When light travels from a less dense medium to a denser medium, it slows down and bends towards the normal. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant called the refractive index. The refractive index is higher for denser materials and determines how much light will bend when passing from one medium to another.

1. Lig ht Refraction of

2. plane  normal  normal center Normal :

3. Angle of incidence, i Angle of refraction, r incident ray Ray emerges parallel to incident ray Refracted ray Refraction of light: The change in the direction, or bending of light when it travels from one medium to another is known as refraction .

5. i r i > r since D air < D glass  a  g  a >  g normal Air Glass When light travels from a less dense medium to a denser medium the speed (or wavelength) of light decreases and the light ray is refracted towards to the normal. Refraction of light:

7. Refractive index 1.0 Air 1.3 Ice 1.33 Water 1.5 Perspex About 1.5 Glass 2.4 Diamond Refractive Index Medium

10. Apparent depth Real depth Fish image of fish Air Water Refractive index of water = (Real depth / Apparent depth)

14. Reversibility of light in reflection Two fig. seen alike, Why ? Explain ! speed v 1 speed v 2 speed v 2 speed v 1  1  1  2  2 n 1 n 1 n 2 n 2

15. air water air water air water i i i = c, critical angle i < c, critical angle i > c i Case 1 Case 2 Case 3  Reflection When light ray traveled from denser material to less dense material (say, from water to air), and angle of incidence, i < c, the critical angle, most of the light ray will be refracted to the less dense medium and part of the light will be reflected. (case 1)

16. air water air water air water i i i = c, critical angle i < c, critical angle i > c i Case 1 Case 2 Case 3  When light ray traveled from denser material to less dense material (say, from water to air), if the angle of refraction equal to 90 0 , then its angle of incidence at this instant is defined as critical angle of the denser material. (case 2) angle i = angle c (if angle r = 90 0 ) Critical Angle

17. air water air water air water i i i = c, critical angle i < c, critical angle i > c i Case 1 Case 2 Case 3  Total Internal Reflection When light ray traveled from denser material to less dense material (say, from water to air), and i f the angle of incidence, i > c, the critical angle, all the light ray will reflected internally. This is called total internal reflection. (case 3)

19. high density low density Optical Fibre ( Group Discussion) light ray

20. Mirages

21. GCE O-Level Past Examination Paper Science (Physics)

22. C O’ level Physics Nov 1995 12. The diagram shows a ray of light moving from air into plastic. What is the refractive index of the plastic ? A 0.71 B 1.22 C 1.41 D 1.50

23. GCE O Nov 1996 10. A ray of light travels from air into glass. The angle of incidence is i and the angle of refraction is r. How is the refractive index of glass calculated ? A i / r B sin i / sin r C sin ( i/r ) D sin i x sin r B

24. Nov 1991 11. Which line shows the path a ray of light would take through a glass block? B Hint: Incident ray parallel to ray B

25. GCE O Nov 1996 11. A ray of red light travelling in glass strike the glass-air boundary. Some light is reflected and some is refracted. Which diagram shows the paths of the ray ? A

26. Nov 1990 7. The bottom surface of a glass block is silvered to act as a mirror. Which diagram best represents the path of a light ray that enters this block through the top surface? E

27. GCE O Nov 1997 10. The bottom surface of a glass black is silvered to act as a mirror. Which diagram could represent the path of a light ray which enters this block through the top surface ? D

28. GCE O Nov 1994 12. Which diagram shows the path of a ray of light through a glass block ? D

29. November 1989 9. A prism is made from glass with a critical angle less than 45 o . Which one of the following diagrams, showing light passing through the prism, is incorrect? C

30. November 1989 11. When a narrow beam of white light passes through a prism, it produces a spectrum. Which one of the following diagrams correctly shows the refraction and dispersion produced by the prism? E Note: not in 1999 syllabus

31. Nov 1990 8. Which diagram correctly shows how a prism can be used to split white light into a spectrum? (Only the colours at the ends of the spectrum are marked on the diagrams.) E

32. 10.(a) Draw a diagram to show a ray of light passing through from air to glass. Label the angle of incidence i and the angle of refraction r. Define refractive index for the glass. [3] GCE ‘O’ LEVEL Nov 1995 i r air glass i > r The refractive index of the glass is equal to the ratio of sin i and sin r. Thus, n = sin i / sin r (continue on next slide)

36. November 1992 3. The diagram shows a ray of light passing thorough a glass block ABCD. (a) Calculate the refractive index of the glass, showing your working. 15 0 25 0 A B C D n = sin i / sin r = sin 25 0 / sin 15 0 = 1.63 (continue on next slide)

37. 3(b) light passing thorough the block is partially reflected at two places. Draw, on the diagram both the reflected rays. [3] 25 0 15 0 25 0 (Cont. …) Q. 3 November 1992

38. Nov 1990 4. The diagram below shows a ray of red light approaching a point P on the boundary between glass and air. a) Which medium, A or B, is the glass? [1] b) What is the size of the angle  ? [1] Since  > 30 0 , therefore median B is the glass angle  = 30 0 (continue in next slide)

39. 4(c) The incident beam was then changed to white light. What effect would this have on the light rays (i) PX, (ii) PY? [2] (Cont. …) Q. 43 Nov 1990 White light Since white light has higher frequency than red light, therefore, (i) PX remains unchanged . (ii) PY will deflect slightly away from normal.