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1

Physics 212 and 222Refraction and Lenses

Refractive Index

Snell’s Law

Dispersion

Rainbows

Total Internal Reflection

Apparent Depth

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2

Physics 212 and 222Refraction and Lenses

Refractive Index

The speed of light in a vacuum is

The speed of light in other materials (media) is always slower.

The index of refraction (refractive index) is the ratio of the speed of light in vacuum over the speed of light in the material.

Refractive index is a property of the material.

s

m8103c

1v

cn

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3

Physics 212 and 222Refraction and Lenses

How does refractive index change the light?

θ1

θ2

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4

Physics 212 and 222Refraction and Lenses

n1n2

θ1

θ1’ θ2

2211 sinsin nn

Snell’s Law

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5

Physics 212 and 222Refraction and Lenses

Dispersion

Index of refraction is a function of wavelength.

Longer wavelengths usually move faster in a medium.

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violetbluegreenyelloworangered nnnnnn

violetbluegreenyelloworangered 222222

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Physics 212 and 222Refraction and Lenses

Rainbows

Primary rainbows come from one reflection.

Secondary rainbows come from two reflections

© 1999 – 2002, HMI, Arbeitsgruppe Nukleare Messtechnik, Prof. W. von Oertzen

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Physics 212 and 222Refraction and Lenses

n1

n2

θ1

θ290o

θc

The critical angle for total internal reflection is θ1 = θc when θ2 = 90o.

oc nn 90sinsin 21

1

2sinn

nc

21 nn

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8

Physics 212 and 222Refraction and Lenses

n1

n2

The apparent depth of the shark is given by as calculated by the equation

'd

21' dnnd

d

d’

21 nn

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9

Physics 212 and 222Refraction and Lenses

Refractive Index

Snell’s Law

Dispersion

Rainbows

Total Internal Reflection

Apparent Depth