@ @ (147):53280,2:53281,4&@g@12)"THE PHYSICS OF LIGHT PART II"q@(""@210)"A PHYSICS STUDY PROGRAM"@<""@F16)"DEVELOPED BY"@P""@Z14)"PAUL W. MCDANIEL"@d14)"4295 WARREN WAY"An14)"RENO, NEVADA 89509"Ax""=A:16)"COPYRIGHT 1988":\A14)"ALL RIGHTS RESERVED"|A:(147):53280,3:53281,5A""A14)" NOTICE ":""'B6)"WHEN THE FLASHING CURSOR AND THE QUESTION MARK APPEAR THE STUDENT MAY PROCEED TO THE NEXT ITEM BY PRESSING THE"B"RETURN KEY. THE LINE NUMBER MAY BE OBTAINED BY PRESSING ANY KEY THEN THE 'RETURN' KEY":B6)"GRAPHIC AREAS WILL BE ERASED AND THE TEXT WILL CONTINUE AFTER 20 SECONDS.":B(147):""C"":53280,0:53281,0;C12)" LASERS CONTINUED ":SC(147):""C6)"THERE ARE MANY DIFFERENT TYPES OF GAS LASERS, BUT THEY ALL MUST MEET THE FOLLOWING REQUIREMENTS":D"(1) A PURE OPTICALLY TRANSPARENT FLUORESCENT MATERIAL MUST BE USED.":D"(2) THE MAJORITY OF ELECTRONS IN THE TRANSMISSION MATERIAL MUST BE IN AN EXCITED STATE, RATHER THAN THE GROUND "D"STATE.":!E"(3) SOME OF THE RADIATION FROM THE STIMULATED EMISSION MUST BE KEPT WITHIN THE TRANSMISSION MATERIAL TO AID IN A"ME""CHAIN REACTION OF PHOTON EMISSION.":eE,(147):""E610)" INJECTION LASERS "::(147)F@6)"THE NEWEST AND SMALLEST MEMBER OF THE FAMILY OF LASERS IS A TINY BLOCK OF SEMICONDUCTOR CRYSTAL CALLED THE "FJ"'INJECTION LASER' OR 'DIFUSSED JUNCTION'LASER. THE INJECTION LASER IS VERY CLOSELY RELATED TO THE COMMON LED, OR "FT"LIGHT EMITTING DIODE. WHEN A VOLTAGE ABOVE A CERTAIN THRESHOLD LEVEL IS APPLIED TO A LED, IT GLOWS. ":zG^6)"IN INJECTION LASERS THERE IS A CRITICAL THRESHOLD POINT, CALLED I-TH. WHEN THE APPLIED VOLTAGE IS BELOW THIS "Hh"THRESHOLD, THE DEVICE FUNCTIONS EXACTLYLIKE AN ORDINARY LED. THAT IS, THE DEVICE GLOWS WITH A RELATIVELY BROAD SPECTRUM OF WAVELENGTHS."HrH|6)"BUT IF THE APPLIED CURRENT TO AN INJECTION LASER EXCEEDS THE THRESHOLD LEVEL, THE EMITTED LIGHT NARROWS DOWN TOA THIN BEAM.":H(147):"" I6)"THE NEXT FIGURES ILLUSTRATES A TYPICAL LED AND A DIFFUSED JUNCTION LASER."::(147).I1,1:1,2_I1,2,0,"PHYSICAL STRUCTURE OF A TYPICAL LED"I1,80,80 80,120 160,120 160,80 80,80I1, 80,100 160,100:1,14,11,"P":1,14,14,"N"I1,80,80 155,50 235,50 235,90 160,120 J1,235,50 160,80$J1,160,100 235,70pJ1,155,35 155,65 157,65 157,35 155,35:1,6,4,"CONTACT WIRE": 5J1,6,18,"WHEN A VOLTAGE ABOVE A CRITICAL POINT IS APPLIED TO WIRE THE LED GLOWS WITH A WIDE PATTERN OF VISIBLE LIGHT": 5#K1,20,4,"^^^^^^^^^^^^":1,20,5,""bK1,26,10,">":1,28,9,">":1,24,11,">":1,22,12,">"K1,6,12,"_":1,7,10,"<"K  J 1 8: K12:1,10J,11K,"" : K:JK 20:(147): 0K(147):"""THROUGH THE SPACINGS BETWEEN THE SCRATCHES. BECAUSE GOOD GRATINGS ARE DIFFICULT TO MAKE REPLICAS ARE OFTEN USED."THTR6)"TO UNDERSTAND THE ACTION OF A GRATING CONSIDER A SET OF PLANE PARALLELWAVES INCIDENT ON A TRANSMISSION GRATING"T\"AS SHOWN ON THE NEXT FIGURE."Tf: (147)Tp 1,1: 1,2Tz I 8 12 4: 1,1,4I,">": I%U I 0 2: 1,(38I),10 38I,20: IQU I 0 2: 1,(38I),30 38I,40: IU I 0 2: 1,(38I),50I 38I,60: IU I 0 2: 1,(38I),70I 38I,80: IU I 0 2: 1,38I,90 38I,100: IV I 0 2: 1,38I,110 38I,120 : I2V I 0 2: 1,38I,130 38I,140 : I_V I 0 2: 1,38I,150 38I,160 : IV I 0 2: 1,38I,170 38I,180 : IV I 0 140 20: 1,40,(25I),10,8,0,180: IV I 0 140 20: 1,40,(25I),18,12,0,180: I W 1,40,25 120,180%W 1,40,45 110,180AW 1,0,100,180,200,0,180aW 1,310,100,180,200,180,360zW 1,280,20 280,180W$ 1,2,45 150,45W. 1, 156,45 280,110W8 1,2,6,"A"WB 1,2,165 150,165WL 1,156,165 280,110WV 1,2,19,"A'"X` 1,40,85 150,55-Xj 1,156,55 280,80FXt 1,40,145 154,108`X~ 1, 157,110 280,80qX 1,11,9,"B"X 1,12,15,"B'"X 1,40,65 100,180X 1,8: 1,158,58,1X 1, 18,12,"LENS"X 1,36,9,"O'"X 1,36,14,"O"Y 