Light and Geometric Optics

1. Light and Geometric Optics

2. Some info on Light • Visible light is part of the electromagnetic spectrum of waves. • Electromagnetic waves are transverse and have a constant speed in space (speed of light) • Light exhibits all the characteristic and properties of all periodic waves • Reflection, refraction, interference, and diffraction • Also exhibits the Doppler Effect

3. The Electromagnetic Spectrum • The electromagnetic spectrum is the complete spectrum or continuum of light including radio waves, infrared, visible light, ultraviolet light, X-rays and gamma rays • An electromagnetic wave consists of electric and magnetic fields which vibrates thus making waves. • All electromagnetic waves are produced by accelerating charged particles.

4. Wavelength, Frequency and Energy • Since all electromagnetic waves travel at the same speed, wavelength and frequency have an indirect relationship. • EM waves with a short wavelength will have a high frequency and high energy. • EM waves with a long wavelength will have a low frequency and low energy.

5. The Electromagnetic Spectrum EM waves differ in their frequency and in the sources used to produce them

6. RADIO WAVES • Have the longest wavelengths and lowest frequencies of all the electromagnetic waves. • A radio picks up radio waves through an antenna and converts it to sound waves. • Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency. • MRI (MAGNETIC RESONACE IMAGING) • Uses Short wave radio waves with a magnet to create an image • DO NOT CONFUSE EM RADIO WAVES WITH LONGITUDINAL SOUND WAVES.

7. Bands of Radio/TV/Microwaves

8. Microwaves • Shorter than radio, longer than light and infrared • Wavelength 1 x 10 - 4 m to 1 x 10-1 m • Used in radar, air – traffic control, long distance telephone communication, medicine and to cook food. • The frequency of microwaves in a microwave oven is the same as the natural rotational frequency of water molecules. Resonance is what causes food to get cooked

9. Invisible electromagnetic waves that are detected as heat Can be detected with special devices such as night goggles Used in heat lamps, and infrared photography. Higher energy than microwaves but lower than visible light Infrared waves

10. Visible Light • The portion of the electromagnetic spectrum that human eyes can detect • Approximately one percent of the EM spectrum • The wavelengths that the human eye can detect are approximately 400 to 700 nanometers. • ROY G BIV (red, orange, yellow, green, blue, indigo, violet) • Red is the lowest frequency and violet is the highest frequency

11. Ultraviolet waves • The part of sunlight that causes sunburn • Higher energy than light waves • Can cause skin cancer and blindness in humans • Used in tanning beds and sterilizing equipment

12. X-Rays • High energy waves • First discovered by Roentgen • Used in medicine, industry and astronomy • Can cause cancer

13. GAMMA RAYS • Shorter wavelength and higher frequency than X-rays • Emitted by radioactive nuclei. • Carry the greatest amount of energy and penetrate the most. • Used in radiation treatment to kill cancer cells. • Can be very harmful if not used correctly.

14. Speed of Light • In 1675 Dutch astronomer, Olaus Roemer, used his observations of Jupiter and the eclipse of one of its moons to measure the speed of light. • In the nineteenth century the American physicist Albert Michaelson used sunlight and rotating mirrors to obtain more precise measurements. • Due to Einstein’s theory of relativity , the speed of light has been set to 2.99792458x108 m/s (approximately 186,000 mi/s) in a vacuum.

15. Visible Light Monochromatic light consists of light of a single wavelength (or frequency). White light is all the colors of visible light mixed together Black is the complete absence of visible light.

16. Review Videos • http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson47/lessonp.html • Electromagnetic Spectrum

17. http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson48/lessonp.htmlhttp://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson48/lessonp.html Reflection

18. Law of Reflection • “the angle that the incident ray makes with the normal to the surface is equal to the angle that the reflected ray makes with the normal to the surface.” • θ1 = θ2 or θi = θr

19. Types of reflection • Polished surfaces such as plane mirrors produce regular or specularreflection. • An irregular surface such as a windblown water surface causes a diffuse reflection.

