Sunlight 1 Sunlight

Sunlight 2 Introductory Question When you look up at the sky during the day, is the light from distant stars reaching your eyes? When you look up at the sky during the day, is the light from distant stars reaching your eyes? A. Yes B. No

Sunlight 3 Observations about Sunlight Appears whiter than most light Appears whiter than most light Casts shadows Casts shadows Makes the sky appear blue Makes the sky appear blue Becomes redder at sunrise and sunset Becomes redder at sunrise and sunset Reflects from many surfaces, not all metallic Reflects from many surfaces, not all metallic Bends and separates into colors in materials Bends and separates into colors in materials

Sunlight 4 Light Medium-wavelength electromagnetic waves Medium-wavelength electromagnetic waves The range of wavelengths we can see The range of wavelengths we can see

Sunlight 5 Spectrum of Sunlight Thermal agitation make charges accelerate Thermal agitation make charges accelerate Highly agitated charges emit light Highly agitated charges emit light The sun is a black-body at 5800° C The sun is a black-body at 5800° C

Sunlight 6 Rayleigh Scattering Passing sunlight polarizes particles in air Passing sunlight polarizes particles in air Fluctuating polarization  light emission Fluctuating polarization  light emission Air particles scatter light (absorb & reemit) Air particles scatter light (absorb & reemit) Air particles too small to be good antennas Air particles too small to be good antennas Long-wavelengths (reds) scatter poorly Long-wavelengths (reds) scatter poorly Shorter-wavelengths (violets) scatter better Shorter-wavelengths (violets) scatter better Scattered light is bluish in appearance Scattered light is bluish in appearance

Sunlight 7 Introductory Question (revisited) When you look up at the sky during the day, is the light from distant stars reaching your eyes? When you look up at the sky during the day, is the light from distant stars reaching your eyes? A. Yes B. No

Sunlight 8 Refraction Polarization of matter delays light’s passage Polarization of matter delays light’s passage Light slows as it passes through matter Light slows as it passes through matter As sunlight slows, it bends – refraction As sunlight slows, it bends – refraction On slowing, bend is toward normal line On slowing, bend is toward normal line As sunlight speeds up, it also refracts As sunlight speeds up, it also refracts On speeding up, bend is away from normal line On speeding up, bend is away from normal line Index of refraction Index of refraction factor by which light’s speed is reduced factor by which light’s speed is reduced

Sunlight 9 Reflection Light polarizes different materials differently Light polarizes different materials differently In different materials, light has different In different materials, light has different speeds of travel speeds of travel relationships between electric & magnetic fields relationships between electric & magnetic fields These changes lead to reflections These changes lead to reflections As sunlight slows, some of it reflects As sunlight slows, some of it reflects As sunlight speeds up, some of it reflects As sunlight speeds up, some of it reflects

Sunlight 10 Dispersion Light’s speed in a material depends on color Light’s speed in a material depends on color Violet light usually moves slower than red Violet light usually moves slower than red Refraction (bending) depends speed change Refraction (bending) depends speed change Violet light usually bends more than red Violet light usually bends more than red

Sunlight 11 Rainbows Refraction, reflection, and dispersion Refraction, reflection, and dispersion

Sunlight 12 Interference Light from different paths can interfere Light from different paths can interfere Constructive – fields are in same direction Constructive – fields are in same direction Destructive – fields are in opposite directions Destructive – fields are in opposite directions The two reflections from a film interfere The two reflections from a film interfere Different colors may interfere differently Different colors may interfere differently

Sunlight 13 Reflection of Polarized Light Angled reflection varies for polarized light Angled reflection varies for polarized light Fluctuating electric field parallel to surface Fluctuating electric field parallel to surface large fluctuating surface polarization large fluctuating surface polarization big reflection big reflection Electric field perpendicular to surface Electric field perpendicular to surface small fluctuating surface polarization small fluctuating surface polarization small reflection small reflection

Sunlight 14 Polarized Sunlight Most glare is horizontally polarized light Most glare is horizontally polarized light Polarizing sunglasses Polarizing sunglasses block horizontally polarized light block horizontally polarized light block glare from horizontal surfaces block glare from horizontal surfaces Much of the blue sky is polarized light, too Much of the blue sky is polarized light, too

Sunlight 15