物理报告实验八辐射定律

实验八实验八Ju4图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.距电热器5～10cm的地方，其金属表面对着温差电堆。色插头插入微伏表的红色插座中。将温差电堆的玻璃窗口打开。开始测量时，按“autocomp”对漂移进行补一、记录下实验开始时黄铜圆筒的温度（T0），温差电堆的最初的输出电