Ch.7 Refraction Index (Ch.7 Refraction Index ( 折射率折射率 ))

1

2

IncidentRay

RefractedRay

Angle ofincidence

Angle of Refraction

air

glass

Angle of reflection Reflected

Ray

Light travelling from air to glass

The light ray bends towards the normal. ( 偏向法線 )

refracted ray

incident ray

normal

angle of incidence

angle of refraction

air

glass

3

glassglassairair

incident ray reflected ray normal

normal

折射線(refracted ray)

折射角 (angle of refraction) 折射角 (angle of refraction)

angle of incidence

angle of incidence

Law of refraction (折射定律 ) Law of refraction (折射定律 )

4r

i

sin

sin= n (refractive index)

Refractive index of some common materials

Material Refractive index

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

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Refractive index (Refractive index ( 折射率折射率 ))

nX – refractive index ( 折射率 ) of medium X

normal

air

medium X

a

X

XX

a nθ

θ

sin

sin

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7

Class Practice 7.1

55

60

air X

Refractive index of x = ?

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Class Practice 7.1

55

60

air Xn = sin i / sin r = sin 60 ° / sin (90-55) ° = sin 60 ° / sin 35 °

= 1.51

Answer is C

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Class Practice 7.2

Which one has the largest refractive index ?

air

X

air

Y

air

Z

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Class Practice 7.2

air

X

air

Y

air

Z

r

i

sin

sin= n (refractive index) r↓ means n↑

∵ rx > ry > rz n∴ x < ny < nz answer is C

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Class Practice 7.3

12

53 °32 °

0.79860.5299

1.511.51

59 °40 °

0.8570.643

1.331.33

Class Practice 7.3

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Class Practice 7.4 (a)

r

50air

water

n = 1.33r = ?

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Class Practice 7.4 (a)

r

50air

water

sin 50° / sin r = 1.33

sin r = sin 50° / 1.33 = 0.576

∴ r = 35.2°

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Class Practice 7.4 (b)

n = 1.33r = ?

r

50 air

water

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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 airwater

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Homework: Assignment Book

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