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Unit5Physicsfrom

creationtocollapseThermalenergy

InvestigaterecogniseandusetheexpressionE=mc

Specificheatcapacityisthequantityofenergyneededtoraisethetemperatureofmaterial,perkilogramperdegreeriseintemperature.

Specific heat capacity can be calculated using this equation,Givingthectheunits

Measuringspecificheatcapacity:1.Weighablockofaluminiumtofinditsmassmandthenplace

itinthelagging.

2.Add a small amount of cooking oil to ensure good thermalcontactwhentheheaterandthermometerandinserted

3.Taketheinitialtemperatureoftheblock.Switchonthepowersupply and start the stopwatch record the current and

potentialdifference

4.Afterthreeminutesswitchofthepowersupplyandrecordthehigheststeadytemperaturereached.

5.You can than find the specific heat capacity using theequation

Explaintheconceptofinternalenergyastherandomdistributionofpotentialandkineticenergyamongstmolecules

IngasthemoleculeshaveKineticenergyduetotheirrandommotion.Inadditionmoleculesthataremadefromtwoormore

atomshavekineticenergyduetorotationandvibration.

Inanidealgastheinternalenergyisentirelytherandomkineticenergyofitsmolecules

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Idealgasassumptions:1.Theintermolecularforcesarenegligibleexceptincollision2.Thatthecollisionsbetweenmoleculesandwiththewallare

elastic

3. JustbeforeacollisionmoleculeshavekineticenergythecloserthemoleculesgetthelargertherepulsiveforcesoK.E

istransferredtopotentialenergyasaresultofworkbeing

donetoovercomeresistiveforcesothemoleculeis

temporarilystationary

4.Timespentincollisionis0comparedtotimespentoutofcollision

Hotbodieshaveahigherconcentrationofinternalenergycomparedtocoldbodies.

Heatistherandominterchangeofenergybetweentwobodiesinthermalcontact.

Energycanbetransferredbetweentwobodiesintheformofworkirrespectiveoftemperaturedifference

Explaintheconceptofabsolutezeroandhowtheaveragekineticenergyofmoleculesisrelatedtotheabsolute

temperatureAtemperatureof0Kiscalledabsolutezerobecauseitisthelowest

temperaturethatcantheoreticallybereached.

ItsvalueontheCelsiusscaleis-273.15degreesAttemperaturescloseto0Kmatterexhibitsquantumeffectssuch

assuperconductivityandsuperfluidity

Asuperconductorisamaterialthatwillconductwithoutanyresistancewhencooledtoacertaintemperature

Thereisacatchtosuperconductors:alotofenergyisneededtomaintainverylowtemperaturesandthisisnotalwaysideal.ForexamplethelargeHadroncolliderneeds96tonnesofliquidheliumtomaintainatemperatureof1.9Kwhichis-271degrees.

Recogniseandusetheexpressionm=3/2kTisthemeansquaredandcancalculatedbysquaringallthe

speedsanddividebythenumberofspeeds.

TistemperaturemeasuredinKelvin istheaverageKineticenergyofamolecule

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TheaverageKineticenergyofmoleculesisproportionaltotheabsolutetemperatureofthegas

UsetheexpressionpV=NkTastheequationofstateforan

idealgasNisthenumberofmoleculesofgask=

InvestigatingtherelationshipbetweenPressureandVolumeforafixedmass:

Thevolumeofafixedmassofairundertestcanbegivenbythelengthofthetubexthecrosssectionalarea.ThereforeifthetubeisuniformthenVisproportionaltoL

Thetotalpressurecanbereadoffthepressuregauge.Openvalvesoairstartsatatmosphericpressurethenincreasethe

pressureusingafootpump.

Recordpressureandvolume.AllowairtoreachthermalequilibriumPisproportionalto1/VPV=constantisBoyelslaw

InvestigatingtherelationshipbetweenPressureandTemperatureofafixedmassofgasandaconstantvolume:

Startbyputtingiceinabeakertogetthetemperatureaslowaspossible,atthistemperaturemeasurethepressureonthepressuregaugeandrecordboth.

Increasethetemperatureby10degreeseachtimeandrecordthecorrespondingpressureuntilboilingpointisreached.

