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Atatomiclevel,ferromagneticmaterialsexhibitlocalmagneticpolarizationeffects–organizedin“domains”.Eachdomainishighlymagnetized,butbecauseitsdirectionisrandom,thebulkeffectisthattheseadduptozero.So,thematerialisnotmagnetized.
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Whenanexternalmagneticfieldispresentinthearea nearaferromagneticmaterial,allthedomainsalign,leadingtoamagnetizedmaterial.Thiswillattract theferromagneticfieldtothesolenoid.
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Whentheferromagnet movesintothecenterofthesolenoid,itwillstopmovingifwedon’tturnthecurrentoff.Thisisbecausethemotionoftheferromagnet intandemwiththesurroundingmagneticfieldinducessomethingcallededdycurrents,whichinfactopposethemotionoftheferromagnet throughthecoil.So….
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Weneedtoturnofthemagneticfield!– Wedothisbyturningoffthecurrent!Momentumcontinuestopropeltheprojectilethrough thecoils.
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Notethetwoswitchesonthecircuit;theyaremeanttoisolateonepartofthecircuitfromtheother; notethatthecapacitorsparticipateinbothcircuitsections.
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Notethetwoswitchesonthecircuit;theyaremeanttoisolateonepartofthecircuitfromtheother; notethatthecapacitorsparticipateinbothcircuitsections.
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Whenwe“close”switch1, wecreateapathforcurrenttoflowthroughthecircuit.Infact,whathappensisthatthesourcewilldepositenough+chargeonthetopcapacitorplate(anddepletethecorrespondingamountfromthebottomplate)sothateventually,thecapacitorswillhaveapotentialdropacrosstheirterminalsequaltothesourcevoltage(useKVLtoprovethatthishastobetrue).Theseriesresistorisslowingdownthecurrent– keepingitatreasonablelevelssoitdoesn’tburnallyourdevices.
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So,inasimplifiedcircuit,ifthesourcesuddenlygoesfrom0Vto5V(V1above,“simulating”theswitchturningon),thecapacitorC1willslowly(redline)becomechargedsothattheimbalanceofchargecreatesavoltagedropacrossthecapacitorequaltothevoltageV1.R1istheretokeepthecurrenttoafinitevalue– soitactuallyslowsdowntheprocessofchargedepositionontheplates.
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Ifyounow“open”switch1(thuscuttingoffcurrentflowinthatbranch)and“close”switch2(thusallowingcurrenttoflowthroughthatbranch),thenyoumight notlooklikeyouhaveasourceofcurrentbutyoudo.Rememberallthechargeyoustoredinyourcapacitorthatdidn’thaveanywheretogo?Nowitdoes.KVLnowwantsthevoltageacrossthecapacitortogotozero,socurrentwillflowintothebranchontheright.
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Currentwillnowflowthroughtheinductor– whichjusthappenstobethecoilyouareusinginyourcoilgun!Thiscoildoesnothavealargeresistance,butitdoeshavesomeresistance. Nevertheless,theRCtimeconstantinthiscaseismuchsmaller,sothishastheeffectofproducingaverylargecurrent overaverysmalltimeperiod.
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Notehow thevoltageacrossthecapacitordischarges throughtheresistorRcoil – yes,thisisnotaninductorbutremember,theinductorhassomeresistance.ThisresistanceisrepresentedbyRcoil inthecircuitabove.
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So,comingbackto thecoil– itwillsuddenlybesubjectedtoaveryhighcurrent,whichwilllastforenoughtimetopulltheprojectileintoitscore.Remember,oncethere,weneedthecurrenttoturnoff. Whichitdoes– naturally,becausethecapacitoritselfonlyprovidesthecurrentforasmallamountoftime.Momentumdoestherest.Yourprojectilewillcontinuetotraveldownthetubeuntilitrunsoutofkineticenergy(dueto?).
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