Physics 2102Physics 2102Lecture 01: MON 12 JANLecture 01: MON 12 JANElectric Charge IElectric Charge IPhysics 2102Jonathan DowlingCharles-Augustin de Coulomb (1736–1806)Version: 1/12/09Benjamin Franklin (1705–1790)Who am IWho am I & Why am I Here?& Why am I Here?Office hours: Nicholson Hall 453, MWF10:30–11:30AM (or by appointment)Phone: 225-578-0887Email: [email protected] Own Research:Quantum OpticsQuantum ComputingPhotonic CrystalsProf. Jonathan P. DowlingHearne Institute for Theoretical Physics Quantum Sciences & Technologies Group1994–98: Research Physicist, US Army Aviation & Missile Command1998–2004: Principal Scientist, NASA Jet Propulsion Laboratory2004–Present: Director, Hearne Institute for Theoretical Physics, LSUCourse DetailsCourse Details• Main Class Website for All Sections:http://www.phys.lsu.edu/classes/spring2009/phys2102/Syllabus, Schedule, Grading Policy, Exam Solutions, …• Lectures will be posted in this section’s website:http://phys.lsu.edu/~jdowling/PHYS21022SP09/• Text: Fundamentals of Physics, Halliday, Resnick, andWalker, 8th edition. We will cover chapters 21-36.• Exams: Midterms 6–7PM: THU 05 FEB, THU 05 MAR, THU02 APR; Final Exam 5:30–7:30PM: FRI 08 MAY• Lab: Meets This Week! Show up or be dropped!• Tutoring: Free Tutors in 102 Nicholson Hall.Course Details: HomeworkCourse Details: HomeworkWeb-based system: Web AssignTo register:• Go to http://www.http://www.webassignwebassign.net/student.html.net/student.html• On the left frame, “student login”• Username: pawsusername@lsu• Institution: lsu• Password: lsuidnumber• Choose “credit card registration” ($$$) or FREE withPurchase of PHYS2102 Book from Bookstore• One Assignment Per Week Due 2AM Wednesdays.• First HW Is Posted This Week Due Next WED 2AM.Course Details: GradingCourse Details: GradingA: ≥90 B: 80-89 C: 60-79 D: 50-59 F: <50Borderline Cases Decided by Class Attendance!What Are We Going to Learn?What Are We Going to Learn?A Roadmap!A Roadmap!• Electric Charge& Electric Force on Other Electric Charges& Electric Field, and Electric Potential• Moving Electric Charges: Current• Electronic Circuit Components: Batteries, Resistors, Capacitors• Electric Currents & Magnetic Field& Magnetic Force on Moving Charges• Time-Varying Magnetic Field & Electric Field• More Circuit Components: Inductors, AC Circuits.• Maxwell’s Equations & Electromagnetic Waves & Light Waves• Geometrical Optics (Light Rays).• Physical Optics (Light Waves): Interference, Diffraction.LetLet’’s Get Started!s Get Started!Electric ChargesElectric Charges……• Two Types of Charges: Positive/Negative• Like Charges Repel• Opposite Charges AttractAtomic StructureAtomic Structure:• Negative Electron Cloud• Nucleus of Positive Protons, Uncharged NeutronsThe Unit of Electric Charge isthe “Coulomb” which is “C”.Proton Charge: e = 1.60 × 10–19 CBenjamin Franklin (1705–1790)Rules of Attraction andRules of Attraction andRepulsion Discovered byRepulsion Discovered byBenjamin FranklinBenjamin Franklin12F1q+21F2q!12F1q+21F2q+12F1q!21F2q!Force Between Pairs of PointForce Between Pairs of PointCharges: CoulombCharges: Coulomb’’s Laws LawCoulomb’s Law — the Force Between Point Charges:• Lies Along the Line Connecting the Charges.• Is Proportional to the Magnitude of Each Charge.• Is Inversely Proportional to the Distance Squared.• Note That Newton’s Third Law Says |F12| = |F21|!!Charles-Augustin De Coulomb (1736–1806)2q!12F1q+21F12rCoulombCoulomb’’s Laws Law F12=k q1 q2r122 k =14!"0with "0= 8.85 #10$12C2N m2 k = 8.99 !109N m2C2The “k” is theelectric constantof proportionality.Usually, we write:Units: F"="[N]"="[Newton]; r"=" [m]"="[meter]; q"="[C]"="[Coulomb]Two Inverse Square LawsTwo Inverse Square LawsNewton’s Law ofGravitational ForceCoulomb’s Law ofElectrical ForceArea of Sphere = 4πr2Number of Lines of Force isConstant.Hence Force Per-Unit-Areais Proportional to 1/r2SuperpositionSuperposition• Question: How Do We Figure Out the Forceon a Point Charge Due to Many Other PointCharges?• Answer: Consider One Pair at a Time,Calculate the Force (a Vector!) In EachCase Using Coulomb’s Law and Finally AddAll the Vectors! (“Superposition”)• Useful To Look Out for SYMMETRY toSimplify Calculations!Feel the Force:Feel the Force:ExampleExample• Three Equal Charges Forman Equilateral Triangle ofSide 1.5 m as Shown• Compute the Force on q1• What are the Forces onthe Other Charges?dq1ddq2q3q1= q2= q3= 20 mCSolution: Set up a Coordinate System, Compute Vector Sum of F12 and F13d123dd12F13Fo60yxαWhat is the Force on Central Particle?Charge +qPlaced at Center Another Example WithAnother Example WithSymmetrySymmetry+qrAll Forces Cancel Except From +2q! ! F =k +2q
View Full Document
Unlocking...