1. Do now! Can you continue/finish the sheet we started at the end of last lesson on POLARISATION?

2. Using ray boxes

3. Reflection Draw around the mirror

4. Reflection normal

5. Reflection normal

6. Reflection normal

7. Reflection normal Angle of incidence

8. Reflection normal Angle of incidence

9. Can you quietly and sensibly follow Mr Porter?

10. Reflection Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror Angle of incidence = Angle of reflection

11. 4.4 Mirrors on the moon! http://www.youtube.com/watch?annotation_id=annotation_877313&feature=iv&src_vid=QNP8wy3S_kY&v=dsRsap 2_RAc

12. 4.4 Mirror Island

13. Aim the laser at the dog! Can you arrange mirrors on the sheet to aim the laser at me? 4.4 Zap the Dog!

14. 4.4 What colour is a mirror? http://www.youtube.com/watch?v=-yrZpTHBEss

15. Possible Homework Design your own worksheet using the law of reflection – you can do something similar to Mirror Island or even better think of an even more interesting way of testing students’ knowledge and understanding of the law of reflection. Print your sheet out and complete it yourself.

16. The mug trick!

18. Why does this happen?

19. Marching soldiers!

20. Light waves Light slows down as it goes from air to glass/water

21. Ripple tank Ripple Tank Simulation

22. Snell’s law There is a relationship between the speed of the wave in the two media and the angles of incidence and refraction θ1θ1 θ2θ2 Ray, NOT wavefronts

23. Snell’s law speed in substance 1 sinθ 1 speed in substance 2 sinθ 2 =

24. Snell’s law In the case of light only, we usually define a quantity called the index of refraction for a given medium as n m = c = sinθ 1 /sinθ 2 c m where c is the speed of light in a vacuum and c m is the speed of light in the medium vacuum c cmcm

25. Snell’s law Thus for two different media sinθ 1 /sinθ 2 = v 1 /v 2 = n 2 /n 1

26. OR! Thus for two different media sinθ 1 /sinθ 2 = v 1 /v 2 = n 2 /n 1 = 1 n 2

27. Refraction – a few notes The wavelength changes, the speed changes, but the frequency stays the same

28. Refraction – a few notes When the wave enters at 90°, no change of direction takes place.

31. 4.4 Refraction worksheet

32. i 4.4 Measuring refractive index r

33. Critical angle

34. i

35. i

37. i

38. Critical Angle http://phet.colorado.edu/en/simulation/bendi ng-lighthttp://phet.colorado.edu/en/simulation/bendi ng-light Critical angle (when angle of refraction is 90º) i

39. Critical angle (C) sinθ 1 /sinθ 2 = n 2 /n 1 At critical angle (C), θ 2 = 90, sinθ 2 = 1 sinC = n 2 /n 1 = 1/n 1 if into air/vacuum

40. Right-angled prisms

41. Right-angled prism? ?

42. Right-angled prisms Bigger than Critical angle

43. Examples of Total Internal Reflection

49. 4.4 Critical angle worksheet

50. Diffraction Waves spread as they pass an obstacle or through an opening

51. Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

52. Diffraction Diffraction is most when the opening or obstacle is similar in size to the wavelength of the wave

53. Diffraction Ripple Tank Simulation

54. Diffraction That’s why we can hear people around a wall but not see them!

55. Diffraction of radio waves

56. Diffraction patterns

57. b θ n = 1 n = 2

58. 4.4 Diffraction worksheet

59. Superposition

60. Principle of superposition When two or more waves meet, the resultant displacement is the sum of the individual displacements

61. Constructive and destructive interference When two waves of the same frequency superimpose, we can get constructive interference or destructive interference. + = + =

62. Superposition In general, the displacements of two (or more) waves can be added to produce a resultant wave. (Note, displacements can be negative)

63. Interference patterns Ripple Tank Simulation

64. If we pass a wave through a pair of slits, an interference pattern is produced

65. Can you follow Mr Porter?

66. Path difference Whether there is constructive or destructive interference observed at a particular point depends on the path difference of the two waves

67. Constructive interference if path difference is a whole number of wavelengths

68. antinode

69. Destructive interference if path difference is a half number of wavelengths node

70. Destructive interference if path difference is a half number of wavelengths

71. 4.4 Interference questions

72. Double slit interference s s

77. s s

78. With white (non-monochromatic) light?

79. Young’s original experiment Coloured filter

80. 4.4 Young’s double-slit worksheet Mr Porter is giving you a worksheet