LASERs and Review. Energy level diagrams- represent energy electron can go to. different height = different energy. e e. e e

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1 Enrgy LASERs and Rviw Enrgy lvl diagrams rprsnt nrgy lctron can go to. diffrnt hight = diffrnt nrgy Class 27: LASERs Rviw Th National Ignition Facility (NIF) is th world's largst lasr. NIF's 92 intns lasr bams [ar] capabl of dircting narly two million jouls of ultraviolt lasr nrgy in billionthofascond pulss to th targt chambr cntr. NIF: Rmindrs/Updats: rading 4.3, 6.3 mor homwork # du Thursday (can t b lat). KM s offic hours Today, Wd 24 Monday 5 th 4 in hlp room RW (sam) For Hydrogn, transitions to ground stat in ultraviolt! No light mittd with colors in this rgion bcaus no nrgy lvls spacd with this nrgy. 2 Important Idas ) Elctrons in atoms only found in spcific nrgy lvls 2) iffrnt st of nrgy lvls for diffrnt atoms 3) photon mittd pr lctron jump down btwn nrgy lvls. Photon color dtrmind by nrgy diffrnc. 4) lctron spnds vry littl tim (0 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 (not to scal) Elctron nrgy lvls in 2 diffrnt atoms Lvls hav diffrnt spacing. Atoms with mor than on lctron lowr lvls filld. 3 Small dtour: Spctra of matrials what it is good for Evry matrial (atom, molcul) has a charactristic mission spctrum ( fingrprint ). Thus by looking at th spctrum of an unknown matrial you can figur out its composition (cool!). This is how w knw th rings of Saturn ar mostly composd of watr ic bfor w actually snt thr a satllit to look closly. Astronomrs larn about th Univrs by obsrving light from distant astronomical objcts, lik stars or galaxis. Light contains information, and sinc it is much asir to obsrv a star than it is to travl to on, thr is clarly a bnfit to bing abl to undrstand what th light is tlling us! Fig. A fals color imag of th watr contnt in Saturn s rings. (Takn in U and not visibl). Mor blu (turquois) mans mor watr, rd mans lss 4 watr. Not th fin structur of th rings. Lasr Light Amplification by Stimulatd Emission of Radiation rpatd cloning of photons to produc LOTS of idntical photons of light. Rquirmnts: ) stimulatd mission (always hav) 2) population invrsion of bunch of atoms (hard) 3) optical fdback (mirror) photon, littl pic of wav, or? w oftn draw as littl ball bcaus lss work. Lasr Light Amplification by Stimulatd Emission of Radiation rpatd cloning of photons to produc LOTS of idntical photons of light. Rquirmnts: ) stimulatd mission (always hav) 2) population invrsion of bunch of atoms (hard) 3) optical fdback (mirror) photon, littl pic of wav, or? w oftn draw as littl ball bcaus lss work. Evrything to know about intraction of light and atoms. 3 asy stps. photon atom lctron in highr nrgy lvl. absorption of light 2. Spontanous mission of light. Elctron jumps 6 down from uppr lvl, givs off light. Randomly in any dirction.

2 Stimulatd mission of light. First ralizd by A. Einstin G Photon hits atom alrady in highr nrgy lvl. original photon continus and atom mits scond idntical on photon atom in xcitd stat scond idntical photon coms out. Atom jumps down. Cloning photon. Only works if photon has th corrct nrgy Nw photon coms out with sam phas (paks and 7 troughs lin up) Thr procsss by which light intracts with atoms in out in out in out absorption (of light) stimulatd mission (of light) Surprising fact. Chanc of stimulatd mission of xcitd atom EXACTLY th sam as chanc of absorption by lowr stat atom. Critical fact for making a lasr but also why it s not asy. spontanous mission (of light) (Aftr lc. coll. or light xcitd atom) Lasr just us stimulatd mission to clon photon many tims (~0 20 /sc) Light Amplification by Stimulatd Emission of Radiation 8 Surprising fact. Chanc of stimulatd mission of xcitd atom EXACTLY th sam as chanc of absorption by ground stat atom. Equal chanc bottom atom will absorb photon laving no photon, as top atom will jump down and so hav two photons. glass tub full of atoms, discharg lamp I would xpct that a. mor photons will com out right hand nd of tub, b. lss com out right, c. sam numbr as go in, d. Can t tll.. It s compltly random 9 b. lss com out right X X X 3 xcitd atoms can mit photons, 6 ground stat atoms will absorb. Absorption wins. Think about statistics / probabilitis A mattr of chanc, somtims could b 0, somtims, somtims 2 or 3, and 3,2, or 0 photons mak it through. pnds on numbr of atoms and how clos thy ar togthr. But most of th tim will b lss photons coming out bcaus mor lowr lvl atoms than uppr. ON AERAGE will gt on out! 0 LASER Light Amplification by Stimulatd Emission of Radiation Nd to clon lots of photons LOTS of idntical light. Thr procss, all play important rols: in out in out in out stimulatd spontanous absorption mission mission Basic rquirmnts for lasr: ) Nd mor atoms in an uppr lvl than a lowr on ( Population Invrsion ) (hard part of making lasr) To amplify numbr of photons going through th atoms I nd a. mor atoms in lowr nrgy lvl, b. half in lowr, half uppr, c. mor in uppr nrgy lvl, d. a sufficint numbr in uppr lvl and it dos not mattr how many ar in th lowr. 2) Nd mthod of rcycling photons to clon mor tims ( fdback ) (mirrors) 2 2

3 To amplify numbr of photons going through th atoms I nd c. mor in uppr nrgy lvl than in lowr. Lowr ats thm up, uppr clons thm (adds nrgy). Equal prob. so amplification or loss is just N uppr N lowr. so gt amplification if mor in uppr lvl than lowr this condition vry unnatural known as population invrsion how to gt population invrsion? N uppr > N lowr, mor out than in. (atoms chang) N uppr < N lowr, fwr out than in. (and atoms chang) try gtting by shining lots of light on atoms. If turn light way up will gt a. population invrsion with all atoms xcitd to uppr lvl, b. no atoms in uppr, c. half th atoms in uppr. If you shin lots and lots of light in (pumping) To incras numbr of photons aftr going through th atoms nd mor in uppr nrgy lvl than in lowr. Nd a Population invrsion (This is th hard part of making lasr, b/c atoms jump down so quickly.) N uppr > N lowr, (mor rproducd than atn) c. Expct 50/50 mix just as asy to xcit (absorb) as to dxcit (stimulatd mission) 5 N uppr < N lowr, fwr out than in. 6 To gt population invrsion, nd at last 3 nrgy lvls involvd. Nd rat into 3 fastr than rat out. What color light could com out on 3 to transition? a. grn, b. blu, c. rd, d. a and b.,. a and c 2 also can kick up by bashing with lctron c. rd. Has to b lowr nrgy than th grn ndd for to 2. Smallr th sparation btwn 3 and, slowr 3 th rat from 3 to. So ths two factors why asir to gt lasrs at longr wavlngths than at shortr wavlngths. pumping procss to produc population invrsion 7 Gtting a population invrsion nd at last on mor nrgy lvl involvd. Trick: us a scond color of light 2 also can kick up by bashing with lctron t t 2 To crat population invrsion btwn G and lvl would nd: a. tim spnt in lvl 2 (t 2 ) bfor spontanously jumping to is long, and tim spnt in lvl (t ) bfor jumping to G is short. b. t =t 2 c. t 2 short, t long G d. dos not mattr pumping procss to ans. c. show on sim produc population invrsion 8 3

