2010+Experifest Physics

8/3/2019 2010+Experifest Physics

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HANDBOOK

Physics

2010

EXPERIMENTFEST

www.newcastle.edu.au


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INTRODUCTION

ExperimentFestisanexperimentprogramdesignedtoprovideenrichingeducationalexperiencesforseniorhighschoolstudentswhoarestudyingPhysics,ChemistryandBiology.ExperimentFestissupportedbytheUniversityofNewcastlesFacultyofScienceandInformationTechnologyandtakesplaceatboththeCallaghanandOurimbah(CentralCoast)campusesoftheUniversityofNewcastle.ItisrunoverfourdaysattheCallaghanCampus

(21-25June2010-PhysicsandChemistry;18-25June2010-Biology)andfourdaysattheOurimbahCampus(28June1July2010).Studentsmayattendeithermorningsessions(9am-12pm)orafternoonsessions(12:45pm-3:45pm).PhysicsExperimentfestisalsorunningatTuncurry(June262010).

Theactivitiesallowstudentstoengageinarangeofhands-onexperimentsthataredifficulttoorganisewithinaschoolsetting,allunderthesupervisionofUniversityStaffandPostgraduatestudents.EachexperimentischosentocomplementtheNSWHSCsyllabusforPhysics,cementingclassroomtheoryandprovidingagoodbasisforexaminationpreparation.

Experimentsinclude: WilsonCloudChamber Michelson-MorleyExperiment ThePhotoelectricEffect Electric&MagneticFields WorldinMotion Superconductivity FramesofReference

Allexperimentsarecomplementedbynotes,follow-updiscussionsand

questionstoenhanceyourlearningexperience.

Forbookinginformationcontact:Larry Miltonon49469159or0404460470;orDavid Rushtonon43336965or0414238464

ExperimentFest2010Page3


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WELCOME

WelcometotheFacultyofScienceandInformationTechnologyattheUniver-sityofNewcastle.ExperimentFestisawonderfulchancetogiveyoupracticalexperiencewhichcomplementsyourclassroomlearningwhilegivingyouafirsthandlookatUniversitylifeandfacilities.Scienceisanexcitingfieldofstudy,allowingyoutomovewiththetimesandcontributeactivelyandrespon-siblytosociety.Therearemanyeducationopportunitiesinscienceafterhigh

school.HereintheFacultyweprovidestudyandresearchprogramsinfast-movingmodernfieldsthatmakeourworldwork.

TheFacultystaffandstudentswhowillbetakingyouthroughtheexperimentstodayareinvolvedincontemporaryscienceresearch.Pleaseaskquestionsandutiliseyourtimewiththem.

Takethisdaytoenjoybeingoutoftheclassroom,exploringsciencewithfel-lowstudentsandparticipatinginvaluableexperimentsanddiscussionswhichwillhelpyouinyourHSCandbeyond.

Iwishyouwellinyourstudies.IhopeyouapplyyourselvestothelearningprocesswithenthusiasmandyouenjoyyourtimeattheUniversity.Wehopetoseeyoustudyingwithusinthefuture!

Bestwishes,

Prof.BillHogarthProVice-ChancellorFacultyofScienceandInformationTechnologyUniversityofNewcastle


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PHYSICS


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STUDYING PHYSICS

Why study physics?Physicsiscrucialtounderstandingtheworldaroundus,theworldinsideus,andtheworldbeyondus.Itisthemostbasicandfundamentalscience.Physicschallengesourimaginationswithconceptslikerelativityandstringtheory,anditleadstogreatdiscoveries,likecomputersandlasers,thatchangeourlives.Physicsencompassesthestudyoftheuniversefromthelargestgalaxiestothesmallestsubatomicparticles.

Moreover,itsthebasisofmanyothersciences,includingchemistry,oceanography,seismology,andastronomy.Allareeasilyaccessiblewithabachelorsdegreeinphysics.

Theimportanceofphysicsisntlimitedtothehardsciences.Increasingly,physicistsareturningtheirtalentstomolecularbiology,biochemistry,andbiologyitself.Evenmedicinehasanicheforphysicists,andsincemedicalphysicistsarehardtocomeby,theyaremuchindemand.

Physicsalsosupportsmanynewtechnologies.Cellphones,theInternet,andMRIsareonlyafewexamplesofthephysics-basedtechnologicaldevelopmentsthathaverevolutionizedourworld.Aphysicseducationequipsapersontoworkinmanydifferentandinterestingplacesin

industrialandgovernmentlabs,oncollegecampuses,andintheastronautcorps.Manytheoreticalandexperimentalphysicistsworkasengineers,andmanyengineershavephysicsdegrees.Inaddition,manyphysicsgradsleavethelabbehindandworkatnewspapersandmagazines,ingovernmentaldepartmentsplaceswheretheirproblem-solvingabilitiesandanalyticalskillsaregreatassets.

Physicsisinteresting,relevant,anditcanprepareyouforgreatjobsinawidevarietyofplaces.

