IDEAS TO IMPLEMENTION QUESTIONS & PROBLEMS SOLUTION QUIDELINES

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1 DO PHYSICS ONLINE IDEAS TO IMPLEMENTION QUESTIONS & PROBLEMS SOLUTION QUIDELINES How to answr a qustion: problm solving (t0_37.pdf) p1.3 Wavs transfr nrgy without any matrial bing transformd. At first cathod rays wr though to b wavs lik X-rays which has bn rcntly discovrd. Cathod rays wr dflctd both by lctric and magntic filds indicating that cathod rays wr a stram of ngativly chargd particls and J J Thompson masurd th q /m ratio providing complling vidnc that cathod rays wr a bam of ngativly chargd lctrons. p1.8 E m = kg q = C a = m.s -. F ma F E q F ma E N.C N.C q q q + I F out of pag B right hand palm rul DO PHYSICS ONLINE 1

2 p1.30 forc on a moving charg in a magntic fild F Bqvsin F forc on charg particl [N] magnitud only B strngth of uniform magntic fild [T tsla] magnitud only magntic flux dnsity q charg of particl [C coulomb] magnitud only v vlocity of chargd particl [m.s -1 ] magnitud only angl btwn magntic fild lins and currnt dirction magnitud only = 0 F = 0 currnt dirction & magntic fild dirction paralll = 90 o F = F max currnt dirction prpndicular to magntic fild dirction p1.34 I v F B right hand scrw rul: magntic fild into pag - right hand palm rul: motion of lctron is dirctly towards th wir p1.44 B = T d =.5 m = m acclrating voltag V a = 10.5 kv = V (a) v =? m.s -1 acclrating voltag dos work on th lctron incrasing its kintic nrgy (b) (c) (d) () V 1 a 7-1 Va mv v m.s m right hand scrw rul magntic forc dirctd up th pag 14 FB Bv N magntic forc & lctric forc must cancl lctric forc dirctd down th pag 14 FB FE N Elctric fild btwn th plats sam dirction as forc on a positiv charg up th pag FE 4-1 FE E E V.m voltag across th plats DO PHYSICS ONLINE

3 bottom plat is positiv (lctron attractd to bottom plat) V 3 E V E d V d (f) J.J Thompson s /m xprimnt V m d Va B From masurmnt of E (or V and d), B and V a th /m ratio can b found. Altrnativly: Thomson adjustd th lctric fild strngth and magntic fild strngth to mak th lctrons pass straight through. This allowd him to calculat th vlocity v of th lctrons (cathod rays). H thn passd th lctrons through th magntic fild B alon, and from th radius R of thir path calculatd th q/m ratio v m B R p1.65 (a) striations (b) right hand sid is th cathod striations ar narr than anod (c) S nots Elctrical dischargs (d) Pattrn will not significantly chang but molculs of diffrnt gass mit radiation of diffrnt frquncis in such transitions. Thrfor, th glow of th positiv column has a charactristic colour for ach gas. () Th prssur of th gas is mainly rsponsibl for th obsrvd pattrns. p1.68 right hand scrw rul forc on positiv charg is dirctd towards th right Th magntic forc acting on th positiv charg will always act towards th cntr of a circl th lctron will mov in a circular path. p1.71 (a) (b) S nots spctral tubs (b) Th tubs hav diffrnt prssurs insid thm. (c) highst to lowst prssur B D A C p1.75 forc on a moving charg in a magntic fild F Bqvsin Th forc only dpnds on th componnt of th vlocity which is at right angls to th magntic fild. it dos not dpndnt on th paralll componnt. DO PHYSICS ONLINE 3

4 p1.76 (a) CRO cathod ray tub (b) Cathod ray tubs using in tlvisions and cathod ray tubs (c) A low voltag to provid currnt to hat cathod B hot cathod lctron gun C acclrating voltag larg usd to acclrat lctrons to giv thm larg kintic nrgis D acclrating voltag plats E lctric dflcting plats to chang th path of th lctron bam F fluorscnt scrn whn an lctron hits th scrn a flash of light is mittd (d) v 0.60c E m v q V 1 k mv 4 V V q () (f) (g) d 3 18 mm m V 54 V V E V.m d 15 F q E.3 10 N 4 1 F a.5 10 m.s m 15 p1.79 right hand palm rul lctron travls in a circular orbit v = m.s -1 q = C m = kg B = T R =? m T =? s f =? Hz Magntic forc = cntriptal forc m v m v B qv R m R B q 9 circumfrnc R vt T s 1 f T Hz R v DO PHYSICS ONLINE 4