4 Photon incidnt on 2 xcitd atoms: What will com out on th right? Think bfor you pick a. photon, b. 2 photons, c. 3 photons, d. 4 photons,. 8 c. 3 oubl at first atom, thn both hit scond but atom only has nough nrgy to giv off on mor photon. atom atom 2 9 so now s how to gt population invrsion, will giv amplification of rd light. If nough atoms in uppr, will las. But much asir if not lt light all scap. Rus. mirror to rflct th light back and forth. Rusing not ncssary. MASER (Microwav ASER)s wr dvlopd first and us spatial sparation to mak invrsion Around forming stars and galactic nucli population invrsion of H2O, CO2 tc. can happn and naturally 20 occurring MASERs and RASERs ar sn Staind glass How do thy gt th colors? Th Lycurgus Cup Lat Roman (4 h cntury) F Mn Au Co 20 fthigh glass at Rio d Janiro Cathdral, Brazil Nasir almulk Mosqu Shiraz, Iran (9 th cntury) Adding impurits adds th color Jabir ibn Hayyan (Grbr) Iran 8 th cntury Islamic fathr of chmistry Adding Mtal oxids controls glass color First systmatic coloring of glass U Gmstons Gmstons Sapphir Al 2 O 3 Clar whn pur F, and Ti impuritis caus th blu color iffrnt impuritis giv diffrnt colors lik in glass Th pur matrial is clar (and boring) 4

5 Ruby Rd Cr atoms in ruby What givs Ruby it s bautiful rd color? Chromium impuritis E m Absorption E h E l E h E l Emission E h E l Making Rubis vn mor bautiful Put thm undr a black light (U light) This proprty fluorscnc is quit common Th Ruby Lasr Maiman, T.H. (960) In fact th trm Fluorscnc is namd for th minral Fluorit (CaF which oftn has this proprty) "Td" Maiman B.S. nginring physics CU Bouldr 949 Th first Lasr Th Ruby Lasr Carfully polishing a ruby and hitting it with bright light rsults in th first lasr Maiman, T.H. (960) Gas lasr lik Hlium Non. Hlium is usd to physically bump into N and xcit a stat that is long livd in th N Just lik non sign with with hlium and non mixtur in it and mirrors on nd. iod lasr sam basic ida, but light producd lik in light mitting diod at PN diod junction. 30 5

6 Many applications of lasrs High nrgy small ara: Cutting: surgry, lasr wlding communication (and wapons) Focus light into xtrmly small spot: (diffraction limit, bcaus in phas!) Cs, s, Collimatd bam Tracking, lvling, Pur color LIAR. 3 What hav w larnd in this sction: ) Lasrs (pump up to population invrsion, put mirrors around it, stimulatd mission will tak car of th rst) 2) For opration, lasrs nd at last 3 nrgy lvls (ground stat and 2 xcitd stats). It hlps if th middl lvl has a long liftim ( mtastabl) 3) How glow in th dark toys work 4) Lots of cool dmonstrations. Lookd at mission spctra. isassmbld a working lasr. 32 Enrgy lvls in solids Enrgy lvls in solids E c E c Conduction band E v E v alnc band Lon atom Lon atom Crystal Th lvls in atoms sprad out whn th atoms arrang in a solid. Ths ar calld bands Th lvls in atoms sprad out whn th atoms arrang in a solid. Ths ar calld bands Why Si is an insulator opd Si is a conductor Conduction band alnc band Conduction band alnc band n typ dopd (P tc.) Conduction band alnc band p typ dopd (Al tc.) In a smiconductor th valnc band is full. Elctrons hat ach othr. To add anothr would tak nrgy W can us out of plac atoms to add or rmov lctrons fring th ons in th matrial to mov and hnc conduct 6

7 LE and Lasr Pushing lctrons LE and Lasr Pushing lctrons Conduction band Conduction band Conduction band Conduction band alnc band alnc band alnc band alnc band n typ dopd (P tc.) p typ dopd (Al tc.) n typ dopd (P tc.) p typ dopd (Al tc.) Push p and n togthr and driv currnt Push p and n togthr and driv currnt LE and Lasr Pushing lctrons Final rviw Physics 00 Conduction band alnc band n typ dopd (P tc.) Conduction band alnc band p typ dopd (Al tc.) Light coms out. That s an LE. LE lasr is only diffrnt bcaus of gomtry A coupl of final xam commnts: Exam will b in this room Exam will b Tusday c 6 th from 4:307 PM This IS NOT includd in th droppd xam. You must tak it. I will b in th hlp room during all of my rgular tims this, nxt and th following wk. Ruls ar gnrally th sam xcpt #qustions and points diffrnt. And you can bring four 3.5 x5 Thr will b a rviw for ~.5 lcturs nxt wk. Thr will b practic problms but prvious xams ar also good to study. Midtrm topics Motion Position, vlocity and acclration finitions, Units Scalars and vctors Graphs of x, v, a vs tim and rlationships btwn graphs Equations of motion and how to us thm: Constant vlocity: x = x 0 vt Constant acclration: v = v 0 at x = x 0 v 0 t ½ at 2 Forcs finition, units, vctor F gravity = mg downwards F friction 0.3 wight in dirction opposing motion F spring = kx in dirction opposing xtnsion/comprssion F nt = ma If a = 0, F nt = 0 Fr body diagrams and finding F nt 7

8 position position Consrvation of nrgy W xt W friction = PE KE Work don by a forc = F d // Lookd at work don by xtrnal forcs and by friction GPE = mgh, KE = ½ mv 2, PPE = P, SPE= ½ kx 2, Thrmal nrgy = constant T Ramps, rollr coastrs, balls. Powr = nrgy/s Brnoulli s quation E tpv = P ½ rv 2 rgh Consrvation of nrgy for an incomprssibl fluid Nuclar Enrgy potntial nrgy wlls of nuclus Alpha dcay Fision & Fusion Radioactivity Midtrm 2 summary Light and E/M Radiation Rviw Topics midtrm 3 Blackbody spctrum Introduction to EM wavs and th EM spctrum Klvin tmpratur scal StfanBoltzman law Shap of BB spctrum at diffrnt tmpraturs why th sun producs visibl light fficintly and incandscnt light bulbs don t. Static lctricity Coulomb s law for forc btwn point chargs oltag and lctric potntial nrgy (EPE) Elctric circuits Ohm s Law Powr dissipation law Battris in sris and Paralll Last sctions of lcturs rviw Sound / Music Wav basics: f, T, l, v (and rlationships) Sound as prssur wavs Amplitud of wavs and associations How to gt diffrnt nots from a violin Harmonics on a violin string WHAT AREA O YOU WANT IN Class Rviw Topics Prioritis: Prioritis: a) position / vlocity a) Consrvation of nrgy / w b) Forc / acclration b) Brnoulli c) Consrvation of nrgy / work c) Nuclar nrgy Lasrs / Quantum Physics Atomic discharg lamps Enrgy lvls of lctron in an atom How light is producd from atom Conditions of a lasr Uniqu charactristics of a lasr Prioritis: a) Light E/M radiation b) Blackbody spctra c) Static lct/ oltag d) circuits Prioritis: a) Mor of th abov b) Sound c) lasrs B B C C E A Tim E A Tim What is th prson s vlocity at A a) Positiv b) Ngativ c) Zro d) Can t b dtrmind What is th prson s vlocity at A a) Positiv b) Ngativ c) Zro d) Can t b dtrmind locity is th slop of a position vs tim graph 8

