Sunlight 1

SunlightSunlight

Sunlight 2

Introductory QuestionIntroductory Question

When you look up at the sky during When you look up at the sky during the day, is the light from distant the day, is the light from distant stars reaching your eyes?stars reaching your eyes?

A.A. YesYes

B.B. NoNo

Sunlight 3

Observations about Observations about SunlightSunlight

Appears whiter than most lightAppears whiter than most light Casts shadowsCasts shadows Makes the sky appear blueMakes the sky appear blue Becomes redder at sunrise and sunsetBecomes redder at sunrise and sunset Reflects from many surfaces, not all Reflects from many surfaces, not all

metallicmetallic Bends and separates into colors in Bends and separates into colors in

materialsmaterials

Sunlight 4

LightLight

Medium-wavelength electromagnetic Medium-wavelength electromagnetic waveswaves

The range of wavelengths we can The range of wavelengths we can seesee

Sunlight 5

Spectrum of SunlightSpectrum of Sunlight

Thermal agitation make charges Thermal agitation make charges accelerateaccelerate

Highly agitated charges emit lightHighly agitated charges emit light The sun is a black-body at 5800° CThe sun is a black-body at 5800° C

Sunlight 6

Rayleigh ScatteringRayleigh Scattering

Passing sunlight polarizes particles in airPassing sunlight polarizes particles in air Fluctuating polarization Fluctuating polarization light emission light emission Air particles scatter light (absorb & reemit)Air particles scatter light (absorb & reemit) Air particles too small to be good antennasAir particles too small to be good antennas Long-wavelengths (reds) scatter poorlyLong-wavelengths (reds) scatter poorly Shorter-wavelengths (violets) scatter betterShorter-wavelengths (violets) scatter better Scattered light is bluish in appearanceScattered light is bluish in appearance

Sunlight 7

Introductory Question Introductory Question (revisited)(revisited)

When you look up at the sky during When you look up at the sky during the day, is the light from distant the day, is the light from distant stars reaching your eyes?stars reaching your eyes?

A.A. YesYes

B.B. NoNo

Sunlight 8

RefractionRefraction

Polarization of matter delays light’s Polarization of matter delays light’s passagepassage

Light slows as it passes through matterLight slows as it passes through matter As sunlight slows, it bends – refractionAs sunlight slows, it bends – refraction

On slowing, bend is toward normal lineOn slowing, bend is toward normal line As sunlight speeds up, it also refractsAs sunlight speeds up, it also refracts

On speeding up, bend is away from normal lineOn speeding up, bend is away from normal line Index of refractionIndex of refraction

factor by which light’s speed is reducedfactor by which light’s speed is reduced

Sunlight 9

ReflectionReflection

Light polarizes different materials Light polarizes different materials differentlydifferently

In different materials, light has differentIn different materials, light has different speeds of travelspeeds of travel relationships between electric & magnetic relationships between electric & magnetic

fields fields These changes lead to reflectionsThese changes lead to reflections

As sunlight slows, some of it reflectsAs sunlight slows, some of it reflects As sunlight speeds up, some of it reflectsAs sunlight speeds up, some of it reflects

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DispersionDispersion

Light’s speed in a material depends Light’s speed in a material depends on coloron color

Violet light usually moves slower Violet light usually moves slower than redthan red

Refraction (bending) depends speed Refraction (bending) depends speed changechange

Violet light usually bends more than Violet light usually bends more than redred

Sunlight 11

RainbowsRainbows

Refraction, reflection, and dispersionRefraction, reflection, and dispersion

Sunlight 12

InterferenceInterference

Light from different paths can interfereLight from different paths can interfere Constructive – fields are in same directionConstructive – fields are in same direction Destructive – fields are in opposite Destructive – fields are in opposite

directionsdirections The two reflections fromThe two reflections from

a film interferea film interfere Different colors mayDifferent colors may

interfere differentlyinterfere differently

Sunlight 13

Reflection of Polarized Reflection of Polarized LightLight

Angled reflection varies for polarized Angled reflection varies for polarized lightlight

Fluctuating electric field parallel to Fluctuating electric field parallel to surfacesurface large fluctuating surface polarizationlarge fluctuating surface polarization big reflectionbig reflection

Electric field perpendicular to surfaceElectric field perpendicular to surface small fluctuating surface polarizationsmall fluctuating surface polarization small reflectionsmall reflection

Sunlight 14

Polarized SunlightPolarized Sunlight

Most glare is horizontally polarized Most glare is horizontally polarized lightlight

Polarizing sunglassesPolarizing sunglasses block horizontally polarized lightblock horizontally polarized light block glare from horizontal surfacesblock glare from horizontal surfaces

Much of the blue sky is polarized Much of the blue sky is polarized light, toolight, too

Sunlight 15