Lect27 - Physics 212 Le cture27: Mirrors Le Mirrors EXAM 3...

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Unformatted text preview: Physics 212 Le cture27: Mirrors Le Mirrors EXAM 3 We De 2 dc Le cture 18 - 25 s OnlineRe w Available vie 50 40 30 20 10 0 Confused Confident Avg = 3.3 Physics 212 Le cture27, S 1 lide Music Who is the Artist? A) B) C) D) E) Stephane Grappelli Pearl Django Mark O’Connor’s Hot Swing Trio Bob Wills Hot Club of Cowtown BB Why?? Over the break, I saw them in person for the Over first time … in Saybrook, IL !! first Great musicians… wide variety of styles Western Swing meets Gypsy Jazz Physics 212 Lecture 27, Slide 2 Physics 212 Le cture27: Mirrors Le Mirrors EXAM 3 We De 2 dc Le cture 18 - 25 s OnlineRe w Available vie 50 40 30 20 10 0 Confused Confident Avg = 3.3 Physics 212 Le cture27, S 3 lide Reflection Angleof incide = Angleof re ction nce fle θi = θr θi θr That’s all of the physics – everything That’s else is just geometry! else Physics 212 Le cture27, S 4 lide Flat Mirror e ache ye • All you se is what re s your e s ct’s re ar e . – You think obje location is whe rays appe t o com from Flat Mirror θr θi Object All rays originating from peak will appear to come from same point behind mirror! Image Physics 212 Le cture27, S12 5 lide Flat Mirror (1) Draw first ray pe ndicular to m rpe irror 0 = θ i = θ r (2) Draw se cond ray at angle θ i = θ r . (3) Line appe to inte ct a distanced be s ar rse hind m irror. This is theim age location. Virtual Im : Virtual age No light actually ge he ts re No θr θi d d Physics 212 Le cture27, S 6 lide AC T A wom is looking at he re ction in a flat ve an r fle rtical m irror. Thelowe part of he body shecan se is he kne . st r e re BB I f shestands close to them , what will bethelowe part of he re ction shecan se r irror st r fle e in them irror. A. Abovehe kne re B. He kne re C. Be he kne low r e Physics 212 Le cture27, S 7 lide AC T A wom is looking at he re ction in a flat ve an r fle rtical m irror. Thelowe part of he body st r shecan se is he kne . I f shestands close to them , what will bethelowe part of e re r irror st he re ction shecan se in them r fle e irror. A. Abovehe kne re B. He kne re C. Be he kne low r e I f thelight doe ge to your sn’t t e the you can’t se it ye n e Physics 212 Le cture27, S 8 lide You will also ge im s fromcurve m t age d irrors: Physics 212 Le cture27, S 9 lide C oncave C : onside thecasewhe theshapeof them r re irror is such that light rays paralle l t o theaxis of them irror areall “focuse to a com on spot a distancef in front of the d” m m irror: The m se irrors areofte n se ctions of sphe s (assum d in re e se this class). t his For such “sphe rical” m irrors, we For assum all angle aresm e n e s all ve t hough wedraw the big to m m it e to se … ake asy e f Physics 212 Le cture27, S 10 lide 10 Aside : For a sphe rical m , R = 2f irror 2f R 2f 2f ce r of sphe nte re som tim s labe d “C ee le ” f Physics 212 Le cture27, S 11 lide 11 Re for finding im : cipe age 1) Draw ray paralle to axis l 2) Draw ray through focus re ction goe through focus fle s re ction is paralle to axis fle l obje ct 2f 2f im age f You now know theposition of thesam point on theim e age Physics 212 Le cture27, S 12 lide 12 S> 2f 2f im is: age re al inve d rte sm r alle 111 += S S′ f S′ M =− S obje ct 2f 2f im age f S S ’ f Physics 212 Le cture27, S 13 lide 13 S= 2f im is: age im re al inve d rte sam size e 111 += S S′ f S′ M =− S obje ct f im age 2f 2f S ’ S f Physics 212 Le cture27, S 14 lide 14 2f > S> f im is: age im re al inve d rte bigge r 111 += S S′ f S′ M =− S 2f 2f obje ct f im age f S ’ S Physics 212 Le cture27, S 15 lide 15 f > S> 0 rays no longe m e r et rays in front of them irror but the do m e but y do e t be hind t hem irror be f obje ct im age (virtual) f S Physics 212 Le cture27, S 16 lide 16 f > S> 0 im is: age im virtual upright bigge r 111 += S S′ f S′ M =− S f obje ct im age (virtual) f S S ’<0 Physics 212 Le cture27, S 17 lide 17 C x: Conside thecasewhe theshapeof them onve r re irror is such that light rays paralle l t o theaxis of them irror areall “focuse to a com on spot a distancef be d” m hind t he be m: irror f Physics 212 Le cture27, S 18 lide 18 S >0 im is: age