初三复习材料docWord格式文档下载.docx

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thenumberoftimestheobjectvibratesinasecond,theunitoffrequencyisHertz,thesymbolHz.Thehigherthefrequency,thehigherthepitch,thelowerthefrequency,thelowerthepitch・

（2）loudness:

thestrengthofthesound,thestrengthofthesoundindB.Amplitude:

theamplitudeofthevibrationofanobject,thelargertheamplitude,thegreaterthesound,thesmallertheamplitude,thesmallerthesound・Thesoundisalsorelatedtothedistanee,thesoundfromthesamesource,thefartherawayfromthesource,theweakerthesound.（3）timbre:

characteristicsofsound・Thefactorsthatdeterminethesoundcolor:

thematerial,structure,etc・Distinguishsoundsbydistinguishingsoundfromsound・5,man，shearingfrequencyfor20hz-20000hz

（1）time:

lessthan20hzfrequencysound,features:

longtransmissiondistance,pervasive,andsoon,mainlyinmajornaturaldisasters:

earthquakes,tsunamis,volcaniceruptions,typhoons,explosion,etc・，

（2）ultrasound:

thesoundofthefrequencyabove20000hz,features:

directionalgood,strongpenetratingpower,easytogetasoundenergyfromarelativelyconcentrated,canbeusedinthedistance,speed,cleaning,welding,graveletc.6,themeaningof:

（1）noisesoundbodydorandomvibrationsound（physicalperspective）・

（2）thesoundthatinterfereswithnormalrest,learningandwork,andthesoundofinterferenceinthesoundofpeoplelistening・（environmentalprotection）7noiselevelsandhazards:

greaterthan50dB,whichaffectsrestandsleep.Greaterthan70dBaffectslearningandwork;

Greaterthan90dBwilldamageyourhearing・Controlnoise:

reducenoiseinthesource,reducenoiseinthetransmissionprocess,andreducenoiseintheear・Theuseofsound:

（1）theuseofsoundtoconveyinformation.Whensoundencounteredobstaclesintheprocessoftransmission,voiceechoeswillbereflectedform,accordingtothetimethevoicereturned,candeterminethelocationoftheobstacles・The/zsonarz，device,whichisnowusedtodetecttheoceanfloor,isusedbymedical"

b-super"

tomakeuseoftheechoprinciple・

（2）usingsoundwavestotransmitenergy.Suchassoundwavescanbeusedtocleanclocksandotherprecisionmachinery;

Surgeonscanuseultrasonicvibrationstoremovestonesfromthebody.Thesecondchapter,thephenomenonoflight,thelightstraightlinedissemination1.thecharacteristicsofthelightsourceLightsourcereferstotheobjectgivingoutlightitselfcdn,thelightofthesun,glowing,litcandlesarelight,someobjectitselfdoesnotshine,butbecausetheycanreflectsunlightorothersourcesoflight,asiftheyareshining,don，tbemistakenforalightsource,suchasthemoonandalltheplanets,theyarenotreferredtoinphysicsofthelightsource・

Inthecourseoffriction,therubberbar,whichisboundbythenucleusofthenucleus,hasattractedthepast,sotherubberstickhasanequalamountofnegativechargebecauseofexcesselectrons・Whenthesolidmatterischargedwithfriction,thechargethathappenstomoveisnegativecharge,whichisthefreeelectron,thepositivechargedoesnotmovethetargetofthe9chargetoformthecurrent,

Thepositivechargemoveinthedirectionoftherulesforthedirectionofcurrent,metalconductivemovewhenthechargeisfreeelectrons,whichmoveinoppositedirectionwiththedirectionofcurrent,conductorconductivebyfreecharge,acid,alkali,saltaqueoussolutionconductivebypositiveandnegativeions10,easilyconductiveobjectiscalledaconductor,commonconductorsaremetals,graphite,theearth,thehumanbody,aswellasacid,alkali,saltsolution,conductoreasilyconductivebecausethereisalotoffreemovingchargesfromaconductor.11,itisnoteasytoconductiveobjectscalledinsulators,commoninsulatorsareceramics,rubber,glass,plastic,oil,etc・，aninsulatorisnoteasytoconductivebecauseinsulatorsinalmostnochargecanbefreetomove・Chapter4circuitcurrentvoltage1.Powersupply:

devicethatprovidescontinuouscurrent（orvoltage）・Poweristheconversionofotherformsofenergyinto

electricity.Forexample,drycellsconvertchemicalenergyintoelectricity・Ageneratorisconvertedbymechanicalenergyintoelectricity.Theconditionofcontinuouscurrent:

musthavepowersupplyandcircuitclosing・Thecircuitconsistsofelectricalpower,wire,switchandelectricalappliances・Thecircuithasthreestates:

（1）access:

thecircuitthatisconnectediscalledthepath;

