12 1 Reflection and refraction Reflection Refraction Total

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12. 1 Reflection and refraction • Reflection • Refraction • Total internal reflection ©

12. 1 Reflection and refraction • Reflection • Refraction • Total internal reflection © Manhattan Press (H. K. ) Ltd. 1

12. 1 Reflection and refraction (SB p. 198) Reflection and refraction Light – travels

12. 1 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 Go to refracted ray © Manhattan Press (H. K. ) Ltd. More to Know 1 2

12. 1 Reflection and refraction (SB p. 198) Reflection and refraction Obey the Laws

12. 1 Reflection and refraction (SB p. 198) Reflection and refraction Obey the Laws of Reflection Obey the Laws of Refraction Go to More to Know 2 © Manhattan Press (H. K. ) Ltd. 3

12. 1 Reflection and refraction (SB p. 199) Reflection 1. Laws of Reflection: 1.

12. 1 Reflection and refraction (SB p. 199) Reflection 1. 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’ © Manhattan Press (H. K. ) Ltd. 4

12. 1 Reflection and refraction (SB p. 199) Reflection 2. Plane mirrors © Manhattan

12. 1 Reflection and refraction (SB p. 199) Reflection 2. Plane mirrors © Manhattan Press (H. K. ) Ltd. 5

12. 1 Reflection and refraction (SB p. 200) Reflection 2. Plane mirrors Note: 1.

12. 1 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 Go to • same size as the object More to Know 3 • laterally inverted 2. The image distance (v) is equal to the object distance (u). © Manhattan Press (H. K. ) Ltd. 6

12. 1 Reflection and refraction (SB p. 200) Refraction 1. Laws of Refraction: (a)

12. 1 Reflection and refraction (SB p. 200) Refraction 1. 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 © Manhattan Press (H. K. ) Ltd. 7

12. 1 Reflection and refraction (SB p. 200) Refraction 1. Laws of Refraction n

12. 1 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. © Manhattan Press (H. K. ) Ltd. 8

12. 1 Reflection and refraction (SB p. 201) Refraction 1. Laws of Refraction In

12. 1 Reflection and refraction (SB p. 201) Refraction 1. Laws of Refraction In vacuum - light travels at c Other media – light travels at lower speed higher n, greater bending of refracted ray © Manhattan Press (H. K. ) Ltd. Go to More to Know 5 9

12. 1 Reflection and refraction (SB p. 201) Refraction 2. Examples of refraction (a)

12. 1 Reflection and refraction (SB p. 201) Refraction 2. Examples of refraction (a) Real depth and apparent depth © Manhattan Press (H. K. ) Ltd. 10

12. 1 Reflection and refraction (SB p. 202) Refraction 2. Examples of refraction (b)

12. 1 Reflection and refraction (SB p. 202) Refraction 2. Examples of refraction (b) Refraction by rectangular glass block © Manhattan Press (H. K. ) Ltd. 11

12. 1 Reflection and refraction (SB p. 203) Refraction 2. Examples of refraction (c)

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

12. 1 Reflection and refraction (SB p. 204) Total internal reflection 1 increases, 2

12. 1 Reflection and refraction (SB p. 204) Total internal reflection 1 increases, 2 is larger © Manhattan Press (H. K. ) Ltd. 1 to finite value (critical angle), 2 =90 o 1 > c, all light are reflected 13

12. 1 Reflection and refraction (SB p. 205) Total internal reflection Examples of total

12. 1 Reflection and refraction (SB p. 205) Total internal reflection Examples of total internal reflection (a) Reflecting prism © Manhattan Press (H. K. ) Ltd. 14

12. 1 Reflection and refraction (SB p. 206) Total internal reflection Examples of total

12. 1 Reflection and refraction (SB p. 206) Total internal reflection Examples of total internal reflection (b) Optical fibre Go to Example 2 © Manhattan Press (H. K. ) Ltd. 15

End © Manhattan Press (H. K. ) Ltd. 16

End © Manhattan Press (H. K. ) Ltd. 16

12. 1 Reflection and refraction (SB p. 198) Ray A ray is a parallel

12. 1 Reflection and refraction (SB p. 198) Ray A ray is a parallel beam of negligible thickness. Return to Text © Manhattan Press (H. K. ) Ltd. 17

12. 1 Reflection and refraction (SB p. 198) It is a good way to

12. 1 Reflection and refraction (SB p. 198) It is a good way to use a laser beam to demonstrate how the light behaves in reflection and refraction. Return to Text © Manhattan Press (H. K. ) Ltd. 18

12. 1 Reflection and refraction (SB p. 200) Moving of object in front of

12. 1 Reflection and refraction (SB p. 200) 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 © Manhattan Press (H. K. ) Ltd. 19

12. 1 Reflection and refraction (SB p. 200) Frequency of light in refraction Only

12. 1 Reflection and refraction (SB p. 200) 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 © Manhattan Press (H. K. ) Ltd. 20

12. 1 Reflection and refraction (SB p. 201) Refractive index and frequency The refractive

12. 1 Reflection and refraction (SB p. 201) 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 © Manhattan Press (H. K. ) Ltd. 21

12. 1 Reflection and refraction (SB p. 203) Q: Light incidents on a 5

12. 1 Reflection and refraction (SB p. 203) 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 © Manhattan Press (H. K. ) Ltd. 22

12. 1 Reflection and refraction (SB p. 204) Solution: Return to Text © Manhattan

12. 1 Reflection and refraction (SB p. 204) Solution: Return to Text © Manhattan Press (H. K. ) Ltd. 23

12. 1 Reflection and refraction (SB p. 206) Q: If you look up from

12. 1 Reflection and refraction (SB p. 206) 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 1. 33. Solution © Manhattan Press (H. K. ) Ltd. 24

12. 1 Reflection and refraction (SB p. 206) Solution: Return to Text © Manhattan

12. 1 Reflection and refraction (SB p. 206) Solution: Return to Text © Manhattan Press (H. K. ) Ltd. 25