5 p1.93 C plats must b conductors V E d plats must b conductors p1.94 (a) Th shadow of th cross showd that th cathod rays travlld in straight lins. Without th cross thr is no shadow. (b) Th glass fluorscs bcaus th nrgy carrid by th lctrons ar absorbd by th glass molculs. Th molculs of th glass bcom and xcitd and thn loss nrgy by mitting photons of visibl light. (c) Th cathod rays ar ngativly chargd lctrons ngativ chargd particls moving in a magntic fild xprinc a forc lctron bam dflctd causing a distortion of th shadow of th cross. (d) Elctrons ar constitunt of atoms, invstigat proprtis of lctrons, masur th q /m ratio. () Nd a high voltag sourc such as an induction coil ******************************************************************* p.05 high voltag sourc spark gaps induction coil rcivr transmittr Sparks across th gap of th transmittr producd th induction coil mittd lctromagntic radiation which includd radio wavs and UV radiation. Whn a sht of glass was placd btwn th transmittr and rcivr, th spark in th rcivr was wakr du to th absorption of th UV by th glass. Hrtz notd th obsrvation but did not follow it up. Th UV absorbd by th mtal rcivr nabld lctrons to b mittd mor asily giving a biggr spark photolctric ffct. DO PHYSICS ONLINE 5

6 Stopping Voltag Vs (V) p.06 Planck nrgy of atomic oscillators is quantizd E = h f Einstin particl modl for light light consistd of photons nrgy of ach photon hf An lctron mittd immdiatly from th surfac by th intraction with a photon Applid th Law of Consrvation of Enrgy Enrgy of incidnt photon = Enrgy to rlas lctron from surfac + KE of jctd lctron h f = ½ m v + = ½ m v max + W W is th min nrgy ndd to rmov an lctron from th surfac work function For lctron to b rlasd h f W thrshold frquncy h f c = W p.08 Stopping voltag Thrshold frquncy Thrshold wavlngth Voltag rquird to rduc photocurrnt to zro Vs is th masurmnt of th maximum kintic nrgy a photolctron Minimum frquncy for th rlas of lctrons from th surfac of th matrial Maximum wavlngth for th rlas of lctrons form th surfac of th matrial h f mv W V W V stopping 1 max stopping h f W frquncy f (Hz) x slop m = (V.Hz -1 ) intrcpt b = V Work function W = 1.7 V = J Planck s constant h = J.s not answr low than accptd valu Thrshold frquncy f c = Hz Thrshold wavlngth c = m = 670 nm Th two lins hav th sam slop = h /. DO PHYSICS ONLINE 6

7 p.13 Max Planck was th first prson to giv a qualitativ xplanation of th curvs for th radiation mittd by a blackbody. H assumd that nrgy is quantizd. Th chang in nrgy of an oscillator is a nhf whr n is an intgr. Th total ara undr th curvs rprsnts to nrgy mittd by th blackbody. Th highr th tmpratur, th mor nrgy radiatd. Win s Displacmnt Law pak T = constant Th highr th tmpratur, th shortr th wavlngth of th m radiation mittd by th blackbody. p.33 (a) Blackbody - objct which givs th maximum amount of nrgy radiatd from its surfac at any tmpratur and wavlngth and th absorbs all th radiation that falls on it. (b) JWS Rayligh & Jams Jans Math modl dscribd blackbody radiation curvs at long wavlngths accuratly but not at shortr wavlngths in th UV, radiation from cavity absorbd and r-mittd with vr smallr and smallr, nrgy mittd from cavity bcoming infinit UV catastroph (c) Max Planck was th first prson to giv a qualitativ xplanation of th curvs for th radiation mittd by a blackbody. H assumd that nrgy is quantizd. Th chang in nrgy of an oscillator is a nhf whr n is an intgr. p.50 Light wav modl intrfrnc ffct Light particl modl - Photolctric Effct Einstin spcial rlativity spd of light is constant indpndnt of motion of sourc or obsrv quivalnc of mass and nrgy E = m c Einstin light stram of particls calld photons nrgy of photon E = hf photon nrgy absorbd by lctron and givn sufficint nrgy to scap th surfac of a mtal photons hav mass m = E/c Photolctric Effct Th photolctric ffct - rlas of an lctron from th surfac of a mtal xposd to lctromagntic radiation. Classical physics was unabl to xplain - th thrshold frquncy, which is th frquncy of light at which lctrons ar mittd from th surfac of a mtal. It prdictd that nrgy from light would b absorbd ovr tim until an lctron had sufficint nrgy to lav th surfac of th mtal. Einstin usd Planck s thory and th concpt that photons carrid nrgy to xplain th photolctric ffct. Einstin assumd that DO PHYSICS ONLINE 7

