Lab 1: Don t Shatter My Image. Reflection and Mirrors. Three types of mirrors. Lab 2: Images The Law of Reflection. Plane Mirror Images

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1 Lab : Dn t Shatter My Image Reflectn and Mrrrs The angle f ncdence equals the angle f reflectn. A plane mrrr results n a vrtual mage (lcated behnd the mrrr). The dstance frm the bject t the mrrr s equal t the dstance frm the mrrr t the mage. Lab 2: Images The Law f Reflectn The reflected rays can be extended behnd the mrrr t lcate the pstn f the vrtual mage. These are the paths yur bran assumes the rays must have fllwed. Three types f mrrrs Plane flat Cncave bumps nward Cnvex bumps utward Ansh Kapr's 23-tn mrrr Plane Mrrr Images Cnvex Sde The Rckefeller Center 2006 Wh Tall Are Yu mrrr Cncave Sde

2 Lght frm an bject n frnt a mrrr spreads ut n all drectns. Only tw f these rays are needed t fgure ut what the mrrr des wth the lght any tw rays wll d. One ray headng upward and ne dwnward wrk well. Draw the nrmals and measure the angles f ncdence. Draw the reflected rays such that the angle f ncdence the angle f reflectn. Because the reflected rays are dvergng (mvng apart) yu trace them backwards t ther magned rgn. 2

3 These reflected rays arrve at yur eye exactly as lght rays frm a real bject wuld. Yur bran desn t knw the dfference between where lght really cmes frm and where t appears t cme frm. Descrbng Images Sze - cmpared t the bject Same Sze Reduced (Smaller) Enlarged (Bgger) Orentatn Uprght Inverted Type f Image Real lght rays actually g there Vrtual lght rays never actually g there Image f an arrw. Hw wuld yu descrbe ths mage? Ths mage s Curved Mrrrs Uprght Same Sze Vrtual It s lcated as far behnd the mrrr as the bject s n frnt f the mrrr. Ths s the nly type f mage frmed by a plane mrrr. Cnvex and Cncave 3

4 Features f a sphercal mrrr Pass Out Small Cncave Mrrrs Where wll ths mage frm? Cllect Small Mrrrs All rays fllw the Law f Reflectn, but sme are easer t predct than thers. Specal Easy t Predct Rays Cncave Mrrrs 4

5 One ray travels n tward the mrrr frm the tp f the arrw n a lne parallel t the prncple axs. Ths ray s reflected frm the mrrr n a path that ges thrugh the fcal pnt. Anther ray travels n tward the mrrr frm the tp f the arrw n a path thrugh the fcal pnt. Ths ray s reflected frm the mrrr n a path parallel t the prncple axs. But where s the mage and what des t lk lke? The mage s lcated where the reflected rays crss. 5

6 The mage s nverted, reduced, and real. Cncave Mrrrs frm many knds f mages Descrbe ths mage. Descrbe each mage. Sphercal Aberratn Results frm the fact that nt all rays pass thrugh the same fcal pnt Fuzzness can be reduced by: Small Aperture Parablc Mrrrs Sphercal Mrrrs are easer t make Specal Easy t Predct Rays Cnvex Mrrrs 6

7 Features f Cnvex Mrrrs One ray travels n tward the mrrr frm the tp f the arrw n a lne parallel t the prncple axs. Ths ray s reflected frm the mrrr n a path that ncludes the fcal pnt. Anther ray travels n tward the mrrr frm the tp f the arrw n a path that ncludes the fcal pnt. Ths ray s reflected frm the mrrr n a path parallel t the prncple axs. Snce the rays dverge, they are extended backwards untl they meet. 7

8 But where s the mage and what des t lk lke? The mage s lcated where the reflected rays seem t crss. Descrbe ths mage. Ths s the nly type f mage frmed by a cnvex mrrr. Uprght Vrtual Reduced Mrrr Wrksheet Part a nly (Dagrams) Use a straght edge! Draw the entre arrw as an mage! Draw the reflected prtn f the ray! Mrrr Frmulae a.k.a. Mrrr Frmulas 8

9 Frmulas apply t bth cncave and cnvex mrrrs. Frmula Cnventns f h h + d d d d M f s the fcal length f the mrrr M s the magnfcatn d s the mage dstance d s the bject dstance h s the heght f the bject h s the heght f the mage. f h h + d d d d M f s pstve fr cncave mrrrs and negatve fr cnvex mrrrs d s always pstve d s pstve fr real mages and negatve fr vrtual mages h always pstve h s pstve fr uprght mages and negatve fr nverted mages M s greater than fr enlarged mages, fr same sze mages, and less than fr reduced mages Example Prblem (Cnvex Mrrr) f -3 cm (cnvex mrrr) h 3 cm d 7 cm Slutn fr mage dstance f + f d d + d d d d 2. Negatve means vrtual mage (behnd mrrr) Seems crrect Slutn fr mage heght Example Prblem (Cncave Mrrr) + f d d h h d d h ( 2.) 3 7 f +3 cm (cncave mrrr) h.7 cm d 8 cm h 0.9 Pstve means uprght Seems crrect 9

10 Slutn fr mage dstance Slutn fr mage heght f + f d d + d d d d 4.8 Pstve means real mage (n frnt f mrrr) Seems crrect + f d d h h d d Negatve means nverted Seems crrect h (4.8).7 8 h.02 Mrrr Wrksheet Reflectn f Sund Parts b, c and d (Calculatns) Rund all answers t 2 decmal places. Marshalltwn Acustcal Cluds Daves Symphny Hall San Francsc 0

11 PV Band Band Shell acustc anechc chamber / ánkók / adj. free frm ech. Acustcal Engneerng Senr NVH Engneer The experenced Harley-Davdsn cmmunty demands a certan dstnctve and unmstakable sund. Yu knw t s a Harley as sn as yu hear t, befre yu even see t. Our prduct s dentfed just as much by hw t sunds as hw t lks. Jhn Deere senr engneer Lren DeVres places small mcrphnes arund the cab f a Jhn Deere 4400 cmpact utlty tractr n the cmpany's nse and vbratn labratry. Mr. DeVres s measurng the sund feld arund the tractr cab fr nput nt a cmputer mdel. Cntrllng Reflected Sund The PV Band Rm Reflectance

12 Reflectance The prtn f the ncdent lght that s reflected. Reflectance the % f lght reflected frm a surface. TO 2 abut 95% Cal Dust abut 5% The Earth s Reflectance Plar ce reflects lght frm the sun. As ths ce begns t melt, less sunlght gets reflected nt space. It s nstead absrbed nt the ceans and land, rasng the verall temperature, and fuelng further meltng. Ths results n a pstve feedback lp called ce albed feedback, whch causes the lss f the sea ce t be self cmpundng. The mre t dsappears, the mre lkely t s t cntnue t dsappear. Reducng Reflectance Aut dmmng mrrrs are based n the scence f electrchrmcs, whch s the prcess f reversbly darkenng materals by applyng electrcty. Dffuse and Specular Reflectn Paper (wth whteut) Each ray stll fllws the Law f Reflectn 2

13 Paper and Ink Dry vs. Wet Cncrete Water flls n the cracks, makng the surface mre smth. It changes frm a dffuse reflectr t a specular reflectr. Vsble Lght Hw Smth? ⅛λ Ham Rad Very Large Array 3