Lecture 1 Charge Chp. 22IntroductionCharged Hair Van de Graaff DemoIntroduction ContinuedSome preliminariesModel of electricityMore preliminariesComparison of which bands are filled and which are empty to explain the difference between metals and insulatorsMethods of Charging Objects: Friction, Contact, and InductionCharging Insulators by Friction/RubbingLeaf ElectroscopeUse UVa ElectroscopeCharged UVa ElectroscopeExplain Electrostatic kit for LabTwo teflon rods on spinnerSummaryTriboelectric series http://www.sciencejoywagon.com/physicszone/lesson/07elecst/static/triboele.htmCharged rods on spinner/similar to picture in bookCharging by Contact / Induction using conductorsShow Uniform Distribution of Charge on Sphere using EEShow induction using two conducting spheres and EEShow Induction using electroscope (small effect)Electrophorous(Induction) http://www.physicsclassroom.com/mmedia/estatics/epn.htmlConservation of chargeSummary: Electrostatics is based on 4 four empirical factsWhat is meant by quantization of charge?Coulombs LawUniformly charged metal spheres of Radius RCoulombs Law examplesSlide 30Principle of SuperpositionExampleExample Cont.In an atom can we neglect the gravitational force between the electrons and protons? What is the ratio of Coulomb’s electric force to Newton’s gravity force for 2 electrons separated by a distance r ?Why are neutral objects always attracted to positive or negative charged objects.Explanation: The neutral objects atoms and molecules orient themselves in the following way so that the Coulomb forces due to attraction are greater than those due to repulsion because the latter are further away. (Inverse square Law)PowerPoint PresentationWhat is the real distribution of charge along a conductor like a wire or tube? How does the charged UVa electroscope really work?How the electroscope works? How is charge distributed along a conducting rod?Slide 40Show hanging charged/conducting pith ball: first attraction by induction, then contact, then conduction of charge, then repulsionFind charge Q on two pith balls separated by distance dWarm up set 1Otto von Guericke in 1660 charged a 7” Sulphur sphereLord Kelvin Water Drop Generator (Early 18’th century)Kelvin Water Drop GeneratorWimshurst MachineVan de Graaff AcceleratorSummer July 04 PHYS632 E&M 1Lecture 1 Charge Chp. 22•Cartoon - Charge is analogous to mass•Opening Demo - Large Van de Graaff•Warm-up problem•Physlet - static cling•Topics–What is electric charge? Point objects, Size. Atomic model–Methods of charging objects. Friction,Contact, Induction, Machines–Instruments to measure charge–Quantization of charge and conservation of charge–Coulombs Law and examples–Principle of superposition and examples•List of Demos–Teflon, glass, wood, spinner, and silk and UVa electroscope and leaf electroscope–Pivoting 2 x 4 balanced on glass illustrates strength of temporary induced charge–Use two metal spheres, measure charge on it, show induction of opposite charge–Two hanging pith balls with double string plus calculation–Electrophorous two aluminum pie plates with styrofoam and handle,–Electrometer and Faraday cage–Small Van de Graaff Generator, lightning rod, electroscope, electric wind,Fluorescent light tube,LED, screen,–Kelvin water drop generatorSummer July 04 PHYS632 E&M 2Introduction•“In the matter of physics, the first lessons should contain nothing but what is experimental and interesting to see. A pretty experiment is in itself more valuable than 20 formulae.” Albert Einstein€ Q =2Lmgdk(secθcsc3θ2+ sec3θ2)Summer July 04 PHYS632 E&M 3Charged Hair Van de Graaff Demo•How does this gadget produce a mini-lightning bolt?•What upward forces are keeping your hair up?•How are these forces produced?•Why do the hair strands spread out from each other?•Why do they spread out radially from the head?•Is hair a conductor or insulator? How can we find out? Does it depend if is wet or dry.•To understand what is going on we need a model of electricity.•Start out with VDG hair raising demo: Need a female teacher to come forward. Take a picture.Summer July 04 PHYS632 E&M 4Introduction Continued•What is charge? How do we visualize it. What is the model. We only know charge exists because in experiments electric forces cause objects to move.–Show cartoon comparing mass and charge•Electrostatics: study of electricity when the charges are not inmotion. Good place to start studying E&M because there are lots of demonstrations.•Atomic Model:- Show overheadSummer July 04 PHYS632 E&M 5Some preliminaries•Electron: Considered a point object with radius less than 10-18 meters with electric charge e= -1.6 x 10 -19 Coulombs (SI units) and mass me= 9.11 x 10 - 31 kg•Proton: It has a finite size with charge +e, mass mp= 1.67 x 10-27 kg and with radius–0.805 +/-0.011 x 10-15 m scattering experiment–0.890 +/-0.014 x 10-15 m Lamb shift experiment •Neutron: Similar size as proton, but with total charge = 0 and mass mn=–Positive and negative charges exists inside the neutron•Pions: Smaller than proton. Three types: + e, - e, 0 charge.–0.66 +/- 0.01 x 10-15 m•Quarks: Point objects. Confined to the proton and neutron,– Not free– Proton (uud) charge = 2/3e + 2/3e -1/3e = +e– Neutron (udd) charge = 2/3e -1/3e -1/3e = 0–An isolated quark has never been foundSummer July 04 PHYS632 E&M 6Model of electricity 1cm long and a radius of 0,005 cm1cm long and a radius of 0,005 cmCopper atom:Copper atom:Z=29(protons), N= 34(neutrons),Z=29(protons), N= 34(neutrons),29 Electrons29 ElectronsQuestion: What is the electrical charge in the material that we are talking about? What is responsible for the conduction of electricity?How many electrons are moving about?Carbon or diamondCopper (Face Centered Cube)Consider solid material like a piece of copper wire. The proton core is fixed in position in a lattice like structure. In a conductor, some electrons are free to move about. How many electrons are there free to move about?Summer July 04 PHYS632 E&M 7More preliminaries Atoms: Below on the left are two widely separated copper atoms. On the right is shown what happens as they come closer together to in a lattice.Summer July 04 PHYS632 E&M 8Comparison of which bands are filled and which are empty to explain the difference between metals and insulatorsIn a metal there are electrons in the ground state of the metal that can easily move to