrors

44. Case 3 (d O = R) Concave Mirrors

45. Case 1: “infinite” distance from mirror Concave Mirrors

46. Case 5 (d O = f) Concave Mirrors

47. Case 6 (d O < f) Concave Mirrors

48. The mirror equation: Finding Image Position + = dIdI dIdI 1 1 f f 1 1 dOdO dOdO 1 1 Distances behind the mirror are assumed to be negative.

49. For all spherical mirrors, the height of the image (H I ) relates to the height of the object (H O ) by: Magnification = - HOHO HOHO HIHI HIHI dOdO dOdO dIdI dIdI

50. The magnification of the image is the absolute value of the image height to the object height: Magnification m = HOHO HOHO HIHI HIHI

51. For a concave spherical mirror, not all incoming rays are reflected so that they actually pass through the focal point. This results in spherical aberration. For a concave spherical mirror, not all incoming rays are reflected so that they actually pass through the focal point. This results in spherical aberration. Spherical Mirrors

52. Spherical aberration is more obvious in highly curved spherical mirrors. Flatter mirrors minimize, but do not eliminate, spherical aberration. Spherical aberration is more obvious in highly curved spherical mirrors. Flatter mirrors minimize, but do not eliminate, spherical aberration. Spherical Mirrors

53. A paraboloidal reflecting surface is not subject to spherical aberration. All rays parallel to the optical axis are reflected through the focus (F). A paraboloidal reflecting surface is not subject to spherical aberration. All rays parallel to the optical axis are reflected through the focus (F). Parabolic Mirrors

54. R = 2f Parabolic mirrors are often used to project rays, with the light source at the principle focus. flashlights, spotlights, etc. R = 2f Parabolic mirrors are often used to project rays, with the light source at the principle focus. flashlights, spotlights, etc. Parabolic Mirrors

55. produce only one type of image virtual (behind mirror) erect smaller f = R/2 (behind mirror) produce only one type of image virtual (behind mirror) erect smaller f = R/2 (behind mirror) Convex Mirrors

56. The mirror equation is still valid, but f and d I are negative numbers. Convex Mirrors + = dIdI dIdI 1 1 f f 1 1 dOdO dOdO 1 1

57. Image size can also be computed: Convex Mirrors = - HOHO HOHO HIHI HIHI dOdO dOdO dIdI dIdI