Ch.7 Refraction Index (折射率)

Incident Ray Refracted Angle of incidence Angle of Refraction air glass reflection Reflected

Light travelling from air to glass refracted ray incident ray normal angle of incidence angle of refraction air glass The light ray bends towards the normal. (偏向法線)

Law of refraction (折射定律) normal reflected ray angle of incidence incident ray glass air 折射角 (angle of refraction) 折射線 (refracted ray) = n (refractive index)

Refractive index of some common materials Air 1.00 Water 1.33 Alcohol (酒精) 1.36 Perspex (有機玻璃) 1.50 Glass 1.50 – 1.70 Diamond (鑽石) 2.42

Refractive index (折射率) normal air medium X a X nX – refractive index (折射率) of medium X

Class Practice 7.1 55 60 air X Refractive index of x = ?

n = sin i / sin r = sin 60 ° / sin (90-55) ° = sin 60 ° / sin 35 ° 55 Class Practice 7.1 55 60 air X n = sin i / sin r = sin 60 ° / sin (90-55) ° = sin 60 ° / sin 35 ° = 1.51 Answer is C

Which one has the largest refractive index ? Class Practice 7.2 air X Y Z Which one has the largest refractive index ?

∵ rx > ry > rz ∴ nx < ny < nz answer is C Class Practice 7.2 air X Y Z = n (refractive index) r↓ means n↑ ∵ rx > ry > rz ∴ nx < ny < nz answer is C

Class Practice 7.3

Class Practice 7.3 53 ° 32 ° 0.7986 0.5299 59 ° 40 ° 0.857 0.643 1.51 1.33

Class Practice 7.4 (a) r 50 air water n = 1.33 r = ?

∴ r = 35.2° r sin 50° / sin r = 1.33 sin r = sin 50° / 1.33 = 0.576 Class Practice 7.4 (a) sin 50° / sin r = 1.33 sin r = sin 50° / 1.33 = 0.576 ∴ r = 35.2° r 50 air water

Class Practice 7.4 (b) r 50 air water n = 1.33 r = ?

∴ r = 28.9° r i = 40 ° sin 40° / sin r = 1.33 sin r = sin 40° / 1.33 Class Practice 7.4 (a) i = 40 ° sin 40° / sin r = 1.33 sin r = sin 40° / 1.33 = 0.483 ∴ r = 28.9° r 50 air water

Homework: Assignment Book Chapter 6 & 7 (p.10-14) Deadline: 2010-11-15 (Mon)