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6b_ec9_soln - Physics 6B Discussion Section Problem —...

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Unformatted text preview: Physics 6B Discussion Section Problem — Week of March 10 A soap film of thickness z = 225 nm is illuminated from the left by blue light with wavelength 1%,, = 400 nm. The film itself has refractive index 11f: 1.333, and is surrounded on both sides by air with index n = 1.000. A observer is stading to the left of the film, looking at the light reflected from the film. The two main ways that light can reach the observer’s eyes are path A and path B, as shown above. % 55‘ Light whicfiravels along path A meets the interface between the air and the soap film only once, at point P. Does this light experience a half—cycle phase shift at this point? Briefly explain why or why not. "769‘; H- ventlecleé‘ of? an “lamb-Ace wheel}, lei ”tr/m {Mr . "(Ado)“- ( #0343, Wu: 55240 {-0 ln‘gle’r lfi£¢ ( S(O‘v~0r wave 3959(1) “Tints alts/3155 gave; a half’ecla PlAuf—L ski—la b) Light which travels along path B meets the interfaces between the air and the soap film three times, at points Q R and S Does this light experience a halfucy‘ (:16 phase shift at any of these points? Briefly explain why or why not Ne, 4+ Polr‘lv’ Q 39/ “W wave 1‘9 "Newt/“9H4; “L‘lcl‘ My”. 9‘ive5 ‘5 IQMseship-l. 44; R, H‘ mcbois‘ 6-H; a h,\7L’lAC(g-K‘l‘0 law \r‘cLK WM “Hall/‘91‘l 9/014 W\’\\ClA alga (‘[email protected]’"1' 71“”? carpi/10% {in FL c) Paths A and B also travel different distances before reaching the observer. How much extra distance does path B travel, and how many extra cycles of phase shift does this result in? (Be careful with the wavelength of' the light!) A. H‘— PX‘E’TA £70499: 490mm _-_— ('g 300mm cl) What type of interference does the observer see between beams A and B: constructive, destructive, or neither? Briefly explain your answer. C0fl9+rflc4rfe. P3!“ A 9.647%); (’ka 511'! 9+ Pram ytlckc‘hov‘. pi’%m€e :_ POW?!" 9 96+; (9; 53,6? 6kig+pmm {’me Ctt9+VlN§f 15"?‘3 / x - Cone—incite e) How would your answers to parts (a) through (d) change if, instead of using blue light, we used red light ln‘krfrn’v‘ct. with a wavelength Pt, = 600 nm? What does this explain about the way soap films look in real life? (Think about how actual soap films look before answering this last question — if your an%er is “they look blue” or “they look redfigfipthen you spend far too little time around soap films!) C(mSvWé ‘I‘o Q 3} chkawgec", C) MOM? A lA ‘E-lllrv‘: % :- 490mm [03%; t‘;--Q)CLJCA Cyfléf 5 -—2-‘¥‘ 5 4:90am -'-’ i ("y-0%. >K ‘ ‘t’gymm - (D pfgl‘rmo‘t- ,{ ink/gorenee (“ Cyofe 0n ,4 1 (70%. am 9/ "L Cycle 56»?me Q4“, Fqflkg) 1‘) When the film is about to pop, it will often grow so thin that its thickness 2 is far smaller than the wavelength of visible light of any color. In this case, what will you see if you observethe light reflected from the film? Have you seen this happen in real life? Yearll 96+ shaming Mariam at a“ Weigh Mfié‘eéjfhj mu Hafiteclzcé li‘filmt RWA HM {Qemuse batik/45+?“ 56:“th ‘f—Lg 1%; C70? 5LMC+ 499m reflecjwvy 3961‘s N? éflivoi 07364 4.75m (it“simtce flfigé) ‘ ...
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