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Electromagnetism Article HowElectromagnetsWork Whatdoesajunkyard,rockconcertandafrontdoorhaveincommon?Theyalluse electromagnets--devicesthatcreateamagneticfieldthroughtheapplicationofelectricity. Junkyardsemployextremelypowerfulelectromagnetstomoveheavypiecesofscrapmetalor evenentirecarsfromoneplacetoanother.Yourfavoritebanduseselectromagnetstoamplify thesoundcomingoutofitsspeakers.Andwhensomeoneringsyourdoorbell,atiny electromagnetpullsametalclapperagainstabell. Mechanically,anelectromagnetisprettysimple.Itconsistsofaconductivewire,usually copper,wrappedaroundapieceofmetal.Acurrentisintroduced,eitherfromabatteryor anothersourceofelectricity,andflowsthroughthewire.Thiscreatesamagneticfieldaround thecoiledwire,magnetizingthemetalasifitwereapermanentmagnet.Electromagnetsare usefulbecauseyoucanturnthemagnetonandoffbyclosingoropeningthecircuit. Asyouknow,magnetshavetwopoles,"north"and"south,"andattractthingsmadeofsteel, ironorsomecombinationthereof.Likepolesrepelandoppositesattract.Forexample,ifyou havetwobarmagnetswiththeirendsmarked"north"and"south,"thenorthendofone magnetwillattractthesouthendoftheother.Ontheotherhand,thenorthendofone magnetwillrepelthenorthendoftheother(andsimilarly,southwillrepelsouth).An electromagnetisthesameway,exceptitis"temporary"--themagneticfieldonlyexistswhen electriccurrentisflowing. Thedoorbellisagoodexampleofhowelectromagnets canbeusedinapplicationswherepermanentmagnets justwouldn’tmakeanysense.Whenaguestpushesthe buttononyourfrontdoor,theelectroniccircuitryinside thedoorbellclosesanelectricalloop,meaningthecircuit iscompletedand“turnedon.”Theclosedcircuitallows electricitytoflow,creatingamagneticfieldandcausing theclappertobecomemagnetized.Thebellrings,the guestreleasesthebutton,thecircuitopensandthe doorbellstopsitsinfernalringing.Thison-demand magnetismiswhatmakestheelectromagnetsouseful. Bycontrollingthecurrent,youcanessentiallyturnthe magnetonandoff.Whenthecurrentisturnedoff,the atomsreturntotheirnatural,randomstateandtherod losesitsmagnetism. Puttingthe“Electro”inElectromagnets Anythingthatproducesacurrentcanpoweranelectromagnet--fromthesmallAAbatteries usedinyourTVremotetolarge,industrialpowerstations. Let’sstartwithalookathowhouseholdbatteriesfunction.Mostbatterieshavetwoeasily identifiablepoles,apositiveandanegative.Whenthebatteryisn'tinuse,electronscollectat thenegativepole.Whenthebatteriesareinsertedintoadevice,thetwopolescomeinto contactwiththesensorsinthedevice,closingthecircuitandallowingelectronstoflowfreely betweenthepoles.Whilethisishappening,themovingelectronsalsocreateamagneticfield. Inanelectromagnet,thebattery'schemicalenergytransformstoelectricalenergyinthewire. Additionally,electromagneticenergyinthenailtransformstoheatenergy.Becausethe magneticfieldsobeytheprincipleofsuperposition,liningupseveralwireswiththecurrentsall pointinginthesamedirectionresultsinthenetmagneticfieldofthefourwiresacting togetherbeingalargerlooparoundallthewires,asillustratedinFigure1. Figure 1. Super position of induced magnetic field of four electric currents going into the page.