1,23,21,"O' = FIRST"$Y 1,23,22,"ORDER IMAGE"CY 1,23,2,"O = FOCAL POINT"_Y 1,23,3,"FOR INCOMING"|Y 1,23,4,"PARALLEL RAYS"Y 12: 0: (147)Y  1,1: 1,2Y I 0 2: 1,140I,30 140I,70: IY I 0 2: 1,140I,80 140I,110 : I-Z( I 0 2: 1,140I,120 140I,160 : IHZ2 1,140,75,30,24,0,180dZ< 1,140,115,30,24,0,180}ZF 1,140,75 210,150ZP 1,140,75,100,80,145,180ZZ 1,140,95 280,95Zd 1,140,95 280,30Zn 1,140,95,100,80,60,90[x 1,30,8,"K=ANGLE OF"[ 1,30,9,"REFRACTION"-[ 1,22,19,"K"B[ 1,12,9,"-----"X[ 1,12,14,"-----"j[ 1,13,12,"D"|[ 1,14,10,"^"[ 1,14,11,""[ 1,14,12,""[ 1,14,13,""[ 1,140,75 155,55[ 1,19,8,"R"6\ 1,4,2,"ACTION OF DIFFRACTION GRATING ON A PARALLEL BEAM OF MONOCHROMATIC LIGHT"R\ 1,2,18,"R=WAVELENGTH"q\ 1,2,19,"D=GRATING SPACE"\ 1,2,21,"SIN K = R/D OR R = D SIN K"\ 12: 0:(147)\"""D],6)"TO UNDERSTAND THE ACTION OF A TRANSMISSION GRATING, CONSIDER A SET OF PARALLEL WAVES INCIDENT ON A GRATING AS"]6"SHOWN IN THE FIGURE. THE LIGHT THAT PASSES THROUGH THE GRATING CAN BE CONSIDERED AS COMING FROM THE SLITS IN "C^@"THE GRATING. ACCORDING TO HUYGEN'S PRINCIPLE, THE SLITS CAN BE CONSIDERED AS SOURCES OF WAVES. THESE WAVES WILL BE"^J"CIRCULAR IN A PLANE PERPENDICULAR TO THERULINGS. LET THE WAVELENGTH OF THE MONOCHROMATIC LIGHT BE R."^T:(147)^^""H_h6)"THE LIGHT EMERGING FROM EACH OF THE SLITS AT ANY ONE TIME WILL BE IN THESAME PHASE AND WILL SPREAD OUT IN"_r"CONCENTRIC CIRCLES FROM EACH SLIT AS A CENTER. THE DISTANCE BETWEEN "`|"SUCCESSIVE WAVEFRONTS IS R, THE WAVELENGTH OF THE INCIDENT LIGHT. THE PARALLEL WAVEFRONTS CAN BE BROUGHT TO A "`"FOCUS BY A CONVERGING LENS AND WILL PRODUCE A CENTRAL IMAGE AT O. ANOTHER SET OF WAVEFRONTS FROM ADJACENT SLITS"a"WILL BE TRAVELLING AT AN ANGLE K TO THE ORIGINAL DIRECTION OF THE BEAM. IT WILL BE OBSERVED THAT EACH SUCH WAVEFRONT IS"za"TANGENT TO CIRCULAR WAVEFRONTS FROM ADJACENT SLITS THAT DIFFER IN PHASE BY ONE WHOLE PERIOD."a:(147)a""b6)"THESE WAVEFRONTS CAN ALSO BE BROUGHT TO A FOCUS AT O' BY A CONVERGINGLENS. FROM THE FIGURE IT CAN BE SEEN"b"THAT THE RESULTANT WAVEFRONT MAKES AN ANGLE K WITH THE PLANE OF THE GRATING SUCH THAT SIN K = R/D WHERE D IS THE " c"DISTANCE BETWEEN TWO SLITS, FROM WHICH R = D SIN K. THUS THE LONGER THE WAVELENGTH, THE GREATER THE ANGLE K."c: (147),c""]c6)"DIFFRACTION-GRATING SPECTROMETER":ic(147)c6)"A SPECTROMETER, WITH A DIFFRACTIONGRATING MOUNTED ON ITS TABLE IS USED TO MEASURE THE WAVELENGTH OF LIGHT."]d"THE NEXT FIGURE IS A SKETCH OF THE PRINCIPAL PARTS OF A SPECTROMETER. LIGHTFROM SOME SOURCE ILLUMINATES THE SLIT S"d"OF THE COLLIMATOR C, AS SHOWN IN THE SKETCH. THE PARALLEL LIGHT COMING OUT OFTHE COLLIMATOR GOES THROUGH THE GRATING"Xe"G, WHICH SENDS OUT WAVES IN VARIOUS DIRECTIONS. IMAGES OF THE SLIT WILL BE FORMED IN DIRECTIONS MAKING ANGLES "e&"K WITH THE DIRECT BEAM WHEN THE N"e0" WAVELENGTHS SATISFY THE GRATING EQUATION"f:12)"NR = D SIN K N"fD:(147)fN6)"AS THE TELESCOPE IS ROTATED ABOUTTHE SPECTROMETER AXIS, THE SHORTEST WAVELENGTH IS OBSERVED IN THE FIRST" gX"ORDER, WHEN THE ANGLE K IS REACHED SUCH THAT R = D SIN K. IF THE SOURCE SENDS OUT WHITE LIGHT, THE SHORTEST WAVWLENGTH"kgb"IS IN THE VIOLET REGION. THE OTHER WAVELENGTHS THEN APPEAR AT LARGER ANGLESUP TO THE "gl"LONGEST VISIBLE WAVELENGTH, WHICH APPEARS RED. THERE IS A BREAK AFTER THE RED IN THE FIRST ORDER SPECTRUM AND THEN"jhv"THE VIOLET APPEARS ONCE MORE. THIS IS THE BEGINNING OF THE SECOND ORDER SPECTRUM AND THE ANGLE OF THE TELESCOPE"h"SATISFIES THE CONDITION":h10)"2R = D SIN K 2"h:(147)h""ai6)"THE NEXT FIGURE SHOWS THE RELATIVEPOSITIONS OF THE FIRST TWO ORDERS OF SPECTRA