Opportunities for further studies in Physics:TheBachelorofSciencedegreeprogramattheUniversityofNewcastleprovidesafoundationofknowledge,skillsand

attributesthatallowsgraduatestobeemployablenotjusttodaybutintothefutureandtocontributeactivelyandresponsiblytosociety.MajoringinPhysics,youhavetheopportunitytosampleand/orspecialiseinanyoneofthefollowing: Biophysics(doublemajor) ComputationalPhysics(doublemajor) Geophysics(doublemajor) MedicalPhysics Nanotechnology OpticalPhysics(doublemajor) ResearchPhysics SpacePhysics/Radar/Surveillance

MajoringinPhotonicsyoucanstudy: OpticalPhysics(doublemajor) OpticalPhysics/LaserEngineering/PhotonicsEngineering

Equipped with his five senses,

man explores the universe

around him and calls the

adventure science

E.PHubble.


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Research in Physics at the University of Newcastle:TherearevariousgroupshereattheUniversitywhicharecommittedtoresearchinphysics.Groupsinclude:

CentreforSpacePhysics MedicalPhysicsGroup SurfaceandNanoscienceGroup ResearchCentreforOrganicElectronics

Careers in Physics:

TheFacultyofScienceandITcareaboutourstudentsandareinterestedingivingasmuchdirectionaspossibletothosemakingcareerchoicesandbeyond.Thepossiblecareerpathslistedbelowincludearangeofopportunitiesforgraduatesatdegree,honours,andpostgraduatestudylevels.

AcousticalPhysicist Astronomer/Astrophysicist Biophysicist Cosmologist FluidDynamicsAnalyst Geophysicist GraduateTrainee(GraduateProgram) HealthPhysicist LaboratoryAnalyst Laboratory/ResearchAssistant Nanotechnologist NuclearPhysicist

OpticalPhysicist

PlasmaPhysicist ResearchScientist RiskAnalyst ScienceInformation/EducationOfficer Science/PhysicsTeacher SciencesTechnician ScientificPatentAttorney/TechnicalAdvisor ScientificPolicyOfficer ScientificWriter SoftwareEngineer/Tester UniversityLecturer/Academic

Possible careers in Photonics:

GraduateTrainee(GraduatePrograms) LaserEngineer ManufacturingEngineer Nanotechnologist NetworkCablingTechnician

NetworkSupportEngineer OpticalResearchScientist PhotonicsEngineer ProjectManager ResearchScientist

SciencesTechnician ScientificPatentAttorney ScientificPolicyOfficer ScientificWriter SystemsEngineer TechnicalSalesRepresentative TechnologyInfrastructureManager TelecommunicationsServiceDelivery TestEngineer UniversityLecturer/Academic

Formoreinformationonthesecareerpaths,pleasevisittheUniversityscareerswebsite:www.newcastle.edu.au/service/careers/majors/

FormoreinformationontheFacultyofScienceandITcheckoutourwebsite:http://www.newcastle.edu.au/faculty/science-it/


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CHARGED PARTICLES INELECTRIC AND MAGNETIC FIELDS

Extract from HSC Syllabus 9.4.1describe quantitatively the force acting on a charge moving through a

magnetic field; F=qvBsin

Solve problems and analyse information using F=qvBsin , F=qE, E=V/d.

Outline Thomsons experiment to measure the charge/mass ratio of an electron

Key WordsMagneticandelectriceldsHelmholtzcoilsElectrongunDeectionplatesCircularMotion

Electriccharge

IntroductionDuringthe1800sitwasbelievedthattheatom(Greekwordmeaningindivisible)wasthefundamentalparticleofallmatter.Inthemid1800sW.Crookes(UK,1832-1919)inventedtheequipmentthatallowedscientiststoinvestigatecathoderays.TheCrookestubeordischargetubeconsistsofaglasstubecontainingapairofseparatedmetalplatesorelectrodes.Theelectrodeswerenamedtheanodeandthecathode.Theexperimentsinvolvedapplyingalargevoltagetotheplatesandinvestigatingthepropertiesoftheraysinthetubeasafunctionofgaspressureetc.

What are Cathode rays ?ThisquestionwasinvestigatedbyJ.JThomson(UK,1856-1940)in1897.Thereare3famousphysicistsnamedThomson.1.WilliamThomson(1824-1907);AlsoknownasLordKelvin,knownfortheabsolutetemperaturescale.2.JosephJ.Thomson(1856-1940);ourguy,discoveryoftheelectron,proposedaplumpuddingatomicmodel3.GeorgeP.Thomson(1892-1975);SonofJ.JThomson,diffractionofelectronstoprovewavenature

Usingtheobservedeffectsofelectricandmagneticeldsonthecathoderays,J.J.Thomsonestimatedthecharge/massratio.FromtheresultsofFaradays(UK,1791-1867)LawofElectrolysis,Thomsonwasabletoestimatethatcathoderaysconsistedofnegativelychargedparticlesthatwereabout1800timeslighterthanhydrogen.Robert

Millikanmorepreciselymeasuredtheelectronchargein1909.