（2）thebrokencircuit:

thebrokencircuitiscalledopenroad:

（3）shortcircuit:

thecircuitdirectlyconnectedtothesourceofthepowersourceiscalledashortcircuit・Circuitdiagram:

adiagramofacircuitconnectedbyasymboliscalledacircuitdiagram・Series:

thecircuitthatconnectsthecircuitelementsinsuccessiveconnections・Thecircuitinwhichthecircuitcomponentisconnectedtogetheriscalledparalle1.Thesizeofthecurrentisindicatedbythecurrentstrength（shortforcurrent）・TheunitofcurrentIis:

theinternationalunitis:

ampere（A）:

Commonunitsare:

miIlian（mA）,microan（A）.1ampere二103miIlian二106microampere・Themeterofthemeasuringcurrentis:

theammeter,whichisusedinthefollowingrules:

themeterisinseriesinthecircuit;

Theconnectionoftheterminalpostiscorrect,andthecurrentisenteredfromthe〃+〃terminal,fromthetermina1.Themeasuringcurrentshallnotexceed

therangeofthecurrentmeter;

Itisabsolutelynotallowedtoconnectthecurrentmetertothepolesofthepowersupplywithoutusingtheappliance・Therearetworangescommonlyusedinthelaboratory:

0~0.6,andthecurrentvalueofeachsmalllatticeis0.02.From0to3,thecurrentvalueofeachsmalllatticeis0.1Ann.Voltage（U）:

voltageisthecauseofelectriccurrentinthecircuit・Thepowersupplyisthedevicethatprovidesvoltage・TheunitofvoltageUis:

volt（V）:

KV,millivolt（mV）,andmicrovolt（V）.Onekilovolt二103volts二106millivolts二109microvolts・Theinstrumentofmeasuringvoltageis:

thevoltmeter,whichUSEStherule:

thevoltmetershouldbeinparallelinthecircuit・Theconnectionoftheterminalpostiscorrect,andthecurrentisenteredfromthe〃+〃terminal,fromthe〃-〃termina1.Themeasuredvoltageshallnotexceedtherangeofthevoltmeter;

Thevoltmetercommonlyusedinthelaboratoryhastworanges:

1,0、3v,andeachsmalllatticehasavoltagevalueof0.1volts・0to15volts,eachsmalllatticehasavoltageof0.5volts・Thevoltagevalueofmemorized:

1,1drybatteryvoltage1.5volts;

1leadbatteryvoltageis2volts;

Thefamilylightingvoltageis220volts;

Thevoltagetosafetyisnohigherthan36volts・Theindustrialvoltageis380volts・Resistance（R）:

theobstructionoftheconductortothecurrent・（aconductor'

sresistancetothecurrentisgreater

Thelargerthenumber,thesmallerthecurrentoftheconductor・Resistance（R）19units:

internationalunits:

ohm（Q）;

Customaryunitsare:

megohmQ（M）,qianQ（K）.1trillioneuros二103・Euro1000二103euro.20factorsdeterminingthesizeofresistance:

theresistanceoftheconductoristhenatureofaconductor,itdependsonthesizeoftheconductormaterial,length,cross-sectionalarea,andthetemperature・

（resistanceandaddintheconductoronbothendsofthevoltageandcurrentthrough）21rheostat（sliderheostatandresistancebox）:

（1）sliderheostatprinciple:

（1）changetheresistancewirelengthtochangeresistanceinthecircuit・Effect:

changesthecurrentandvoltageinthecircuitbychangingtheresistanceinthecircuit・（3）nameplate,suchasasliderheostatmarked〃50Q2a"

said:

isthesignificanceofmaximumvalueis50Q,allowsthemaximumcurrentis2a.Properuse:

a.shouldbeinseriesincircuit.B.Theconnectionshouldbe〃onego，z;

C.youshouldadjusttheresistorstothelargestplacebeforeyougettheelectricity・

（2）resistancebox:

arheostatthatcanrepresentaresistor・Ohm'

slaw:

theelectriccurrentinaconductorisproportionaltothevoltageintheconductor'

send,andinverselyproportionaltotheresistanceoftheconductor・Theformula:

（）theunit:

I,（A）;

UandV（V）;

R-European（Q）・1Ann二1volt/o.TheI,UandRintheformulamustbeinthesamecircuit;

IhavetwoquantitiesinI,U,andR,andIcantakeanotherquantity.Theunitshouldbeunifiedwhencalculating・4.Theapplicationofohm，slaw:

（1）thesameresistance,resistanceisconstantandhasnothingtodowithcurrentandvoltage,butaddonbothendsoftheresistorvoltageincreases,thethroughcurrentisincreased・（R二U/I）whenthevoltageisconstant,thegreatertheresistance,thelessthecurr