物理報告實驗八輻射定律

實驗八實驗八Ju4圖Allbodiesradiateheat.Theintensityofthisthermallyexcitedelectromagneticradiationincreaseswithtemperatureofthebody,andisalsodependentonthesurfaceofthisbody.Atagivenwavelength,theheatabodyradiates,thebetteritcanabsorbthisheatabodyradiates,thebetteritcanabsorbthisAbodywhichcompletelyabsorbsheatradiationofallwavelengthsiscalledablackbody.ItwasKirchhoffwhofirstproposedusingacavityasavirtuallyidealblackbody.Theblackbodyhasthegreatestabsorptionfactor,andthus,atagiventemperatureandwavelength,thehighestpossibleemissivityaswell.TheStefan-BoltzmannlawstatesthatthetotalemittedradiationofablackbodyincreasesproportionallytheabsolutetemperatureTraisedtothefourthpower.Moreprecisely,theradiantexitanceM,i.e.thetotalpowerradiatedononesideofthesurfacewithreferencetotheareaoftheradiatingsurface,isdefinedasM=(=5.67w10–8 mAtthesametime,theblackbodyabsorbsradiationfromitsenvironment.Thus,wedonotmeasuretheradiatedradiantexitanceM,butrathertheradiantexitanceM’withdrawnfromtheblackbodybyradiation.TheradiantexitanceabsorbedfromtheenvironmentisM=T400M’=(T4–T04)Inthisexperiment,anelectricovenwithablackbodyaccessoryisusedasthe“blackbody”.Theblackbodyaccessoryconsistsofaburnishedbrasscylinderandascreen.Thebrasscylinder,whichissealedatoneend,isslidintotheelectricovenandheatedtothedesiredtemperature.Thescreen,whichcanbewater-cooledifnecessary,isarrangedinfrontoftheelectricoven,sothatessentiallyonlythethermalradiationoftheburnishedcylinderismeasured,andnottheouterwallofthehotoven.AnNiCr-Nitemperaturesensorisusedtomeasurethetemperatureatthebrasscylinder.ThethermalradiationismeasuredusingaMoll’sthermopiletowhichamicrovoltmeterisconnected.Thethermopilecontainsanumberofthermocouplesconnectedinseries.Themeasuringpointsabsorbtheincidentradiationalmostcompletely,whilethecomparisonpointsareattheambienttemperatureWecanthustaketheoutputvoltageofthethermopileasarelativemeasureoftheradiantexitanceM＇。CompensatingtheSetfunctionswitch3topositionWhenthemeasuringcircuitisconnectedbutvoltage-free,presskey8forautomaticcompensationofexternalandinternaloffsetvoltages.Ifthezerosettingofthedigitaldisplayandanalogoutputisnotachievedwhenthekeyisreleased,carryoutfineadjustmentusingthepotentiometer7.3.2VoltageSetfunctionswitch3toposition3.2.1VoltageConnectthemeasuringcircuitatsocketpair1,butmakesurethismeasuringcircuitisinitiallyde-energized(switchoffallexternalvoltageandcurrentSetfunctionswitch3toposition3.2.1VoltageConnectthemeasuringcircuitatsocketpair1,butmakesurethismeasuringcircuitisinitiallyde-energized(switchoffallexternalvoltageandcurrentsources).Selecttheappropriatemeasuringrange.Forsensitivemeasurements(U<1mV):hemeasuringcircuittodiminish(approx.1minute),then:Compensatetheoffsetbypressingkey8(alsocarryoutfineadjustmentusingpotentiometer7ifnecessary)tosetthedigitaldisplayandanalogoutputtozero.ApplythevoltageUtobemeasuredbyswitchingonthevoltageandcurrentsourcesinthemeasuringcircuit;readthevoltagefromthemeter.距電熱器5～10cm的地方，其金屬表面對著溫差電堆。色插頭插入微伏表的紅色插座中。將溫差電堆的玻璃窗口打開。開始測量時，按“autocomp”對漂移進(jìn)行補(bǔ)一、記錄下實驗開始時黃銅圓筒的溫度（T0），溫差電堆的最初的輸出電