9 position position position position position position B B C C E A Tim A Tim E Nam all points whr th prson is stationary Nam all points whr th prson is stationary a) E, B and b) E and c) All points d) E, C and ) B only a) E, B and b) E and c) All points d) E, C and ) B only prson is stationary whn vlocity = 0. locity is th slop of a position vs tim graph. prson is stationary whn th graph has zro slop (horizontal), vn is only instantanously B B C C E A Tim E A Tim Nam all th points whr th prson is acclrating a) A, B and C b) B only c) All points d) A and C ) A and B Nam all th points whr th prson is acclrating a) A, B and C b) B only c) All points d) A and C ) A and B Whn th prson is acclrating his vlocity is changing locity is th slop of a position vs tim graph So whn h is acclrating, th slop of this graph is changing (w could argu about E) B B E F A C G Tim C F G A Tim E What is th prson s avrag vlocity btwn points F and G? What is th prson s avrag vlocity btwn points F and G? a) Somthing gratr than zro (positiv) b) Somthing lss than zro (Ngativ) c) Zro d) Can t dtrmin from this graph a) Somthing gratr than zro (positiv) b) Somthing lss than zro (Ngativ) c) Zro d) Can t dtrmin from this graph Avrag vlocity = chang in position/tim takn At F and G th prson is at th SAME position, so th chang in position is 0. Avrag vlocity is zro 9

10 Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. Which diagram shows th nt forc on a loadd box whn it is at rst? A B C E Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. Which diagram shows th nt forc on a loadd box acclrating to th right at 2m/s 2? A B C E E: F nt = ma : F nt = ma Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. Which diagram shows th nt forc on a loadd box whn it is bing pushd to th right at a stady vlocity? Nt forcs and acclration Which diagram shows th nt forc on a loadd box whn it is dclrating to a stop? (Prior to dclrating it was moving to th right at a stady vlocity) A B C E A B C E E: F nt = ma C: locity was to right and now box is dclrating to a stop irction of vlocity CHANGE (v = v f v i ) is to th lft a = v / t also to lft F nt = ma nt forc in sam dirction as acclration Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. What is th magnitud of th horizontal forc that I am applying to th box whn it is sliding across th floor at a constant vlocity? a. 392 N b N c N d. 2.9 N. Non of th abov Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. What is th magnitud of th horizontal forc that I am applying to th box whn it is sliding across th floor at a constant vlocity? a. 392 N b N c N d. 2.9 N. Non of th abov F friction F push F nt = F push F friction = ma = 0 F push = F friction = m mg = (0.3) (40) (9.8) = 7.6 N 0

11 Nt forcs and acclration I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. What is th magnitud of th horizontal forc that I am applying to th box whn it is acclrating across th floor at.5m/s 2? a. 60 N F friction F push b N c N d N F nt = F push F friction. Non of th abov F push F friction = ma F push = F friction ma = (0.3)(40)(9.8) (40)(.5) = 77.6 N Springs I hav a spring which is labld Spring constant = 8 N/m. I assum that this is corrct and us it to masur th mass of an appl. I attach th appl to th bottom of th spring and it strtchs 2.5cm (or 0.25m) from quilibrium. What is th mass of th appl? (assum g = 0m/s 2 ) a) 0. kg b) kg c) 0kg d) 00kg ) Can t b dtrmind. In quilibrium, nt forc on appl = 0. ownwards forc of gravity is xactly qual and opposit to upwards forc from spring. mg = kx m = kx /g = (8N/m)(0.25m)/(0m/s 2 ) = 0. kg Rlaxd Spring: Zro xtnsion Strtchd spring kx mg x Now I hang th sam appl on a diffrnt spring and it strtchs much lss than 2.5cm. What is th spring constant of this spring? a) Lss than 8N/m b) 8N/m c) Mor than 8N/m d) Can t dtrmin from information givn Now I hang th sam appl on a diffrnt spring and it strtchs much lss than 2.5cm. What is th spring constant of this spring? a) Lss than 8N/m b) 8N/m c) Mor than 8N/m d) Can t dtrmin from information givn Lss xtnsion for sam forc stiffr spring highr valu of k. mg = kx in quilibrium whn nt forc = 0. k = mg/x Smallr x biggr k Which spring xrtd th biggr upwards forc on th appl? a) Th wak spring which had a larg xtnsion b) Th stiffr spring (smallr xtnsion) c) Thy xrtd th sam upwards forc d) Can t tll from this information Which spring xrtd th biggr upwards forc on th appl? a) Th wak spring which had a larg xtnsion b) Th stiffr spring (smallr xtnsion) c) Thy xrtd th sam upwards forc d) Can t tll from this information In BOTH cass, in quilibrium, th nt forc = 0 mg = kx mg is th wight of th appl and th sam in both cass Th upwards forc th th spring (kx) is th sam in both cass

12 I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. Whn th box is travlling at a constant vlocity of 3m/s, what is its KE? a. 360 J b. 80 J c. 60 J d. 20 J. Non of th abov Enrgy & Work Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. Whn th box is travlling at a constant vlocity of 3m/s, what is its KE? KE = /2 mv a. 360 J 2 b. 80 J c. 60 J d. 20 J. Non of th abov I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. If I suddnly lt go and stop pushing th box whn it is travlling at 3m/s across th floor, how far dos th box travl bfor it coms to a stop? a. 0m b. 0.5 m c. m d..5m. 2m Enrgy & Work Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. Th warhous floor is mad of concrt and thr is a cofficint of sliding friction of 0.3 btwn th boxs and th floor. If I suddnly lt go and stop pushing th box whn it is travlling at 3m/s across th floor, how far dos th box travl bfor it coms to a stop? Wxt W friction = PE KE a. 0m b. 0.5 m c. m d..5m. 2m F friction d = KE f KE I (0.3mg)(d) = 0 ½ mv 2 (0.3g)(d) = ½ v 2 d = ½ v 2 /(0.3g) = (0.5*9) / (0.3*9.8) =.5m Work don by friction = KE lost Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. How much work do I do pushing th cart at a slow stady spd from th bottom of th ramp to th top? a. 392 N b. 392 J c. 568 J d. 40 J. 39 N Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m How much work do I do pushing th cart plus box at a slow stady spd from th bottom of th ramp to th top? W xt W friction = PE KE a. 392 N b. 392 J c. 568 J d. 40 J. 39 N Work don = GPE gaind by box = mgh = (40) (9.8) (4) = 568 J 2

13 I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. What forc do I hav to apply (paralll to th surfac of th ramp) to push th cart up th ramp? a. 392 N b. 96 N c. 568 N d. 0 N. Non of th abov Enrgy & Work 4m Work don = Forc distanc travlld paralll to forc 568 J = F push 8m I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. What forc do I hav to apply (paralll to th surfac of th ramp) to push th cart up th ramp? a. 392 N b. 96 N c. 568 N d. 0 N. Non of th abov Enrgy & Work 4m Work don = Forc distanc travlld paralll to forc 568 J = F push 8m Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. Suppos that I can only push with a maximum forc of 00 N. What is th minimum lngth of ramp that I nd to us? a. 5. 7m b. 8m c. 9.3 m d m. Non of th abov 4m Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. Suppos that I can only push with a maximum forc of 00 N. What is th minimum lngth of ramp that I nd to us? a. 5. 7m b. 8m c. 9.3 m d m. Non of th abov 4m Work don = Forc distanc travlld paralll to forc 568 J = 00N d Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. At th top of th ramp I lt th cart go. What is its spd whn it rachs th bottom of th ramp? a. 568 J b m/s c. 8.9 m/s d. 6.3 m/s. Non of th abov W xt W friction = PE KE GPE lost = KE gaind mgh = ½ mv 2 2gh = v 2 v = sqrt(2gh) = sqrt(2*9.8*4) = 8.9 m/s Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. This tim I tak th box off th cart and lt it slid down th ramp. Thr is a frictional forc btwn th box and ramp of 00N. Assum that w ar using th 8m ramp. What is th KE of th box at th bottom of th ramp? W xt W friction = PE KE a. 568 J b. 784 J (F friction )(d ramp ) = mgh KE = mg (h c. 496 J f h i ) KE f KE i = mg (0 4) KE d. 768 J f 0 = 4mg KE. Non of th abov f KE f = 4mg (F friction )(d ramp ) = 4(40)(9.8) (00)(8) = 768 J 3