8 light xistd as photons, ach with an nrgy qual to E = h f and that th numbr of photons dtrmind th light intnsity. Photons with th highst nrgy corrspond to th highst frquncy, and an lctron would not b mittd from a mtal surfac unlss th photons possssd nrgy qual to or gratr than th nrgy ndd to ovrcom th nrgy holding th lctron on th mtal surfac. Th nrgy rquird to rlas th lctron from th surfac was calld th work function, W. Einstin was abl to combin th photon nrgy with th work function and th KE of th mittd lctrons in th quation h f = E Kmax + W p.61 E =? V =? J f =? Hz = 550 nm = m c = f E = h f = h c / f = c / = Hz E = J =.3 V visibl p.6 (a) (b) (c) Using a rvrs voltag to rduc th photocurrnt to zro stopping voltag. 1 mv V max stopping h f W m v h Wmin Vs f s nots Plot V s against f slop = h/ h 1 p.66 violt 1 = 400 nm = m f 1 =? Hz E 1 =? J =? V grn = 400 nm = m f =? Hz E =? J =? V rd 3 = 715 nm = m f 3 =? Hz E 3 =? J =? V c f c 19 f E h f 1 V J f 1 = Hz E 1 = J = 3.1 V f = Hz E = J =. V f 3 = Hz E 3 = J = 1.7 V hf W m v W V 1 min max min Violt light photons hav 0.9 V mor nrgy rlasd lctrons will hav 0.9 V xtra kintic nrgy. Th nrgy of th rd photons is lss than th work function of th surfac no lctrons rlasd from surfac. s DO PHYSICS ONLINE 8

9 p.70 (a) high voltag sourc spark gaps induction coil rcivr (b) (c) transmittr In ordr of incrasing nrgy radio microwav IR visibl UV X-rays -rays Oscillating chargs oscillating lctric filds oscillating magntic filds production of radio wav Radio wav oscillating lctric & magntic filds oscillating lctric forc on fr lctrons in wirs dtction of radio wavs (d) () (f) (g) Th glass in transparnt to radio wavs. UV dos not pass through glass. Whn glass plat blocks UV, spark shortr bcaus lss nrgy absorbd by lctrons lss asily rmovd mor difficult to crat th spark. Photolctric ffct rlas of lctrons from a surfac by absorption of incidnt m radiation. p.7 Photolctric ffct rlas of lctrons from a surfac by absorption of incidnt m radiation. Th prdictions of classical physics could not xplain th xprimntal obsrvations mad. Einstin usd Planck s ida of nrgy quantization to xplain th photolctric ffct by applying th law of consrvation of nrgy whr light bhavs as a stram of particls calld photons and th nrgy of ach photon is givn by E = hf. This xplanation also supportd th radical ida introducd by Planck. Th impact of his xplanation was grat and was th starting point for modrn physics whr th idas of classical physics wr not valid. p.90 In classical physics, th nrgy of a systm could has a continuous rang of valus, but Planck introducd for th first tim th concpt of discrt changs in nrgy of a systm in his xplanation of blackbody radiation. This was a radical ida at th tim and on of th first stps in dvloping a nw way to dscrib th world in trms of th idas in modrn physics. DO PHYSICS ONLINE 9

