普通物理英语课件30_TemperatureEtc.pdfVIP

Temperature,Expansion,IdealGasLaw

Physics1425Lecture30

MichaelFowler,UVa

Everything’sMadeofAtoms

•Thisideawasonlyfullyacceptedabout100

yearsago—inpartbecauseofEinstein’s

analysisofBrownianmotion.

•Brown,whostudiedthesexlifeofplants,

noticedalotofjigglingpollengrainsunderhis

microscopein1827.Heassumeditwas

becausetheywerealive,butlaterfoundthe

identicaljigglingwithdefinitelydeadstone

powder.

•Thiswasnotunderstoodforhalfacentury….!

AppletMovie

SizeandMassofAtoms

•Thehydrogenatomisabout10-10macross,

othersareafewtimesbigger.

•Avogadro’sNumber:NA=6.02x1023,the

numberofatoms(ormolecules)inonegram-

mole,22.4LvolumeatNTP.

•Theatomicmassunitis1.66x10-27kg.The

massofamoleculeinamu=massofNatoms

A

ingrams:onegrammoleofH2Ois18grams.

•NOTE:thisisjustareminder—youshouldbe

veryfamiliarwithallthisfromchemistry!

ClickerQuestion

•AssumethemoleculesShakespearebreathedoutin

hislastbreath(say,oneliter)arenowuniformly

distributedthroughouttheatmosphere.Whatisthe

probabilityyoubreathedoneinjustnow,inyour

mostrecentbreath?

A.1in10,000

B.1in1,000

C.1in100

D.1in10

E.Morelikelythannot.

ClickerAnswer

Theansweris:morelikelythannot.

Thereare6X1023moleculesin22.4L,soabout

3X1022inoneliter.

TheEarth’satmospherehasvolume4πR2d,take

R=6x106m,d=2x104m.Thisgivesa

volumeabout1015321

m,or10L.

MeasuringTemperature

•Wecantellb