Allowafewminutesbeforetakingresultstoallowanequilibriumtemperaturetobereached.

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OscillationsRecallthattheconditionforsimpleharmonicmotionisF=-kx,andhenceidentifysituationsinwhichsimpleharmonicmotion

willoccurInoscillationthemotionisrepetitiveaboutafixedpositionwiththe

objectatrestateitherextremesandhasmaximumspeedatmidpoint

Foranoscillationtheforceactingontheoscillatingbodyandthereforeitsaccelerationmustbeproportionaltothedisplacement

Theforceandthereforeaccelerationalwaysactinoppositedirectionstowardstheequilibriumposition

Anobjectwhosemotionsatisfiestheaboveconditionsissaidto

haveSHM

Recogniseandusetheexpressionsa=-2x,a=-A2cost,v=Asint,x=AcostandT=1/f=2/asappliedtoasimpleharmonicoscillator

Sinceforceisproportionaltoaccelerationwecanexpressionintermsofa where istheconstant

FindingthespringconstantofaspringfromHookeslaw:

Suspenda100gmasshangerfromaverticalspringUseasetsquareagainstameterruletomeasuretheinitialheightAddextramassesin50gincrementsuntil300g.AftereachmassisaddedrecordtheextensionPlotagraphofFagainstXthegraphshouldbeastraightlineand

thegradientwillbethespringconstantFindingthespringconstantusingsimpleharmonicmotion

Setupapparatussimilartothatforthepreviousexperiment.

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Thistimemeasurethetimetakenforthemassestomake10oscillations

Tohelpjudgethestartandstopofanoscillationsputamarkeratthecentreofanoscillation,e.g.apinsecuredtoaverticalruler

usingbluetack Plotagraphof against thisshouldgiveastraightline

throughtheorigin.ThegradientwillgiveyouthevalueofkEquationsofsimpleharmonicmotion:

Inperfectsimpleharmonicmotionthefrequencyoftheoscillationdoesnotdependontheamplitudeofoscillation

Ift=0atoneendofthemotionxatthattimewillbe=totheAmplitude.TheSolutionisequalto

Fortheaboveequationthegraphwillbeacosinegraph(displacement-time)thegradientofthiswillbethevelocity

Thevelocitycanthereforebefoundbydifferentiatingtheaboveequationwhichwillgiveus .Thismeansthatthe

velocitytimegraphlookslikeanegativesinewave

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Obtainadisplacementtimegraphforanoscillatingobjectandrecognisethatthegradientatapointgivesthevelocityatthatpoint.Acardisattachedtomassestogiveagoodreflectivesurface.Dataloggersettorecordfor10secondsatasamplingrateof100

persecond.

Computercanbeprogramedtogivegraphsofdisplacement,velocityandaccelerationagainsttime.

Rotarysensor

Apendulumisconnectedtoarotarysensor.Thismeasurestherotationalmotionandinthecaseofapendulumismeasurestheangulardisplacement.

Recallthatthetotalenergyofanundammedsimpleharmonicsystemremainsconstantandrecogniseanduseexpressionsfortotalenergyofanoscillator

AsthependulumswingsthereisacontinuouschangeofKinetic

energytoPotentialenergy.AteitherextremestheKineticenergyis0andG.P.Eismax

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TheheavydensebobispulledbackandreleasedThispendulumwilloscillateatitnaturalfrequency ,

determinedbyitslengthandgivenbytheequation

Allotherlightpendulumsarecoupledtothisdiverpendulum

byastringsotheywillexperienceaforcedoscillation=infrequencytothatofthedrivingpendulum

Pendulumsclosertothedrivingpendulumabsorbmoreenergybecausetherenaturalfrequencyisclosertothenaturalfrequencyofthedrivingpendulum.Theywilloscillatewithlargeamplitudes

OscillationsoflargeamplitudesiscalledresonanceForasystemwilllittleornodampingtheresonantfrequency

occursatthenaturalfrequency

Forasystemwhichhasbeendampedtheresonantfrequencyislowerthanitsnaturalfrequency

ExplainhowdampingandtheplasticdeformationofductilematerialsreducetheamplitudeofoscillationDampingisimportantindesignsofmachinesandbuildingto

preventunwantedvibrations

Theshapeofthelatheisdesignedsothattheresonantfrequencyisnowherenearthefrequencyoftherotationofalathe

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Latesttechnologyistocoatturbinebladeswithductilematerial.(Amaterialthatcanbeplasticallydeformedwithoutfracture)whichmeansthatitcanabsorbalotofenergy.