10 p.95 (a) Light was thought to b a wav phnomna (b) Light could produc as intrfrnc pattrn a wav bhaviour (c) Light a stram of particls photons (d) Both th obsrvations mad on th photolctric ffct and blackbody radiation could not b xplaind in trms of classical physics radial nw idas had to b introducd.g. nrgy quantization and light as both a particl and a wav ******************************************************************** p3.13 Boron valnc 3 p typ smiconductor Conduction by th movmnt of hols to th right p3.18 Mtal fr lctrons moving through crystal lattic collisions btwn lctrons and lattic ions rsistanc p typ smiconductor hols (+) n typ smiconductor lctrons p3. Small nrgy band gap btwn th valnc band and th conduction band p3.3 p typ smiconductor small numbr impuritis atoms of valncy 3 (B Al Ga) addd to vry pur silicon p3.4 Early radio communications was basd upon valv tchnology (diods and triod valvs) Valvs xpnsiv, fragil, larg, nrgy infficint With th introduction of smiconductor dvics such as th transistor valvs bcam obsolt in radio communications Solid stat dvics far suprior no warm tim, rquir lss nrgy input, smallr, lss fragil, mor robust, chapr, can construct intgratd circuits on a singl chip of smiconducting matrial Nxt dvlopmnt intgratd circuits compltd circuits containing millions of componnts on th on silicon chip DO PHYSICS ONLINE 10

11 p3.7 (a) Doping of vry pur silicon involvs th additions of small amount of impurity atoms of Group 3 or 5 lmnts. n typ smiconductor Group 5 phosphorus P, arsnic As, antimony Sb p typ smiconductor - Group 3 aluminium, gallium Ga (b) Elctrons producd by photolctric ffct whr an lctron is frd by th absorption of a photon. (c) A potntial diffrnc is stablishd btwn th diffrnt silicon layrs whn a photon is absorbd, th hols migrat through th p typ smiconductor whil fr lctrons cross th n typ smiconductor and a currnt is maintaind by th continual absorption of photons. n-si _ - undopd Si + p-si + photon absorbd crats a fr lctron & hol lctron flow p3.30 (a) At first it was difficult to obtain larg quantitis of vry pur silicon (b) Chips mad with silicon ar much lss tmpratur snsitiv than using grmanium Pur silicon was not availabl whn th first transistors wr dvlopd. It was thn vry difficult to produc silicon of sufficint purity, whil it was possibl to produc high purity grmanium. p3.33 S nots p3.39 Solar cll currnt photolctric ffct whn a incidnt photon of sufficint nrgy (gratr than work function of surfac) is absorbd by an lctron in th smiconductor layr it crats a fr lctron and a hol Th lctrons acts as charg carrirs in th n typ smiconductor matrial and hols act as charg carrirs in th p typ smiconductor matrial potntial diffrnc btwn th n and p smiconductor layrs xtrnal circuit connctd currnt. As long as light falls on th photocll, th lctrons and hols ar mobilizd to giv a currnt through th light glob DO PHYSICS ONLINE 11

12 lctron nrgy p3.44 Valvs thrmionic dvics - vacuatd glass containrs (gas at low prssur) lctrons rlasd from hot filamnt thrmionic mission larg (bulky) hot usd lots of nrgy diods rctification triods amplifirs, switchs Solid stat dvics - miniaturisation diods (pn junctions) transistors (npn, pnp) IC - intgratd circuits consum littl powr Suprconductor zro rsistanc blow critical tmpratur Applications solid stat dvics switching amplification Applications suprconductors powr transmission magntic lvitation p3.5 insulator smiconductor conductor n typ smiconductor a donor impurity atom has a 5 th valnc lctron that dos not participat in th covalnt bonding and is vry loosly bound. It is rlativly asy for an lctron to b xcitd from th donor lvl into th conduction band whr it acts as a charg carrir charg carrirs ar mainly ngativ lctrons in th conduction band. p typ smiconductor accptor impurity atom has only 3 valnc lctrons, so it can borrow an lctron from a nighbouring atom. An lctron can mov from th valanc band to th accptor lvl crating a hol in th valanc band. Th rsulting hol is fr to mov about th crystal positiv charg carrirs moving in valnc band. DO PHYSICS ONLINE 1

