Physics 2102 Lecture 01: MON 12 JANWho am I & Why am I Here?Course DetailsCourse Details: HomeworkCourse Details: GradingWhat Are We Going to Learn? A Roadmap!Let’s Get Started! Electric Charges…PowerPoint PresentationForce Between Pairs of Point Charges: Coulomb’s LawCoulomb’s LawSlide 11SuperpositionFeel the Force: ExampleSlide 14Slide 15Physics 2102 Physics 2102 Lecture 01: MON 12 JANLecture 01: MON 12 JANElectric Charge IElectric Charge IPhysics 2102Jonathan DowlingCharles-Augustin de Coulomb (1736–1806)Version: 01/14/19QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Benjamin Franklin (1705–1790)Who am I & Why am I Here?Who am I & Why am I Here?Office hours: Nicholson Hall 453, MWF 10:30–11:30AM (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, LSU 1994–98: 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, and Walker, 8th edition. We will cover chapters 21-36. • Exams: Midterms 6–7PM: THU 05 FEB, THU 05 MAR, THU 02 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: Course Details: HomeworkHomeworkWeb-based system: Web Assign To register:• Go to http://www.webassign.net/student.htmlhttp://www.webassign.net/student.html• On the left frame, “student login”• Username: pawsusername@lsu• Institution: lsu• Password: lsuidnumber• Choose “credit card registration” ($$$) or FREE with Purchase 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: <50100100100302001st exam2nd exam3rd examHomeworkFinal ExamBorderline Cases Decided by Class Attendance!What Are We Going to What Are We Going to Learn?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.Let’s Get Started!Let’s Get Started!Electric Charges…Electric Charges…• Two Types of Charges: Positive/Negative• Like Charges Repel• Opposite Charges AttractAtomic StructureAtomic Structure: • Negative Electron Cloud• Nucleus of Positive Protons, Uncharged Neutrons The Unit of Electric Charge isthe “Coulomb” which is “C”.Proton Charge: e = 1.60 × 10–19 CQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Benjamin Franklin (1705–1790)Rules of Attraction Rules of Attraction and Repulsion and Repulsion Discovered by Discovered by Benjamin FranklinBenjamin Franklin12F1q+21F2q−12F1q+21F2q+12F1q−21F2q−Force Between Pairs of Force Between Pairs of Point Charges: Coulomb’s Point Charges: Coulomb’s LawLawCoulomb’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)QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.2q−12F1q+21F12rCoulomb’s LawCoulomb’s Law€ F12=k q1 q2r122€ k =14πε0with ε0= 8.85 ×10−12C2N m2€ k = 8.99 ×109N m2C2The “k” is the electric constant of proportionality.Usually, we write:QuickTime™ and a decompressorare needed to see this picture.Units: FS=S[N]S=S[Newton]; rS=S[m]S=S[meter];qS=S[C]S=S[Coulomb]Two Inverse Square Two Inverse Square LawsLawsQuickTime™ and a decompressorare needed to see this picture.Newton’s Law of Gravitational Force Coulomb’s Law of Electrical Force Area of Sphere = 4r2Number of Lines of Force is Constant. Hence Force Per-Unit-Area is Proportional to 1/r2SuperpositionSuperposition•Question: How Do We Figure Out the Force on a Point Charge Due to Many Other Point Charges?•Answer: Consider One Pair at a Time, Calculate the Force (a Vector!) In Each Case Using Coulomb’s Law and Finally Add All the Vectors! (“Superposition”)•Useful To Look Out for SYMMETRY to Simplify Calculations!Feel the Force: Feel the Force: ExampleExample•Three Equal Charges Form an Equilateral Triangle of Side 1.5 m as Shown•Compute the Force on q1•What are the Forces on the Other Charges?dq1ddq2q3q1= q2= q3= 20 mCSolution: Set up a Coordinate System, Compute Vector Sum of F12 and F13d123dd12F13Fo60yxQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.What is the Force on Central Particle?Charge +qPlaced at Center Another Example With Another Example With SymmetrySymmetry+qrAll Forces Cancel Except From +2q! € r F =k +2q +qr2FQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this
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