14 Enrgy & Work I m working in a warhous packing goods into boxs and moving thm to th loading bay. Onc loadd, ach box has a mass of 40kg. On th far sid of th warhous I load a box onto a light frictionlss cart. I push th cart plus box up a loading ramp. Th hight of th ramp is 4m abov th floor. Th lngth of th ramp is 8m. This tim I tak th box off th cart and lt it slid down th ramp. Thr is a frictional forc btwn th box and ramp of 00N. Assum that w ar using th 8m ramp. What is th spd of th box at th bottom of th ramp? a. 6.2 m/s b m/s c. 2.7 m/s d. 4.8 m/s. 0m/s KE = ½ mv 2 v = sqrt(2 KE /m) = sqrt (2*768/40) (KE at bottom ramp from prvious Q) = 6.2 m/s Brnoulli s quation E tpv = P ½ rv 2 rgh PPE KE GPE Consrvation of nrgy for a unit volum of an incomprssibl liquid (.g. watr) Assums: No pumps, no friction in systm of intrst Mthod: Pick 2 points in systm On whr w know vrything On whr w want to calculat a quantity Writ an xprssion for E tpv at both points Equat xprssions E tpv at both points Solv quation to find unknown quantity My hous is on th sid of a hill. Th watr at th fauct has a mains prssur of 30 psi (200,000 Pa) abov atmosphric. (St AP as th zro of prssur). I attach a hos to th fauct and lt th hos run down th hill. Th fauct is opn but th valv at th outlt of th hos is closd. If th outlt of th hos is 6m vrtically blow th fauct, what is th prssur (abov atmosphric) bhind th outlt valv? a. 200,000 Pa b. 4,200 Pa c. 258,000 Pa d. 324, 400 Pa. Non of th abov E tpv = P ½ rv 2 rgh At fauct: P = 200,000Pa, v = 0, h = 0 E tpv = 200,000 Pa At valv: P = P valv, v=0, h = 6m E tpv = P valv rg(6) 200,000 = P valv 000*9.8*6 P valv = 200, *9.8*6 = 258,800 Pa My hous is on th sid of a hill. Th watr at th fauct has a mains prssur of 30 psi (200,000 Pa) abov atmosphric. I attach a hos to th fauct and lt th hos run down th hill. Th fauct is opn but th valv at th outlt of th hos is closd. Th outlt valv is still closd and 6m blow th hous. I pok a small hol in th hos nar th outlt valv. What is th vlocity of th watr laving this hol? E tpv = P ½ rv 2 rgh a m/s b m/s c. 5.4 m/s d. 9.0 m/s. 4.6 m/s At fauct: P = 200,000Pa, v = 0, h = 0 E tpv = 200,000 Pa Outsid hol: P = 0, v=?, h = 6m E tpv = ½ rv 2 rg(6) 200,000 = ½ rv 2 000*9.8*6 ½ rv 2 = 200, *9.8*6 = 258,800 v = sqrt(2*258800/000) = 22.8 m/s My hous is on th sid of a hill. Th watr at th fauct has a mains prssur of 30 psi (200,000 Pa) abov atmosphric. I attach a hos to th fauct. If I run th hos up th hill instad and opn th outlt valv, what is th maximum vrtical hight of th hos outlt abov th fauct at which any watr will com out? a m b m c. 4.7 m d. 9.8 m. 0 m E tpv = P ½ rv 2 rgh My hous is on th sid of a hill. Th watr at th fauct has a mains prssur of 30 psi (200,000 Pa) abov atmosphric. I attach a hos to th fauct. If I run th hos up th hill instad and opn th outlt valv, what is th maximum vrtical hight of th hos outlt abov th fauct at which any watr will com out? E tpv = P ½ rv 2 rgh a m b m c. 4.7 m d. 9.8 m. 0 m At fauct: P = 200,000Pa, v = 0, h = 0 E tpv = 200,000 Pa At outlt : P = 0, v=0, h = h max E tpv = rgh max 200,000 = 000*9.8*h max h max = 20.4 m 4

15 Watr distribution in skyscraprs Th skyscrapr watr problm: Lss prssur on th highr floors, Watr won t mak it to th top floor. What about spd in a pip? E tpv = GPE hr How can you solv this problm? Put vry high prssur pump at bottom (giv watr nough PPE at bottom) Us a sris of pumps up th building Pump watr to a tank on th roof, thn you will always hav prssur on th floors blow. P ½ rv 2 rgh = E total / (E total pr unit volum ) m 8m I m dsigning a fountain for a city park. I want th watr in th fountain to squirt 8m vrtically in th air. What prssur will I nd in th larg pip just bfor th nozzl? (Assum that friction can b ignord) a Pa b. 80 Pa c. 80,000 Pa d Pa. Mor information rquird E tpv = P ½ rv 2 rgh I m dsigning a fountain for a city park. I want th watr in th fountain to squirt 8m vrtically in th air. What prssur will I nd in th larg pip just bfor a Pa th nozzl? (Assum that friction E tpv can = b P ignord) ½ rv 2 rgh b. 80 Pa Top of watr jt: v = 0, P = c. 80,000 Pa In pip: v = 0, h = 0, P =? d Pa. Mor information rquird E tpv is sam in both locatio P pip = rgh jt = 000*0*8 = 80,000 Pa Mor Brnoulli!! I hav a tank of watr that is 4m dp. What is th prssur of watr at th bottom on th tank? (St AP as th zro of prssur, r = 000kg/m 3 for watr) Mor Brnoulli!! I hav a tank of watr that is 4m dp. What is th prssur of watr at th bottom on th tank? (St AP as th zro of prssur) I m going to st th zro of hight at th surfac of th w At surfac: P = 0, v = 0, h = 0 E tpv = 0 At bottom of tank: P =?, v = 0, h = 4m E tpv = P rg(4) 0 = P 4rg P = 4*000*9.8 = Pa 5

16 Mor Brnoulli!! I hav a tank of watr that is 4m dp. (St AP as th zro of prssur) I drill a small hol in th sid of th tank 2m blow th sur What is th vlocity of watr laving th hol? Mor Brnoulli!! I hav a tank of watr that is 4m dp. (St AP as th zro of prssur) I drill a small hol in th sid of th tank 2m blow th sur What is th vlocity of watr laving th hol? I m going to st th zro of hight at th surfac of th w At surfac: P = 0, v = 0, h = 0 E tpv = 0 Just outsid hol: P = 0, v =?, h = 2m E tpv = ½ rv 2 rg(2) Rarrang 0 = ½ to rv solv 2 2rg for v: v = 6.3 m/s Mor Brnoulli!! I hav a watr pump that producs watr at prssur P pump at th outlt. If I want to pump watr to a hight of 8m abov th pump, what is th minimum prssur that th pump nds to produc? Mor Brnoulli!! I hav a watr pump that producs watr at prssur P pump at th outlt. If I want to pump watr to a hight of 8m abov th pump, what is th minimum prssur that th pump nds to produc? At output of pump: P = P pump, v = 0, h=0 E tpv = P pump (v is qual to zro bcaus whn th pump has this minimum prssur only a tiny bit of watr is JUST flowing out of th top nd of th pip. Th flow rat in th pip is ngligibl). At top of pip: P = 0, v = 0, h = 8m. E tpv = rg(8) Ppump = 000*9.8*8 = Pa Mor Brnoulli!! I hav a watr pump that producs watr at prssur P pump at th outlt. If I want th watr to lav a small nozzl at th nd of th pip (8m abov th pump) at a vlocity of 2m/s, what prssur must th pump produc? Mor Brnoulli!! I hav a watr pump that producs watr at prssur P pump at th outlt. If I want th watr to lav a small nozzl at th nd of th pip (8m abov th pump) at a vlocity of 2m/s, what prssur must th pump produc? At pump: P =?, v = 0 (amount of watr laving small nozzl is ngligibl), h = 0. E tpv = P pump Just outsid nozzl: P = 0, v = 2m/s, h = 8m Etpv = ½ r (2 2 ) 8rg P pump = ½ r (2 2 ) 8rg = ½ * 000* 4 8*000*9.8 = Pa 6