13 p3.55 conduction band (narly mpty) conduction band ( mpty) E gap valanc band (full) smiconductor valanc band (full) diamond conduction band - lctrons mov in conduction band h f valanc band + hols mov in valanc band Smiconductor =? m E gap = 0.8 V = (0.8) q J q = C c = 3.0 m.s -1 h = J.s min nrgy of photon and max wavlngth of photon E = h f = h c / = E gap = C = h c / E gap = m = 1.55 m infrard Diamond =? m E gap = 5.0 V = (5.0) q J q = C c = 3.0 m.s -1 min nrgy of photon and max wavlngth of photon E = h f = h c / = E gap = C = h c / E gap = m = 48 nm ultraviolt p3.57 As th tmpratur is incrasd, lattic vibrations incras and som lctrons gain sufficint nrgy to b xcitd across th nrgy gap form th valanc band to th conduction band. Mor lctrons can tak part in conduction lowring th rsistanc of th smiconductor. For mtals, th incrasd lattic vibrations causs nrgy to b lost from lctrons by collisions with th lattic, incrasing th rsistanc. Th conductivity of a matrial dpnds upon th numbr of charg carrirs availabl. In a mtal thr ar nrgy lvls availabl for lctrons to gain nrgy and tak part in conduction sinc th band gap is zro - approximatly on lctron pr atom is fr to act as a conduction lctron. In a insulator, th band gap is vry larg and at room tmpraturs thr ar almost zro fr lctrons in th conduction band and hnc th high rsistanc. In a smiconductor thr is a smallr band gap ar thr ar a fw lctrons in th conduction band at room tmpraturs and th rsistanc is lss than than of an insulator. DO PHYSICS ONLINE 13

14 photo currnt I (ua) p3.77 Changd socity gratly lctronics rvolution small scal circuits nrgy fficint compard with valus - intgratd circuits computr rvolution microprocssors, robots information rvolution world wid wb - GPS p3.90 Diagram shows accptor lvl p typ smiconductor valnc 3 lmnts B, Al, Ga p3.9 right hand scrw rul chargs moving in a magntic fild Hols(+) mov up Elctrons (-) mov down p3.95 (a) (b) (d) incrasd intnsity photon nrgy E (V) (c) Work function W = 1.6 V c =? m W = 1.6 V = (1.6) q J q = C c = 3.0 m.s -1 W = h f c = h c / c = C = h c / W = m = 780 nm IR () For photon nrgy lss than th thrshold frquncy, no lctrons ar rlasd from th surfac irrspctiv of th intnsity. For nrgis abov th thrshold, as th nrgy is incrasd th numbr of lctrons rlasd incrass as shown by th incras in th currnt th gratr th intnsity mor photons mor lctrons rlasd gratr currnt. Whn th nrgy bcoms sufficintly high, almost all th availabl lctrons ar rlasd from th surfac and thr is only a vry small incras in currnt for incrasd nrgy of th photons saturation ffct. ********************************************************************** DO PHYSICS ONLINE 14

15 p4.04 (a) intrfrnc of wavs constructiv and dstructiv (b) By making masurmnts on th intrfrnc pattrn producd by impacting X-ray bams onto crystallin structurs, th spacing btwn atoms could b stimatd. This lad to th important fild of X-ray crystallography which is usd to dtrmin th structur of matrials. p4.14 (a) (b) Magntic Lviation - Missnr Effct Whn matrial coold blow th transition tmpratur in th prsnc of a magntic fild, a spcimn bcoms prfctly diamagntic (a diamagntic objct is rplld by a prmannt magnt) du to xpulsion of th xtrnal magntic fild from th intrior of th suprconductor by th canclling th magntic flux insid. If a small magnt is brought nar a suprconductor, it will b rplld bcaus inducd supr-currnts around th surfac will produc mirror imags of ach pol. If a small prmannt magnt is placd abov a suprconductor, it can b lvitatd by this rpulsiv forc. Trains magntic lvitation (Missnr Effct) Us powrful suprconducting lctromagnts mountd on bottom of train and normal lctromagnts on th tracks rpl th suprconducting magnts and giv ris to th forcs for propulsion. Bnfits rducd rsistanc to th motion Limitations- nd vry strong magnts producd by suprconducting lctromagnts but nd vry low tmpraturs for suprconducting stat xpnsiv. p4.0 (a) A matrial bcoms suprconducting (rsistanc = 0 and xpls xtrnal magntic filds) whn its tmpratur drops blow a crtain tmpratur known as th critical tmpratur. (b) -57 o C -181 o C -140 o C (c) High tmpratur suprconductors goal to find a matrial that would b suprconducting at room tmpratur DO PHYSICS ONLINE 15