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Effect of the Electric FieldAvoltageisappliedacrossthedeflectionplatesinthetube.Iftheelectricfieldisassumedtobeuniform,thentheexpressionfortheelectricfield,Eis

E =

andtheelectronsexperienceaforcegivenby

F =

Theelectronbeamismadevisiblebycollisionsofgasatomsinthetubeandwiththemicascreen.

a) Draw a diagram showing the expected path of an electron after it enters

the electric field.

b) How can you tell if the charge on the particles is +ve or -ve?

Assumeanelectrontravelswithaninitialvelocity,v0inthehorizontal(x)directionandencountersauniformelectricfieldintheydirection.

c) In which direction is the force on the electron?

d) What is the shape of the curve traced out by the path of the electron?

electrongun

V


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Effect of the Magnetic FieldThemagneticfieldisgeneratedbyaHelmholtzcoilarrangement.

e) In what direction is the magnetic field when it intersects the electron beam?

Inthemagneticfield,theelectronsexperienceaforcegivenby

F =

f) In what direction is this magnetic force?

g) What is the shape of the curve traced out by the electron due to the force caused by the magnetic field?

Thismeansthatthemagneticforce(Bqvsin)actsasacentripetalforce:Fc=mv2

r

so,Bqvsin=mv2,andifis900thenBqv=mv2

rr

Byrearrangingtheaboveequationthecharge/massratio:q/m=

Theradiusofcurvature,risgivenbyr=(x2+y2)/(2y).Thiscanbemeasuredfromthegridscaleonthetube.Thevalueofris=............................

Charge to Mass Ratio1.EnsurethecurrentintheHelmholtzcoilsiszero(nomagneticeld).2.Switchontheelectriceld.3.IncreasethecurrenttotheHelmholtzcoilsuntilthecathoderaybeamattensout.Atthispointtheforcesfromthe

twoelds,actingonthecathoderaybeam,areequal.

ie,Felectriceld=Fmagneticeldor, Eq=Bqvsimplifyingthiswillgive E=Bvandrearrangingforv: v=E (Equation2) B

Adjustthecurrenttothecoilsuntilthetraceintersectsthecoordinate(10,0)onthegrid.Usethevalueofthecurrent,I,tocalculatethemagneticeld,B,by: B=0.00423Ih) Calculate the value of B from the given value of I.

i) Estimate the deflection plate separation from the grid scale. This is the value for d.

d=...................m.

Thepotentialdifferencebetweenthechargedplates,V,hasavalueof...........................V

j) Calculate the value of the electric field E using: E = V E = ............................Vm-1

d

k) Combine equations 1 and 2 by substituting for v in equation 1 and find the charge/mass ratio, q/m for a cathode

ray particle.

q/m =

l) What is the accepted value for q/m ?

(Equation1)


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MICHELSON-MORLEY EXPERIMENT

HSC Syllabus 9.2.4Describe and evaluate the Michelson-Morley attempt to measure the

relative velocity of the Earth through the aether

Gather and process information to interpret the results of the Michelson-

Morley experiment

What is the nature of Light?Around1800itwasthoughtthatlightwasawavebecauseitproducedinterferenceanddiffractionpatterns.Michelsons(in1879)calculatedthespeedoflight,usinganarclampandrotatingmirrors,tobe186,350milespersecond.

Like waves travelling through water it was thought that light must be similarly travelling in some mysterious material,

which was called the aether, surrounding and permeating everything even space. Since light travels so fast, the aether

must be very light and very hard to compress. It must also allow solid bodies to pass through it freely, without ether

resistance, or the planets would be slowing down.

How could the Aether be detected?Michelsonexplainedthepuzzletohischildrenasfollows:Suppose we have a river of width w (say, 100 units), and two swimmers who both swim at the same speed,(say, 5

units per second). The river is flowing at a steady rate, say 3 units per second. The swimmers race in the following

way: they both start at the same point on one bank. One (Joe) swims directly across the river to the closest point

on the opposite bank, then turns around and swims back. The other (Bob) stays on one side of the river, swimming

upstream a distance (measured along the bank) exactly equal to the width of the river, then swims back to the start.

Who wins?

Lets consider Bob who goes upstream and back. Going 100 units

upstream, the speed relative to the bank is only 2 units per second,

so that takes 50 seconds. Coming back, the speed is 8 feet per

second, so it takes 12.5 seconds, for a total time of 62.5 seconds.

Now Joe goes across the flow which is little trickier. To succeed in

going directly across, Joe must actually aim upstream at the correct

angle. If the angle is correctly chosen so that the net movement

is directly across, in one second Joe must have moved four units

across (see diagram). So, at a crossing rate of 4 units per second,

Joe gets across in 25 seconds, and back in the same time, for a total

time of 50 seconds so Joe wins. This turns out to true whatever theirswimming speed. (Of course, the race is only possible if they can

swim faster than the current!)A

CB

flow

vt

ct

Bank

river

Bank


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Michelsonthoughtthat just as the speed of sound is relative to the air, so the speed of light mustbe relative to the ether. So if you could measure the speed of light then you could measure the

speed of light travelling upwind, and compare it with the speed of light travelling downwind, and

the difference of the two measurements should be twice the windspeed.

