1© Manhattan Press (H.K.) Ltd. Reflection Refraction Refraction 12.1 Reflection and refraction Total internal reflection Total internal reflection

2 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 198) Reflection and refraction Light – travels in straight lines (diffraction and interference of light are not prominent) Light incidents on glass, it is reflected and refracted incident ray reflected ray refracted ray Go to More to Know 1 More to Know 1

3 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 198) Reflection and refraction Go to More to Know 2 More to Know 2 Obey the Laws of Reflection Obey the Laws of Refraction

4 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 199) Reflection 1. Laws of Reflection Laws of Reflection: 1. The incident ray, the normal to the surface and the reflected ray are all lie in one plane. 2. The angle of reflection is equal to the angle of incidence. i.e. θ 1 = θ 1 ’

5 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 199) Reflection 2. Plane mirrors

6 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 200) Reflection 2. Plane mirrors Note: 1. The properties of the image: virtual (image cannot be formed on screen) erect same size as the object laterally inverted 2. The image distance (v) is equal to the object distance (u). Go to More to Know 3 More to Know 3

7 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 200) Refraction 1. Laws of Refraction Laws of Refraction: (a) The incident ray, the normal and the refracted ray at the point of incidence are all lie in one plane. (b) At the interface between any two different media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for any particular wavelength of the ray. This is named as Snell’s Law and defined as: Go to More to Know 4 More to Know 4

8 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 200) Refraction 1. Laws of Refraction n 1 sinθ 1 = n 2 sinθ 2 n = n 2 /n 1 Note: For air, n  1.00.

9 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 201) Refraction 1. Laws of Refraction Go to More to Know 5 More to Know 5 In vacuum - light travels at c Other media – light travels at lower speed higher n, greater bending of refracted ray

10 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 201) Refraction 2. Examples of refraction (a) Real depth and apparent depth

11 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 202) Refraction 2. Examples of refraction (b) Refraction by rectangular glass block

12 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 203) Refraction 2. Examples of refraction (c) Refraction by prism Go to Example 1 Example 1

13 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 204) Total internal reflection  1 increases,  2 is larger  1 to finite value (critical angle),  2 =90 o  1 > c, all light are reflected

14 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 205) Total internal reflection Examples of total internal reflection (a) Reflecting prism

15 © Manhattan Press (H.K.) Ltd Reflection and refraction (SB p. 206) Total internal reflection Examples of total internal reflection (b) Optical fibre Go to Example 2 Example 2

16 © Manhattan Press (H.K.) Ltd. End

17 © Manhattan Press (H.K.) Ltd. Ray A ray is a parallel beam of negligible thickness. Return to Text 12.1 Reflection and refraction (SB p. 198)

18 © Manhattan Press (H.K.) Ltd. It is a good way to use a laser beam to demonstrate how the light behaves in reflection and refraction. Return to Text 12.1 Reflection and refraction (SB p. 198)

19 © Manhattan Press (H.K.) Ltd. Moving of object in front of mirror When an object moves towards a fixed mirror at a speed v, its image moves at the same speed v towards the mirror too. Return to Text 12.1 Reflection and refraction (SB p. 200)

20 © Manhattan Press (H.K.) Ltd. Frequency of light in refraction Only the speed and the wavelength of the light changes when it travels from one medium to another. Its frequency remains unchanged. Return to Text 12.1 Reflection and refraction (SB p. 200)

21 © Manhattan Press (H.K.) Ltd. Refractive index and frequency The refractive index varies with the frequency of light. The higher the frequency of light, the greater the refractive index. Return to Text 12.1 Reflection and refraction (SB p. 201)

22 © Manhattan Press (H.K.) Ltd. Q: Q: Light incidents on a 5 mm thick of glass plate with refractive index 1.48 at angle of incidence of 50°. What is the lateral displacement x of the light ray after transmitting through the glass? (The refractive index of air is about 1.00.) Solution 12.1 Reflection and refraction (SB p. 203)

23 © Manhattan Press (H.K.) Ltd. Solution: Return to Text 12.1 Reflection and refraction (SB p. 204)

24 © Manhattan Press (H.K.) Ltd. Q: Q: If you look up from the bottom of a swimming pool, you can see the objects above water subtended within a cone as shown in the figure. Find the angle θ. Given that the refractive index of water is Solution 12.1 Reflection and refraction (SB p. 206)

25 © Manhattan Press (H.K.) Ltd. Solution: Return to Text 12.1 Reflection and refraction (SB p. 206)