im virtual upright sm r alle 111 += S S′ f obje ct im age (virtual) f<0 S >0 S ’<0 Physics 212 Le cture27, S 19 lide 19 Exe cutiveS m – Mirrors & Le s: um ary nse S> 2f 2f 2f > S> f re al inve d rte sm r alle concave re al re inve d rte bigge r virtual virtual upright bigge r (conver ging) f conver ging f f > S> 0 111 += S S′ f S′ M =− S S >0 virtual virtual upright sm r alle convex (diver ging) diver ging f f Physics 212 Le cture27, S 20 lide 20 I t’s always thesam : e 111 += S S′ f S′ M =− S You just haveto ke p thesigns straight: e s’ is positivefor a re im al age f is positivewhe it can producea re im n al age Le sign conve ns ntions S positiveif obje is “upstre ” of le : positive ct am ns S : positiveif im is “downstre ” of le ’ age am ns f: positiveif conve rging le ns Mirrors sign conve ntions S positiveif obje is “upstre ” of m : positive ct am irror S : positiveif im is “upstre ” of m ’ age am irror f: positiveif conve rging m irror (concave ) Physics 212 Le cture27, S 21 lide 21 Pre flight 2 BB BB 60 50 Cis not corre as it doe not go through thefocal ct s point. 40 30 20 10 0 Physics 212 Le cture27, S 22 lide 22 Pre flight 4, 5 80 80 60 60 40 40 20 20 0 0 Physics 212 Le cture27, S 23 lide 23 Pre flight 7 BB 2f > S > f image is: i mage r eal inver t ed bigger 111 += S S′ f S′ M =− S f >S >0 r ays no longer meet in f r ont of t he mir r or b ut t hey do meet but do meet behind t he mir r or b ehind 2f 2f obj ect f f obj ect image (vir t ual) image f S’ S 50 f S If theobje is be ct hind thefocal le ngth it will re ct an inve d fle rte im . age 40 30 20 10 0 If theobje is in front of the ct f ocal le ngth it will producea virtual upright im . age Physics 212 Le cture27, S 24 lide 24 Pre flight 9 BB S >0 image is: vir t ual upr ight smaller obj ect obj image (vir t ual) 70 60 f <0 < 0 S> 0 S’< 0 50 40 30 20 10 It's liketheback of a spoon, or oneof thosem irrors in the corne of a conve ncestore r nie . 0 Physics 212 Le cture27, S 25 lide 25 C alculation An arrow is locate in front of a conve d x An sphe rical m irror of radius R = 50cm . 50cm Thetip of thearrow is locate d The at (-20cm ,-15cm ). (-20cm (-20,-15) y R=5 0 x Whe is thetip of thearrow’s im ? re age Whe • Conceptual Analysis • Mirror Equation: 1/s + 1/s’ = 1/f • Magnification: M = -s’/s • Strategic Analysis irror e quation to figureout thex coordinateof theim age • Usem agnification e quation to figureout they coordinateof thetip of theim age • Usethem Physics 212 Le cture27, S 26 lide 26 Calculation An arrow is locate in front of a conve d x An sphe rical m irror of radius R = 50cm . 50cm Thetip of thearrow is locate d The at (-20cm ,-15cm ). (-20cm What is thefocal le ngth of them irror? A) f =50cm B) f = 25cm C) f = -50cm D) f = -25cm y R= 5 0 BB (-20,-15) x For a sphe rical m irror | f | = R/2 = 25cm . For R/2 25cm Rulefor sign: Positiveon sideof mirror wherelight goes after hitting mirror Positive y R f <0 f = - 25 cm 25 Physics 212 Le cture27, S 27 lide 27 Calculation An arrow is locate in front of a conve d x An sphe rical m irror of radius R = 50cm . 50cm Thetip of thearrow is locate d The at (-20cm ,-15cm ). (-20cm (-20,-15) y R= 5 0 f = -25 cm -25 x What is thex coordinateof theim ? age A) 11.1 cm B) 22.5 cm C -11.1 cm ) D) -22.5cm BB Mirror e quation 111 =− s′ f s fs s = 20 cm s− f f = -25 cm (−25)(20) s′ = = -11.1 cm 20 + 25 s′ = S s’ < 0 theim is virtual (on the“othe sideof them ince age r” irror) Physics 212 Le cture27, S 28 lide 28 Calculation An arrow is locate in front of a conve d x An sphe rical m irror of radius R = 50cm . 50cm Thetip of thearrow is locate d The at (-20cm ,-15cm ). (-20cm What is they coordinateof thetip of theim ? age A) -11.1 cm B) -10.7 cm C) -9.1 cm M =− S′ S y R= 5 0 x = 11.1 cm 11.1 f = -25 cm -25 x (-20,-15) (-20,-15) D) -8.3cm BB Magnification Magnification e quation s = 20 cm s’ = -11.1 cm M = 0.556 yimage = 0.55yobject = 0.556*(-15 cm = -8.34 cm obje 0.556*(-15 ) Physics 212 Le cture27, S 29 lide 29 ...
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This note was uploaded on 03/05/2011 for the course PHYS 212 taught by Professor Kim during the Spring '08 term at University of Illinois, Urbana Champaign.

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