Electrostatics Chapter 23What’s HappeningProbable First Observation ElectricityIdiot!A Quick ExperimentHistoryAmberDemo – Lets make some observationsExperimental ProcedurePredictionsExperiment #1Experiment #2Experiment #3What is the effect ofExperiment #4What’s Going On?From whence this charge???Experiment #5Neutral ObjectInductionPolarizeGroundRemove GroundPositive !Slide 25Same as before: PolarizationFrom WebAssignExampleAnother ExampleExample - TapeSlide 31Effect of ChargeWe have also observed that there must be TWO kinds of charge.What happens when two surfaces touch or rub?Slide 35Summary - RubbingsWhat have we found?Forces Between ChargesTypes of MaterialsSlide 40This is WARNothing Happens! The Green thing is a Force Field!Side ViewProperties of a FORCE FIELDFieldsExample – Gravitational Field.The Gravitational Field That We Live In.Coulomb’s Law – Force between chargesRememberCoulomb’s LawSlide 51Slide 52The Electric FieldSlide 54Slide 55Slide 56Slide 57Slide 58Mysterious ForceElectric FieldTwo ChargesDoing itGeneral-Force  FieldSlide 65Two Charges What is the Electric Field at Point P?The two S’sWhat is the electric field at the center of the square array?Kinds of continuously distributed chargesContinuous Charge DistributionymmetryLet’s Do it Real TimeThe mathA Harder ProblemSlide 75Completing the MathDare we project this??The GeometrySlide 79Final ResultLook at the “Field Lines”What did we learn in this chapter??What else did we learn in this chapter?Slide 84The SphereSummaryTo be remembered …Electrostatics Chapter 23Week-1-2What’s Happening•Clicker use will start on Friday (maybe).•Today we begin the study of charge with make-believe clickers.•There will NOTNOT be a quiz this week.•There WILLWILL be a quiz next Friday.•WebAssigns are now active.Probable First Observation ElectricityElectricityIdiot!If lightening had actually traveled down the kite string, old Ben Franklin would have been toast!Probably never happened, but good story!A Quick ExperimentHistory600 BCThales of Miletos rubs amber (electron in Greek) with cat fur and uses it to pick up feathers.Important questions:Why was he doing this?Didn’t he have a job??What happened to the skinned cat?AmberMillion years ago large stands of forests in some parts of the world began to seep globs of sticky resin! This aromatic resin oozed down the sides of trees, as well as filling internal fissures, trapping debris, such as seeds, leaves, feathers and insects. As geologic time progressed the forests were buried and the resin hardened into a soft, warm, golden gem, known as amber. Amber is the fossilized resin of ancient trees which forms through a natural polymerization of the original organic compounds. Most of the world's amber is in the range of 30-90 million years old.Demo – Lets make some observationsRubberDead Cat or RabbitGlassWoolNOT Shown: Aluminum RodsExperimental ProcedurePivotThe sequence of Experiments1. Identify the two rods2. Treat each rod3. Bring one rod near to the other4. PREDICT WHAT WILL HAPPEN5. VOTE ON POSSIBILITIES6. Observe what happens7. Did we learn anything?Predictions1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenExperiment #1PivotRubber rodRubber rod1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenExperiment #2PivotRubber rubbed withskin of dead rabbitRubber rubbed withskin of dead rabbit1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenExperiment #3PivotGlass rubbed with wool1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenGlass rubbed with woolWhat is the effect ofDISTANCE??Experiment #4Pivot1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenGlass rubbed with woolRubber rubbed withskin of dead rabbitWhat’s Going On?All of these effects involve rubbing two surfaces together.Or pulling two surfaces apart.Something has “happened “to each of these objects.These objects have a new PROPERTYOther properties are mass, colorWe call this NEW PROPERTY CHARGE.From whence this charge???-+PivotExperiment #5Rubber rubbed withskin of dead rabbitMetal Rod1. Rods will attract each other2. Rods will repel each other3. Nothing will happen4. Something not listed above will happenNeutral ObjectPositive charge attracts negative charges.Rod becomes “polarized.Negative end is closer to positive chargeDistance effect causes attraction.InductionPolarizeGroundRemove GroundPositive !Balloon PhysicsSame as before: PolarizationFrom WebAssignThree are brought close to each other, two at a time. When objects A and B are brought together, they attract. When objects B and C are brought together, they repel. From this, we conclude which of the following? (Select all that apply.) [_] Objects A and C possess charges of the same sign. [_] All three of the objects possess charges of the same sign. [_] One of the objects is neutral.[_] Objects A and C possess charges of opposite sign. [_] We need to perform additional tests to determine information about the charges on the objectExamplePITH BALLSAnother ExampleExample - TapeEffect of ChargeWe have also observed that there must be TWO kinds of charge.Call these two typespositive (+)negative(-)We “define” the charge that winds up on the rubber rod when rubbed by the dead cat to be NEGATIVE.The charge on the glass rod or the dead cat is defined as POSITIVE.What happens when two surfaces touch or rub? Bonding!Bonding!The Triboelectric SeriesNo! No!When two of the following materials are rubbed together under ordinary circumstances, the top listed material becomes positively charged and the lower listed material becomes negatively charged.MORE POSITIVE rabbit's fur glass mica nylon wool cat's fur silk paper cotton wood acrylic cellophane tape polystyrene polyethylene rubber balloon saran wrap MORE NEGATIVE No! No!Summary - RubbingsWhat have we found?There are TWO types of charge.PositiveNegativeLike Charges AttractUn-Like charges repelThe force between charges increases as they are brought closer together.This charge separation results from chemical bonds which are severe in the pocess.Forces