PRODUCED BY A DIFFRACTION "i"GRATING ON EITHER SIDE OF THE CENTRAL WHITE IMAGE.":i(147)i 1,1: 1,2i 1,0,80 320,80i 1,0,120 320,120,j 1,2: 1,20,80 20,120 24,120 24,80 20,80: 1,22,82,1Aj 1,0,16,"WHITE"Xj 1,0,17,"CENTRAL"pj 1,0,18,"SPECTRUM"j  1,14: I 1 10 : 1,48I,80 48I,120: Ij 1,7: I 1 10: 1,60I,80 60I,120: Ik  1,6: I 1 10: 1,61I,80 61I,120: I:k* 1,8: I 1 10: 1,74I,80 74I,120: Ilk4 1,9: I 1 10: 1,87I,80 87I,120: Ik> 1,3: I 1 10: 1,100I,80 100I,120: IkH 1,2: 1,6,9," I "kR 1,14: I 1 10 : 1,137I,80 137I,100: I(l\ 1,7: I 1 10: 1,149I,80 149I,100: I\lf 1,6: I 1 10: 1,162I,80 162I,100: Ilp 1,8: I 1 10: 1,175I,80 175I,100: Ilz 1,9: I 1 10: 1,188I,80 188I,100: Il 1,3: I 1 10: 1,201I,80 201I,100: Im 1,2: 1,17,9," II "7m 1,0,19,"I = FIRST ORDER"Xm 1,0,20,"II = SECOND ORDER"m 1,14: I 1 10 : 1,137I,80 137I,100: Im 1,7: I 1 10: 1,149I,80 149I,100: Im 1,6: I 1 10: 1,162I,80 162I,100: I*n 1,8: I 1 10: 1,175I,80 175I,100: I^n 1,9: I 1 10: 1,188I,80 188I,100: In 1,3: I 1 10: 1,201I,80 201I,100: I:1,2n 1,0,19,"I = FIRST ORDER"n 1,0,20,"II = SECOND ORDER"n 12: 0: (147)n 1,1: 1,2%o 1,6,4,"TOP VIEW OF SPECTROMETER" 1, 60,100 164,100yH 1, 84,112 164,100yR 1, 112,122 164,100z\ 1,138,126 164,100+zf 1, 150,112 164,100Gzp 1, 160,114 164,100Yzz 1,20,12,"1"nz 1,2,14,"LYMAN"z 1,2,15,"SERIES"z 1,164,85 164,20z 1,162,86 155,37z 1,160,86 146,55z 1,160,87 141,74{ 1,14,1,"BALMER SERIES"{ 1,192,76 231,441{ 1,198,82 230,64J{ 1, 202,87 220,82a{ 1,32,5,"PASCHEN"w{ 1,32,6,"SERIES"{ 1,224,100 264,100{ 1,224,110 242,112{ 1,32,13,"BRACKETT"{ 1,32,14,"SERIES"{$ 1,232,134 250,140 |. 1,33,17,"PFUND""|8 1,33,18,"SERIES"6|B 1,21,13,"N=2"J|L 1,21,16,"N=3"^|V 1,21,18,"N=4"r|` 1,21,20,"N=5"|j 1,21,22,"N=6"|t 1,2,23,"SPECTRA RESULTING FROM QUANTUM JUMPS"|~ 1,2,2,"HYDROGEN"| 1,2,3,"SPECTRAL"| 1,2,4,"SERIES"} 12: 0:(147)#}""@}14)" HOLOGRAMS ":T}(147):""}6)"AN INTERESTING INTERFERENCE EFFECTIS ACCOMPLISHED USING THE COHERENT LIGHTFROM A LASER. IN THE NEXT FIGURE A "K~"PARTIALLY SILVERED MIRROR IS INSERTED INTHE PATH OF A LASER BEAM. ABOUT 90% OF THE INCIDENT BEAM IS DIRECTED TOWARD AN"~"OBJECT WHILE THE REMAINING 10% (THE REFERENCE BEAM) IS ALLOWED TO TRAVEL TOWARD A PIECE OF PHOTOGRAPHIC FILM."F"SOME OF THE LIGHT THAT STRIKES THE OBJECT IS REFLECTED TOWARD THE FILM WHERE IT INTERFERES WITH THE REFERENCE ""BEAM. THE FILM IS THEN PROCESSED IN A REGULAR PHOTOGRAPHIC LABORATORY. ":(147) 1,1:1,2 1,8,2,"HOW TO MAKE A HOLOGRAM" 1,20,40 20,140 16,140 16,40 20,40:1,18,44,1:1,0,4,"FILM"z1,130,120 190,60 196,60 136,120 130,120:1,134,118,1:1,16,6,"BEAM SPLITTER"(1,160,160,10,8:1,160,160,1:1,20,22,"OBJECT"21,300,100 156,100 148,160:1,156,100 20,100<1,300,90 168,90 160,160:1,168,90 20,90uF1, 300,80 177,80 171,160:1,177,80 20,80:1,23,14,"INCIDENT LASER":1,28,15,"BEAM"P1,160,160 20,100:1,160,160 20,80:1,160,160 20,90ρZ1,6,8,"REFERENCE BEAM"d1,6,18,"REFLECTED":1,11,19,"BEAM"n I0 2:1,2,10I,":": I+x 20:(147): 0;""6)"THE NEXT FIGURE SHOWS HOW THE HOLOGRAM CAN BE VIEWED. THE INTERFERENCEPATTERN SET UP WHEN THE HOLOGRAM WAS"2"MADE SETS UP A DIFFRACTION PATTERN WHEN THE FILM IS HELD IN THE PATH OF A LASER BEAM. THIS RESULTS IN A VIRTUAL IMAGE "l"AND A REAL IMAGE AS SHOWN IN THE FIGURE."::(147){ 1,1:1,21,8,2,"HOW TO VIEW THE HOLOGRAM"1,10,8,"EYE":1,24,6,"DIFFRACTION":1,24,7,"PATTERN ON FILM":1,162,90 220,6071,160,60 160,140 164,140 164,60 160,60:1,162,62,1\ I0 2:1,20,11I,":": I: 5v1,27,10,"LASER BEAM"1,300,100 164,100 60,1401,300,90 164,90 60,140ڄ1,300,110 164,110 60,1401,260,140 130,72 1,260,140 120,80"1,260,140 110,92W 1,60,140,10,8:1,60,142,1:1,3,20,"REAL