Post on 04-Aug-2020
Electrostatics isthestudyofchargesatrestElectricity putsthosechargesinmotionForthat,youneedapotentialdifference(a.k.a voltage)andaconductiveloopforelectronstoflow.
Current:FlowofelectricchargeI(unit:amperes)=Q/t=Coulombs/second
0.001Acanbefelt0.005Aispainful0.010Acausesinvoluntarymusclecontractions0.015Acauseslossofmusclecontrol0.070Acanbefatalifthecurrentlastformore
than1second
Lightgoeson‘instantly’whenswitchturnedonElectronsdonotmoveatspeedoflight
Speedoflight(c)=3x108m/sElectrons– 6x105 m/sinrandomdirections
Signal(energy)movesatspeedoflightduetoelectricenergyfield
Electronsincircuitdonotcomefrombatterybutarefromthewire
Batteriessupplyelectricenergytoasystem➤ TheydoNOTcreatecharge➤ TheydoNOTsupplyelectriccharge➤ theypush charge➤ Batteriesuseachemicalreactiontocreateapotentialdifferenceacrossitspositiveandnegativeterminals
Thinkofvoltageasakindofelectricpressure,likeahose.Morevoltage=greater“push”ontoelectrons
1.Makesurebothcarsareturnedoff.2.Connectoneendofthered(positive)jumpercabletothepositiveterminalonthestalledbattery.3.Connecttheotherred(positive)cable tothepositiveterminalofthegoodbattery.4.Connectoneendoftheblack(negative)jumpercabletothenegativeterminalofthegoodbattery.5.Connecttheotherblack(negative)cabletoaclean,unpaintedmetalsurfaceunderthedisabledcar’shood.Somewhereontheengineblockisagoodplace.Unlessyouwanttoseeflyingsparksandapossibleexplosion,donotconnectthenegativecabletothenegativeterminalofthedeadbattery.6.Startthecarthat’sdoingthejumping; runfor2to3minutesbeforestartingdeadcar.7.Removecablesinreverseorder.8.Keepjumpedcarrunningforatleast30minutestogivebatterysufficienttimetorecharge.
Howtojumpadeadcarbattery(don’tneedtomemorizeforquiz)
V
Acidremoveselectronsfromthezinc(anode,black)PositivelychargedzincionsmoveintosolutionElectronsremovedbytheacidflowintothewireintothecopper(cathode,red)CopperwantselectronsmorethanzincdoesHydrogenionsintheacidmeetelectronsinthecopper,makingbubblesofhydrogengasonthecopper
Toknowforquiz:- Electronsmovefromanode,throughwire,into
cathode- Currentmovesfromcathode,throughwire,into
anode- Anodeandcathodecan’tbesamemetal- youneed
apotentialdifferenceinorderforcurrenttoflow- Fruitisn’tgeneratingelectricity– itisprovidingthe
acidthatreactswiththeanode(zinc)toproducefreeelectronsthatleavethroughthewire
Whichhasagreaterresistance?R1:greatestslopeOhm’sLawEquation:V=IRV=voltage(a.k.a.potentialdifference,involts)I=Current(inamperes)R=resistance(inOhms)
Blue(Y3):thickestwire,red(Y2):thinnestwire
Resistance:measureofamaterial’sabilitytoresisttheflowofofelectronsΩ (ohms)Conductor– lowresistivity
materialswithfreeelectronse.g.copper,aluminum,gold,mostmetals
Insulator– highresistivitymaterialswithnofreeelectronse.g.glass,plastics,ceramics,wood
SUPERCONDUCTORS➤ Eventhebestconductorsputupsomeresistancetoelectriccurrent➤ Theresistivityofamaterialdependssomewhatontemperature➤ Generally,resistivityincreaseswithtemperature➤ Somematerials,oncecooledbelowaparticularcriticaltemperature,willofferexactlyzeroresistance➤Materialsinsuchastatearesaidtobesuperconducting
Turned on
ResistivityalsodependentontemperatureLightbulbismostlikelytoburnoutrightafteryouturniton–Filamentiscold,soithaslowerresistance,sohighercurrent.(V=IR)Whenitgetswarmer,itsresistanceincreases,soithasalowercurrent.(V=IR)
Whenwesayanappliance“useselectricity”,wearereallysayingthat
A.CurrentdisappearsB.ElectricchargesaredissipatedC.ThemainpowervoltageisloweredD.ElectronsaretakenoutofthecircuitE.Electronkineticenergyisconvertedinto
heatenergy,lightenergy,ormechanicalwork.
PowerP=Energy/time
P=IV
Allelectronicdevicesofferresistancetotheflowofcurrent➤ Anythingthatoffersresistance“eatsup”electricenergy➤ often(readinevitably)byconvertingittoheatenergy➤ sometimesinordertodowork
Electricenergyisusefulbecauseitcanbeeasilytransformedintootherformsofenergy➤motorsturnitintomechanicalwork➤ electricheaters,stoves,toasters,andhairdryersturnitintothermalenergy➤ lightbulbsturnitintolightandthermalenergy➤
Anelectricirondrawsacurrentof4Aat250V.Whatisitspowerusage?
A. 0.0166WB. 60WC. 1000W
Acommonlightbulb reads60W,120V.Howmuchcurrentinampereswillflowthroughthebulb?
A. 7200ampsB. 0.5ampsC. 2.0amps
Whatvoltageisthislightbulbmeantfor?(120V)Howmuchcurrentispassingthroughthis?(110mA=0.11A)Mostbulbsocketsdelivereither12or120V.Whatwouldhappenifwepluggedthisbulbintoa12Vsocket?P=IVCalculateresistance:V=IR,R=V/I=120/.11=1100Ohms
Determinethecostofusingthefollowingappliancesforthetimeindicatediftheaveragecostis9cents/kWh.
(a)160WcolorTVfor3hoursand30minutes0.16kWx(3.5h) x9cents = 5.04cents
kWh(b)Six60Wbulbsfor7hours.
6x.06kWx(7h) x9cents = 22.68centskWh
Whichwillhavegreaterresistance?A.1B.2C.Theywillhavethesameresistance
Thesimplecircuit
Calculatethecurrentthroughthelightbulb(R1)andthepowerdissipatedthroughthebulbWhatisthedirectionofcurrentvs.thedirectionofelectronflow?V=IR,P=IVI=V/R=10V/5Ohms=2AP=2Ax10V=20W