17 8m 8m What is th spd of th watr immdiatly aftr th nozzl? a. ~5.3 m/s b. ~2.5 m/s c. ~8.7 m/s d. ~ 4.3 m.s. Watr dos not com out What is th spd of th watr immdiatly aftr th nozzl? a. ~5.3 m/s b. ~2.5 m/s c. ~8.7 m/s d. ~ 4.3 m.s. Watr dos not com out E tpv = P ½ rv 2 rgh Insid pip: v = 0, P = 80,000 Pa, h = 0 Aftr nozzl: v =?, h = 0, P = 0 E tpv is sam in both locations P pip = ½ r v 2 v = sqrt (2P pip /r) = sqrt ( 2* 80,000 /,000 ) = 2.6 m/s If th fountain squirts 2m 3 of watr in th air vry scond, what is th powr producd by th pump that is supplying th prssurizd watr to th nozzl? a W b. 2 W c. 000 W d. 237,806 W. 56,800 W 8m If th fountain squirts 2m 3 of watr in th air vry scond, what is th powr producd by th pump that is supplying th prssurizd watr to th nozzl? a W b. 2 W c. 000 W d. 237,806 W. 56,800 W 8m Powr = nrgy supplid to watr / sc = GPE gaind by watr /sc = mgh/s = (m/s) g h Mass of watr squirtd pr scond = 2m 3 000kg/m 3 Powr = = 56,800 W = 2000kg Rcip how to mak an atom: Ingrdints: taspoon protons taspoon nutrons cup of lctrons Proton (positiv charg) Nutron (no charg) Elctron (ngativ charg) Each lmnt has diffrnt numbr of protons. Atom ingrdints: Proton (positiv charg) charg =.6 x 0 9 Coulombs mass =.66 x 0 27 kg. Nutron (no charg) no charg mass =.66 x 0 27 kg. Elctron (ngativ charg) charg =.6 x 0 9 Coulombs mass = 9.0 x 0 3 kg.. Mix protons and nutrons thoroughly. 2. Bak at 00 million dgrs until sticks togthr to form solid dns nuclus (about s). 3. Frost with lightly with fluffy layr of ngativ lctrons. 4. Chill bfor srving! atom siz: Radius of nuclus is 0,000 tims smallr than nucluslctron distanc 0 hydrogn p dutrium p, n hlium 2 p, 2 n Uranium p, 46 n 7

18 What if thrw proton so starts out going towards nitrogn nuclus with a lot of spd (lots of kintic nrgy)? Starts with lots of kintic nrgy Rplling forc from nuclus slows down proton Proton s kintic nrgy convrtd into lctrostatic potntial nrgy, as it gts closr to nuclus r, sparation distanc Potntial nrgy curvsrprsnt nrgy to bring particls togthr. Potntial nrgy Potntial nrgy curv for proton approaching nuclus lctrostatic rpulsion attractiv nuclar Enrgy scal gigantic compard to chmical nrgy. Why? Simpl coulomb s law. F= k (charg of #)(charg of #2) sparation distanc, r r 2 Chmistry forcs btwn lctrons and protons on distanc scal of atomic siz (> 0 0 m). Nuclar forcs forcs btwn Kintic nrgy protons on distanc scal combinationral nuclus 000,000 tims smallr. 0,000 tims closr mans forcs 00,000,000 tims biggr bcaus of /r Gravity nrgy analogy. sparation 2. Lots mor potntial nrgy stord!!! distanc, r 03 sparation distanc, r 04 if at cntr, want to roll down hill/fly apart lots of lctrostatic potntial n Atomic nucli Gts dpr until iron (26 P, 30 N) lss dp if biggr. tunnling difficulty = width x dpth of tunnl hlium Rally stabl: Hav to add a whol bunch of nrgy to brak up! bryllium hardr to push togthr, but biggr drop whn do. Rally big nuclus, >00 P, >00 N, lik Uranium or plutonium 05 E nuclus hard taks long tim, billions of yars! 2 mdium 3 asy!, happns in millionths of a scond! How much nrgy rlasd? a. most, 2 scond, 3 last nrgy is diffrnc from b. 2 most,, 3 last bottom of cratr to outsid. c. 3 most, 2, last 3 is most, 2 scond, is las d. 3 most,, 2 last 06 Anothr Sim (bcaus this is hard to do at hom) N N Nutron Inducd fission ky to atomic bo two smallr nucli fw xtra fr nutrons LOTS OF ENERGY!! parnt nuclus (somtims othr bad stuff) daughtr nucli 07 Uranium p, 43 n Nutron absorbd Excits U235 nuclus up abov potntial barrir Splits into two smallr nucli which zoom apart du to lctrostatic rpulsion! simulation 08 8

19 BACK TO CHAIN REACTION Fission Nuclar xplosion: atomic bomb 2nd gnration Many Gnrations: 3 rd, 4 th, 5 th, U235 and U238 atoms ar placd into a containr, which ar likly to rsult in a chain raction (rsulting in xplosion) whn a fr nutron triggrs fission of on of th U235: st gnration ry spcial stuff: Uranium 235 or plutonium Why Ur 235 not 238? U 238 has 3 xtra nutrons hlp hold it togthr. pr cratr in potntial nrgy. urp! Eats xtra nutrons! vs # #2 #3 #4 a. #2 only b. #, #2, and #5 c. #2 and #4 d. #2, #3, and #4. #2, #4, and #5. Lots of uranium in th ground why not just blow up? Corrct answr is c. (#2 and #4) Analysis: # is too spars.. most nutrons will lav box bfor hitting anothr U235. #2 is good.. Pur U235, dnsly packd, larg packag #3 has too many U238 s mor U238 s than 235 s. Fr nutrons mor likly to b absorbd by 238 s than to hit and fission anothr 235. #4 is OK Mor U235 s than 238 s, still dnsly packd, larg packag #5 is too small of packag nutrons likly to scap packag bfor hitting anothr U #5 Fusion bomb or hydrogn bomb Basic procss lik in sun. Stick small nucli togthr. Fusion bomb or hydrogn bomb Basic procss lik in sun. Stick small nucli togthr. activation nrgy of 00 million dgrs utrium on utrium utrium on Tritium Stick hydrogn isotops togthr to mak hlium. = push togthr nrgy rquird hlium nrgy rlasd if push ovr th hump Which will rlas mor nrgy during fusion? a. utrium combining with dutrium b. utrium combining with tritium Simpl if can push hard nough just us sun or fission bomb. Mor nrgy pr atom than fission. Can us LOTS of hydrogn. End up with GIGANTIC bombs 000 tims biggr than first fission bombs Answr is b. Incoming dutrium particl has comparativly mor potntial nrgy! 2 Elctromagntic wavs can hav any wavlngth Scintific notation is usful! 4 9