IMAGE"" 1,260,140,10,8:1,260,142,1:1,26,20,"VIRTUAL IMAGE", 20:(147): 06""@8)" ABSORPTION OF LIGHT BY MATTER "::(147)hJ6)"WHEN AN ELECTROMAGNETIC LIGHT WAVEINTERACTS WITH THE CHARGES OF AN ATOM, AMOLECULE, OR A NUCLEUS, THE ELECTRIC"T"AND MAGNETIC FIELDS OF THE WAVE IMPRESSES A FORCED OSCILLATION ON THE NATURAL MOTION OF THE CHARGES WITH THE "e^"RESULT THAT ENERGY IS ABSORBED BY THE SYSTEM OF CHARGES. IF THE FREQUENCY OF THE FORCED OSCILLATIONS IS THE SAME AS"h"THE NATURAL FREQUENCY OF THE SYSTEM OF CHARGES THE RATE OF ABSORPTION OF ENERGYBY THE SYSYTEM IS A MAXIMUM. WE CALL "pr"THIS SITUATION 'RESONANCE'. ANY ASSEMBLYOF CHARGED PARTICLES, ATOMS, MOLECULES, OR NUCLEI, HAVE A SERIES OF RESONATING FREQUENCIES.":|(147):""6)"THE RESONATING FREQUENCIES CONSTITUTE THE 'ABSORPTION SPECTRUM' OF THE SUBSTANCE. EXPERIENCE HAS SHOWN THAT""THE FREQUENCIES OBSERVED IN THE ABSORPTION SPECTRUM OF A MATERIAL ARE ALSO OBSERVED IN ITS EMISSION SPECTRUM ":(147):""ԉ" SCATTERING OF LIGHT BY BOUND ELECTRONS ":(147)V6)"WHEN AN ELECTROMAGNETIC LIGHT RAY PASSES THROUGH AN ATOM (OR MOLECULE), ITDISTURBS THE MOTION OF THE BOUND "֊"ELECTRONS AND THE ATOM MAY BE LEFT IN ANEXCITED STATE. THE EXCITED ATOM MAY LATER EMIT LIGHT WAVES OF THE SAME "V"FREQUENCY AS THE INCIDENT WAVE. THE ENERGY THE ATOM EMITS HAS BEEN ABSORBED FROM THE INCIDENT WAVEBY THE ATOM'S "֋"BOUND ELECTRONS. THIS PROCESS IS CALLED 'SCATTERING' AND THE RADIATION EMITTED IS CALLED 'THE SCATTERED WAVE'. THE NEXT""FIGURE ILLUSTRATES THIS PROCESS." :(147) 1,1A1,10,2,"SCATTERING OF RADIATION": 3d I 1 10:1,8,8I,"->": I1,5,4,"INCIDENT":1,7,5,"WAVE"ь1,200,108,4,3:1,200,108,1:1,32,12,"BOUND":1,31,13,"ELECTRON": 3& J 0 10:1,10J,13,"": J01,12,18,"ELECTRON ABSORBS ENERGY":1,12,19,"AND RADIATES A SPHERICAL":1,12,20,"WAVE THUS REDUCING INTENSITY":1,12,21,"OF PRIMARY RADIATION"ݍ:1,200,108,3,2:1,200,108,8,6:1,200,108,13,10:1,200,108,18,14:1,200,108,23,18D1,200,108,28,22N1,20,4,"SCATTERED":1,23,5,"WAVE".X 12: 0:(147)Yb(147):"":52380,3:53281,3l8)" WHY THE SKY IS BLUE "::(147)v6)"THE BRIGHTNESS AND BLUE COLOR OF THE SKY ARE ATTRIBUTED TO THE SCATTERINGOF SUNLIGHT BY THE AIR. THE BLUE COLOR ""IS THE RESULT OF THE MORE INTENSE SCATTERING OF THE SHORTER WAVELENGTHS. THE SAME PROCESS ACCOUNTS FOR THE BRIGHT""RED COLORS OBSERVED AT SUNRISE AND SUNSET, WHEN THE SUN'S RAYS TRAVERSE A VERY LARGE THICKNESS OF AIR BEFORE"|"REACHING THE EARTH'S SURFACE,RESULTING IN A STRONG ATTENUATUON OF THE SHORT WAVELENGTHS ON ACCOUNT OF SCATTERING.":(147):53280,0: 53281,06)"A FREE ELECTRON CANNOT ABSORB ELECTROMAGNETIC ENERGY WITHOUT VIOLATING THE PRINCIPLE OF CONSERVATION ""OF MOMENTUM. THIS FOLLOWS FROM THE FACT THAT A FREE ELECTRON CANNOT ABSORB AN AMOUNT OF ENERGY E AND AT THE SAME TIME ""ACQUIRE A MOMENTUM OF P = E/C,BECAUSE THE RELATION BETWEEN BETWEEN KINETIC ENERGY AND MOMENTUM FOR AN ELECTRON IS":76)" "\6)" 2 2 2 2"6)"E = C M C + P C - M C"6)" K E E E":6)"THUS E IS ABOUT EQUAL TO K":14)" 2"14)"P /2M" 14)" E E" :!(147)a 6)"THIS RELATION IS INCOMPATATIBLE WITH THE RELATION":v*14)"P = E/C":46)"IF E = E ">6)" K"H6)"AS REQUIRED BY THE CONSERVATION OFENERGY. THUS SCATTERING OF LIGHT BY FREEELECTRONS SHOULD NOT BE POSSIBLE.":3R(147):""Y\10)" THE COMPTON EFFECT ":ef(147)p6)"IN THE CASE OF THE BOUND ELECTRON ENERGY AND MOMENTUM ARE ABSORBED AND SHARED BY BOTH THE ELECTRON AND THE ION"9z"AND SO IT IS POSSIBLE TO SPLIT ENERGY AND MOMENTUM IN THE CORRECT PROPORTIONS."6)"IN THE CASE OF THE FREE ELECTRON, THERE IS NO OTHER PARTICLE WITH WHICH THE ELECTRON CAN SHARE THE ENERGY AND ""MOMENTUM. THUS NO ABSORPTION OR SCATTERING SHOULD BE POSSIBLE."