The Ultimate IGCSE Physics Guide.docx

The Ultimate IGCSE Physics Guide.docx

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TheUltimateIGCSEPhysicsGuide

TheUltimateIGCSEGuidetoPhysics

ByCGPwned

Unit1:

Solids,LiquidsandGases

Density

SOwhat’sdensity?

Well,allsolids,liquidsandgaseshavedifferentpropertiesandcharacteristics.Onesuchcharacteristicisdensity.Solidsareoftenverydense,liquidsarelessdensethansolids,andgaseshaveverylowdensities.Densityishowmuchmasssomethinghasforacertainvolume–inotherwords,how‘squashedup’somethingis.

Tocalculatedensity,usethisequation:

Density=Mass/Volume

P=m/v

Example:

Apieceofironhasamassof390kgandavolumeof0.05m3.Whatisitsdensity?

P=m/v

P=390kg/0.05m3

=7800kg/m3Remembertheunit!

Densitycanbekg/m3,g/cm3…etc

CalculatingVolumesfortheDensity

Foracuboidlikethis,simplymultiplyitslength,widthandheight.I’massumingyouknowthis,butifnot,workupyourmathsman…

Asforirregularsolids,measureoutacertainamountofwaterwithameasuringcylinder.Thisisthecontrol（somethingtocompareresultsto）.Dothesamewithanothermeasuringcylinder,anddropthesolidin.Notetheriseinthelevelofwater.Thedifferencebetweenthetwomeasurementsisthevolumeofthesolid,inthiscase,10ml.

Pressure

PressureinSolids

Letsstartlikethis:

Youcaneasilypushapinintoapieceofwoodquiteeasily,butitisprettymuchimpossibletomakeaholeinthewoodwithyourfinger.Youcantrywithlittlesuccess（andendupwithsplintersalloveryourfingers）.Whyisthat?

Thesmallpointofthedrawingpinconcentratesallyourpushingforceintoatinyarea,sothepingoesintothewoodeasily.

Togettothepoint,pressureisdefinedastheforceperunitarea.Forceismeasuredinnewtons（N）andareaismeasuredinsquaremetres（m2）.TheunitforpressureisN/m2orPa（forPascals）.

Unfortunately,thereisanequationthatcomeswithpressureandthisisONLYFORSOLIDS:

Pressure（inPascals）=Force（innewtons）/Area（insquaremetres）

p=f/a

Example:

Awomanweighs600Nandthetotalareaofhershoesincontactwiththegroundis0.0015m2.Findthepressuresheisexertingtotheground.

p=f/a

p=600N/0.0015m2

=400000Pa（or400kPa）

PressureinLiquidsandGases

Pressureinliquidsactequallyinalldirectionsaslongastheliquidisnotmoving.Thisisthesameforgases.Thepressureinairisastaggering100000Pa,butsincethepressureinsideourbodiesaresimilar,wedon’tfeelthepressure.Thepressureinairisalsoreferredtoas1.0atmosphere.

Tocalculatepressureinliquidsusethefollowingequation:

Pressure（inPa）=Height/Depth（inm）xDensity（inkg/m3）xGravitationalFieldStrength（inN/kg）

Orp=hdgNotethatgisusually10N/kgv

Example:

JustinBieber’s（ohmygod!

）swimmingpoolhasadepthof3m.Whatisthetotalpressureoftheswimmingpool?

Takethegravitationalfieldstrengthtobe10N/kgandthedensityofwatertobe1kg/m3（ignoretheswimmingpoolbeingchlorinated‘causeJB’sswimmingpoolisalwayscleananyways）.

p=hdg（theactualequationisp=hpg,butI’mnotbotheredfindingthatspecialpfordensity）

p=3mx1kg/m3x10N/kg

p=30Pa

TheBrownianMotion

BrownianMotion:

Thecontinualrandommovementofmicroscopicparticles.Whenparticlescollideintooneanother,thiscausesachangeinspeedanddirectionoftheparticles,makingthemrandomlymoveabout.

Boyle’sLaw

Thisisallsummarizedintothefollowingequation:

Pressure1xVolume1=Pressure2xVolume2

Orp1V1=p2V2

Example:

Atmosphericpressureis100kPa.Someairinasealedcontainerhasavolumeof2m3atatmosphericpressure.Whatwouldbethepressureoftheairifyoureduceditsvolumeto0.2m3?

100kPa=100000Pa

P1V1=p2V2

100000Pax2m3=p2x0.2m3

200000=0.2p2

P2=1000000Pa

=1000kPa

Andinwords…

Boyle’sLaw:

Ataconstanttemperatureandwithafixedmassofgas,pressureisinverselyproportionaltovolume.

Question:

Howdoesagasexertapressureonthewallsofitscontainer?

Billionsoftinyairparticlesmoveaboutincontinualrandommotion.Particlecollisionswiththewallsofthecontainerexertsaforce,whichgetsdistributedovertheareaofthewallofthecontainer,hence,exertingapressure.

PressureLaw

Temperaturealsohasaneffectonthepressureofagas.Thisisshowninanexperimentsetupontheright.Whenwaterisheatedgradually,theairisalsoheated,changingthereadingonthepressuregauge.Plotdowntheresultsandyou’dgetagraphthatlookssomethinglikethis.

Waitaminute…shouldn’tthepressurebeatzeropascals?

No.ThisisbecausepressureisNOTproportionaltotemperateinCelsius.Butwhathappensifyoucontinuecoolingthegas?

