Ch. 4 Refraction (折射)

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

Incident Rays (入射線) Refracted Rays (折射線) Normal (法線) The light ray in air Refracted Rays (折射線) The light ray in the glass block Normal (法線) The line perpendicular to the glass block Angle of incidence (入射角) The angle between the incident ray and the normal. Angle of refraction (折射角) The angle between the refracted rays and the normal.

(r) is NOT equal to (i) (i = r = 0) air glass i = 0 r = 0 air glass (r) is NOT equal to (i) (i = r = 0)

i r glass air Normal i r air glass The light ray bent away from (偏離) the normal. The light ray bent towards (偏向) the normal.

c

c 8

c 9

Experiment (實驗) 半圓膠塊 電源 光箱 量角器

Method i / 30 45 60 75 r /

is a constant and is called refractive index (折射率) of glass. sin i 0.500 0.707 0.866 0.966 sin r is a constant and is called refractive index (折射率) of glass.

Method i / 30 45 60 75 r / 0 20 28 35 40

i / 30 45 60 75 r / 20 28 35 40 sin i 0.500 0.707 0.866 0.966 sin r Correct to 3 significant figures. 14

refractive index (折射率) of glass. sin i 0.500 0.707 0.866 0.966 sin r 0 0.342 0.469 0.574 0.643 --- 1.46 1.51 1.51 1.50 is a constant (about 1.5) and is called refractive index (折射率) of glass.

Laws of refraction (折射定律) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant. = constant The relation is called Snell’s law (斯湼耳定律). The constant is called the refractive index (折射率) of the material.

Refractive Index (折射率) Material (物質) Refractive Index (折射率) vacuum (真空) 1.0000 air 1.0003 water 1.33 glass 1.5 to 1.7 diamond 2.42

1. sin i is directly proportional (正比) to sin r. Graphical Method to find Refractive Index sin r sin i 1. sin i is directly proportional (正比) to sin r. 2. The slope (斜率) of the graph is refractive index of the material.

Class Exercise 6.1 i / 30 45 60 75 r / sin i 0.500 0.707 0.866 0.966 sin r Plot the graph of sin i against sin r in the graph paper. (b) What is the relationship between sin i and sin r ? (c) Hence, calculate the refractive index of the material.

i / 30 45 60 75 r / sin i 0.500 0.707 0.866 0.966 sin r 0 20 28 35 40 0 0.342 0.469 0.573 0.643

(a)

(b) The graph is a straight line which passes through Therefore, sin i is __________ to sin r.

(正比) to sin r. (b) The graph is a straight line which passes through the origin (0,0) Therefore, sin i is directly proportional (正比) to sin r. 23

(c) slope = 0.90 0 = 0.60 0 = 1.5 The refractive index is 1.5