The ExperimentLightisdirectedatanangleof45degreesatahalf-silvered,halftransparentmirror,sothathalfthelightgoesonthroughtheglass,halfisreected.Theybothgoontodistantmirrorswhichreectbacktothehalf-silveredmirror.Atthispoint,thelightisagainhalfreectedandhalftransmitted,butatelescopeisplacedbehindthehalf-silveredmirrorasshownintheguresothatthecombinedlightwillarriveinthistelescope.Now, if there is an ether wind blowing, someonelooking through the telescope should see the effect of a slightly longer time for the 2 light beams

to arrive, since one would have gone more upstream and back, one more across stream in

general.

Takingthespeedoflighttobecrelativetotheaether,andtheethertobeowingatv:

togoadistancelupstreamwilltake l/(c-v)secondsandldownstreamwilltake l/(c+v)seconds,thereforethetotalroundtriptakes2 l / (c (1- v2/c2))seconds.

We can safely assume the speed of the aether is much less than the speed of light,

otherwise it would have been noticed long ago, for example in timing of eclipses of

Jupiters satellites.

Thismeansv2/c2isasmallnumbersoweapproximatetheroundtriptimetogoupstreamanddownstreamtobe(2l/c)(1+v2/c2).FromPythagorastheorem,thecross-streamspeedis(c2-v2).Theroundtripcrossstreamtimewillbe2l/(c2-v2).Thiscanbeapproximatedas(2l/c)(1+v2/2c2).

Thetworoundtriptimesdifferbyanamount(l)(v2/c3).Now,2l/cisjustthetimethelightwouldtakeiftherewerenoaetherwindatall,say,afewmillionthsofasecond.Ifwetaketheetherwindspeedtobeequaltotheearthsspeedinorbit,thenv2/c2isabout1/100,000,000.Thismeansthetimedelaybetweenthepulsesreectedfromthedifferentmirrorsreachingthetelescopeisaboutone-hundred-millionthofafewmillionthsofasecond.Itseemscompletelyhopelessthatsuchashorttimedelaycouldbedetected.


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Michelsonwasthefirsttofigureouthowtodoitusingtheinterferencepropertiesofthelightwaves.Onesetofwavesgoesupstreamanddownstream,theothergoesacrossstreamandback.Finally,theycometogetherintothetelescopeandtheeye.Iftheonethattooklongerishalfawavelengthbehind,itstroughswillbeontopofthecrestsofthefirstwave,theywillcancel,

andnothingwillbeseen.Ifthedelayislessthanthat,therewillstillbesomedimming.However,slighterrorsintheplacementofthemirrorswouldhavethesameeffect.Tomaximizetheeffect,thewholeapparatus,includingthedistantmirrors,wasplacedonalargeturntablesoitcouldbeswungaround.

Observe how the interference pattern changes as the turntable is rotated through 90

degrees. What happens?

How does this change compare to that expected if there is an aether?

Why was the null result difcult to accept?


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WILSON CLOUD CHAMBERExtract from HSC Syllabus 9.8.3Perform a rst-hand investigation or gather secondary information to observe radiation emitted from a nucleus using Wilson

Cloud Chamber or similar detection device

Thecloudchamber,alsoknownastheWilsonchamber,isusedfordetectingparticlesofionisingradiation.Initsmostbasicform,acloudchamberisasealedenvironmentcontainingasupercooled,supersaturatedalcoholvapour.Whenanalphaparticleorbetaparticleinteractswiththemixture,itionizesit.Theresultingionsactascondensationnuclei,aroundwhichamistwillform(becausethemixtureisonthepointofcondensation).Thehighenergiesofalphaandbetaparticlesmean

thatatrailisleft,duetomanyionsbeingproducedalongthepathofthechargedparticle.Thesetrackshavedistinctiveshapes(forexample,analphaparticlestrackisbroadandstraight,whileanelectronsisthinnerandshowsmoreevidenceofdeectionbycollisions).Whenanyuniformmagneticeldisappliedacrossthecloudchamber,positivelyandnegativelychargedparticleswillcurveinoppositedirections,accordingtotheLorentzforcelawwithtwoparticlesofoppositecharge

(http://en.wikipedia.org/wiki/Cloud_chamber)

InthisdemonstrationwewilluseaDiffusionCloudChamber600(AndrewsUniversity,MI,USA)toobserveionizingradiationfromcosmicraysandalsofromaPb210source.

Pb210hastwodecaypaths.

(i) ItdecaystoHg206byemissionofa3.72MeValphaparticle.Hg206thendecaystoTl206bybetaparticleemission.

(ii) Pb210alsodecaystoBi210bybetaparticleemission.

Inbothdecaypathsgammaraysarealsoemitted.

Observe the tracks from the Pb210 source. Can alpha particle and beta particle tracks be identied?

Observe tracks when the source is removed. Where do those tracks come from?

