Sunlight 1 Sunlight Sunlight 2 Introductory Question n

Sunlight 1 Sunlight

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

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

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

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

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

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

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

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

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

Sunlight 11 Rainbows n Refraction, reflection, and dispersion

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

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

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

Sunlight 15