Ifaductilematerialfeelsvibrationsitgoesthroughhysteresisloopseachvibration.Astrophysicsandcosmology

UsetheexpressionF=Gm1m2/r2Newtonproposedthateveryparticleintheuniverseattractsevery

otherparticlewiththeForceF.

GisthegravitationalconstantM1M2istheproductofthemassesofthetwoparticlesandristhe

distancebetweenthem

Deriveandusetheexpressiong=-Gm/r2forthegravitationalfieldduetoapointmass

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Recallsimilaritiesanddifferencesbetweenelectricandgravitationalfields Gravitationaleffects Electrostaticeffects

Fieldstrength

P.d.

Energyconservation

ForceLaws

RadialFields

Differences:Gravitationalforceaffectsallparticleswithamass,but

electrostaticforceonlyaffectsparticlewithchargeGravitationalforceisalwaysattractivewhereaselectrostaticforce

canbeattractiveorrepulsive

Itisnotpossibletoshieldmassfromgravitationalfieldbutitispossibletoshieldachargefromanelectrostaticfield

Recogniseandusetheexpressionrelatingflux,luminosityanddistanceF=L/4d2applicationtostandardcandles

Ilightyearisthedistancetravelledbylightinoneyear

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Luminosity,Lisusedtodescribethetotaloutputpowerofastar,

unitsW

Theelectromagneticwaveenergypersecondperunitareafromastarreachingusonearthiscalledtheradiationflux,F

RadiationfluxisalsoknownaslightintensityFandLarelinkedbytheinversesquarelaw

Standardcandles

Theproblemwithusing tomeasurethedistancebetweenearthandastaristhatitistoofarsoitwontexhibitparallax.

ACepheidstarchangeluminositywithtimeThemaximumluminosityLofCepheidstarisrelatedtotheperiod

Tofitsluminosityvariation

Supernovaexplosionscanbeusedasstandardcandlestofindthedistancetoevenmoredistantgalaxies

RecogniseanduseasimpleHertzsprung-Russelldiagramtorelateluminosityandtemperature.Usethisdiagramtoexplainthelifecycleofstars.

TheHertzsprung-Russelldiagramisaplotofstellarluminosityandsurfacetemperature

Lifecycleofthestar

Onthehorizontalaxisthe

temperaturegoes

fromHigh

temperaturesonthelefttolow

temperatureson

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Onceastarisformeditadoptsapositiononthemainsequenceandspendsmostofitslifeatafairlyconstantsurfacetemperatureandluminosity

Moremassivestarsspendashortertimeonthemainsequencecomparedtolessmassivestars1. Itwasformedfromacloudofhydrogenandhelium2. Itjoinedthemainsequenceabout5billionyearsagoanditwill

leavethemainsequence5billionyearfromnow3.Afterleavingthemainsequenceitswillexpandandbecomea

redgiantandafterlosingabout50%ofitsmassitwillbecomeawhitedwarf

4. Itwillcoolslowlyforbillionsofyearsandeffectivelydie

Recogniseandusetheexpression:maxT=2.898x10-3mK(Wienslaw)forblackbodyradiatorsThesunisayellowstarbutstarsthatarehotterthanthesun

appearwhiteWienslawmaxT=2.898x10-3mKtellsusthatmaxandTare

inverselyproportional

OnlyappliestoblackbodyradiatorsAllstarsactasblackbodyradiatorswhichmeanstheyabsorbany

electromagneticradiationfallingonthem

Recogniseandusetheexpressionsz=/f/fv/cforasourceofelectromagneticradiationmovingrelativetoanobserverandv=Hodforobjectsatcosmologicaldistances

Neutrino star

or black hole

Birth of

stars in a

dark cloud

Massive stars

Stars like

our sun

Supergiant Supernova

Red GiantPlanetary

nebula

White dwarf