QUESTION 1 1. Suppose, for the sake of argument, that instead of scattering blue light, the air scattered green light. What color would the Sun look to the human eye (remember: the sunlight hitting the top of the Earth's atmosphere is close to white in color)? A. Bluish B. Reddish C. Purplish (magenta) D. Black 5 points QUESTION 2 1. Suppose, for the sake of argument, that instead of scattering blue light, the air scattered only infrared light. What color would the SKY look like to the human eye? A. It would look Red B. It would still look Blue C. It would look Black D. It would look White 5 points QUESTION 3 1. An electromagnetic wave traveling through space encounters an electron sitting at rest. Upon being hit by the wave, which way will the electron move? A. It will bob up and down with the crests and troughs B. It'll be pushed entirely along the direction the wave is moving (perpendicular to the crests and troughs) C. It won't move at all D. It'll both bob up and down and be pushed along the direction the wave is moving 5 points QUESTION 4 1. The reason why light reflected off a surface often has significant horizontal polarization is that A. The atoms reflecting the light can only oscillate at specific frequencies B. The atoms reflecting the light can only wiggle parallel to the direction they're re-emitting the light, so they can't produce light having polarization vertical to the surface C. The atoms reflecting the light can only wiggle perpendicular to the direction they're re-emitting the light, so they can't produce light having polarization vertical to the surface D. None of the above 5 points QUESTION 5 1. How much of the incident light is transmitted through the third polarizer? A. All B. Some C. None D. Not enough information 5 points QUESTION 6 1. In the polarizer question above, what is the polarization of the light transmitted through the third polarizer? A. Vertical B. Horizontal C. 45 degrees D. None of these, since the light doesn't make it through the 3rd polarizer 5 points QUESTION 7 1. Unpolarized light with brightness I0 encounters a polarizer which is oriented approximately vertically, letting through only vertically polarized light. This is then passed through a second polarizer oriented at an angle of the first polarizer. The person on the right receives only about 1/3 of the original light ( I0 /3). What is the approximate angle, θ, of the second polarizer? (Hint:use Malus's Law). θ to A. 57◦ B. 17◦ C. 70◦ D. 0◦ 5 points QUESTION 8 1. The Sun is directly overhead and you are facing toward the north. Light coming to your eyes from the sky just above the horizon is A. partially polarized north-south B. partially polarized east-west C. partially polarized up-down D. linearly polarized up-down 5 points QUESTION 9 1. For light shining onto a surface at Brewster's angle, the angle between the light reflected off the surface and the light transmitted into the surface is A. 0◦ B. 180◦ C. 90◦ D. depends on the index of refraction, n, of the medium 5 points QUESTION 10 1. How much brighter is blue sky at 350 nm than at 800 nm? A. Approximately 2x B. Approximately 25x C. Approximately 0.04x D. it's the same brightness! 5 points Click Save and Submit to save and submit. Click Save All Answers to save all answers. Lecture!23:!Polarization!and!Scattering! (cont’d) Monday, November 17, 14 Looking%toward%the%Sun,%the%light%is A)%linearly%polarized B)%circularly%polarized C)%elliptically%polarized D)%mostly%unpolarized Monday, November 17, 14 incoming' unpolarized' light'from'the' Sun light!scattered! 