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李薩如圖線與頻率比Horizontal

intersectionVerticalintersection7Functiongenerator8空氣中聲速的測(cè)量

MeasurementofSoundVelocityinAirTheLab'centerofphysics9IntroductionAcousticsmaybedefinedasthegeneration,transmission,andreceptionofenergyintheformofvibrationalwavesinthematter.Astheatomsormoleculesofafluidorsolidaredisplacedfromtheirnormalconfiguration,aninternalelasticrestoringforcearises.Examplesincludingthetensile(張力)forceproducedwhenaspringisstretched.Itisthiselasticrestoringforce,coupledwithinertia(惰性)ofthesystem,thatenablesmattertoparticipate(參與)inoscillatoryvibrationsandtherebygenerateandtransmitacousticwaves.10Themostfamiliaracousticphenomenonisthatassociatedwithofsound.Fortheaverageyoungperson,avibrationaldisturbanceisinterpretedassoundifitsfrequencyliesintherangeofabout20to20000Hz.Howeverinabroadersenseacousticalsoincludestheultrasonicfrequenciesabove20000Hzandtheinfrasonicfrequenciesbelow20Hz.11Themeasurementofspeedofsoundisofinterestingforunderstandingthemainpropertyofsound.Onecaneasilyobtainthevelocityofsoundthroughthefollowingexpression:12Purpose學(xué)會(huì)用不同的方法測(cè)定空氣中的聲速。掌握數(shù)字式函數(shù)發(fā)生器、示波器的使用方法。學(xué)會(huì)用逐差法處理測(cè)量結(jié)果，并對(duì)結(jié)果的不確定度進(jìn)行分析。13ExperimentalmethodsResonancefrequencyResonanceMethod(amplitudemethod)PhasemethodLissajousFigures

method14Ultrasonic

velocimeter

Piezoelectric-ceramictransducerDigitalruler15Resonancefrequency當(dāng)一個(gè)振動(dòng)系統(tǒng)受到另一個(gè)系統(tǒng)周期性的激勵(lì)時(shí)，若激勵(lì)系統(tǒng)的激勵(lì)頻率與振動(dòng)系統(tǒng)的固有頻率相同時(shí)，振動(dòng)系統(tǒng)將獲得最大的激勵(lì)能量，此現(xiàn)象稱為共振（諧振）。實(shí)驗(yàn)中使用的超聲壓電陶瓷換能器具有固有諧振頻率，當(dāng)換能器系統(tǒng)的工作頻率等于諧振頻率時(shí)，換能器處于諧振狀態(tài)，發(fā)射器發(fā)出的超聲波功率最大，是最佳工作狀態(tài)。

161、諧振頻率的調(diào)整改變信號(hào)發(fā)生器的頻率時(shí)，看到……17Standingwave當(dāng)兩個(gè)換能器之間的距離,等于半波長(zhǎng)的整數(shù)倍時(shí)將發(fā)生共振，產(chǎn)生共振駐波現(xiàn)象，波幅達(dá)到極大。182、利用共振駐波法測(cè)量聲速 將換能器的接收端接入示波器的CH1通道，當(dāng)改變換能器之間的距離時(shí)……19Phasemethod

(1)travelingwavemethod沿傳播方向上的任何兩點(diǎn)，其振動(dòng)狀態(tài)相同（相位差為2π的整數(shù)倍）時(shí)，兩點(diǎn)間的距離應(yīng)等于波長(zhǎng)λ的整數(shù)倍，即:(n=positiveinteger)203、利用行波法測(cè)量聲速 保持剛才的接線，同時(shí)將發(fā)射波接入CH2,選擇觸發(fā)與發(fā)射波同步，當(dāng)改變換能器之間的距離時(shí)……21(2)CirculartracemethodIncidencesignalReflectedsignalCompositionalsignal224、利用李薩如圖法測(cè)量聲速 保持剛才的接線，水平顯示選擇X-Y，當(dāng)改變換能器之間的距離時(shí)……23ExperimentalequipmentsUltrasonic

Veloc