20 Th lctromagntic spctrum All EM radiation is a priodic modulation of th lctric fild All EM radiation travls at spd c = m/s c = l f isibl light is just on part of th lctromagntic spctrum with spcific rang of l (and f) Purpl light has a wavlngth of 400 nm. What is its frqu ( nm = 0 9 m) a Hz b Hz c Hz d. 333 Hz Hz f = c/l Purpl light has a wavlngth of 400 nm. What is its frqu ( nm = 0 9 m) a Hz b Hz c Hz d. 333 Hz Hz f = c/l Us standard units! What is Elctric fild? Light is priodic modulation of lctric fild Strong fild Elctric fild distanc l Elctric fild xists vrywhr in spac scribs th forc on a chargd particl at ach point in spac ctor has a magnitud and dirction Units: Nwtons/Coulomb Contains nrgy Cratd by chargs (and cratd in othr ways) Analogy: Lik gravitational fild dscribs th forc on a particl with ma Balloon dmo Th spctrum of whit light? A spctromtr masurs th spctrum (rang of wavlngths or frquncis) in light incoming whit light bam light mad up of many colors dtctd powr isibl IR U Whit light find as th spctrum of EM radiation mittd by th sun All visibl l prsnt with roughly qual intnsity (wavlngth or color) 20

21 Intnsity Blackbody spctrum and tmpratur Evrything that has a nonzro tmpratur mits a spctrum of EM radiation Th spctrum of EM radiation coming from a black objct is calld th blackbody spctrum. Black objct: Absorbs and mits all EM l asily Go to th blackbody spctrum simulation BB spctrum dtrmind by tmpratur only. Th tmpratur of th objct affcts both Th total powr of EM radiation mittd by th objct Th rang of wavlngths mittd (th spctrum) Tmpratur and total mittd powr (brightnss) StfanBoltzman law givs total lctromagntic powr (nrgy/scond) out of a hot objct at tmpratur T Powr = X X T 4 X a StfanBoltzmann constant, = 5.67 x 0 8 J/(s m 2 K 4 ) = missivity ; how wll th light gts out Ara of surfac Tmpratur of objct (in Klvin!) What is 2400 dgrs C in dgrs K? a. 227 K b K c. 8.8 K d K. Non of th abov What is 2400 dgrs C in dgrs K? a. 227 K Tmp (K) = Tmp (C) 273 b K c. 8.8 K d K. Non of th abov Th Klvin Tmpratur Scal: Links T to motion Idntify spctrum of radiation givn off by prson (37 C) and a block of barly frozn ic (0 C). 3 Room tmp 65F 8C 29K 2 dgr Klvin = dgr Clsius = 9/5 dgr Fahrnhit 0 dgr Clsius = 273 K All motion stops Wavlngth a. 2 is prson, is ic, b. is prson, 2 is ic, c. Non, bcaus ic givs off no thrmal radiation, d. is both ic and prson bcaus thy ar almost idntical. 3 is prson, on of th othrs is ic. 2

22 Powr Idntify spctrum of radiation givn off by prson (37 C) and a block of barly frozn ic (0 C). 3 2 Th plot abov shows th BB spctrum of an objct at th tmpratur of a typical lightbulb. Why is th lightbulb <20% fficint? b. is prson, 2 is ic, Wavlngth Anything with a non zro tmpratur mits EM radiation. Th ic and th prson ar both so cold that th radiation is not visibl. Th prson is a bit hottr than ic, so givs off mor radiation ( T 4 ), and has pak powr at a slightly shortr l ( /T). a. Not all of th lctrical powr going into th lightbulb gts convrtd into EM powr b. Lss than 20% of th lctrical powr in gts convrtd to IR powr c. All th lctrical powr going in gts convrtd to EM powr but lss than 20% is at visibl wavlngths d. isibl light is at shortr wavlngths and thrfor dosn t contain EM nrgy. Th surfac ara of th lightbulb filamnt is too small for an fficint convrsion of lctrical powr to visibl EM powr. Th plot abov shows th BB spctrum of an objct at th tmpratur of a typical lightbulb. Why is th lightbulb <20% fficint? a. Not all of th lctrical powr going into th lightbulb gts convrtd into EM powr b. Lss than 20% of th lctrical powr in gts convrtd to IR powr c. All th lctrical powr going in gts convrtd to EM powr but lss than 20% is at visibl wavlngths d. isibl light is at shortr wavlngths and thrfor dosn t contain EM nrgy. Th surfac ara of th lightbulb filamnt is too small for an fficint convrsion of lctrical powr to visibl EM powr. What typ of EM radiation is mittd from th surfac of th arth? a. Primarily U b. Primarily visibl c. Primarily IR d. IR and visibl. All parts of th EM spctrum at roughly qual intnsitis Sourc of lctricity: Elctric chargs l max ~ / T Rmmbr to us T in K Evrything (arth, you, th tabl tc) mad of tiny particls calld atoms Atoms ar mad up of 3 vn tinir particls: Elctrons, nutrons and protons Th atom What typ of EM radiation is mittd from th surfac of th arth? a. Primarily U b. Primarily visibl c. Primarily IR d. IR and visibl. All parts of th EM spctrum at roughly qual intnsitis Particl Charg Mass Elctron kg Proton kg Nutron kg = Coulombs Coulomb (C) is th unit of charg Look at BB pht at tmpratur of arth Static lctricity: What happns whn chargs ar stationary Elctricity (and lctric currnts): What happns whn chargs (usually lctrons) ar moving 22

23 F lik chargs rpl opposit chargs attract F F Considr 2 point chargs, A and B. What forc dos charg A fl? Obsrvd bhavior: Forc dpnds on q A and q B : Mor charg, mor forc Forc dpnds on distanc btwn thm (r) : lss distanc, mor forc Coulomb s Law: F onafromb = k q Aq B r 2 Putting this togthr: Elctric Forc q A F r q B scribs th forc btwn 2 point chargs k is Coulomb constant = 8.99 x 0 9 N m 2 /C 2 q A and q B ar amount of charg in coulombs (C ) r is sparation in m Coulomb = 6 x 0 8 lctron chargs! Forc Elctric Hocky Simulation! of B on A = kq A q B Plac charg (B) 2cm from chargd puck (A). S chargd puck fly away r 2 Now plac charg (B) cm away from chargd puck (A). Compard to prvious situation forc on A will b: a. half as larg, b. sam siz, c. twic as larg, d. four tims largr. somthing ls. d. four tims largr sinc forc dpnds on /r 2 distanc smallr, forc largr Plac charg (B) cm away from chargd puck (A) as in prvious Q. Add a scond charg to B, right on top of first. Compard to prvious qustion, forc on A is: a. ½, b. sam, c. x 2, d. x 4,. somthing ls. c. x 2 bcaus forc on A gos lik (charg of A x charg of B), in this Q w doubld th charg on B Bring unchargd mtalizd mylar balloon up to an d Graaf Bring unchargd mtalizd mylar balloon up to andrgraff. Prdict what will happn:. Bfor it touchs 2. Aftr it touchs. Bfor touching a. Not affctd by dg b. Attractd to it c. Rplld Prdict what will happn:. Bfor it touchs 2. Aftr it touchs. Bfor touching a. Not affctd by dg b. Attractd to it c. Rplld 2. Aftr touching a. Not affctd by dg b. Attractd to it c. Rplld Chargs in nutral ball ar polarizd by charg on dg chargs mov closr to dg, chargs mov away Forc btwn chargs = kq A q B r 2 chargs on ball ar closr to dg, so forc of attraction is strongst Bring unchargd mtalizd mylar balloon up to andrgraff. Prdict what will happn:. Bfor it touchs 2. Aftr it touchs 2. Aftr touching a. Not affctd by dg b. Attractd to it c. Rplld oltag has to do with conditions of systm Amount of charg istanc from that charg Lik th lctric forc (rlatd but diffrnt) Whn balloon touchs, chargs ar pushd onto it by th othr chargs on th dg Now balloon is ngativly chargd lik dg Lik chargs rpl 23