90∘ is!completely! polarized oxygen%molecule light!scattered! 90∘ is!completely! polarized Monday, November 17, 14 some! unpolarized! light!is! forward! scattered Monday, November 17, 14 Polarization!Pattern!of!the!Sky %The%sky%is%linearly%polarized,%along%lines%tangent%to%a%circle%centered% on%the%Sun% %Maximum%polarization%90∘%away%from%Sun%(i.e.,%on%the%horizon%when% the%sun%is%directly%overhead,%and%on%a%N9S%line%when%sun%is%setting) Monday, November 17, 14 Polarization!Pattern!of!the!Sky %The%sky%is%linearly%polarized,%along%lines%tangent%to%a%circle%centered% on%the%Sun% %Maximum%polarization%90∘%away%from%Sun%(i.e.,%on%the%horizon%when% the%sun%is%directly%overhead,%and%on%a%N9S%line%when%sun%is%setting) circles+of+constant+angle+from+ the+Sun Monday, November 17, 14 Sun%Overhead Sunset Monday, November 17, 14 Amount%of% Polarization 1.0%=%100% %Bees%have%polarization9sensitive%cones%in%their%eyes % Bees% use% the% polarization% pattern% of% the% sky% to% determine% where% the% Sun%is,%even%when%it’s%cloudy%(!!) %Use%the%Sun%as%a%compass%to%mark%where%food%is%to%other%bees %The%angle%between%food%direction%and%Sun%direction%is%marked%in%their% dance%(Sun+Compass+Angle)! Monday, November 17, 14 Why!Clouds!Are!White % If% particles% are% huge% compared% to% wavelength% of% incoming% light,% they% look% like% big% spheres% and% scatter% all% wavelengths% equally,%many%times%over% Mie'Scattering:'more'radiation'scattered' forward'than'for'Rayleigh'scattering %%Called%Mie+Scattering,%named%after%Gustav% Mie,% a% German% physicist,%who% studied% this% in% 1908 %%Mie%scattering%off%water%droplets%gives%the% ‘milky% haze’% we% see% on% hot,% humid% days:% lots% of%H2O%in%air % The% air% also% often% contains% dust% particles% that%are%larger%than%O%and%N%atoms % These% larger% particles% scatter% red% light% more% than% blue% (opposite% of% Rayleigh% scattering).%% %%Give%reddish%hue%we%see%on%smoggy%days! Monday, November 17, 14 haze:%particulates,%aerosols,%water% vapor,... Why!Clouds!Are!White % If% particles% are% huge% compared% to% wavelength% of% incoming% light,% they% look% like% big% spheres% and% scatter% all% wavelengths% equally,%many%times%over% Mie'Scattering:'more'radiation'scattered' forward'than'for'Rayleigh'scattering %%Called%Mie+Scattering,%named%after%Gustav% Mie,% a% German% physicist,%who% studied% this% in% 1908 %%Mie%scattering%off%water%droplets%gives%the% ‘milky% haze’% we% see% on% hot,% humid% days:% lots% of%H2O%in%air % The% air% also% often% contains% dust% particles% that%are%larger%than%O%and%N%atoms % These% larger% particles% scatter% red% light% more% than% blue% (opposite% of% Rayleigh% scattering).%% %%Give%reddish%hue%we%see%on%smoggy%days! Monday, November 17, 14 milk:%very%large%particulates%9% scatter%all%wavelengths%equally% (called%Mie+Scattering)% Rayleigh!Scattering!and!Mie!Scattering! Together!in!the!Sky Sun Monday, November 17, 14 Rayleigh!Scattering!and!Mie!Scattering! Together!in!the!Sky Sun Monday, November 17, 14 Color'of''Water From:% http://starryskies.com/articles/ 2003/03/water.html Ocean% waters:% % Water% absorbs% red% better% than% blue,% with% the% blue% being% transmitted% into% the% ocean% (kind% of% like% Rayleigh% scattering% inside% the% water!)% %Blue%is% also%scattered% by% particles% and%plants,%enhancing%the%blueness Tropical% waters:% Like% oceans,% tropical% waters% also% absorb% red% and% transmit% blue,% but% don’t% reWlect% as% much% of% that% blue% back% (lots% more% algae,%dead% plants,%etc,%which% don’t%reWlect%blue% very%well) Rivers%and%lakes:%Mud%acts%in%the%opposite%way% from%water%9%it%reWlects%red%light%more%than%blue.