PHYSICS 632 SUMMER 2006 Orientation 8:30 – 10:30 Room 203 Electricity & Magnetism Richard A. Lindgren, Office Room 302Lecture 1 Charge Chp. 21IntroductionCharged Hair Van de Graaff DemoIntroduction ContinuedSome preliminariesMethods of Charging Objects: Friction, Contact, and InductionPowerPoint PresentationSlide 9Slide 10Model of electricityCharging Insulators by Friction/RubbingSummary CommentsTriboelectric series http://www.sciencejoywagon.com/physicszone/lesson/07elecst/static/triboele.htmSummary: Electrostatics is based on 4 four empirical factsConservation of chargeWhat is meant by quantization of charge?Coulombs LawUniformly charged metal spheres of Radius RCoulombs Law Two Positive ChargesCoulombs Law Two Pennies without electronsPrinciple of Superposition Three charges In a lineSlide 23Example Three point chargeSlide 25Slide 26In 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)Slide 30PHYSICS 632 SUMMER 2006Orientation8:30 – 10:30 Room 203Electricity & MagnetismRichard A. Lindgren, Office Room 302Your Goals: Get a degree, crossover teaching, fill in knowledge gaps, review, learn new teaching ideas, peer learning, modeling, inquiry learning, group learning, new demos, computer technology, solidify concepts, learn how to do problems.Format: Daily graded homework focuses on problems solving using WebAssign. Work on problems in recitation before lecture, discuss with TA’s and others in the apartments at night. Due at 8:00 am next day. Math review in recitation. Trigonometry, unit vectors and vectors, derivatives and integration. How do you improve problem-solving skills. Lots of practice and more practice. Test on first three Tuesdays fourth test and final on WebAssign, 30% conceptual questions, 70% problem oriented. There will also be 4 homework assignments due in August, September, and October. Final exam in October on WebAssign.Text: Halliday, Resnick, and Walker 7’th edition, extended, Sarting with chapter 21. Class organizationCartoonDemonstrationsGraded problems due 8:00 AMWarm-up problems due 8:00 AM. Not graded.Lecture and discussionDemos with explanationsHandworked Problems on ElmoMisconception/Polling problemsPhysletsSummer July 06 PHYS632 E&M 2Lecture 1 Charge Chp. 21•Cartoon - Charge is analogous to mass•Opening Demo - Large Van de Graaff•Warm-up problems•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•Example problems•Clicker Misconception/polling problems•Demonstrations•PhysletsSummer July 06 PHYS632 E&M 3Introduction•“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 EinsteinF =kq1q2/r2k =1/ 4πε0Summer July 06 PHYS632 E&M 4Charged 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.• Need a female teacher to come forward.Summer July 06 PHYS632 E&M 5Introduction Continued•What is charge?• How do we visualize it.• What is the model.• We only know charge exists because in experiments electric forces causeobjects 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:Summer July 06 PHYS632 E&M 6Some 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 and radius–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 06 PHYS632 E&M 7Methods of Charging Objects:Friction, Contact, and Induction•Normally atoms are in the lowest energy state. This means that the material is electrically neutral. You have the same number of electrons as protons in the material. •How do we change this? •How do we add more electrons than protons or remove electrons?Summer July 06 PHYS632 E&M 8QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Summer July 06 PHYS632 E&M 9QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Summer July 06 PHYS632 E&M 10QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Summer July 06 PHYS632 E&M 11Model 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