How dos light intract with mattr? And what dos (this say about) mattr? REGISTER!!! If Schrödingr s Cat walks into a forst, and no on is around to obsrv it, is h rally in th forst? sourc unknown Phys 1010 Day 27 Qustions? On th natur of modls Farmr/sds Light intracting with atoms Rmindrs: Nxt:spctra, applications lik lasrs HW will chang 1 FCQs 2 Class Updats Th Farmr and th Sds (a parabl of scintific rasoning) Scors will b updatd by nd of wk Lasrs this wk Rviw nxt wk Final & grads HW for nxt wk rviw A) I want both du at sam tim Monday B) mak th HW (short du Monday); Rviw on Wd? A sd is a squar with som dots on it. Th farmr always plants 4 sds in a group. First Group: Scond Group: Farmr obsrvs # of sprouts ach group producs. 3 4 Th Farmr and th Sds First Group: Scond Group: 4 sprouts 6 sprouts What do you think? What schms can w com up with that would prdict th numbr of sprouts basd on th dot pattrn showing whn th sds ar plantd? 5 Th Farmr and th Sds First Group: Scond Group: 4 sprouts 6 sprouts What dos your group think? Whn vryon has com up with at last on schm, shar your schms with your group 6 1
Th Farmr and th Sds Th Farmr and th Sds Possibl Schms 1. Totally Random (Numbrs arn t rlatd to # of sprouts) 2. (Largst Numbr) = (# of Sprouts) 3.... 4.... 12 Possibl Schms 1. Totally Random (Numbrs arn t rlatd to # of sprouts) 2. (Largst Numbr) = (# of Sprouts) 3. (Numbr that is vn) = (# of Sprouts) 4. (Scond Largst Numbr) + (Smallst Numbr) = (# of Sprouts) 5. [(Sum of all Numbrs) 3] / 2 = (# of Sprouts) 13 Anothr sd grouping th farmr trid: Anothr sd grouping th farmr trid: 2 sprouts! Possibl Schms 1. Totally Random (???) 2. (Largst Numbr) = 3. (Numbr that is vn) = 4. (Scond Largst Numbr) + (Smallst Numbr) = 5. [(Sum of all Numbrs) 3] / 2 = Possibl Schms 1. Totally Random (???) 2. (Largst Numbr) = 3 Sprouts 3. (Numbr that is vn) = 2 Sprouts 4. (Scond Largst Numbr) + (Smallst Numbr) = 3 Sprouts 5. [(Sum of all Numbrs) 3] / 2 = 2 Sprouts 14 15 Qustions from this story: Possibl Schms 1. Totally Random (???) 2. (Numbr that is vn) = 2 Sprouts 3. [(Sum of all Numbrs) 3] / 2 = 2 Sprouts A MODEL 1. How could w dcid if any of ths thr schms is th corrct on? 2. If th farmr had to wait to plant mor sds, ar thr rasons w might in th mantim favor on schm ovr anothr? 3. How do w know if w v figurd out all th possibl schms? 4. Whr did ths schms w v bn discussing com from? (Not: This qustion is not about th lmnts of th schms, but th dcisions as to what lmnts to us and how to us thm.) 16 16 17 17 2
COMPETING THEORIES INTERPRETATION EVEN NUMBER THEORY OF SPROUTS & SEEDS (# OF SPROUTS) = 2 SPROUTS 2 sprouts! Why vn? EVEN NUMBER THEORY OF SPROUTS & SEEDS (# OF SPROUTS) = 2 SPROUTS 2 sprouts! COMPLEX THEORY OF SEEDS & SPROUTS (# OF SPROUTS) = [(1 + 1 + 2 + 3) 3] / 2 = 2 SPROUTS COMPLEX THEORY OF SEEDS & SPROUTS (# OF SPROUTS) = [(1 + 1 + 2 + 3) 3] / 2 = 2 SPROUTS Why subtract 3? constraind by obsrvaaon 19 18 18 What dos combining ths numbrs physically rprsnt? 19 Summary Scintists mak up thoris to xplain th vidnc thy s. Ths thoris ar constraind by xprimnt. W can t always opn up th sd and look insid. Hav to mak infrncs from indirct vidnc. A thory with a plausibl mchanism is mor convincing than a rot algorithm. Th mor diffrnt cass our thory works on, th mor w bliv it. But it could always b wrong 20 20 Larning Goals 1. How Ruthrford scattring stablishd atom mad up of small havy nuclus with larg cloud of light lctrons. 