16 p4.44 BSC thory namd aftr Bardn, Coopr, Schriffr who proposd it. Whn th tmpratur drops blow th critical tmpratur th bhaviour of th conduction lctrons suddnly changs lctrons pair up forming Coopr pairs which hav opposit spin and linar momntum and all pairs mov cooprativly this stat rducs th total nrgy of th systm wll blow all othr stats Th conduction lctrons acting as a collction of Coopr pairs ar in th ground stat. Thr is a larg nrgy gap to th nxt highr nrgy stats which would dstroy th Coopr pairs th conduction lctrons can no longr intract with th lattic and xchang nrgy with th lattic which is th mchanism that producs rsistanc, thrfor th matrial is suprconducting th conduction lctrons flow through th matrial with zro loss in nrgy. p4.49 Th suprconductor xcluds magntic filds at vry low tmpraturs. s p4.14 p4.50 Mtals at room tmpratur movmnt of fr or conduction lctrons lctrons in th conduction band. Suprconductor collctiv flow of Coopr pairs stat of lowst nrgy zro rsistanc to th flow of lctrons. p4.60 Tin - suprconducting ( m) tin 10 silvr p4.75 Powr transmission s nots Magntic lvitation trains s nots p T C = 3.7 K T (K) Abov th critical tmpratur th magntic fild can pntrat and pass through th matrial. Blow th critical tmpratur th matrial bcoms suprconducting and xpls th magnt fild from its intrior th magntic fild lins can not pass through it. abov critical tmpratur blow critical tmpratur DO PHYSICS ONLINE 16

17 Max KE of photo-lctrons KE (V) p4.80 Th capacity of microprocssors and th fficincy of thir opration is in apart limitd by th hating ffct in th dvics thy oprat in. Having zro rsistanc circuits would allow thir capacity and spd of opration to b incrasd substantially. Th us of suprconductors in transistors (Josphson junction) and suprconducting connction films also allow procssing of signals to b gratly spdd up. p4.88 (a) A matrial bcoms suprconducting (rsistanc = 0 and xpls xtrnal magntic filds) whn its tmpratur drops blow a crtain tmpratur known as th critical tmpratur. (b) If a small magnt is brought nar a suprconductor, it will b rplld bcaus inducd supr-currnts around th surfac will produc mirror imags of ach pol. If a small prmannt magnt is placd abov a suprconductor, it can b lvitatd by this rpulsiv forc. (c) Missnr Effct (d) Magntic lvitation trains, motors rduction in frictional forcs ********************************************************************** m008 (a) (b) Rliability rpating an xprimnt a numbr of tims - us man valu graphing th rsults. Ignor th data point that is obviously wrong (c) No chang to graph. (d) Critical frquncy min frquncy blow which photo-currnt is zro. f c = Hz () Work function min nrgy to rmov an lctron from th surfac. W = J 8 x frquncy f (Hz) x m013 Whn th tmpratur of a mtal is dcrasd its lctrical rsistanc dcrass bcaus conduction lctrons loss lss nrgy in collisions with th lattic ions whos vibrations dcras by lowing th tmpratur. m00 Powr transmission s nots Magntic lvitation trains s nots DO PHYSICS ONLINE 17

18 m045 f = 10.8 MHz = Hz E =? J =? V =? m q = C c = 3.0 m.s -1 h = J.s E = h f E(V) = E(J)/q c = f = c / f E = J = V vry small photon nrgy sinc in radio part of m spctrum =.9 m long wavlngth bcaus of small frquncis m047 (a) Cathod rays wr dflctd by lctric and magntic filds ngativly chargd particls. J.J. Thompson was abl to masur q /m ratio lctrons (b) To produc an lctrical discharg nd vry high voltags > V (c) mak sur that your do not com into contact with th high voltag sourc m049 proton q = C v = 6.00 m.s -1 B = 1.8 T R = m m =? kg m 0 =? kg Magntic forc = Cntriptal forc mv q v B R p mv q B R q B R m v m0 m v 1 c m kg v c 7 0 m kg m050 Paddl whl spins whn struck by cathod ray bam bam carris momntum DO PHYSICS ONLINE 18