Observe what happens to the tracks when a magnet is placed in the cloud chamber.


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THE PHOTOELECTRIC EFFECTExtract from HSC Syllabus: 9.4.2Explain the particle model of light in terms of photons with particular energy and

frequency.

Solve problems, analyse information and identify the relationship between photon

energy, frequency, speed of light and wavelength

Whenlightshinesonametalsurfaceelectronsareejected.Theenergycarriedawaybyeachelectrondependsonthefrequencybutnotontheintensityoflight.Therefore,lightcanbeconsideredtobeastreamofparticles(photons)ratherthanawave.

Theemittedelectronshavearangeofkineticenergies.Theelectronswithmaximumkineticenergyareemittedfromrightatthesurfaceafterhavingreceivedalltheenergy,E,fromthephoton.However,inleavingthesurfacetheelectronsloseanamountofenergy (calledtheworkfunctionofthesurface).

Read the above section and write down an expression for the maximum

kinetic energy of the electrons in terms of the photon energy E and workfunction .

Max kinetic energy = (1)

TheenergyofaphotonisgivenbyE=hf,wherePlancksconstanthis6.63x10-34JsandfisthefrequencyofthephotoninHzandc=f wherethespeedoflightcis3.00x108ms-1andthewavelengthofthephotonis .

Write down an expression for E in terms of . E = (2)

Combine (1) and (2) to write down a relation between maximum kinetic energy and

Maximum kinetic energy = (3)


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The Experiment Todeterminemaximumkineticenergyofemittedelectrons.

Thephototube(Fig2)istheessentialpartoftheinstrumentyouwilluse.Itisanevacuatedglasstubecontainingacoatedelectrode(cathode)shapedlikehalfofacylinder.Anotherelectrode(anode)intheformofastraightrodispo-sitionedatapproximatelythefocalpointofthecurvedsurface.Whenlightstrikesthecathodesurface,electronsareejectedandcollectedbytheanode.Thecolouredlters,placedintothelightpath,cutoffallwavelengthsaboveaparticularvalue,thereforetheminimumwavelengthoflightreachingthetubeisknown.Eqn3canthenbeusedtodeterminethemaximumkineticenergyoftheemittedelectrons.Tomeasurethehighestelectronenergyweapplyasmallreversevoltagecalledthebacking

voltage(iewithanodenegativeandcathodepositive)thatisjusthighenoughtocompletelystoptheowofelectronsreachingtheanode(absolutelyzerocurrent).

Note:Ifthebackingvoltageiscontinuedtobeincreased,thecurrentwillbegintoowbackwardsbecauseelectronsbegintoowfromtheanodetothecathode.

The Experimental Method

1. Havethedemonstratorchecktheequipment.Turnonthelight sourcelightsourcetoilluminatethephototubethroughthe

apertureintherearfaceoftheinstrument.Notethatthelight sourcewillbecomewarm. 2. Insertoneoftheltersintothewiderpairoftheslidegrooves providedinfrontofthelightsource. 3. Selecttube current onthemeter switchtomonitorthecurrent throughthephototube.Select the 0-20A range.

4. Usingthe backing voltagecontrol,adjustthevoltagefromzerovoltsuntilthecurrentthroughthetube reducesbelow 0.1 microamp.

5. Nowselectthesensitive 0-200nA range andincreasethebacking volts untiltheelectronowthroughthe tubeisreducedto0.0 nanoamps.Ifthecurrentgoesnegativereducethebacking volts until0.0 nanoamps isachieved.Atthispointthemostenergeticelectronsarepreventedfromreachingtheanode.

Fig 3


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6. Withoutdisturbinganything,selectbacking voltsonthemeter switchandobservetheexactvoltagethat isbeingappliedtothephototubeinreversetostopallelectronsfromreachingtheanode.Recordthis backingvoltageintable1.

7. Removethecolourlterandrepeattheexperimentfromsteps3to7fortheremainingcolourlters.

8. Usingthewavelengthvaluemarkedonthebluelter,calculatethefrequency(inHertz)ofthelighttransmitted bythislterandenteritintotable1.Recordyourmeasurementsofbackingvoltageintable1.

9. PlotagraphofthefrequencyinHz(Xaxis)againstthebackingvoltsinVolts(Yaxis)usingthesupplied graphpaper.

Table1

Filter Wavelength

(nm)

Frequency

f=c/ (Hz)

BackingVolts

(V)blue 450

yellow 480 6.25x1014

orange 545 5.50x1014

red 590 5.08x1014

Discussion

Thestoppingvoltageisrelatedtothemaximumkineticenergyoftheelectronssinceiftheelectronshavemoreen-ergyitwillrequirealargervoltagetostopthem.

So which colour light generates electrons with the highest kinetic energy?

Which colour light generates electrons with the lowest kinetic energy?

Is this expected from equation 3?

What can we say about the slope of the line in this graph?


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The intercept on the Y axis is related to the workfunction of the cathode. Using eqn 1, determine the work-

function of the cathode in eV.

