Refraction of light

1. Refraction of light

2. No, because the fish is actually located somewhere else. Yes, of course. No, because size of objects changes when they are put under water. 1 John says, ‘When hunting a fish under water, you should aim your spear directly at the fish.’ Do you agree? 

3. It refracts into the water. It is reflected back to the air. It is absorbed by water and turned into heat. 2 When sunlight falls on the water surface, which of the following occur(s)?   

4. Introduction Refraction is the bending of light when the light passes from one medium to another. air glass

5. Introduction Useful words to describe refraction of light angle of incidence incident ray normal air glass refracted ray angle of refraction

6. air glass Introduction From a less dense to a denser medium • e.g. from air to glass normal incident ray refracted ray • Light is benttowards the normal.

7. water air Introduction From a denser to a less dense medium • e.g. from water to air normal incident ray refracted ray • Light is bentaway from the normal.

8. Relation between angle of incidence and angle of refraction sin i i = angle of incidence r = angle of refraction sin r O straight line passing through the origin  sin i is directly proportional to sin r.

9. Laws of refraction Video Simulation

10. Laws of refraction • The incident ray, the refracted ray, and the normal all lie in the same plane. normal normal incident ray air air glass glass refracted ray refracted ray

11. Laws of refraction • The ratio of the sin i to sin r is constant. sin i i.e. = constant sin r – This is called Snell’s law. In general, n1 sin 1 = n2 sin 2

12. sin i sin r sin qa sin qg Refractive index • refractive index n = • e.g. for glass, ang= where a: air g: glass

13. Refractive index Refractive indices of some materials Material Refractive index Glass 1.5 – 1.7 Water 1.33 Perspex 1.5 Diamond 2.42

14. Refractive index and speed of light vacuum (or air) 3  108 m water (n = 1.33) 2.25  108 m glass (n = 1.5) 2  108 m diamond (n = 2.42) 1.25  108 m distance that light travel in 1 s

15. 3 Refractive index and speed of light distance that light travel in 1 s vacuum (or air) 3  108 m water (n = 1.33) 2.25  108 m glass (n = 1.5) 2  108 m diamond (n = 2.42) 1.25  108 m fastest Refractive index slowest Speed of light

16. Example 3 air water A ray of light passes from air into water. Angle of incidence = 30 What is angle of refraction in water? nwater = 1.33 30

17. Example 3 30 air water 22.1 nw sin w= na sin a Applying Snell’s law,  1.33  sin w = 1  sin 30 = 0.376  sin w = sin 30/1.33  w = 22.1

18. Example 4 a g 15 30 45 60 75 11 18 28 34 40 Towards A ray of laser hits a rectangular block. The table gives a set of results. Notes: a = angles of incidence, g = angles of refraction. (a) Is the refracted ray bent towards or away from the normal?

19. Example 4 0.259 0.500 0.707 0.866 0.966 0.191 0.309 0.470 0.559 0.643 sina sin g a g 15 30 45 60 75 11 18 28 34 40 (b) Find out how sin aand sin gare related by plotting a graph of sin aagainst sin g.

20. Example 4 sin a 1.0 0.8 0.6 0.94  0.30 0.62  0.20 0.259 0.500 0.707 0.866 0.966 0.191 0.309 0.470 0.559 0.643 sin a sin g slope = = 1.52 0.4 0.2 sin g 0 0.2 0.4 0.6 0.8 0.94  0.30 = 0.64 0.62  0.20 = 0.42

21. Example 4 sin a sin g Refractive index = = slope of graph (c) Find the refractive index ng of the glass block in used in the experiment. = 1.52 The refractive index of the glass block used is 1.52.

22. Q1 A boy shines a torch under… A boy shines a torch under water as shown. Which one shows the correct path of the light ray? A Path X. B Path Y. C Path Z. D All of them.

23. Q2 A beam of light travels air to… A beam of light travels from air to water. Which of the following is equal to the ratio sin r: sin i? normal A nwater : 1 i air B nair : 1 water C 1 : nwater D 1 : nair r

24. Q3 A light rays is incident on a… A = sin 30 sin 20 sin  sin 40 sin 30 sin 20 sin 40 sin  sin  sin 40 B = C = 1.5 A light ray is incident on a glass prism. Which equation can be used to find  ? 30  20 40 D sin 40 = 1.5 sin 

25. Q4 True or false: When light is… True or false: When light is incident on a surface along the normal, only refraction occurs; there is no reflection. (T/F)

26. Q5 Statements:... 1st statement 2nd statement Light is bent towards the normal when it passes from air to glass. Glass has a greater refractive index than air. true? true? Yes Yes

27. 4 Examples of refraction of light a Bent chopstick • The chopstick appears bent because of refraction

28. 4 Examples of refraction of light real depth I O b Shallower in water • The depth that the object isactually at is called the real depth. Simulation

29. 4 Examples of refraction of light c Flickering objects in hot air • The object you see through the unstable hot air appears blurred and flickering.

30. Q1 True or false: Light slows… True or false: Light slows down when it enters a material from air. (T/F)

31. Q2 True or false: The refractive… True or false: The refractive index cannot be smaller than 1. (T/F)

32. Q3 True or false: If light travel… True or false: If light travel at the same speed in all materials, refraction would still occur when it passes from air to water. (T/F)

33. Q4 True or false: If the speed of… True or false: If the speed of light in raindrop is equal to that in air, there would be no rainbows. (T/F)

34. Q5 Sketch a ray diagram for the... Sketch a ray diagram for the tip of the chopstick to show why the chopstick looks bent when dipped into water.