24 oltag is lik th hight of mountain Think Topographical maps oltag tlls you what a charg will do is lik top of hill Is lik vally Whr is 0? What will a q do at 0: a) B attractd to highr voltag b) B attractd to lowr voltag c) Not b impactd b) Just lik a ball rolls down hill oltag is lik th hight of mountain oltag Charg, q Elctrical Potntial Enrgy EPE = q Hight (and gravity) Mass, m Gravitational potntial Enrgy GPE = m g h Two mtal plats connctd by a battry. Battry maintains a voltag diffrnc of btwn th plats A Plat A is groundd (st to zro ) What is th voltag of plat B? a) 0 b) c) d) Can t dtrmin from information givn q B Two mtal plats connctd by a battry. Battry maintains a voltag diffrnc of btwn th plats A Plat A is groundd (st to zro ) What is th voltag of plat B? a) 0 b) c) d) Can t dtrmin from information givn q B Not: Conductors (bits of mtal, wirs tc) ar a constant voltag all ov A q What will happn to th charg q if w lt go of it (ignor gravity)? a) Nothing b) It will fly ovr to plat A c) Sparks will fly d) Somthing ls B 24

25 A What will happn to th charg q if w lt go of it (ignor gravity)? a) Nothing b) It will fly ovr to plat A c) Sparks will fly d) Somthing ls q q has a charg. It will b rplld by chargs on plats B and attractd to chargs on plat A B Elctrostatic potntial nrgy and voltag Nw forc: Elctrostatic forc btwn chargs Nw PE: Elctric Potntial Enrgy (EPE) Forcs and PE go in pairs Rmmbr gravitational forc: o work against gravitational forc (mg) to rais an objct s GPE (mgh) Similarly, do work against lctric forc to rais an objct s EPE EPE = q, whr q = charg of objct and is voltag diffrnc Lik GPE with q m and h oltag () tlls you EPE of any charg at that location in spac Tlls you work rquird to bring a unit charg from = 0 to that location trmind by surrounding chargs. Closr you ar to charg th mor th voltag A groundd objct is always at = 0 Usually most intrstd in : voltag diffrnc btwn 2 locations Bst undrstood by doing practic qustions! Elctrostatics Summary Positiv and ngativ charg: Lik chargs rpl, opposits attract Coulombs law for point chargs: F = k q A q B r 2 Forc acts along lin joining particls oltag: trmins EPE of charg at that location in spac EPE: = q Clos to chargs voltag is mor and vic vrsa Groundd objct is at 0 (Also calld Elctric Potntial) Nw form of potntial nrgy Lots of analogis to GPE ( h, q m) Flashlights, circuits, battris, and powr = Givn battris, light bulbs, and wir, how can w dsign a light bulb circuit a) that will burn brightst, b) that will last longr, c) that will b dim, d) that will turn on and off. How can you control and prdict currnt and powr in light bulbs? All this basic circuit stuff applis to hom wiring, hom lctronics, hatrs tc. Thursday lctur hlp sav livs physics of dangrs of lctrocution. Builds on lctrostatics (lik chargs rpl, opposit chargs attract, voltag, EPE) but now lctrons ar moving. nd to start thinking lik an lctron! Elctric circuits: som important idas light bulb circuit: Wiring. Currnt is consrvd (lctrons don t appar/disappar) 2. Chang in ovr circuit = of battry, or nrgy sourc 3. = I R (Ohm s law) usful for whol circuit (R total, total, giv I total) or individual componnt (.g. R bulb, bulb giv I bulb ),.on t mix and match. 4. P = I = I (IR) = I 2 R powr dissipatd by rsistanc R = (/R) = 2 /R 5. Rsistors in sris: Rsistancs add: R tot = R R 2 Currnt through all rsistors is th sam 6. Rsistors in paralll: oltag drop across paralll lgs of circuit is sam What will happn whn hook up battry to flashlight bulb with 2 wirs as shown? a. light up b. barly light up c. not light up 49 25

26 light bulb circuit: Wiring What will happn whn hook up battry to flashlight bulb with 2 wirs as shown? a. light up b. barly light up c. not light up Complt circuit: lctrons ar abl to flow all th way around and back into battry, producing a stady currnt (I) If thr is a brak in th circuit thy will pil up at th brak and push back(coulomb's law) prvnting any mor from flowing (I=0) Elctrons must hav a complt conducting circuit to flow oltag diffrnc btwn nds of battry.5 olts, 9 olts, 2 olts EPE = q light bulb circuit: Battry What happns to EPE of lctrons as thy flow around th loop? a) EPE is always th sam. b) EPE incrass through battry; EPE dcrass through circuit. c) EPE dcrass through battry EPE incrass through circuit. Circuit lmnts summary Wirs: Mak complt circuit ncssary for stady flow of lctrons Usually hav ngligibl (zro) rsistanc Battry: Has positiv chargs pild up at on trminal and ngativ chargs at th othr Provids voltag diffrnc around circuit Provids ach lctron with q = of EPE to spnd in circuit Provids push for lctrons around circuit (biggr, biggr push) Enrgy changs in circuit Battry: Chmical to EPE of lctrons In circuit wirs: EPE to KE of lctrons In bulb: KE of lctrons to thrmal nrgy (random KE) of filamnt atoms Filamnt surfac: Thrmal nrgy of filamnt atoms to radiatd nrgy (light) In Battry: hat and light Bulb: Filamnt is a high rsistanc wir in which lctrons los thir nrgy as hat. Start: Lots of nrgy This is a task for Elctron man! Circuits Think lik an lctron 4. End: Exhaustd! All nrgy usd up gtting through cours. Usful tip: In qustions, assum conncting wirs hav zro R 2. Wirs: Not much to bump into Low R. Los just a littl bit of nrgy and los zro nrgy in thm, unlss told othrwis 3. Filamnt Lots to bump into Highr R (Lik trudging through mudpit) Los lots of nrgy. Sam currnt through conncting wirs and filamnt. R filamnt >> R wirs Almost all nrgy lost in filamnt. Rsistanc (R) of a circuit lmnt is masur of how hard it is for lctrons to pass through. Units: Ohms (W) Currnt (I) : charg pr scond flowing past a point in th circuit (= # lctrons pr scond charg on lctron) Units : Amps ( A = C/s) oltag (diffrnc) () a) Across battry: Masur of EPE givn to ach as it passs through battry. EPE givn =. Rlatd to pushing forc on lctrons in circuit b) Across a rsistor (wir, filamnt tc): Masur of EPE lost by ach as it passs through. EPE lost =. Unlss told othrwis voltag diffrnc across conncting wir = 0. Units: olts () Not: All quantitis Ohm s Law: = IR spcific to on Rsistanc of componnt componnt. Currnt through componnt on t mix and match! oltag droppd across componnt 26