What is the metal cathode surface most likely made from? Use the list workfunctions on the graph paper to

determine your answer.

Extension

Withtheredlterselected,placeanapertureinthelightpathtoreducetheintensityoflight.

Does this markedly change the backing volts? Is this result expected?


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REFERENCE FRAMES

Extract from HSC Syllabus 9.2.4Students perform an investigation to help distinguish between inertial and noninertial

frames of reference

Areferenceframewhichmovesatconstantvelocitywithrespecttoanotheriscalledaninertialreferenceframe.Forcesactthesamewayinthisframeasintheoriginalframe.Intheexperimentbelow,acartcarryingapendulumsitsonaninclinedplane.

Intheframeofthecartthependulumhangsdirectlydown,ifthecartisstationary.Predicthowthependulumhangsifthecartismovingdownthetrackatconstantvelocity.

Is this what happens experimentally?

Ifthecartismovingatconstantvelocitywehaveaninertialframeofreference.ThebehaviourofinertialframeswasdescribedinEinsteins

specialtheoryofrelativity.

Butwhathappensiftheframeisacceleratingi.e.ifwehaveanon-inertialframeofreference?So how should the pendulum hang if the cart is accelerating down the

track? Should it

(i) hang straight down

(ii) hang perpendicular to the incline or

(iii) in some other direction?

Is this what happens experimentally?

Wecanexplainthisbehaviourbysayingthat (i)Newtonslawsdontworkinanacceleratingframeofreferenceor (ii)thatweneedextractitiousforcestomakeNewtonslawswork.

Newtonsprincipleofequivalencesaysthatphysicscanbeexplainedinacceleratingframesbytheuseofgravitationalforces. In what direction shouldgravity point in the carts frame of reference to explain the position of the

pendulum?


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SUPERCONDUCTIVITY

Extract from HSC Syllabus 9.4.4Process information to identify some of the metals, metal alloys and compounds that have been identified as exhibiting

the property of superconductivity and their critical temperatures

Process information to discuss possible applications of superconductivity and the effects of those applications on

computers, generators and motors and transmission of electricity through power grids

Discuss the advantages of using superconductors and identify limitations to their use

Gather and process information to describe how superconductors and the effects of magnetic fields have been

applied to develop a maglev train

Process information to discuss possible applications of superconductivity and the effects of those applications oncomputers, generators and motors and transmission of electricity through power grids

Earlyinthe20thcentury,DutchphysicistHeikeKamerlinghOnnesobservedthatmercurydisplayednoelectricalresistancewhencooledtoverylowtemperatures.Superconductivitybecameascienticcuriositywithfewpracticalapplications.Theninthe1960sapracticalsuperconductingmetalwiremadeofniobiumandtinwasdeveloped.Theniobiumandtitaniumalloy,stillinusetoday,isamongthematerialscalledlow-temperaturesuperconductors.

Low-temperaturesuperconductorsmustbecooledtobelow20Kelvin(-253oCelsius)inordertobecomesuperconducting.Theyarenowwidelyusedinmagneticresonanceimaging,orMRI,machines,andintheeldsof

high-energyphysicsandnuclearfusion.Additionalcommercialusehasbeenlimitedlargelybythehighrefrigerationcostsassociatedwithliquidhelium,whichisneededtocoolthematerialstosuchlowtemperatures.

Thehopeforlow-costsuperconductivitywasignitedbytwosignicantdiscoveriesinthe1980s.In1986,twoIBMscientistsinZurich,AlexMullerandGeorgBednorz,discoveredanewclassofsuperconductors.Unlikethelow-temperaturesuperconductors,whichweremetallicorsemimetallic,thesenewcompoundswereceramicandweresuperconductingupto35K(-238oC).MullerandBednorzwonaNobelPrizefortheirdiscovery.Thenin1987,PaulChuattheUniversityofHoustontookthediscoveryonestepfurtherandannouncedacompoundthatbecamesuperconductingat94K(-179 oC).Thisdiscoverywasparticularlysignicantbecausethiscompoundcouldbecooledwithcheapandreadilyavailableliquidnitrogen.Thesenewmaterialswerecalledhigh-temperaturesuperconductors.

Bismuth-basedcompoundsarebeingfashionedintosuperconductingwiresandcoils,whicharebecomingessentialtoelectricpoweruses.Thallium-andyttriumbasedcompoundsarebeingformedintothethinlmsusedinelectronicdevices.Identify metals, alloys and compounds used as superconductors and their critical temperatures.

metals, metal alloys and compounds critical temperatures


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Some current uses of Superconductors1. Powertransmissioncablesthatcarrycurrentwithoutenergylosseswillincreasethecapacity

ofthetransmissionsystem,savingmoney,space,andenergy.PrototypepowertransmissioncableshavebeendevelopedandarebeingtestedbyteamsledbyPirelliCableCompanyand

SouthwireCompany.2. Motorsmadewithsuperconductingwirewillbesmallerandmoreefficient.A1,000-horsepowermotorhasbeenconstructedandisundergoingtestingbyanSPIteamledbyRockwellAutomation/RelianceElectricCompany.

