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Welcome to Physics 102! Electricity & Magnetism(forces that hold atoms & molecules together,living cells) Light Atomic & Nuclear PhysicsPhys. 102, Lecture 1, Slide 1

Course contentPhysics 101Physics 102Macroscopic KinematicsForcesEnergyFluidsWaves (Sound)Microscopic Electricity & circuitsMagnetism & inductionOpticsModern PhysicsPhys. 102, Lecture 1, Slide 2

Meet the course directors Lecturer:Research:Office Hours: Discussion coordinator: Lab & exam coordinator:Phys. 102, Lecture 1, Slide 3

When emailing me: Email must be sent from @illinois.edu Subject line should begin with “PHYS102 question:” