Answers to the Conceptual Questions

Transcription

1 hapter 17 Lght 205 shne re laser lght nt a tube f REST tthpaste. The re seems t sappear. Next we use ur clr aer. It s a bx cntanng lght bulbs fr each f the three prmary clrs behn a translucent screen. We can pruce a arety f clrs by aryng the ntenstes f the lghts. We en the class wth a emnstratn f the blue sky/yellw Sun phenmenn. Place a pece f carbar wth a hle n t n the erhea prjectr. Place a beaker flle wth water n tp f the hle. Yu shul see a run whte sun n the prjectr screen. Nw slwly pur pwere cffee cream (apprprate frm the schl cafetera) nt the water. As the water gets mlky, t lks blush an the sun turns yellw. The blush water s seen because f scatterng. The yellw sun s the clr left when yu subtract blue lght frm whte lght. lawe Reasnng Explres the bseratns f clre bjects uner clre lghts. Physcs n Yur Own Stuents are aske t use a magnfyng glass t examne clr phtgraphs an rawngs n magaznes. Ve Encyclpea 23 #23 lrs n Spectral Lght #25 Newtn s lr Dsc #26 Ate lr Mxng 24 # Artfcal Sunset mputer Anmatns Acte gure Anmatns are aalable n the Multmea Manager Instructr s Resurce D. They are rganze by textbk chapter, an each anmatn cmes wthn a shell that pres nfrmatn n hw t use the anmatn, explratn acttes, an a shrt quz. Answers t the nceptual Questns 1. Unless there s ust n the ar, nne f the lght gets scattere nt yur eyes untl the lght hts the wall. 2. The ust clu scatters sme f the lght n ranm rectns. Sme f ths scattere lght reaches yur eyes. 3. The mrrr s a reflectng surface s n lght scatters back twar yur eyes. 4. The ust has ranmly rente surfaces that reflect sme f the lght n all rectns. Sme f that lght returns t yur eyes. 5. A pnt surce f lght s neee t pruce an umbra wthut a penumbra. 6. The penumbra wll be much mre prnunce fr the extene lght surce n the celng. The Sun cers an angle f nly abut half a egree an behaes almst lke a pnt surce. 7. Intally, the umbra s nfnte as n lght reaches the flr. When the bk s near the flr, the umbra becmes the same sze as the bk. Whle the bk s rppng, the umbra must be shrnkng.. Intally, the umbra s nnexstent as the lght surce s bgger than the bk an sme lght hts all pnts n the flr. When the bk s near the flr, the umbra becmes the same sze as the bk. Whle the bk s rppng, the umbra must be grwng. 9. There wll be n umbra when the shaw s nt lng enugh t reach the screen. Ths ccurs when the Mn's umbral shaw es nt reach the Earth. 10. In these stuatns there wll be n umbra because the Mn's shaw s nt lng enugh t reach the Earth. The bserers wul see an annular eclpse n whch the rm f the Sun s seen arun the Mn. 11. Enlargng the pnhle wll make the mage brghter an fuzzer. 12. The mage gets smaller an brghter. 13. The mage s upse wn an left-rght reerse. 14. The small gaps between the leaes act lke nepenent pnhle cameras each prucng an mage f the Sun.

2 206 hapter 17 Lght 15. ; the angle f reflectn must equal the angle f ncence. 16. D; the mage must le alng a lne perpencular t the (extene) mrrr. 17. Only the bserer at A can see the mage. 1. Stuent 1 s crrect. 19. The chl's mage s the same sze as the chl, 0.7 meter. 20. The mage pruce by a flat mrrr s the same sze as the bject an the same stance behn the mrrr as the bject s n frnt f the mrrr. Therefre, yur mage wll reman the same sze an appear t walk twar the mrrr. 21. The mage can nly be seen by bserers at B an. 22. mage 23. The magnfcatn f a lat mrrr s ne. Its fcal pnt s at nfnty. 24. Because yur mage at all tmes s the same stance behn the mrrr as yu are frnt f t, the mage's spee must be the same as yur spee. The relate spee must be twce yur spee r 2.4 meters per secn. 25. The shrtest pssble mrrr s half her heght an s nepenent f hw far she stans frm the mrrr. 26. Wrs appear reerse n a mrrr nt because the mage s reerse but because yu are effectely lkng at t frm the ther se. 27. The mages appear t get prgressely smaller because they are prgressely farther frm the ewer. The mages are all rtual because they are behn the mrrrs. 2. The bject plus the mages frm an eght-fl symmetrc arrangement. Therefre, seen mages wll be seen. 29. The backs f autmte healghts are cure t pruce a beam f lght. The small bulb s place near the fcal pnt f the cure mrrr. 30. A cncae mrrr. 31. The rtual mage frm the plane mrrr s behn the mrrr far frm yur eyes. The real mage frm the cncae mrrr s n frnt f the mrrr clser t yur eyes. Ths mage s mre lkely t stran yur eyes. 32. The mage f cnex mrrr s always smaller than the bject. 33. A cncae mrrr wll pruce a magnfe rtual mage f yur face f yur face s place nse the mrrr's fcal pnt. 34. Because the mages pruce by cnex mrrrs are always smaller than the bjects, ther smaller szes make them seem lke they are farther away than they really are. 35. The mage s ery clse t the mrrr n the back se an nly slghtly magnfe. As yu me away, the mage gets larger an mes away. 36. The mage s ery clse t the mrrr n the back se an nly slghtly reuce n sze. As yu me

3 hapter 17 Lght 207 away, the mage gets smaller an mes away. 37. The lght actually cnerges t frm a real mage; there s n lght at the lcatn f a rtual mage. 3. Bth real an rtual mages can be phtgraphe because the lght cmes (r appears t cme) frm the mage. 39. The bulb shul be place at the fcal pnt. If parallel rays all reflect frm the mrrr an cnerge t the fcal pnt, rays rgnatng at the fcal pnt wll reflect frm the mrrr such that they are parallel. 40. The new mage s frme at the rgnal lcatn f the bject. Ths s a cnsequence f the reersblty f lght rays. 41. The spee f lght s much faster than the spee f sun. 42. Because the lght reachng Earth nw left the bjects many years ag, we see eents that tk place n the past. 43. By the tme a e sgnal frm the Sjurner reache Earth an a cmman was sent back, n the rer f twenty mnutes wul hae elapse. Ths s t lng t a an accent. 44. The lag tme f ther respnses t yur questns wul be ntceably lnger f they were n Mars. 45. Blue lght plus re lght yels magenta. 46. The substance wul appear magenta (a resh purple) uner whte lght because whte lght cntans bth re an blue, an t wul appear re uner re lght. 47. Uner re lght, the surface wll appear re. Uner green lght, the surface wll appear green. Uner blue lght, the surface wll appear black. 4. If the sptlghts nt hae any blue n them, the ress wll appear black. 49. The letter wul blen nt the backgrun as bth wul appear re. 50. N lght wul pass thrugh bth flters. The re flter remes all lght but re, whch cannt then pass thrugh the blue flter. 51. Wth lght beams yu are ang clrs whereas wth pgments yu are subtractng clrs. Each atnal pgment absrbs anther set f clrs. Re pant absrbs all but re an green pant wll then absrb the re leang muy brwn. 52. Magenta an cyan pants wll pruce a ark blue. 53. yan s the cmplementary clr t re because cyan lght (whch can be thught f as blue plus green) plus re lght makes whte lght. 54. Green s the cmplementary clr t magenta because green lght plus magenta lght (whch can be thught f as blue plus re) makes whte lght. 55. Yu wul see the cmplement f green, whch s magenta (whch can be thught f as blue plus re). 56. Yu wll get the cmplementary clr t yellw, that s, blue. 57. The sky wul appear green ue t the scattere lght, an the Sun wul appear magenta because f the remal f green frm the Sun s whte lght. 5. The Sun wul lk mre re because the ncrease number f mlecules wul scatter een mre f the blue en f the spectrum, nclung the greens an yellws. Answers t the Exercses 120 cm s = = 5cm 4 = 20cm 30 cm 1. ( )( )

4 20 hapter 17 Lght 10 cm 1 h h = = = 50 cm 5 2. ( 5cm) 1cm 3. bject mage ncent angle reflecte angle nrmal 4. The bttm f the mrrr must be half way between Gerge's eyes an belt buckle 60 n. 36 n. heght abe flr = 36 n. + = 4 n The mage s 2 m behn the mrrr. ( ) ( ) 2 2 = 3m + 4m = 5m 6. The lght traels 2 m hrzntally an 1.5 m ertcally t strke the mrrr. ( ) ( ) 2 2 = 2 2m + 1.5m = 5m 7. θ= m tan 2m = r f ( ) = 2 = 2 4m = m r 6m 10. f = = = 3m The mage s real, nerte, an reuce n sze. 12. The mage s real, nerte, an magnfe.