3. Generatorswillusesuperconductingwireinplaceofironmagnets,makingthemsmallerandlighter.Newgeneratorsalsomaygetmorepowerfromlessfuel.AnSPIteamledbyGeneralElectrichasdevelopedadesignfora100-megavoltamperegenerator.

4. Currentcontrollers(i.e.,fault-currentlimiters)helputilitiesdeliverreliablepowertotheircustomers.HTSfault-currentlimitersdetectabnormallyhighcurrentintheutilitygrid(causedbylightningstrikesordownedutilitypoles,forexample).Theythenreducethefaultcurrentsothesystemequipmentcanhandleit.AnSPIteamledbyGeneralAtomicsrecentlyproducedasuccessfulHTSfault-currentlimiterthatwillsoonbereadytomarket.

5. Energystorageinflywheelsystemswillensurethequalityandreliabilityofthepowertransmittedtoutilitycustomers.Inaddition,energystorageprovidesutilitieswithcostsavingsbyallowingthemtostoreenergywhenthedemandforelectricityislowandgeneratingthepowerischeap.Thisstoredenergyisthendispensedwhendemandishighandpowerproductionismoreexpensive.

6. Magneticresonanceimaging(MRI)machinesenhancemedicaldiagnosticsbyimaginginternalorgansofteneliminatingtheneedforinvasivesurgeries.MRIs,whichcurrentlyaremadewithlow-temperaturesuperconductors,willbesmallerandlessexpensivewhenmadewithHTS.

7. Maglevtrainsseemtofloatonairasaresultofusingsuperconductingmagnets.ThesetrainshavebeenunderdevelopmentinJapanfortwodecades;thenewestprototypemayexceed

547kilometersperhour.

Discuss possible applications of superconductors and the effect of those applications as

well as advantages or limitations of superconductors

applications of

superconductivityeffects advantages or limitations


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ExperimentPerformaninvestigationtodemonstratemagneticlevitationAnalyseinformationtoexplainwhyamagnetisabletohoveraboveasuperconductingmaterial

thathasreachedthetemperatureatwhichitissuperconducting

Observe the demonstrator fill the foam container with liquid nitrogen to slightly cover the

superconductor and let the liquid nitrogen boil off until the surface is uncovered the

Yttrium Barium Copper Oxide (YBCO) sample will be near 77K and superconducting. Place

the magnet on the superconductor and observe that it is levitating. Observe what happens

when the nitrogen all boils off and the sample warms up.

What happens?

ExplanationSuperconductorsexcludemagneticelds,apropertycalledtheMeissnereffect.Thiseffectcausesasmallmagnettolevitateabovethesuperconductorsurface.Asthemagnetisbroughttowardsthesuperconductor,currentloopsaresetupinthesuperconductorwhichgeneratemagneticeldstoopposethemagneticeldcreatedbythemagnet.Theeldsetupbythesuperconductorwillpropagateoutsidethesuperconductorandcausethemagnettolevitateeventhoughthemagnethascometoastopabovethesuperconductorsurface.Thisisbecausethesuperconductorhaszeroresistanceandsothecurrentswillcontinuetoowafterthemagnethas

stopped.

Thelevitatingmagnetdoesnotslideoffthesuperconductor.ThisisamanifestationofFluxPinning,aphenomenaassociatedwithTypeIIsuperconductors,suchashightemperatureceramicsuperconductors.Herelinesofmagneticuxassociatedwithamagnetcanpenetratethebulkofthesuperconductorintheformofmagneticuxtubes.Theseuxtubesarethenpinnedtoimperfectionsorimpuritiesinthecrystallinematrixofthesuperconductortherebypinningthemagnet.

RareearthmagnetSuperconductorYBa2Cu3O7

Inducedcurrents


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PROJECTILE MOTION UNIFORMLYACCELERATED MOTION IN TWOSPATIAL DIMENSIONSExtract from HSC Syllabus: 9.2.2Describe the trajectory of an object undergoing projectile motion within the Earths gravitational field

Perform a first hand investigation, gather information and analyse data to calculate the initial and final velocity,

maximum height reached, range and time of flight of a projectile for a range of situations by using simulations,

dataloggers and computer analysis

Inphysicsweclassifydifferenttypesofmotionsothatwecanpredictwherethingswillendup.Usually,studyofmotioninphysicsbeginsbyconsideringdistanceandspeedwhere

Distance = speed x time (1)

Thiswillpredictacarsdistancetravelledprovidedthecarneitherspeedsupnorslowsdown,i.e.foraconstantspeed.Speedisascalarquantity(itonlyhasasizeormagnitude).Ifwegivethespeedadirectionaswellasamagnitudethenwemakeavectorquantitycalledvelocity.Distanceisalsoascalarquantitywhiledisplacementisavectorquantity.