19 m065 CRO Transistor circuit stp-up transformr stp-down transformr E m07 m = kg V = 49 V d =.0 cm = m E =? V.m -1 q =? C lctric fild V E.5 10 V.m d 3-1 lctric forc (up) = gravitational forc (down) charg must b positiv q E m g mg q E C m076 diagram of an induction coil with a spark gap ~ 5 mm diagram of a radio not tund to a radio station Th sparking across th trminals of th induction coil producd radio wav. Ths radio wavs wr dtctd by a radio not tund to a radio station. A static or crackling nois was hard and this was hard whn tunr was scannd ovr th frquncy rang for th AM radio stations. DO PHYSICS ONLINE 19

20 m080 V = 134 V + +q v = m.s -1 - d = m F B F E magntic fild into B pag lctric fild E down E =? V.m -1 B =? T Elctric fild E = V / d = V.m -1 For bam of positiv chargs to mov un-dflctd, magnituds of th lctric and magntic forcs must b qual. F E = F B q E = q v B B = E / v = 3.85 T m08 Nd to link th work don by Einstin and Planck to outsid factors influncing thir work. Einstin spcial rlativity photolctric ffct light as a stram of particls - photons nrgy quantizd E = h f Planck xplanation of blackbody radiation nrgy of oscillators quantizd E = h f World War II Einstin lft Grmany pacifist Planck continud working and supportd th Grman govrnmnt m08 work function W = J = ( ) / ( ) V = 5.44 V min nrgy of photon to produc photo-lctrons h = J.s c = m.s -1 h f = h c / = W f = W / h = Hz = h c / W = m UV DO PHYSICS ONLINE 0

21 m095 lctrons fr lctrons that can mov du to an applid lctric fild lctrons acquird sufficint nrgy to b in th conduction band. hols rmoval of an lctron from a bond, hols as if a positiv charg du to an applid lctric fild hols locatd in valanc band. m111 incidnt radiation = 187 nm = m c = f c = m.s -1 f = c / = Hz max KE E Kmax =.5 V = ( )(.5) J = J Photolctric Effct h f = E Kmax + W W = h f c Nd to find thrshold frquncy fc f c = f E Kmax / h = Hz Al m115 Whn mrcury is coold blow its critical tmpratur of 4. K is bcoms suprconducting, that is th conductor has zro rsistanc. Mrcury is a mtal and is a good conductor and conduction is du to th movmnt of th fr lctrons in th conduction band at room tmpraturs (0 o C). S nrgy band diagram. Blow th critical tmpratur, mrcury is a suprconductor, th conduction is du to th cooprativ movmnt of Coopr pairs through th lattic. Conduction in a P typ smiconductor is primarily du to th movmnt of hols in th valnc band S nrgy band diagram. Th rsistanc of a smiconductor is highr than that of a mtal such as mrcury. m10 Th frquncy of th incidnt light was lss than th thrshold frquncy. DO PHYSICS ONLINE 1

22 m00 Max Planck (19 Oct 1900) - hypothsis radiation mittd & absorbd by walls of a blackbody cavity radiation quantizd chang in nrgy E E 1 = n h f n = 1, 3, His assumption of nrgy lvls quantizd nabl him to obtain an quation to succssfully dscrib th blackbody radiation curv: Planck radiation law agrd with xprimnt. Each atom bhavd as a small antnna (lctromagnt oscillator) nrgy of an oscillator n h f (n = 0, 1,,.) - nrgy of oscillator was quantizd. Chang in nrgy of oscillator (mission & absorption) quantizd E = intgr h f atomic oscillators do not radiat or absorb nrgy in continuously variabl amounts Birth of Quantum Physics - Planck did not bliv that atomic oscillators bhavd this way - usd his modl to simply account for th shap of th blackbody curv Curv shows th radiation mittd from a blackbody at a fixd tmpratur. Th tmpratur dtrmins th pak in th curv Win s Displacmnt Law pak T = constant Th total ara undr th curv rprsnts th rat of th total nrgy mittd by th blackbody. m400 Undrstanding of crystal structurs many advancs in scinc undrstanding of conduction ld to th dvlopmnt of th smiconductor industry dvlopmnts in lctronics, computrs, information tchnology. X ray diffraction X ray bam incidnt on th matrial X rays diffractd from atoms that mak up th crystallin structur to produc an intrfrnc pattrn. By xamining th distanc btwn maxima in th intrfrnc pattrn Bragg wr abl to dtrmin th distanc btwn paralll plans of atoms. DO PHYSICS ONLINE