5 hapter 17 Lght Ths prblem has the same agram as fr Exercse 11. Measurements n ths rawng shw that the mage s lcate 37.5 cm n frnt f the mrrr an s 2 cm tall. 14. Snce the bject s stll 3 tmes the fcal length frm the mrrr, the mage s exactly between the bject an the mrrr. The mage s 60 cm frm the mrrr an 3 cm tall. 15. The rawng shws that the mage s lcate 20 cm behn the mrrr. 16. Snce the bject s stll 2 tmes the fcal length frm the mrrr, the mage s ne-thr as far frm the mrrr as the bject s. The mage s 30 cm behn the mrrr. 17. The rawng shws that the mage s lcate 20 cm behn the mrrr an has a magnfcatn f 2/3. 1. The rawng shws that the mage s lcate 60 cm behn the mrrr an has a magnfcatn f The bject s lcate at the center f curature fr the mrrr, s the mage s at the same lcatn, 40 cm n frnt f the mrrr. 20. Yu wul want the canle an ts nerte mage t be at the same lcatn. Ths happens when the canle s place at the center f curature fr the mrrr, whch s twce the fcal length r 60 cm m 4 10 s t = = = 10 s ; = 3 10 m s 0.2 s m = = = t 0.2 s m s

6 210 hapter 17 Lght 23. t 24. t t 400 km 1000 m = = = = 3 10 m s 1km mn max s 16 ms 9 9 ( ) m m mn = = = 520 s =.67 mn 3 10 m s 9 9 ( + ) m m max = = = 2520 s = 42 mn 3 10 m s 15 1 LY = 3 10 m s 1y = m 25. ( )( ) 365 ays 24 h 3600 s 1y 1 1h ct ( ) ( ) = = 3 10 m s 10 s = 0.3m 1ft Answers t the Prblems n Prblem Slng 2m h = h = m = 0.m 20 m 1. ( ) 1.5 m h = h = 1m = 0.3m 5m 2. ( ) h 0.1 m = = m = 10 m h ( 10 m) 3. ( ) h 1 4. = = 0.5 m = 2 m h = h ; s cnstant n ths prblem h h h 75cm = = = 6.25 h 12cm = 3 cm 6.25 = 237 cm 6. ( ) 50 m h = h = 0.3 m = 7.5 m 2m 7. The mrrr s equstant frm the ppste wall f the ance hall an the mage f the ppste wall. The ance hall wll therefre appear twce as large.. A agram wll shw that the fe clsest mages are lcate at 1 m, 7 m, an 9 m behn the near mrrr, an 3 m an 5 m behn the far mrrr = 1 1 = 1 1 = 1 = 60 cm f s 30 cm 60 cm 60 cm Because s' > 0, the mage s real.

7 hapter 17 Lght cm m = = = 1 s 60 cm = = = = 60 cm f s 20 cm 30 cm 60 cm 60 cm m = = = 2 h = m h = 2 ( 15 cm) = 30 cm s 30 cm = = 3 5 cm = 15 cm 11. s m s ( ) The mage s rtual s = 15 cm = + = + = f s 5cm 15cm 15cm f = 7.5 cm = = = = 30 cm f s 60 cm 20 cm 60 cm ( 30 cm) m = = = 1.5 h = m h = 1.5 ( cm) = 12 cm s 20 cm = = = = 20 cm f s 15 cm 60 cm 60 cm 20 cm 1 m = = = 13 h = mh = ( 12cm) = 4cm; nerte s 60 cm s 30cm s = f = 10 cm 15 cm = 30 cm = 15 cm h cm m = = = 0.5 h = = = 16 cm ; nerte s 30 cm m = = = 0 = ( nfnty) f s f f = = s s f s f s = 2 f = = 3 15 cm = 5 cm = + = + = f = 7.5 cm f s 15cm 5cm 15cm s ms ( ) r 12 cm 1. f = = = = 3cm = = = = 2.1 cm f s 3 cm cm 24 cm = f s Because f s negate an s s pste, the rght-han se s always negate. Therefre, s always negate. Ths ncates that the mage s always rtual.

8 212 hapter 17 Lght 20. m = 1 s = = s = s f = = s s s f s = 2 f 21. t 22. t km km y = = = km km y = = = ( ) 51. y 14 y 1LY km = 169,000 y km km LY = km 1LY 24. ( )