electrostatics is the study of charges at rest · 4. connect one end of the black (negative) jumper...

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