2. What on ss if bash atoms with anything, particularly lctrons, as in a discharg lamp. 3. What light coming from atoms ( spctra ) imply about bhavior of lctrons in atom. W will combin with undrstanding of light as a wav and a particl. W will rturn to this onc w undrstand th atom bttr and whr light coms from. 23 Prior modls of atom Atom Grk indivisibl unit But wait w can gt lctrons from thm (scraping, or chmical) + + + + + + + + + 24 Dvlop modl of how light intracts with and is producd by individual atoms & what that tlls us about how to dscrib atoms and about bhavior of lctrons in atoms How to look at structur of atoms? Exprimnt! Hit atoms with various things and s what happns. Elctrons Atom Light Larning Goals: 1. How Ruthrford scattring stablishd atom mad up of small havy nuclus with larg cloud of light lctrons. 2. What on ss if bash atoms with anything, particularly lctrons, as in a discharg lamp. 3. What light coming from atoms ( spctra ) imply about bhavior of lctrons in atom. 25 3
Invstigating Atoms: An analogy with JELLO ball Hav a havy blob that sms lik grap JELLO, and you hav gun with rubbr bullts. How to find out what th middl of th blob is lik? Hav a havy blob that sms lik grap JELLO, and you hav gun with rubbr bullts. How to find out what th middl of th blob is lik? Shoot bunch of bullts into it and s this. Studnt suggstions 26 Hav a havy blob that sms lik grap jllo, and you hav gun with rubbr bullts. How to find out what th middl of th blob is lik? Shoot bunch of bullts into it and s this. What is th insid lik? a. hollow b. solid JELLO c. hard havy cor surroundd by JELLO 27 d. bunch of hard littl objcts distributd through blob Atom Sim What is th insid lik? c. hard havy cor surroundd by JELLO Objct must b hard and havy to rflct. Essntially Ruthrford xprimnt and conclusion. Ruthrford shot alpha particls = 2 protons, 2 nutrons Bullts = n pn p Positiv charg 28 Atom: Tiny nuclus with protons and nutrons (99.9% of mass) Surroundd by larg diffus cloud of low mass lctrons 29 Googl map prspctiv 50 is th nuclus (that s Gamow Towr) 100mi is th dg that s Wyoming! 1010 m n n pnp p pn p 1014 m 30 31 4
Itm 2: Bash atoms with lctrons and s what happns Look at with diffraction gratings and atomic discharg lamps. Mrcury, Sodium, non Hold grating only by dgs...oil from hands ruins grating. Hold clos to y... S rainbow from lights. Turn so rainbow is horizontal. In atomic discharg lamps, lots of lctrons givn bunch of nrgy (voltag). Bash into atoms. ( Non lights, Mrcury strt lamps) 120 Volts voltag diffrnc or mor with long tub Moving lctrons Colliding with atoms Cathod 32 33 What colors from whit light? What colors from hydrogn? What from sodium? What from mrcury? What colors from non? Hydrogn Hydrogn Whit light = whol spctrum Each typ of atom producs uniqu st of colors. Calld its spctrum, plural spctra. Na Hydrogn Each typ of atom producs uniqu st of colors. Discussion: if w know that diffrnt colors of light rprsnt diffrnt nrgis, what dos this man about atoms? Studnt suggstions: a. b. c. d.. 34 35 Rviw of atom discharg lamps non signs. Enrgy lvls mtal, bulb filamnt, or not stuck in atom (lik sun). If hot, jump btwn all diff. lvls. Wiggl around, all colors. In discharg lamps, lots of lctrons givn bunch of nrgy (voltag). Bash into atoms. ( discharg tub ) 120 V or mor with long tub Enrgy lvls in isolatd atom. kick