Lecture 1-2What’s Happ’nin?YesterdaySummary - RubbingsTRIBOELECTRIC SERIES When we rub two different materials together, which becomes positively charged and which becomes negative? Scientists have ranked materials in order of their ability to hold or give up electrons. This ranking is called the triboelectric series. A list of some common materials is shown here. Under ideal conditions, if two materials are rubbed together, the one higher on the list should give up electrons and become positively charged. You can experiment with things on this list for yourself .Forces Between ChargesPithPith BallA PITHY DEMOPithy HappeningsMetal Rod InteractionInductionMore InductionSlide 14Slide 15Magic?How many ways can we transfer charge? Let us count the ways. ……………..Willie the ShakeCoulomb’s LawVery Important Concepts in PhysicsLet’s Do Some ProblemsSlide 21In the figure, particle 1 of charge +1.0 µC and particle 2 of charge -4.0 µC, are held at separation L = 11.0 cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the coordinates of particle 3? x=[-11] cm y=[0] cmSlide 23A mechanics problem from the past!Free Body Forces?Slide 26Slide 27What is this “charge” thing?What is e??How Do We Know??? Millikan Oil Drop ExperimentWhat have we found?Slide 32The ElectroscopeLecture 1-2Charge - ContinuedWhat’s Happ’nin?By now you should have registered on WebAssign and tried the initial assignment.Watch for the appearance of a REAL assignment.You should be reading the first chapter.You should have read the syllabus (web).YesterdayWe looked at charge.and MagicSummary - Rubbings-- - + - +- -TRIBOELECTRIC SERIES your handglassyour hairnylonwoolfursilkpapercottonhard rubberpolyesterpolyvinylchloride plasticTRIBOELECTRIC SERIESWhen we rub two different materials together, which becomes positively charged and which becomes negative? Scientists have ranked materials in order of their ability to hold or give up electrons. This ranking is called the triboelectric series. A list of some common materials is shown here. Under ideal conditions, if two materials are rubbed together, the one higher on the list should give up electrons and become positively charged. You can experiment with things on this list for yourself .GIVES UP MORE ELECTRONS+-Forces Between Forces Between ChargesChargesQ1Q2Attract Repel+ + X+ - X- + X- - XPith Main Entry: 1pith Pronunciation: 'pithFunction: nounEtymology: Middle English, from Old English pitha; akin to Middle Dutch & Middle Low German pit pith, pit1 a : a usually continuous central strand of spongy tissue in the stems of most vascular plants that probably functions chiefly in storage b : any of various loose spongy plant tissues that resemble true pith c : the soft or spongy interior of a part of the bodyPith BallGenuine Pith !!!Genuine Pith !!!A PITHY DEMOPithy HappeningsCharge Transfer by ContactMetal Rod InteractionInductionMore InductionMagic?How many ways can we transfer charge? Let us count the ways.……………..Willie the ShakeDirect ContactSeparation of bonds (rubbing, etc,)ConductionInductionMagic.Coulomb’s LawF is a vector.magnitudedirection1/40=k=8.99 x 109 Nm2/C2DEFINITION – Unit of Charge is the coulomb221041rQQ FVery Important Very Important Concepts in PhysicsConcepts in PhysicsSSuperposition SSymmetryLet’s Do Some ProblemsStrategy1. Think about how you will proceed.2. What information is given, what is missing?3. Develop the equations in an algebraic format.4. Solve for an algebraic solution.5. Plug in the numbers at the end.6. Look at some special cases to check on consistancy.7. Think about what you have learned that is worth retaining.In the figure, a central particle of charge -2q is surrounded by a square array of charged particles, separated by either distance d or d/2 along the perimeter of the square.In the figure, particle 1 of charge +1.0 µC and particle 2 of charge -4.0 µC, are held at separation L = 11.0 cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the coordinates of particle 3? x=[-11] cm y=[0] cmA mechanics problem from the past!Free Body Forces?Find force on lower left Find force on lower left particle.particle.What is this “charge” thing?There are two charged particles we will be concerned with:ElectronsProtonsElectrons have a charge of –eProtons have a charge of +eALL charges are an integral multiple of this fundamental charge “e”What is e??|e|=1.6 x 10-19 CoulombsExact value in textbookHow Do We Know???Millikan Oil Drop ExperimentA Critical BalanceWhat have we found?There are TWO types of charge.PositiveNegativeLike Charges AttractUn-Like charges repelThe force between charges increases as they are brought closer together.This charge separation results from chemical bonds which are severed in the process.Forces Between ChargesQ1Q2Attract Repel+ + X+ - X- + X- - XThe
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