Ifthecaracceleratesuniformlywithacceleration,a,thenthedistancetravelledinatime,t,is

Distance = ut + at2 (2)

Equation(2)alsoallowsforthecasewherethecarhasaninitialconstantspeed,u,andthenaccelerates.Wenowhavethemainingredientsforexaminingmotionontwodimensions.Accelerationandforcearerelatedtothemassoftheobject,i.e.itismoredifculttomoveaheavyobject.Gravityprovidesaforceintheverticaldirectionandwellcalltheverticaldirection,y.Projectilemotionisviewedintwodimensionsasthecombinationoftwocomponentmotions,oneinthehorizontal,thexdirection,andtheotherintheverticalortheydirection.

Equations1and2arethebasis(inphysics)ofprojectilemotion.Equation(1)describesmotionalongthehorizontalwhiletheainequation(2)istheaccelerationduetogravity.

Thefollowingtableshowsthequantitiesusedinthehorizontalandverticalcomponentsofprojectilemotion,asvectorsorscalars.

Vectors Scalars

DisplacementxandyInitialvelocityu

xandu

y

Finalvelocityvxandv

y

Accelerationax

anday

Time


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Thevectorcomponentsrequiretheuseofpositive(+)andnegative(-)signstoshowthedirectionoftravel.Arbitrarilywechoseapositive(+)signformotioninanupwardorverticaldirectionandaminus(-)signformotioninthedownwardsorhorizontaldirection.

Usingthesymbolsfromthetableequations1and2become:

x=uxt (3)

y=uyt+a

yt2 (4)

Typicallyforprojectilemotionay=-gwhereg=9.8ms-2.Thenequations(3)and(4)canbesolvedtodeterminethe

maximumheight,H,reachedandthemaximumhorizontaldistance,R,travelledbeforetheobjectreturnstoitsoriginalheight. H=u

y2/2g (5)

R=2uxuy/g (6)

Inthisexerciseyouwillbeabletoexamineavideoofprojectilemotion.Thecomputersoftwareallowsyoutoobtainthex,ycoordinatesofasoftballatvarioustimesduringthemotion.Fromthesedata,variousphysicalquantitiescanbestudiedastheballtracesoutprojectilemotion.Bynow,youwouldhavecompletedaunitonprojectilemotionatschool.


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Section AByaskingmembersinyourgroup,writeshortanswerstothefollowing:Asoftballisthrownfromoneplayertoanother.

What shape does the ball trace out in space? Can you show (mathematically) why?

Does the energy of the ball change during the motion? How does the friction from the air affect the energy of

the ball?

What is the relationship between the potential and kinetic energies of the ball?

Does the momentum of the ball change? In what way?

Does the acceleration of the ball change?

Would there be any difference in plots of the balls position compared with its displacement?


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Section BThevideosoftwareiscalledWorldinMotionandyoushouldseeashortcuttowimonthecomputerscreen.Thissoftwareisgreatforanalysingvideofootagebutratherpoorinpresentingthevariousoptions,navigationandinformation.Itiseasytogetlost!

Herearethestepsyouneedtogettoplayandanalysethevideo:1.Afterstartingthesoftware,thecomputerscreenshouldlooksomethinglikethis;

2.YoucanusethesymbolseithersideofHistorytonavigate

3.ClickontheProjectileMotionoptionintheleftmenu

4.ChooseVideoExperimentsSet1

5.Clickinthee1710.htmtext

6.Bynow,youshouldseethefirstframeofthevideowithoptionsontheright

7.ClickonMarkingtheVideofollowedbyClickHeretoopenthevideo

8.Youhavearrivedatthevideomarkingenvironment.ClickonPlaytoseethefootage.YoucannowuseSteptosee

theimagesoneframeatatime.

9.Movingthemouseovertheimagechangesthecursortoanarrow.Leftmouseclickandyoucandigitisethe

positionoftheball

10.Whenyouhavedigitisedthroughthewholemotion,clickonGraph>>,followedbyNext

11.ChooseObjectmovinginXandYdirections,andYisVertical,Next

12.Selectalltheplotsavailable,Next

13.Thescreenshouldnowlooklikethis:


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Onthisscreen,clickonGraph>>

Thefirstgraphispositionversustimeintermsofxandycomponentsandthevectorresultant.In the space below draw the graphs you see on the screen and explain the brown (X) and green (Y) curves.


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Thenextgraphisdisplacementwithtime.On the following axis draw the graphs shown on the screen.

What are the differences between this and the position versus time graph?

The gradient of this graph will allow you to nd what property of the motion?

Thenextgraphisvelocity.Draw the velocity/time graphs on the following axis.Notethestraightatlineforthexcomponent.

Why is the y component a straight line? Isnt the ball accelerating in this direction?

What is the numerical value of the slope of the green (vy) line?


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Thenextgraphisthemomentum.Draw the graph on the following axis. Which other graph does it look likeand why?

Finally,theaccelerationisshown. Draw the acceleration/time graph on the following axis.Notethatthexcomponentisclosetozerowhiletheycomponentisnear9.8m/s2.

Calculate values for the maximum height, H, reached (above the original starting height) and the

range, R, and compare your values to the results from equations 5 and 6.

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