23 m550 Acclrating voltags incrass KE of lctrons 1 qv mv Elctron in a uniform magntic fild xprincs a magntic forc that is always dirctd towards th cntr of a circl cntriptal forc mv B q v R mv B qr m v m q V B m q V qr q = C m = kg V = 5.00 kv = V R = 557 mm = m B = T B =? T m680 (a) UV radiation on mtal photolctric ffct lctrons mor asily rmovd largr spark. (b) Incrasing th gap btwn th trminals of th rcivr dcrass th strngth of th spark across th trminals. (c) A spark producd by th transmittr mits som UV placing th glass plat rducd th UV from raching th rcivr dcras in th strngth of th spark. m690 Th kintic nrgy of th mittd lctrons was proportional to th frquncy of th incidnt radiation and indpndnt of th intnsity of th light. No lctrons wr mittd unlss th incidnt light was abov a crtain thrshold frquncy. For frquncis abov th thrshold frquncy, lctrons wr rlasd immdiatly from th surfac vn for vry low intnsity incidnt light. m700 It was Hinrich Hrtz who first obsrvd th photolctric ffct whil prforming his xprimnts on th production and rcption of radio wavs. H noticd that whn light producd by th spark producd by th spark of his transmittr loop fll dirctly onto th rciving loop, th spark at th rcivr was strongr (mor asily producd). H noticd that somthing to do with th light falling on th rcivr was allowing th discharg to b mor asily achivd, but h did not invstigat furthr. DO PHYSICS ONLINE 3

24 m80 Win s Displacmnt Law (a) pak T = m.k pak = 550 nm = m T =? K T K (b) pak blu < rd T blu > T rd m950 Magntic forc on chargd particl is dirctd towards cntr of a circl circular motion lctron charg = q = C lctron mass m = m = kg lctron vlocity v = m.s -1 magntic fild B = T lctron moving at right angls to B fild = 90 o sin = 1 Forc on charg moving in magntic fild F Bqvsin Magntic forc = Cntriptal forc F c = m v / R R = m v / B q = m m955 Cathod rays travl in straight lins m960 Magntic fild dirctd into pag Right hand rul Cathod bam dflctd down th pag South pol brought nar bam Magntic fild dirctd out of pag Right hand rul Cathod bam dflctd up th pag m964 S nots DO PHYSICS ONLINE 4

25 m965 Einstin Spcial Rlativity Spd of light is constant indpndnt of th motion of th sourc or an obsrvr (indpndnt of th fram of rfrnc in which it is masurd) Inrtial frams of rfrncs tim and spac not absolut lngth contraction, tim dilation, mass / nrgy E = mc, mass dpndnt upon vlocity Einstin Quantum Thory Explanation of photolctric Effct (Nobl Priz) Particl natur of light photons E = hf Emission of photolctron dpnds upon frquncy of incidnt radiation Th contributions mad by Einstin wr instrumntal in th start and dvlopmnt of Modrn Physics whr idas wr compltly at odds with classical physics of th tims. m970 Obsrvation light on a mtal surfac photo-lctrons Classical physics light as wav could not xplain obsrvations Radical nw thory light as a stram of particl photons E = h f Nw thory could xplain th obsrvations m 990 Planck and Einstin good frinds supportd ach othr scintific rsarch but thir viws on th rol of scinc and scintific rsarch wr vry diffrnt. Einstin Activist for world pac and was only on of four scintists to sign a partition for pac at th start of WW1. Maintaind that scintific rsarch should b rmovd from social and political forcs and dvotd to th pursuit of knowldg and undrstanding. Did support th dvlopmnt of th atomic bomb. aftr WWII, totally opposd th rsarch, dvlopmnt and us of nuclar wapons warnd of th dvastating nrgy that could b rlasd. Planck Staunch patriot support th Grman govrnmnt and th ris of th Nazi rgim. Work for th th Nazi during WWII. Scinc to support a social and political agnda. Rapid progrss in Grman scinc as a bnfit to all Grmans and a clar indication of thir suprior abilitis. DO PHYSICS ONLINE 5