初三复习材料doc.docx
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初三复习材料doc
初三复习材料
12physicalknowledgereviewdata(mid-termexamtips,internaluse)thefirstchapter1,soundisproducedbythevibrationoftheobjects,vibrationtostop,stop・Thesoundofthevocalchordsofthevocalcords,thesoundofthebird,svoicefromthesoundofthetracheaandthebronchialjunction,thecricketsarevocalinthevibrationsoftheleftandrightwings.Thetransmissionofsoundrequiresmedium.Solids,liquids,andgasescantransmitsound.Avacuumcannottransmitsound.Thespeedofsoundindifferentmediaisdifferent・15°Csoundintheairattherateof340m/s・Ingeneral,thevelocityofsoundinsolid,liquid,andgasisgas-liquidsolidVV.
V
Itis.Soundtravelsthroughthemedium,andusuallythesoundwehearcomesfromtheair・Echo:
anobstaclewillreflectback.Theechoreachesaperson,searmorethan0.1sabovetheoriginalsound,andtheearcanseparatetheechofromtheoriginalandheartheechoatleast17m・Threecharacteristicsofsound:
pitch,loudness,andtimbre.
(1)thepitchofavoice・Frequency:
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:
theinternationalunitis:
volt(V):
Commonunitsare:
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