T6 L6 transers mk1ppt Physics4IGCSE.ppt

1 gcsephysics magnetismandelectromagnetism 2 lesson6 transformers aims torecallthestructureofatransformer andunderstandthatatransformerchangesthesizeofanalternatingvoltagebyhavingdifferentnumbersofturnsontheinputandoutputsides toknowandbeabletousetherelationshipbetweeninput primary andoutput secondary voltagesandtheturnsratioforatransformer 3 whatisatransformer 4 whatisatransformer wherearetransformersused whatdowecallatransformerthatincreasesvoltage whatdowecallatransformerthatdecreasesvoltage adeviceusedtoincreaseordecreasevoltage inthenationalgridandhouseholdappliances astep uptransformer astep downtransformer 5 transformers atransformerhastwoelectromagneticcoils whentheelectricitychangesinthefirstcoilanelectricvoltageiscreatedacrossthesecondcoil transformersareusedtochangethevoltageandcurrentoftheelectricitythatcomesfrombelco 6 howdoesitwork 7 transformers atransformercanchangethevoltageandcurrentofanelectricalsupply somedevicesneedlowvoltageandsomeneedsomeneedhighvoltage onlya c voltagecanbetransformedfromonevoltagetoanother thisiswhymainselectricityneedstobea c tounderstandatransformerweneedtolearnmoreaboutcoilsandcores 8 rememberthis anelectricvoltageisonlyinducedwhenthemagnetismoving weneedachangingmagnetismtomakeelectricity barmagnethaveasimilarmagneticfieldpattertoasolenoidwithcurrent 10 whatiswhat inputa c voltage inputorprimarycoil outputorsecondarycoil asoftiron o core outputa c voltage 11 whatiswhat theinputorprimaryvoltage theoutputorsecondaryvoltage numberofprimarycoils numberofsecondarycoils 12 inputside theprimaryvoltagecreatesamagneticfieldwhenitscurrentpassesthroughthecoil thea c voltagemeansthatthemagnetismthroughthecoilisalwayschanging 13 outputside themagnetismfromtheprimarycoilispassedthroughtheirontothesecondarycoil becausethemagnetismischangingavoltageisinducedinthesecondarycoil thesizeoftheoutputvoltagedependsonthesizeofthetwocoils changingthemagnetismisjustlikemovingamagnet onlyeasier 14 softironcore ironisasoftmagneticmaterial thismeansthatitisveryeasytomagnetizeandveryeasytodemagnetize inatransformerthedirectionofelectricityischangingmanytimeseachsecond everyfractionofasecondthecoreneedstochangeitsmagnetism weuseironbecauseitcanchangeitsmagnetismfromonedirectiontoanotherveryeasily 15 lampdemonstration 16 transformers transformerschangethevoltageandcurrentofana c electricalsupply inthefollowingexperimentmainselectricityat220voltsentersthecircuit afterleavingthetransformerthevoltagehasbeenreducedtoapproximately11volts 17 18 inputcircuit thevoltageentersthecircuitthroughthethick220voltwireandpassesthroughthecoilwith3600turns 19 outputcircuit thevoltageisinducedinthesmallerpartofthetransformerthatonlyhas300turnsofwire itthentravelsthroughthethinnerwirestothe11voltlamp 20 thelampisoffbecausethemagnetismisnotstrongenoughtogofromonecoiltheother 21 the c coreincreasesthemagnetism 22 the o coreisevenstronger 23 stepupandstepdown andanequationtolearn 24 isthisastep uporastep downtransformer primarycoil secondarycoil 25 isthisastep uporastep downtransformer primarycoil secondarycoil 26 lessturns lessvoltage 27 transformerformula theformulaforcalculatingvoltagesandcoilsinatransformerhasfourvariables 28 whichwayup theformulaisaboutvariables itdoesnotmatterwhichwayupyourememberthesymbols 29 transformerexample1 astep downtransformerisrequiredtotransform240va c to12va c foramodelrailway iftheprimarycoilhas1000turns howmanyturnsshouldthesecondaryhave v2 v1 t2 t1t2 t1 v2 v1 t2 1000 12 240 t2 50turns 30 transformerexample2 atransformerisdesignedtohave2500primaryturnsand5000secondaryturns whatistheoutputvoltageiftheinputvoltageis120v v2 v1 t2 t1v2 v1 t2 t1 v2 120v 5000 2500 v2 240v 31 230v transformerexample3 atransformerhas200turnsonitsprimarycoiland50turnsonitssecondarycoil theinputvoltageis920v whatistheoutputvoltage 32 500turns atransformerhas100turnsonitsprimarycoil ithasaninputvoltageof35vandanoutputvoltageof175v howmanyturnsareonthesecondarycoil transformerexample4 33 transformers transformersareusedto orstepdown theyonlyworkonacbecausean currentintheprimarycoilcausesaconstantlyalternating thiswill analternatingcurrentinthesecondarycoil words alternating magneticfield induce stepup voltage wecanworkouthowmuchatransformerwillstepuporstepdownavoltage ifatransformeris100 efficient thepowerproducedinthesecondarycoilshouldequalthepowerinputoftheprimarycoil powerstation homeappliance longtransmissionline lookslike rload rwire rwire powertransmission powerdissipatedinanelectricitydistributionsystem wecanfigureoutthecurrentrequiredbyasinglebulbusingp visoi p v 120watts 12volts 10amps estimateresistanceofpowerlines 0 001 m 2 105m 20ohms 120wattlightbulb 12voltconnectionbox powerplantoncoloradoriver 10km powerdissipate wasteintransmissionalineisp i2r 102 20 2 000watts efficiency ise 120watts 2120watts 5 6 whatcouldwechangeinordertodobetter thetradeoff thethingthatkillsusmostisthehighcurrentthroughthe fixedresistance transmissionlinesneedlesscurrentit sthatsquareini2rthathasthemostdramaticeffectbutourapplianceneedsacertainamountofpowerp visolesscurrentdemandshighervoltage solutionishighvoltagetransmissionrepeatingtheabovecalculationwith12 000voltsdeliveredtothehousedrawsonlyi 120watts 12kv 0 01ampsforonebulb givingp i2r 0 01 220 20 10 4watts sop 0 002wattsofpowerdissipatedintransmissionlineefficiencyinthiscaseise 120watts 120 004 99 996 39 example anaverageof120kwisdeliveredtoasuburb10kmaway thetransmissionlineshaveatotalresistanceof0 40 calculatethepowerlossift