% So% muddy% water% looks% brown.%Since% rivers% are% big% transporters% of% mud,% they% usually% appear% brown Monday, November 17, 14 More!on!Polarization:!Malus’!Law!and! Brewster’s!Angle Monday, November 17, 14 Brewster’s'Angle ! Light! hitting! the! surface! at! Brewster’s! angle! does! TWO! things: Brewster’s% incident%light% angle,%θB coming%in%at% Brewster’s% angle:% unpolarized reIlected'light:' horizontal' polarization 90˚ transmitted% light:%partial% polarization Monday, November 17, 14 1 .! I t s! r e h l e c t e d! a n d! transmitted! parts! are! at! 90˚! angle!to!each!other 2.! The! rehlected! component! h a s! n o! p o l a r i z a t i o n! perpendicular! to! the! surface! ( i t ’ s! f u l l y! h o r i z o n t a l l y! polarized) ! Most! light! rehlected! off! surfaces! isn’t! exactly! at! Brewster’s! angle,! so! it’s! partially!polarized Brewster’s'Angle ! Light! hitting! the! surface! at! Brewster’s! angle! does! TWO! things: Brewster’s% incident%light% angle,%θB coming%in%at% Brewster’s% angle:% unpolarized ✗ reIlected'light:' horizontal' polarization 90˚ transmitted% light:%partial% polarization Monday, November 17, 14 1 .! I t s! r e h l e c t e d! a n d! transmitted! parts! are! at! 90˚! angle!to!each!other 2.! The! rehlected! component! h a s! n o! p o l a r i z a t i o n! perpendicular! to! the! surface! ( i t ’ s! f u l l y! h o r i z o n t a l l y! polarized) ! Most! light! rehlected! off! surfaces! isn’t! exactly! at! Brewster’s! angle,! so! it’s! partially!polarized Brewster’s!Angle!Simulator!From!Light! and!Color!Tutorial!Website http://micro.magnet.fsu.edu/primer/java/scienceopticsu/polarizedlight/brewster/index.html Monday, November 17, 14 Brewster’s!Angle horizontally polarized light % There% is%a% special% incidence% angle% (θB)% for% light% hitting% a% surface% where% the% reWlected% part% and% transmitted% part% are% at%90 %to%each%other %Whenever%this%happens,%the% reWlected% light% comes% out% c o m p l e t e l y% h o r i z o n t a l l y% polarized B θB%+%θ2%=%90˚ charge’s' movement polarization%out%of%page Monday, November 17, 14 B polarization%along%page What’s%Brewster’s%angle%for%light%traveling%in%water%(n=1.33)% reWlecting%off%crown%glass%(n=1.55)? A)%53∘% B)%49∘ C)%41∘ D)%34∘ Monday, November 17, 14 Waves!Can!Have!Any!Polarization! !In!general,!waves!have!a!polarization! t h a t ’ s! s o m e w h e r e! i n+ b e t w e e n+ horizontal+and+vertical !How#do#we#represent#such#a#wave? vertical ! Easy:! As! a! SUM! of! amplitudes! of! a! horizontal!wave!and!a!vertical!wave!! ! In!general,! any! quantity! that! can! be! represented! as! the! sum! of! two! components!is!called!a!vector.++ + + Electric% Wields,% magnetic% Wields,% velocities,% accelerations% are% a% few% examples... ! Tweak! the! amplitude! of! each! component!to!hinebtune! Monday, November 17, 14 y vertical% =% horizontal x y horizontal = vertical vertical% (small) x horizontal (large) Polarization!Doesn’t!Have!to!Be!Purely! Horizontal!or!Purely!Vertical polarization!simulation Monday, November 17, 14 Using%Polarizer/Analyzer%to%Create%Arbitrary% unpolarized%light Polarization%Direction 30˚ polarizer% rotated%to%0˚ polarizer% rotated%to% 30˚ Monday, November 17, 14 As# long#as#we# keep#track#of# the# vertical# and# horizontal# pieces# at# every# step,# we# can#
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