|"HOWEVER WHEN ELECTROMAGNETIC RADIATION HAS PASSED THROUGH A REGION CONTAINING FREE ELECTRONS ONE OBSERVES THAT ""RADIATION OF A DIFFERENT FREQUENCY FROM THE INCIDENT RADIATION IS PRESENT. THIS RADIATION IS INTERPRETED AS DUE TO THE "v"SCATTERING OF THE INCIDENT RADIATION BY THE FREE ELECTRONS. THE FREQUENCY OF THENEW RADIATION IS SMALLER THAN THE ""INCIDENT RADIATION. FURTHERMORE THE INTENSITY OF THE SCATTERED RADIATION IS DIFFERENT FOR EACH DIRECTION OF SCATTERING.":(147):"""THIS PHENOMENUM IS CALLED 'THE COMPTON EFFECT' FOR ARTHUR COMPTON(1892-1962) WHO FIRST OBSERVED IT IN THE EARLY 1920'S.":6)"THE NEXT FIGURE ILLUSTRATES THE COMPTON EFFECT."::(147) 1,11,6,2,"GEOMETRY OF COMPTON SCATTERING"=1,13,3,"BY FREE ELECTRON"]1,160,100,4,3:1,160,100,1 I 1 18:1,0I,12,"": I1,2,14,"INCIDENT":1,2,15,"RADIATION"ؙ1,20,18,"ELECTRON":1,19,17,"SCATTERED" $1,160,100 250,60:1,21,12,"--------------"6.1,17,7,"SCATTERED":1,17,8,"RADIATION"d8 1,250,55,260,65,90,1:1,31,6,"DETECTOR"ӚB1,160,100,50,40,60,90:1,28,10,"A":1,160,100,55,45,90,120:1,160,100 256,150:1,31,18,"":1,27,14,"B"L1,258,150,4,3:1,258,150:1,160,100,55,45,90,120:1,27,14,"B": 20+V(147): 0`6)"LET L BE THE WAVELENGTH OF THE INCIDENT RADIATION AND L' BE THAT OF THESCATTERED RADIATION. COMPTON FOUND THAT"j"L' IS DETERMINED SOLELY BY THE DIRECTION OF THE SCATTERING (ANGLE A), THE EXPERIMENTAL RELATION BEING":Bt10)"L' - L = L (1-COS A) A"]~10)" C0M":6)"WHERE L ,IS A CONSTANT, 'THE"6)" COM"ǜ"COMPTON WAVELENGTH' AND IS EQUAL TO":霦8)"2.4262 X 10 METERS.":(147):""68)" ANALYSIS OF COMPTON EFFECT "::(147)6)"RECALLING THAT L = C/F WE MAY REWRITE EQUATION A THE FORM"4)" L"4)" COM"4)"1/F' - 1/F = (1-COS A) (B)"4)" C":~6)"WE HAVE LEARNED THAT PHOTONS BEHAVE LIKE PARTICLES SO WE MAY TREAT COLLISIONS BETWEEN PHOTONS AND ELECTRONS""BY ELEMENTARY MECHANICS."::(147)  1,1Ӟ1,12,1,"THE COMPTON EFFECT"1,160,100,4,3:1,160,100,1( I 1 18:1,0I,12,"": Ib21,2,14,"INCIDENT":1,2,15,"PHOTON":1,2,16,"E = HF":1,2,17,"P = HF/C"<1,7,6,"FREE ELECTRON":1,7,8,"E = M C :P = 0":1,8,7," 2":1,12,9,"0":F1,160,100 250,60:1,21,12,"--------------"4P1,30,4,"SCATTERED":1,30,5,"PHOTON":1,30,6,"E'= HF'":1,30,7,"P = HF'/C"\Z1,160,100,50,40,60,90:1,28,10,"A"d 1,160,100 240,145:1,30,18,""Ƞn1,250,150,4,3:1,250,150,1:1,160,100,55,45,90,120:1,27,14,"B"Ox1,17,17,"SCATTERED":1,17,18,"ELECTRON":1,20,22,"E = M C + P C ":1,20,21," 2 4 2 21/2":1,20,23," 0 "i1,20,20,"P = P": 20y 0:(147)6)"NOW THE LOSS IN ENERGY BY THE INCIDENT PHOTON MUST BE EQUAL TO THE GAIN IN ENERGY BY THE SCATTERED ELECTRONHENCE":,6)"HF/C - HF'/C = T (1)":"WHERE T IS THE KINETIC ENERGY OF THE SCATTERED ELECTRON. IF WE TREAT THE PROCESS AS A COLLISION OF TWO PARTICLES,""WE CAN APPLY THE PRINCIPLE OF CONSERVATION OF MOMENTUM. WE THUS HAVE":"46)"HF/C = HF'/C COS A + MV COS B (2)":6)"THIS EQUATION STATES THAT THE INITIAL MOMENTUM ALONG THE ORIGINAL DIRECTION OF THE PHOTON BEAM IS EQUAL TO"#"THE COMPONENTS IN THIS DIRECTION OF THE FINAL MOMENTA OF THE SCATTERED PHOTON AND THE RECOIL ELECTRON.":/(147)H6)"WE ALSO HAVE":w6)"0 = HF'/C SIN A - MV SIN B (3)":6)"THIS EQUATION STATES THAT THE COMPONENTS OF THE MOMENTA AT RIGHT ANGLES TO THE ORIGINAL DIRECTION BEFORE ":"THE COLLISION MUST EQUAL THE COMPONENTS AFTER THE COLLISION.":6)"IF EQUATIONS (1), (2), AND (3) ARESOLVED FOR THE FREQUENCY OF THE SCATTERED PHOTON, AND THE RESULTS ""CONVERTED TO THEIR CORRESPONDING WAVELENGTHS, THE RESULT IS":"6)" H"?,6)"L' - L = (1-COS A) (4)"X66)" MC":ʦ@"WHERE L' IS THE WAVELENGTH OF THE