示波器的使用及声速的测量

示波器的使用

ApplicationofOscilloscopeTheLabcenterofphysics1Basicstructure

返回oscilloscopetube

Circuitelectrongun

electronbeam

Level

deflector

verticaldeflectorFluorescentscreen2displayprincipleofOscilloscope3sinusoidalwavesawtoothwave4Evenrotationofthedrum–evenmotionoftheelectronbeamalongthex-direction.Motionofthepeniny-direction–deviationofthebeaminy-directionproportionaltothemeasuredvoltage.Aquestion:Theelectronbeammovingalongx-directionreachestheendofthescreenatsomepointandhastojumpbackandstartwritingagainfromthebeginningofthescreen.

Howcomethatyounormallyonlyseeonecurveonthescreenatanytime?

Bytheway,howfastdoesthebeamgofromlefttoright?5Theansweristriggering.

Afterdrawingonecurve(sinusoidal,triangular,square…)onthescreentheelectronbeamreturnsbacktoitsstartingpoint,butitdoesnotstartdrawinganothercurve,beforethevoltagereachessomepresetvalue–triggerlevel.triggerlevel6LissajousFigures李萨如图线与频率比Horizontal

intersectionVerticalintersection7Functiongenerator8空气中声速的测量

MeasurementofSoundVelocityinAirTheLab'centerofphysics9IntroductionAcousticsmaybedefinedasthegeneration,transmission,andreceptionofenergyintheformofvibrationalwavesinthematter.Astheatomsormoleculesofafluidorsolidaredisplacedfromtheirnormalconfiguration,aninternalelasticrestoringforcearises.Examplesincludingthetensile(张力)forceproducedwhenaspringisstretched.Itisthiselasticrestoringforce,coupledwithinertia(惰性)ofthesystem,thatenablesmattertoparticipate(参与)inoscillatoryvibrationsandtherebygenerateandtransmitacousticwaves.10Themostfamiliaracousticphenomenonisthatassociatedwithofsound.Fortheaverageyoungperson,avibrationaldisturbanceisinterpretedassoundifitsfrequencyliesintherangeofabout20to20000Hz.Howeverinabroadersenseacousticalsoincludestheultrasonicfrequenciesabove20000Hzandtheinfrasonicfrequenciesbelow20Hz.11Themeasurementofspeedofsoundisofinterestingforunderstandingthemainpropertyofsound.Onecaneasilyobtainthevelocityofsoundthroughthefollowingexpression:12Purpose学会用不同的方法测定空气中的声速。掌握数字式函数发生器、示波器的使用方法。学会用逐差法处理测量结果，并对结果的不确定度进行分析。13ExperimentalmethodsResonancefrequencyResonanceMethod(amplitudemethod)PhasemethodLissajousFigures

method14Ultrasonic

velocimeter

Piezoelectric-ceramictransducerDigitalruler15Resonancefrequency当一个振动系统受到另一个系统周期性的激励时，若激励系统的激励频率与振动系统的固有频率相同时，振动系统将获得最大的激励能量，此现象称为共振（谐振）。实验中使用的超声压电陶瓷换能器具有固有谐振频率，当换能器系统的工作频率等于谐振频率时，换能器处于谐振状态，发射器发出的超声波功率最大，是最佳工作状态。

161、谐振频率的调整改变信号发生器的频率时，看到……17Standingwave当两个换能器之间的距离,等于半波长的整数倍时将发生共振，产生共振驻波现象，波幅达到极大。182、利用共振驻波法测量声速 将换能器的接收端接入示波器的CH1通道，当改变换能器之间的距离时……19Phasemethod

(1)travelingwavemethod沿传播方向上的任何两点，其振动状态相同（相位差为2π的整数倍）时，两点间的距离应等于波长λ的整数倍，即:(n=positiveinteger)203、利用行波法测量声速 保持刚才的接线，同时将发射波接入CH2,选择触发与发射波同步，当改变换能器之间的距离时……21(2)CirculartracemethodIncidencesignalReflectedsignalCompositionalsignal224、利用李萨如图法测量声速 保持刚才的接线，水平显示选择X-Y，当改变换能器之间的距离时……23ExperimentalequipmentsUltrasonic

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