up, only crtain wavlngths whn com down. 36 Discussion: Givn what w know about light, what dos this imply about lctrons in atoms? Implis that lctrons only chang btwn vry spcific nrgis. Only way for individual atoms to giv off nrgy is as light. Each tim a photon is mittd an lctron must b changing in nrgy by that amount (rlasing nrgy). (basics, applications) Atoms ar lazy always want to go back to lowst nrgy stat. 2. Excitd atom..lctron 3. Elctron 1. Fast lctron in atom gos to highr jumps back to hits atom nrgy low nrgy Lss KE Highr nrgy Ground stat Excitd stat 10ns 37 5
Nuclus Elctron Nuclus Elctron Highr Enrgy Enrgy lvls Highr Enrgy Enrgy lvls Whn lctron movs to location furthr from th nuclus, a. nrgy of lctron dcrass bcaus nrgy is rlasd as positiv and ngativ chargs ar sparatd, and thr is a dcras in lctrostatic potntial nrgy of lctron sinc it is now furthr away b. nrgy of lctron incrass bcaus it taks nrgy input to sparat positiv and ngativ chargs, and thr is an incras in th lctrostatic potntial nrgy of th lctron. c. nrgy of lctron incrass bcaus it taks nrgy input to sparat positiv and ngativ chargs, and thr is a 38 dcras in th lctrostatic potntial nrgy of th lctron. Whn lctron movs to location furthr from th nuclus, a. nrgy of lctron dcrass bcaus nrgy is rlasd as positiv and ngativ chargs ar sparatd, and thr is a dcras in lctrostatic potntial nrgy of lctron sinc it is now furthr away b. nrgy of lctron incrass bcaus it taks nrgy input to sparat positiv and ngativ chargs, and thr is an incras in th lctrostatic potntial nrgy of th lctron. c. nrgy of lctron incrass bcaus it taks nrgy input to sparat positiv and ngativ chargs, and thr is a dcras in th lctrostatic potntial nrgy of th lctron. (Forc on lctron is lss, but Potntial Enrgy is highr!) 39 Nuclus F Elctron Highr Enrgy Enrgy lvls nrgy lvls of lctron stuck in atom 3 2 nrgy of colliding 1 lctron Elctron fls forc toward nuclus. Must work against that forc to mov lctron farthr away, so incras in PE. Whn lctron movs to location furthr from th nuclus, Answr is b. nrgy of lctron incrass bcaus it taks nrgy input to sparat positiv and ngativ chargs, and thr is an incras in th lctrostatic potntial nrgy of th lctron. It s lik pushing a bouldr out of a ditch (stp at first and shallow latr on). 40 So lctrons at highr nrgy lvls ar furthr from th nuclus! G (ground) If th colliding lctrons hav an nrgy btwn that of lvl and lvl 3 whn thy hit th atom a. no lvls will b xcitd, and so no light will com out. b. 1 color of light will com out c. 2 colors of light will com out d. 3 colors of light will com out. 4 colors com out. ans. d. nough nrgy to xcit lvl 2, thn gt 2 1 followd 41 by 1 G, but also can go 2 G. Enrgy lvl diagrams rprsnt nrgy lctron can go to. diffrnt hight = diffrnt nrgy For Hydrogn, transitions to ground stat in ultraviolt! No light mittd with colors in this rgion bcaus no nrgy lvls spacd with this nrgy. Enrgy Important Idas 1) Elctrons in atoms only found in spcific nrgy lvls 2) Diffrnt st of nrgy lvls for diffrnt atoms 3) 1 photon mittd pr lctron jump down btwn nrgy lvls. Photon color dtrmind by nrgy diffrnc. 4) lctron spnds vry littl tim (10 8 s) in xcitd stat bfor hopping back down to lowst unfilld lvl. 5) If lctron not stuck in atom, can hav any nrgy. Hydrogn Lithium Elctron nrgy lvls in 2 diffrnt atoms Lvls hav diffrnt spacing. Atoms with mor than on lctron lowr lvls filld. 42 (not to scal) 43 6