SCATTERED PHOTON AT AN ANGLE A AND L IS ITS ORIGINAL WAVELENGTH.":J(147):""\T6)"THE CHANGE IN WAVELENGTHS AS PREDICTED BY EQUATION (4) DEPENDS ONLY ON THE ANGLE OF SCATTERING AND NOT ON"֧^"THE SUBSTANCE. THIS IS IN ACCORD WITH EXPERIMENTAL RESULTS. FURTHERMORE THE ENERGY AND MOMENTUM OF THE RECOIL ""h"ELECTRON AGREE WITH THE RESULTSAS PREDICTED BY EQUATION (4).":r" THIS AGREEMENT CONSTITUTES STRONG SUPPORT FOR THE QUANTUM THEORY OF RADIATION. ":|(147)è""2)" THE NATURE OF ELECTROMAGNETIC WAVES "::(147) ""6)"WHEN CHARGES ARE ACCELERATED, THEYPRODUCE CHANGING ELECTRIC AND MAGNETIC FIELDS, WHICH PROPOGATE IN THE FORM OF""ELECTROMAGNETIC WAVES. THESE WAVES TRANSPORT ENERGY AND MOMENTUM THAT HAS BEEN TRANSFERRED TO THEM FROM THE ""ACCELERATING CHARGES."6)"IN EMPTY SPACE SYMMETRY REQUIRES THAT THE MAGNETIC AND ELECTRIC FIELDS BEMUTUALLY PERPENDICULAR. FURTHERMORE THE""FIELDS MUST CHANGE AND MOVE AT A PARTICULAR RATE. THIS TURNS OUT TO BE THE VELOCITY OF LIGHT. IT THEREFORE IS "{"EASY TO ASSERT THAT LIGHT IS, IN FACT, SIMPLY MOVING ELECTRIC AND MAGNETIC FIELDS.":(147)""12)" POLARIZATION ":ë(147)<6)"UNPOLARIZED LIGHT IS LIGHT IN WHICH THE ELECTRIC FIELDS IN THE DIFFERENT WAVE TRAINS ARE AT PURELY ""RANDOM ANGLES TO ONE ANOTHER. LINEARLY POLARIZED LIGHT IS LIGHT IN WHICH THE ELECTRIC FIELDS OF ALL THE DIFFERENT"B"WAVETRAINS ARE ORIENTED PARALLEL TO EACHOTHER. POLARIZATION OF LIGHT OCCURS WHENLIGHT IS REFLECTED FROM A SMOOTH SURFACE.":&6)"AT THE PROPER ANGLE OF INCIDENCE, CALLED BREWSTER'S ANGLE, THE REFLECTED BEAM OF LIGHT IS POLARIZED WITH THE"/0"ELECTRIC FIELD VECTORS PARALLEL TO THE INTERFACE. THE NEXT FIGURE ILLUSTRATES POLARIZATION BY REFLECTION.":F:1,1:53280,8:1,2D1,6,0,"POLARIZATION BY REFLECTION AT BREWSTER'S ANGLE"خN1,0,100 320,100 320,170 0,170 0,100:1,160,30 160,140X1,2,11,"REGION I":1,2,13,"REGION II"Hb1,22,5,"INCIDENT":1,22,6,"RAY":1,2,5,"REFLECTED":1,2,6,"RAY"l1,280,40,3,2:1,260,50,3,2:1,240,60,3,2:1,220,70,3,2:1,200,80,3,2:1,180,90,3,2:1,160,100,3,2&v1,270,30 290,50:1,250,40 270,60:1,230,50 250,70:1,210,60 230,80:1,190,70 210,90:1,170,80 190,100n1,140,90,3,2:1,120,80,3,2:1,100,70,3,2:1,80,60,3,2:1,60,50,3,21,280,40 160,100:1,160,100 90,170:1,160,100 60,50ﰔ1,127,114 153,128:1,108,133 132,147:1,88,153 113,1671,11,6,178,3,2:1,0,186 12,195P1,2,22,"= ELECTRIC FIELD PARALLEL TO INTERFACE"1,2,23,"= ELECTRIC FIELD PARALLEL TO SCREEN":1,2ұ1,21,9,"I":1,17,9,"I":1,160,100,42,34,0,50:1,160,100,42,34,310,3601,18,17,"R":1,160,100,42,34,180,220o1,1:1,21,14,"I = INCIDENT ANGLE":1,21,15,"(BREWSTER'S ANGLE)":1,21,16,"R = ANGLE OF":1,25,17,"REFRACTION"²1,2:1,160,100,50,40,220,300:1,15,12,"A":1,1:1,21,18,"A = 90 DEGREES":1,2в 20:1,2(147): 0\6)"IF THE INCIDENT BEAM APPROACHES THE INTERFACE AT BREWSTER'S ANGLE, I IN THE PREVIOUS FIGURE, THE REFLECTED BEAM"ܳ "IS POLARIZED WITH THE ELECTRIC FIELD COMPONENT PARALLEL TO THE INTERFACE. IN THIS CASE THE ANGLE BETWEEN THE ""REFRACTED AND THE REFLECTED RAY IS 90 DEGREES.":G 6)"IT IS LEFT TO THE STUDENT TO SHOW THAT"^*12)" N "u412)" 2">12)"TAN I = "H12)" N "R12)" 1":\6)"WHERE N AND N ARE THE INDEX OF"f6)" 1 2":Ep"REFRACTION OF REGION I AND REGION II RESPECTIVELY.":Qz(147)a""" PRODUCTION OF ELECTROMAGNETIC WAVES "::(147):"" 6)"WHEN A BEAM OF HIGH ENERGY ELECTRONS ARE CAUSED TO STRIKE A METAL PLATE THE ELECTRONS ARE SLOWED DOWN TO ""REST. THIS DECELERATION OF THE ELECTRONS WILL CAUSE THE EMISSION OF ELECTROMAGNETIC WAVES, USUALLY X-RAYS.":6)"SIMILARLY, THE PRODUCTION OF RADIOWAVES, MICROWAVES, GAMMA RAYS, AS WELL AS LIGHT RAYS CAN BE TRACED BACK TO THE "I"ACCELERATION OF CHARGED PARTICLES.":Ƿ6)"THE SUBJECT OF ELECTROMAGNETIC WAVES WILL BE TREATED MORE FULLY IN ANOTHER PROGRAM IN THIS SERIES."::(147)׷""10)" MOLECULAR SPECTRA ":y6)"WHEN A MOLECULE ROTATES AS A WHOLEOR WHEN ITS CONSTITUENT ATOMS VIBRATE ORWHEN THERE ARE CHANGES IN ITS ELECTRONIC""CONFIGURATION 'MOLECULAR ENERGY STATES' MAY ARISE. SPECTRA ARISING FROM TRANSITIONS AMONG THIS MULTIPLICITY OF"o"LEVELS ARE QUITE COMPLEX BUT WHEN UNDERSTOOD CAN LEAD TO A GREATER UNDERSTANDING OF THE MOLECULAR ""STRUCTURE INVOLVED."::(147):""6)"THE LOWEST ENERGY LEVELS OF A DIATOMIC MOLECULE ARISE FROM ROTATION ABOUT ITS CENTER OF MASS. THE NEXT ""FIGURE SHOWS SUCH A ROTATION OF A MOLECULE CONSISTING OF ATOMS OF MASSES M AND M' A DISTANCE R APART."::(147) 1,1$1,0,1,"A DIATOMIC MOLECULE CAN ROTATE ABOUT ITS CENTER OF MASS.".1,160,40 160,150:1,18,4,"AXIS":W81,160,100,2,1:1,160,100 260,50:1,26,6,"CENTER OF MASS"B1,115,107,12,10:1,115,107,1:1,11,13,"M":1,261,85,4,3:1,261,85,1:1,35,10,"M'"ƻL1,115,107 261,85V1,160,100,50,15:1,19,8,"_":1,160,100,120,30:1,19,10,"_"@` DRAW1,115,107 TO 115,125:DRAW1,261,85 TO 261,115_j1,18,12,"R":1,27,11,"R'"t1,4,18,"R = R + R'":1,4,17,""~ 20:(147): 06)"THE MOMENT OF INERTIA OF THIS MOLECULE ABOUT AN AXIS PASSING THROUGH ITS CENTER OF MASS AND PERPENDICULAR TO"8"A LINE JOINING THE ATOMS IS"R8)" 2 2"n8)"I = MR + M'R' ":׽"WHERE R AND R' ARE THE DISTANCES OF ATOMS 1 AND 2 RESPECTIVELY FROM THE CENTER OF MASS.":(6)"SINCE MR = M'R' BY DEFINITION,THE MOMENT OF INERTIA MAY BE WRITTEN"J6)" MM' 2"l6)"I = () (R + R') "6)" M + M'6)" 2 "6)"I = M'R , WHERE M IS THE REDUCED MASS OF THE MOLECULE. THUS THE ROTATION OF A DIATOMIC MOLECULE IS EQUIVALENT TO "K"THE ROTATION OF A SINGLE PARTICLE OF "Y" " "MASS M. LOCATED AT A DISTANCE OF R AWAY."::(147)˿6)"THE ANGULAR MOMENTUM L OF THE MOLECULE IS"12)"L = IW WHERE W IS ITS "(12)" R"|2"ANGULAR FREQUENCY. NOW WE HAVE LEARNED THAT ANGULAR MOMENTUM OF THE ELECTRON INTHE HYDROGEN ATOM IS QUANTIZED AND CAN"<"HAVE ONLY THE VALUES"F10)" 1/2"P10)"L = (L(L+1)) H/2":;Z6)"LIKEWISE THE ANGULAR MOMENTUM OF AROTATING MOLECULE TURNS OUT TO BE SIMILARLY QUANTIZED"Vd10)" 1/2"tn10)"L = (K(K+1)) H/2"x10)" R":"WHERE K, THE ROTATIONAL QUANTUM NUMBER IS RESTRICTED TO"10)"K = 0, 1, 2, 3,...":(147)j 6)"LET US NOW RELATE THE FREQUENCIES OF THE SPECTRAL LINES THAT RESULT FROM TRANSITIONS BETWEEN ROTATIONAL ENERGY"ª"LEVELS WITH THE MOLECULAR MOMENT OF INERTIA. THE ENERGY OF A ROTATING MOLECULE IS"´14)" 2"¾14)"E = 1/2 I W":14)" 2"%14)" L "814)" R"M14)" = "c14)" 2I":14)" 2"14)" K(K+1)(H/2)"14)" = "14)" 2I"::(147)V"6)"ONLY TRANSITIONS INVOLVING A CHANGE IN QUANTUM NUMBER K OF + OR -1 CAN OCCUR. THIS RESTRICTION IS CALLED A "p," -4 -1"6"'SELECTION RULE'. A TRANSITION BETWEEN AROTATIONAL STATE K+1 AND A STATE K MEANSAN ENERGY CHANGE OF":@8)"DELTA E = E - E"J8)" K+1 K":""wH6)"THE MOLECULAR ENERGY DUE TO BOTH ROTATION AND VIBRATION CAN BE EXPRESSED BY"R8)"E = E + E "\8)" V R" :f8)" 2"p8)" (V+1/2)HF + K(K+1) (H/2) "z8)" = ";Є8)" 2 I":^Ў6)"WHEN THE SELECTION RULES"И8)"DELTA V = +OR- 1 AND DELTA K = +OR- 1":Ѣ6)"ARE TAKEN INTO ACCOUNT FOR A TRANSITION BETWEEN TWO ROTATIONAL LEVELSBELONGING TO TWO ADJACENT VIBRATIONAL"WѬ"LEVELS,THE ROTATION-VIBRATION SPECTRUM RESULTS.":cѶ(147)s""12)" ELECTRONIC SPECTRA ":(147)!6)"A MOLECULE MAY HAVE SEVERAL ELECTRONIC STATIONARY STATES, EACH WITH ITS OWN ENERGY. ABOUT 1 TO 10 ELECTRON ""VOLTS OF ENERGY ARE REQUIRED TO EXCITE THE ELECTRON MOTION IN MOLECULES. WHEN AMOLECULE EXPERIENCES AN ELECTRONIC""TRANSITION THE RADIATION FALLS IN THE VISIBLE OR ULTRAVIOLET REGIONS OF THE SPECTRUM.":x6)"TO A GIVEN ELECTRONIC STATE THERE CORRESPOND MANY VIBRATIONAL STATES, EACHWITH CORRESPONDING ROTATIONAL STATES.""THUS FOR A GIVEN ELECTRONIC TRANSITION THE SPECTRA CONSIST OF A SERIES OF BANDSEACH BAND CORRESPONDS TO A GIVEN VALUE OF"%6)"F AND ALL POSSIBLE VALUES OF F "R6)" V R":$6)"MANY PROPERTIES AND STRUCTURES OF MOLECULES MAY BE LEARNED FROM THE STUDY OF MOLECULAR SPECTRA."::(147)."" 