27 R Battris in sris (nos to tail) R Battris in sris (nos to tail) cas Compar th brightnss of th bulbs in cas and cas 2. All bulbs and battris ar idntical cas c. cas 2 is mor than twic as bright Elctrical powr into bulb = EM powr out. R cas 2 a. Cas 2 twic as bright as cas b. Cas 2 sam brightnss but runs twic as long c. Cas 2 mor than twic as bright as cas d. Cas 2 producs no light R cas 2 Mthod : P in = bulb2 /R Cas: P in = 2 /R Cas 2: P in = (2 ) 2 /R = 4 2 /R (In addition, sinc filamnt is hottr in cas 2 a gratr fraction of th radiatd EM powr is in visibl rang.) Mthod 2: P in = I bulb x bulb Both I and doubl in cas 2 P in = 4 R Battris in paralll R Battris in paralll R cas cas 2 Compar th brightnss of th bulbs in cas and cas 2. All bulbs and battris ar idntical a. 2 twic as bright as b. 2 sam brightnss c. 2 mor than twic as bright as d. 2 producs no light R cas cas 2 Compar th brightnss of th bulbs in cas and cas 2. All bulbs and battris ar idntical a. 2 twic as bright as b. 2 sam brightnss c. 2 mor than twic as bright as d. 2 producs no light Why? Think lik an lctron. In ithr battry in cas two, th lctron has th sam Elctric potntial nrgy = EPE = q Not: an lctron dosn t gt to go through What is both th diffrnc battris, thn? it s on or th othr R R cas Battris in paralll What is th diffrnc thn? Each battry can produc a givn amount of Currnt (lctrons/ scond) for a crtain amount of tim R R Summary: Sris: mor nrgy for ach lctron! (brightr) how you mak a 9 out of Clls, or AAAs cas 2 Not: rating on battris is in Amp Hours! (what Zoinks.. is an With amphour?) two battris I hav a gratr rsrvoir of lctrons to draw from. Cas 2: last twic as a long! Paralll: longr lasting diffrnc btwn AAAs and clls 27

28 Air prssur How much powr from bulb. How much powr in bulb (or circuit): = 2 (givn) R = 5 Ohms I =??? How much in visibl? I = / R= 2 / 5 Ohms =0.8 Amps P=? Sound so far Sound is a prssur or dnsity wav carrid by air molcul Sound wav is a vry small fluctuation on th background p Musical not: Rgularly spacd sris of high and low prs olum of th not is dtrmind by th AMPLITUE of th Pitch of th not is dtrmind by th FREQUENCY of th p atm. Amplitud P = I = 0.8 A x 2 = 9.6 W 0%20% ~ Watt!! Tim (s) Thinking about wavs: Frquncy (f) # of oscillations/sc (Hz = /s) olum and amplitud Microphon Wavlngth (l) istanc of on complt cycl (m) (.g. distanc btwn prssur maximums) Priod (T) Tim for on complt oscillation (s) Spd (v) istanc travld pr scond (m/s) P x t Rlationships among ths variabls: v= l f istanc pr scond = distanc pr oscillation # of oscillations pr scond f = /T # oscillations pr scond = /tim for on oscillation v = l /T Qustion: If I incras th volum, what will happn to th signal from th microphon? a. Th paks will go up and th vallys will go down. b. Th paks will gt closr togthr. c. Th whol signal will go up. d. Both a and b.. Nothing will happn O EXPERIMENT. How to chang th pitch (not) of th spakr? To gt a highr pitch sound, w nd to adjust th spakr to: a. vibrat back and forth mor rapidly, taking a smallr amount of tim for ach cycl b. vibrat back and forth at th sam rat as bfor, but th rang of it s back and forth motion is largr. c. rciv mor powr d. vibrat back and forth mor slowly, taking a longr amount of tim for ach cycl. vibrat back and forth at th sam rat as bfor, but th rang of it s back and forth motion is smallr. What if w wantd to chang th pitch of th ton producd by th spakr? To gt a highr pitch sound, w nd to adjust th spakr so that: a. It vibrats back and forth mor rapidly, taking a smallr amount of tim for ach cycl b. It vibrats back and forth at th sam rat as bfor, but th rang of it s back and forth motion is largr. c. It rcivs mor powr d. It vibrats back and forth mor slowly, taking a longr amount of tim for ach cycl. It vibrats back and forth at th sam rat as bfor, but th rang of it s back and forth motion is smallr. In physics/wav languag this is calld adjusting th frquncy (f) 28

29 How do w gt nots of diffrnt pitch from a violi Gt th strings to vibrat at diffrnt frquncis Must control th vibrations or wav motion of th strings Rmmbr, for ANY wav: v = f l f = v / l Frqun cy (pitch) of Spd of wav (on motion To chang th violin pitch (frquncy) string) of a not w can a) Chang v not th spd of wavs on th string chang thicknss or tnsion of th string b) Chang l th wavlngth chang th lngth of th string Wavlngth of string a) Changing pitch by spd of wavs on a string v string ~ F T m L v f λ string a) How do violinists tun thir strings? Adjust th tnsion (F T ) Mass on spring tlls us: Incrasing F T lik incrasing th stiffnss of th Biggr spring forc acclrats and oscillat b) Why dos th G string produc a lowr not than th E G string is thick larg mass pr lngth (m L ) E string is thin small mass pr lngth Mass on spring xpts: Thickr string lik biggr mass (sam spring) Mor mass acclrats and oscillats mor s b) Chang not by Wavlngth of wavs on a string If w could only control th frquncy of a violin string with thicknss and tnsion, th violin would hav 4 nots.. vstring But, f so w can also chang th frquncy by chan λ Wavlngth of wavs on a string If w could only control th frquncy of a violin string with thicknss and tnsion, th violin would hav 4 vstring nots.. f So w can also chang th frquncy by chang λ L Simplst or fundamntal oscillation of a violin string How much of a wavlngth dos this fundamntal motion dmonstrat? a) wavlngth b) 2 wavlngths c) ¼ wavlngth L Simplst or fundamntal oscillation of a violin string How much of a wavlngth dos this fundamntal motion dmonstrat? a) wavlngth b) 2 wavlngths c) ¼ wavlngth Wavlngth of wavs on a string If w could only control th frquncy of a violin string with thicknss and tnsion, th violin would hav 4 vstring nots.. f So w can also chang th frquncy by chang λ L L = ½ l l 2L vstring vstring f λ 2L Fundamntal wavlngth and hnc frquncy dirctly rla Can chang fundamntal frquncy by shortning th strin Fundamntal frquncy of string dtrmins that pitch that v f λ string Fingr v string 2L Longr string Longr wavlngth, lowr frquncy Shortr string Shortr wavlngth Highr frquncy EMO CAPO 29

30 Harmonics String is tid down at ach nd. It oscillats back and forth. Th simplst way for th string to flx is lik this: Fundamntal frquncy, st harmon f = v string /2L But it can also flx in mor complicatd ways and w call th 2 nd harmonic: half th wavlngth, twic th frquncy 3 f rd harmonic: 2 = 2f = v string /L third th wavlngth, thr tims th frquncy, It is th mixtur of harmonics f 3 = 3f that = 3v ach string /2L instrumnt producs along with th fundamntal that givs EMO it STANING its Mor qustions on harmonics A string is clampd at both nds and thn pluckd so that it vibrats in th mod shown blow, btwn two xtrm positions A and C. Which harmonic mod is this? a. fundamntal, b. scond harmonic, c. third harmonic, d. 6 th harmonic A B A, B and C ar snapshots of th C string at diffrnt tims. answr: 6 th harmonic thr ar 6 points of maximum displa Harmonic dm 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. Enrgy lvls in isolatd atom. kick up, only crtain wavlngths whn com down. Atomic Modls & Light In discharg lamps, lots of lctrons givn bunch of nrgy (voltag). Bash into atoms. ( discharg tub ) 20 or mor with long tub 77 Non / ischarg Lamps Sim atoms lazy always want to go back to lowst nrgy stat Hav to gt rid of nrgy, snd it off as light. Fast lctron or right color light hits atom 2 Excitd atom 3 Atom back to low nrgy or Light mittd Not: diffrnt atoms hav diffrnt nrgy lvls (orbits rsulting in diffrnt nrgis of light (colors) coming ou 79 Ground stat (lowst possibl) 80 30