Sunlight Sunlight Yes Yes Y Y A. A. No No B. B. Sunlight - PDF document

Sunlight 1 Sunlight 2 Introductory Question Introductory Question When you look up at the sky during the day, is When you look up at the sky during the day, is � the light from distant stars reaching your eyes? the light from distant stars reaching your eyes? Sunlight Sunlight Yes Yes Y Y A. A. No No B. B. Sunlight 3 Sunlight 4 Observations about Sunlight Observations about Sunlight Reading Question 14.1a Reading Question 14.1a � Sunlight appears whiter than most light Sunlight appears whiter than most light � The sky is blue because The sky is blue because � � Sunlight makes the sky appear blue Sunlight makes the sky appear blue � � Sunlight becomes redder at sunrise and sunset Sunlight becomes redder at sunrise and sunset A. blue light scatters off air better than red light blue light scatters off air better than red light � A. � It reflects from many surfaces, even nonmetals It reflects from many surfaces, even nonmetals B. air glows blue when exposed to sunlight air glows blue when exposed to sunlight B. � It bends and separates into colors in materials It bends and separates into colors in materials C. sunlight reflected from the earth surface is blue sunlight reflected from the earth surface is blue C. � Sunlight a key source of renewable energy Sunlight a key source of renewable energy D. sunlight contains more blue light than red light sunlight contains more blue light than red light D. Sunlight 5 Sunlight 6 Reading Question 14.1b Reading Question 14.1b 5 Questions about Sunlight 5 Questions about Sunlight � Light partly reflects from transparent objects Light partly reflects from transparent objects � Why does sunlight appear white? Why does sunlight appear white? � because light because light � Why does the sky appear blue? Why does the sky appear blue? � How does a rainbow break sunlight into colors? How does a rainbow break sunlight into colors? A. changes speed as it enters or leaves objects. changes speed as it enters or leaves objects. h h d d i i l l bj bj A. � Why are soap bubbles and oil films so colorful? Why are soap bubbles and oil films so colorful? B. can’t travel well through transparent objects. can’t travel well through transparent objects. B. � Why do polarizing sunglasses reduce glare? Why do polarizing sunglasses reduce glare? C. is unstable inside transparent objects. is unstable inside transparent objects. C. D. has no magnetic field in nonmagnetic objects. has no magnetic field in nonmagnetic objects. D. 1

Sunlight 7 Sunlight 8 Question 1 Question 1 Light Light � Why does sunlight appear white? Why does sunlight appear white? � Light is Light is a class of electromagnetic waves a class of electromagnetic waves � � Long Long- -wavelength EM waves: Radio & Microwave wavelength EM waves: Radio & Microwave � Medium Medium- -wavelength: IR, Visible, UV light wavelength: IR, Visible, UV light � Short � Sh rt Sh rt Short-wavelength: X wavelength: X- l n th X l n th X r -rays & Gamma r rays & Gamma- & G mm & G mm r -rays rays Sunlight 9 Sunlight 10 Clicker Question Clicker Question Spectrum of Sunlight Spectrum of Sunlight � How does the sun’s hot surface emit light? How does the sun’s hot surface emit light? � Sunlight is thermal radiation Sunlight is thermal radiation— —heat from the sun heat from the sun � Charges in the sun’s hot photosphere jitter thermally Charges in the sun’s hot photosphere jitter thermally � Accelerating charges emits electromagnetic waves Accelerating charges emits electromagnetic waves A. Its hot atoms glow with their characteristic Its hot atoms glow with their characteristic A. � Th � The sun emits a black The sun emits a black- Th n mit n mit bl bl k k b d -body spectrum at 5800 K body spectrum at 5800 K b d p p tr m t 5800 K tr m t 5800 K colors, like those in a neon sign. colors, like those in a neon sign. l l lik lik h h i i i i � We perceive thermal light at 5800 K as “white” We perceive thermal light at 5800 K as “white” B. Its hot atoms escape from its surface and Its hot atoms escape from its surface and B. become light waves. become light waves. C. Thermal energy causes its charged particles to Thermal energy causes its charged particles to C. accelerate rapidly and thus emit EM waves. accelerate rapidly and thus emit EM waves. Sunlight 11 Sunlight 12 Clicker Question Clicker Question Question 2 Question 2 � If you compare a sheet of white paper that’s If you compare a sheet of white paper that’s � Why does the sky appear blue? Why does the sky appear blue? illuminated by direct sunlight to an identical illuminated by direct sunlight to an identical � Why is the sun reddish at sunrise and sunset? Why is the sun reddish at sunrise and sunset? sheet illuminated by an incandescent sheet illuminated by an incandescent lightbulb lightbulb, , A. both sheets will appear equally white. both sheets will appear equally white. A. B. the sunlit sheet will appear more blue. the sunlit sheet will appear more blue. B. C. the sunlit sheet will appear more green. the sunlit sheet will appear more green. C. D. the sunlit sheet will appear more red. the sunlit sheet will appear more red. D. 2

