1. Refraction of Light LIGHT CHAPTER 10.2

3. LIGHT REFRACTION OF LIGHT Refraction is the change in direction of light when it passes from one medium to another.

4. LIGHT REFRACTION OF LIGHT If light ray enters another medium perpendicular to boundary, the ray does not bend.

5. LIGHT REFRACTION OF LIGHT When the light ray travels from air to water, the refracted ray bends towards the normal. i r air water Incident ray Refracted ray normal i – angle of incidence r– angle of refraction

6. LIGHT REFRACTION OF LIGHT When the light ray travels from water to air, the refracted ray bends away from the normal. i r air water Incident ray Refracted ray normal i – angle of incidence r– angle of refraction

7. LIGHT REFRACTION OF LIGHT During refraction, light bends first on passing from air to glass and again on passing from the glass to the air.

8. LIGHT REFRACTION OF LIGHT During refraction, light bends first on passing from air to glass and again on passing from the glass to the air. i r Incident ray Emergent ray Refracted ray Reflected ray air air glass

9. LIGHT OPTICAL DENSITY Light slows down when it enters an optically denser medium. The refracted ray bends towards the normal when the second medium is optically more dense than the first. i r air water Incident ray Refracted ray normal

10. LIGHT OPTICAL DENSITY Light speeds up when it enters an optically less dense medium. The refracted ray bends away from the normal when the second medium is optically less dense than the first. air water i r Incident ray Refracted ray normal

11. LIGHT OPTICAL DENSITY Among the 3 transparent mediums (air, water and glass), glass has the highest optical density. air water i 1 r 1 Incident ray Refracted ray glass i 2 r 2 Refracted ray air water i 1 r 1 Incident ray glass i 2 r 2 Refracted ray Refracted ray

12. LIGHT REFRACTION OF LIGHT Complete these ray diagrams. air glass glass water

13. LIGHT REFRACTION OF LIGHT Complete these ray diagrams. air water glass air

14. LIGHT LAWS OF REFRACTION The incident ray, the refracted ray and the normal at the point of incidence all lie in the same plane. Law #1

15. For two given media, the ratio sin i ÷ sin r is a constant , where i is the angle of incidence and r is the angle of refraction LIGHT i r air water Incident ray Refracted ray normal LAWS OF REFRACTION Law #2 Refractive Index, n = sin i sin r

16. LIGHT REFRACTIVE INDEX The higher the optical density, the greater the refractive index. The greater the refractive index, the greater the bending of light towards the normal. air water i 1 r 1 Incident ray Refracted ray glass i 2 r 2 Refracted ray air water i 1 r 1 Incident ray glass i 2 r 2 Refracted ray Refracted ray

17. LIGHT REFRACTIVE INDEX If light is incident upon a piece of glass (refractive index 1.52) at an angle of 45 o , what is the angle of refraction?

18. LIGHT REFRACTIVE INDEX Given that the refractive index of water is 1.33, calculate the angle of refraction when the incident ray comes in at 60 o to the normal. 60 o r air water Solution n = sin i sin r 1.33 = sin 60 o sin r sin r = sin 60 o 1.33 r = 40.6 o

19. LIGHT SPECIAL CASE! When light travels from a less dense medium to a denser medium… n = sin i sin r i r air water When light travels from a denser medium to a less dense medium… n = sin r sin i i r air water

20. LIGHT REFRACTIVE INDEX The figure shows light travelling from water into the air. The ray is incident upon the boundary at 30 o . What is the angle of refraction if the refractive index of water is 1.33? 30 o r air water Solution n sin r sin i = 1.33 sin 30 o sin r = sin r = 1.33 sin 30 o r = 41.9 o

21. LIGHT REFRACTIVE INDEX Other ways of calculating the refractive index… Refractive index, n = Also... Speed of light in vacuum / air Speed of light in medium = c v

22. LIGHT REFRACTION OF LIGHT Take a look at this...

23. LIGHT The critical angle is the angle of incidence in the optically denser medium for which the angle of refraction is 90 o . When i = critical angle,c r = 90 o . REFRACTION OF LIGHT

24. LIGHT This is called TOTAL INTERNAL REFLECTION . When i > critical angle, the ray gets reflected internally. REFRACTION OF LIGHT

25. LIGHT For TOTAL INTERNAL REFLECTION to take place: The light ray must travel from an optically denser medium towards a less dense one. TOTAL INTERNAL REFLECTION The angle of incidence must be greater than the critical angle. Direction of light path i

26. LIGHT How do we calculate the critical angle? TOTAL INTERNAL REFLECTION We know that r = 90 o …

27. LIGHT TOTAL INTERNAL REFLECTION We know that when light travels from a less dense medium to a denser medium Refractive Index, n = sin r sin i We know that when light travels from a denser medium to a less dense medium Refractive Index, n = sin r sin i

28. LIGHT How do we calculate the critical angle? TOTAL INTERNAL REFLECTION We know that r = 90 o … Refractive Index, n = sin r sin i n = sin c sin 90 o = sin c 1

29. LIGHT How do we calculate the critical angle? TOTAL INTERNAL REFLECTION n = sin c = c 1 sin -1 n 1

30. LIGHT Medium: TOTAL INTERNAL REFLECTION Refractive Index: Critical Angle: = c sin -1 n 1 Glass 1.50 = sin -1 1.50 1 = 41.8 o

31. LIGHT Medium: TOTAL INTERNAL REFLECTION Refractive Index: Critical Angle: = c sin -1 n 1 Water 1.33 = sin -1 1.33 1 = 48.8 o

32. LIGHT Medium: TOTAL INTERNAL REFLECTION Refractive Index: Critical Angle: = c sin -1 n 1 Diamond 2.42 = sin -1 2.42 1 = 24.4 o

33. LIGHT TOTAL INTERNAL REFLECTION Applications of Total Internal Reflection in Prisms

34. LIGHT TOTAL INTERNAL REFLECTION Applications of Total Internal Reflection in Prisms

35. LIGHT TOTAL INTERNAL REFLECTION Applications of Fibre Optics