RefractionRefraction

Changing SpeedChanging Speed The speed of light in a material The speed of light in a material

depends on the depends on the electromagnetic properties.electromagnetic properties.• Permittivity and permeabilityPermittivity and permeability

The ratio of the speed in a The ratio of the speed in a material to that of a vacuum is material to that of a vacuum is the index of refraction.the index of refraction.

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cn

Clear MediaClear Media AirAir 1.000291.00029 IceIce 1.311.31 WaterWater 1.3331.333 AlcoholAlcohol 1.361.36 QuartzQuartz 1.45841.4584 PlexiglasPlexiglas 1.511.51 Crown glassCrown glass 1.521.52 Flint glassFlint glass 1.661.66 ZirconZircon 1.9231.923 DiamondDiamond 2.4172.417

• Values at 589 nmValues at 589 nm

Every transmitting medium has Every transmitting medium has its own index of refraction.its own index of refraction.

Refraction GeometryRefraction Geometry The geometry for refraction The geometry for refraction

follow the same rules as follow the same rules as reflection.reflection.• Normal to the surfaceNormal to the surface

• Incident angle Incident angle ii• Reflected angle Reflected angle rr

There is also a refracted ray.There is also a refracted ray.• Transmitted angle Transmitted angle tt

Snell’s LawSnell’s Law The ratio of the sines of the The ratio of the sines of the

incident and reflected angles is incident and reflected angles is proportional to the relative proportional to the relative wavelengths in the material.wavelengths in the material.

The wavelength is inversely The wavelength is inversely proportional to the index.proportional to the index.

Combined they become Snell’s Combined they become Snell’s law of refraction.law of refraction.

t

i

t

i

sin

sin

i

t

t

i

n

n

ttii nn sinsin

Bending InBending In Light is refracted into a crown Light is refracted into a crown

glass slab at 30.0glass slab at 30.0°°. Find the . Find the angle in crown glass.angle in crown glass.

• nn11 = 1.00 and = 1.00 and nn22 = 1.52 = 1.52

• θθ22 = sin = sin-1-1(n(n11 / n / n22) sin ) sin θθ11 = = 19.219.2oo

The ray bends toward the The ray bends toward the normal.normal.• Always true for the higher Always true for the higher

index of refractionindex of refraction

Bent RaysBent Rays The refraction at the interface The refraction at the interface

between water and air can between water and air can cause objects to appear in the cause objects to appear in the wrong place.wrong place.

A split spoon in a clear glass of A split spoon in a clear glass of water is a common example. water is a common example.

MirageMirage

Air temperature affects the index of refraction.Air temperature affects the index of refraction.• Lower for less dense, hot airLower for less dense, hot air

The difference causes refraction.The difference causes refraction.

InversionInversion

At some times of the year there is a layer of cool air near At some times of the year there is a layer of cool air near the ground.the ground.• Inverted mirageInverted mirage

PrismPrism The index of refraction The index of refraction

depends on the wavelength.depends on the wavelength.• Longer wavelengths - lower Longer wavelengths - lower

indexesindexes

A triangular prism has two A triangular prism has two refracting surfaces.refracting surfaces.• One into glassOne into glass

• One back to airOne back to air

The wavelengths are The wavelengths are separated into a spectrum.separated into a spectrum.

PolarizationPolarization At an interface light becomes At an interface light becomes

partially polarized.partially polarized.• Separated beams reflected Separated beams reflected

and transmittedand transmitted If the beams are perpendicular If the beams are perpendicular

then the reflected ray is fully then the reflected ray is fully polarized.polarized.• Brewster’s angleBrewster’s angle

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triB 90

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tB n

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BiBt nn sin)90sin(