Sunlight 13 Sunlight 14 Clicker Question Clicker Question Rayleigh Scattering Rayleigh Scattering � Rayleigh scattering occurs when Rayleigh scattering occurs when � When a light wave encounters an atom, its When a light wave encounters an atom, its electric field polarizes that atom slightly electric field polarizes that atom slightly � passing sunlight electrically polarizes tiny particles in the air. passing sunlight electrically polarizes tiny particles in the air. � That alternating polarization That alternating polarization acts as a source of light waves acts as a source of light waves, , � so air particles scatter light so air particles scatter light— —they absorb and then reemit it. they absorb and then reemit it. A. so the atom can absorb and reemit the wave. so the atom can absorb and reemit the wave. h h b b b b d d i i h h A. � Air particles are too small to be good antennas for light, Air particles are too small to be good antennas for light, B. but the atom cannot absorb the wave. but the atom cannot absorb the wave. � so long so long- -wavelengths (reds) scatter poorly wavelengths (reds) scatter poorly B. � while shorter while shorter- -wavelengths (violets) scatter better. wavelengths (violets) scatter better. C. but the atom cannot emit a wave. but the atom cannot emit a wave. C. � Rayleigh scattered sunlight is bluish in appearance Rayleigh scattered sunlight is bluish in appearance � The missing blue light reddens the solar disk itself The missing blue light reddens the solar disk itself � particularly at sunrise and sunset particularly at sunrise and sunset Sunlight 15 Sunlight 16 Introductory Question Introductory Question (revisited) Question 3 Question 3 (revisited) When you look up at the sky during the day, is When you look up at the sky during the day, is � How does a rainbow break sunlight into colors? How does a rainbow break sunlight into colors? � the light from distant stars reaching your eyes? the light from distant stars reaching your eyes? Y Yes Yes A. A. No No B. B. Sunlight 17 Sunlight 18 Light and Refraction Light and Refraction Clicker Question Clicker Question � Sunlight slows while it passes through matter Sunlight slows while it passes through matter � Glass is much more Glass is much more polarizable polarizable than air. When a than air. When a light wave moves from air into glass, the sudden light wave moves from air into glass, the sudden � Light waves electrically polarize matter Light waves electrically polarize matter increase in polarization causes increase in polarization causes � That polarization delays the light wave’s passage That polarization delays the light wave’s passage � Each material has an “index of refraction” � E Each material has an “index of refraction”—the factor E h m t ri l h h m t ri l h n “ind n “ind f r fr f r fr ti n” ti n” th f the factor th f t r t r by which it reduces light’s speed. by which it reduces light’s speed. A. part of the wave to be reflected. part of the wave to be reflected. A. � When light changes speed at an interface, When light changes speed at an interface, B. part of the wave to be absorbed. part of the wave to be absorbed. B. � it bends toward the perpendicular if it slows down it bends toward the perpendicular if it slows down C. all of the wave to be transmitted. all of the wave to be transmitted. C. � it bends away from the perpendicular if it speeds up it bends away from the perpendicular if it speeds up D. some of the wave to travel along the surface. some of the wave to travel along the surface. D. 3