You’dfindthatwhenpressureiszero,thetemperatewouldbeat-2730C.Thistemperateisknownasabsolutezero.Whenconvertedtokelvins（anothertypeofmeasurementfortemperature）,absolutezeroiszerokelvins.Butbacktothepoint,whatwouldhappenifyouconvertedthetemperaturesintokelvins?

ConvertingbetweenKelvinsandCelsius

Kelvins=Celsius+273

Celsius=Kelvins–273

Ifyouconvertthetemperaturesintokelvins,thisiswhathappens:

Thereisapositivecorrelation!

ThisshowsthatpressureofgasisproportionaltotemperatureinKelvin.ThisleadsintothePressureLawequation:

（NotethattemperaturesmustbeinKelvin）

Pressure1/Temperature1=Pressure1/Temperature1

Orp1/T1=p2/T2

Example:

Youtakeanemptytinandputthelidontightly.YouheatitusingaBunsenburneruntilthetemperatureoftheairinsideis500C.Whatisthepressureoftheairinsidethetin?

Thetemperatureoftheroomis200Candatmosphericpressureis100kPa.

WemustfirstconvertthetemperatureinKelvin,so:

T1=20+273=293K（ThisisthetemperatureOUTSIDEthetin）

T2=50+273=323K（ThisisthetemperatureINSIDEthetin）

p1/T1=p2/T2

100kPa/293K=p2/323K

p2=110kPa

NowtosummarisethePressureLaw:

PressureLaw:

Withafixedmassofgasataconstantvolume,pressureisproportionaltotemperature（inKelvins）.

StatesofMatter

Solids

Liquids

Gases

Particlesarecloselypacked.

Regularstructure.

Vibrateaboutfixedpositions.

Particlesarecloselypacked.

Irregularstructure.

Randommotionwithinstructure.

Nofixedpositions.

Moveatrapidrandommotion.

Areveryspreadout.

ChangeinStatesofMatter

Unit2:

Energy

Whatthehellisenergy?

Well,energyisusedeverywhere!

Weneedtouseenergytowalk,tolifeobjects,topush,topull,andinmostcases,tothink.Machinesalsoneedtouseenergytopowerup.That’swhyyouriPodcan’tlastforeverwithoutelectricity!

Wegetourenergyfromfoodanditisthentransferredintootherformsofenergysuchaskineticenergyandheatenergy.Whatthehellareyoutalkingabout?

Wellyouwillfindoutlater.

DefineEnergy:

Energyistheabilitytodowork.

TypesofEnergyandEnergyConversions

ThistablesummarisessomeofthedifferenttypesofenergythatyouwillneedtolearnaboutinGCSE.

Energy

Description

Chemical

Energythatisstoredinfoodorbatteries.Weburnitintootherformsofenergy.

Thermal

Alsoknownasheatenergy.Mostenergyiswastedbyturningintothis.Weusethermalenergytokeepourselveswarm.

Sound

Alsoapossibleformofwasteenergy.ButI’msureyouknowwhatsoundis.Itisaseriesoflongitudinalwaves–butwe’llgettothatlater.

Light

Thisenergyemitsalight.Weneedlighttoseethings.Thingslikelightbulbshaveenergythatisconvertedtothis.

Electrical

Mostoftheenergyweneedisconvertedfromelectricalenergy.Electricalenergycanbemadefromotherformsofenergy.

GravitationalPotential

Storedenergythatvariesdependingonwhereyouare.Thehigher,themore.

Kinetic

Alsoknownasmovementenergy.Electricalenergyisconvertedtokineticenergytomakemotorswork.Wegetthisfromchemicalenergy.

Geothermal

Energyfromtheheatunderground–storedintheEarth’score.Thisisfoundinvolcanoesandthermalsprings.

ElasticPotential

Energythatisstoredinsprings.Thistypeofenergyisfoundincatapultsandbows.

NuclearEnergy

Theenergyreleasedwhenunstableuraniumatomsinthenuclearreactorbreakdownandformachainreaction.

Energyisconvertedindifferentways.Herearesomeexamples:

▪Whenwerun,chemicalenergyfromourfoodisconvertedtokineticenergy.Someofitiswastedbybeingconvertedintothermalenergy,makingushot.

▪Whenavibratorisused,chemicalenergyfromthebatteryisconvertedintoelectricalenergy,whichisthenconvertedintokineticenergy.Someiswastedthroughsoundenergy.

Efficiency

Energywillneverdisappear.Itcanonlybewasted–orconvertedintootherformsofenergy.PhysicistsbelievethattheamountofenergyintheUniverseisconstant–whichmeanswecannotuseenergyup.

ThisleadsustotheLawofConservationofEnergy.

TheLawofConservationofEnergystatesthat:

Energyisnotcreatedordestroyedinanyprocess.Itisjustconvertedfromonetypetoanother.

DrawingSankeyDiagrams

Whenweareconsideringenergytransfers,wemustrememberthataproportionoftheenergyinputiswasted.Realsystemscanneverhave100%efficiency.Theusefuloutputenergywillalwaysbelessthantheinput.Efficiencyisgiveninpercentage–usuallyanyway,butreadthequestionforthespecificunit.

ThisisaSankeydiagram.

Howdoesitwork?

WelltheSankeydiagramalwayspointsright.Theinputenergyiswrittenatthebeginningofthearrow,withtheamountofenergyspecifiedinjoules.Thenthearrowsplitsintomorearrows.Thearrowthatgoesstraightrightistheusefulenergy（whichneedstobestatedtoo）.Thearrowpointingdowniswastedenergy.

W