20. http://www.stmary.ws/highschool/physics/home/animations3/waves/reflectionInt.swfhttp://www.stmary.ws/highschool/physics/home/animations3/waves/reflectionInt.swf • Remember ... reflection always makes a V • What is the smallest mirror you need to see your whole body? • 1/2 your height

21. Plane Mirrors • When an object is viewed in a plane mirror, the image that is formed is erect (upright), left-right reversed, and the same size as the object. • Incident ray, normal line, and reflected rays are all in the same plane • The distance the object is in front of the mirror equals the distance the image is behind the mirror

22. Angle of Reflection? (with respect to normal) 60 degrees (Angle from normal)

23. http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson48/lessonp.htmlhttp://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson48/lessonp.html Refraction

24. Refraction • Refraction – the bending of light that occurs when a light wave passes through a boundary between two media • Any device with a lens refracts light • http://www.stmary.ws/highschool/physics/home/animations3/waves/refraction2.swf

25. Speed and Refraction • The faster the medium, the larger the angle a light ray makes with the normal Velocity of Air > Velocity of Water (light always crosses over normal)

26. If Light goes from fast medium to slow, light bends toward the normal

27. Ifθin = 0 degrees,no refraction (Light must come in at an angle to be refracted)

28. REFRACTION IS ALWAYS ACCOMPANIED BY REFLECTION Find the missing ray in the ray diagram The reflected ray at the glass/air boundary is  missing. 

29. Which ray diagram is correct? Choice 2 (Angle ray leaves air = Angle ray enters air)

30. At what angle will the ray reenter the air? 35 degrees

31. A sunset is an optical illusion Refraction allows you to see the sun even after it has set. 

32. Bill Nye video

33. Index of Refraction (n) – a comparison of speed of light in a substance to its speed in a vacuum n = c/v • c = speed of light in a vacuum (3.00 x 108 m/s) v = speed of light in a medium • Ex. If a substance has an index of refraction of 2.00 it means light is twice as fast in a vacuum than it is in that medium • http://www.stmary.ws/highschool/physics/home/review/waves/refractionHarrison.htm

34. Which substance slows down light the most when light enters from air? Diamond – has the highest index of refraction Which slows down the least? Water – lowest n

35. Ex 1) Speed of light in alcohol? • Alcohol: n = 1.36 (Reference Table)    n = c/v • 1.36 =(3.00 x 108 m/s)/V •     V = 2.21 x 108 m/s

36. c= nv n and v are inversely related • The more light is slowed down or sped up, the more it changes direction.

37. Snell's Law n1sinθ1 = n2sinθ2 • 1 – incident medium • 2 – refractive medium

38. Ex: Calculate θ2 Air/Lucite n1sinθ1 = n2sinθ2 1.00 sin53 = (1.50) sinθ2 .798 = 1.50sinθ2 θ2 = 320

39. n and v and λ n1v1 = n2v2 1 - incident medium 2 – refractive medium When a light changes media, its wavelength changes NOT its frequency n2λ2 = n1λ1 When light refracts it BENDS, CHANGES SPEED and WAVELENGTH

40. Total internal reflection • http://video.mit.edu/watch/mit-physics-demo-refraction-a-total-internal-reflection-12044/

41. sinθc = 1/n1 • Critical Angleθc– angle of incidence for which the angle of refraction equals 900 when light travels inside one medium that borders on air or a vacuum • Deriving Critical Angle Equation n1sinθ1 = n2 sinθ2     Substitute θc, θ2 = 90, n2 = 1  n1sinθc = 1sin90  n1sinθc = 1       sinθc = 1/n1

42. Ex) Find θc for Lucite sin θc = 1/n1  From reference table, n1 = 1.50  sinθc = 1/1.50 θc = 41.8

43. Relationships with θ1 & θc • When θ1 > θc Total Internal Reflection (Outside Medium Must Be Faster) • When θ1 = θc θ2 = 900 • When θ1< θc Refraction

44. Total internal reflection θ1 > θc

45. When θ1 = θc θ2 = 900

46. Which diagram shows: a) Total Internal Reflection? Choice 2 (Outside Medium Must be Fast) b) Refraction? Choice 3 c) Impossible? Choice 1 (Light always crosses over normal)

47. Dispersion • Dispersion – separation of polychromatic light into its component wavelengths (colors)

48. Each Color hasA Different Wavelength Red – fastest (slowed least), bent leastViolet – slowest (slowed most), bent most

49. http://www.stmary.ws/highschool/physics/home/notes/waves/Dispersion.htmhttp://www.stmary.ws/highschool/physics/home/notes/waves/Dispersion.htm • (youtube video)

50. http://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson46/lessonp.htmlhttp://www.montereyinstitute.org/courses/AP%20Physics%20B%20II/course%20files/multimedia/lesson46/lessonp.html Diffraction