86)"THE NEXT FIGURE ILLUSTRATES THE BANDS IN MOLECULAR SPECTRA.":*B 1,1RL1,8,0,"BANDS IN MOLECULAR SPECTRA"lV1,2,2,"E":1,4,2,"^"`1,35,20 35,150:1,40,60 90,60:1,40,150 300,150j1,5,8,"FIRST":1,5,9,"EXCITED":1,5,10,"STATE"t1,5,19,"GROUND":1,5,20,"STATE"~1,0,22,"ELECTONIC"rֈ I 0 40 10:1,100,55I 150,55I: I: L0 4010:1,180,55L 220,55L: L֒ J 0 50 10:1,100,140J 150,140J: J֜1,14,22,"ELEC +":1,14,23,"VIBRATION"/צ1,19,17,"0":1,19,16,"1":1,19,15,"2":1,19,13,"3":1,19,12,"4":1,19,11,"5":1,19,20,"V"bװ K 0 50 10:1,180,140K 220,140K: K׺1,24,22,"ELEC +":1,24,23,"VIBR +":1,24,24,"ROTATION" L 0 7:1,180,110L 220,110L: L N0 7:1,180,25N 220,25N: Nn1,28,13,"]":1,30,13,"":1,30,12,"":1,30,11,"":1,30,10,"":1,30,9,"":1,30,14,"":1,30,15,"":1,30,16,""1,260,130 300,130:1,260,123 300,123:1,260,110 300,110:1,260,95 300,95:1,260,75 300,75(1,38,16,"0":1,38,15,"1":1,38,13,"2":1,38,11,"3":1,38,9,"4":1,38,20,"K"> 20: 0:(147)N""n 12)" INTERFERENCE ":(147):""6)"THE PHENOMENON OF 'INTERFERENCE' OCCURS WHEN TWO OR MORE WAVES COINCIDE IN SPACE AND TIME. A COMMON METHOD FOR"("PRODUCING INTERFERENCE IS TO ALLOW INCIDENT AND REFLECTED WAVES TO COINCIDEIN SPACE. ANOTHER EXAMPLE IS THE USE OF"2"COHERENT SOURCES. AN EXAMPLE OF THE TWO COHERENT SOURCES IS ILLUSTRATED IN THE FOLLOWING FIGURE.":<(147): 1,1:1,2\F1,2,0,"INTERFERENCE OF TWO COHERENT SOURCES":1,5,1,"YOUNG'S DOUBLE-SLIT EXPERIMENT"tP1,20,100 300,100Z1,40,100,2,1:1,5,13,"S"d I 0 40 10: 1,40,100,50I,40I,65,120: In1,135,40 135,160:1,11,4,"DOUBLE SLIT"!"IS THE CONDITION FOR MAXIMUM REFLECTION AND MINIMUM TRANSMISSION, AND":H!8)"2TN COS R = N'(LAMBDA)":7R!"IS THE CONDITION FOR MAXIMUM TRANSMISSION AND MINIMUM REFLECTION.":\!6)"THESE EQUATIONS GIVE DIFFERENT VALUES FOR THE ANGLE OF REFRACTION R, AND THE ANGLE OF REFLECTION I FOR EACH",f!"WAVELENGTH. THIS EXPLAINS THE COLORS OBSERVED IN THIN OIL FILMS ON WATER SURFACES. LIKEWISE A SUCCESSION OF"p!"COLORED BANDS IS PRODUCED IF THE FILM IS OF VARIABLE THICKNESS."::(147)z!""!14)" THE DOPPLER EFFECT "::(147):""":1,22,10,"S":1,23,11,"V":1,4,5,"1":1,6,7,"2":1,9,9,"3":1,11,11,"4"0"1,20,14,"WAVES MORE CLOSELY"q$"1,20,15,"SPACED ON SIDE IN":1,20,16,"WHICH BODY IS MOVING"."1,18,18,"AN OBSERVER AT REST AT":1,18,19,"O OBSERVES A SHORTER":1,18,20,"EFFECTIVE WAVELENGTH"48"1,18,21,"THAN AN OBSERVER WHO":1,18,22,"SEES THE SOURCE AS IT":1,18,23,"IS RECEEDING"IB" 20:(147): 0L"6)"THE DOPPLER EFFECT FOR LIGHT WAVESDEPENDS ONLY ON THE VELOCITY OF THE OBSERVER RELATIVE TO THE SOURCE. THIS IS"FV""THE CONSEQUENCE OF THE CONSTANCY OF THE VELOCITY OF LIGHT. IT CAN BE SHOWN THATTHE FREQUENCY F' MEASURED BY AN OBSERVER"`""MOVING WITH A VELOCITY V RELATIVE TO A SOURCE HAVING A FREQUENCY F IS":"f"8)" 1/2"h"8)" ' [ 1 - V/C]"j"8)"F = F "l"8)" 1/2",t"8)" [ 1 + V/C]":~"6)"THE DOPPLER EFFECT CAN BE OBSERVEDIN THE SPECTRUM OF STARS AND IS CALLED 'THE RED SHIFT'. THIS FACTOR ALLOWS US """TO ESTIMATE THE VELOCITY OF RECEEDING STARS."::(147)"""Y"6)"OTHER PROGRAMS IN THIS SERIES MAY BE OBTAINED DIRECTLY FROM THE AUTHOR BY WRITING TO":c""""12)"DR. PAUL W. MCDANIEL""12)"4295 WARREN WAY""12)"RENO, NEVADA 89509"(#12)"702 826-3560"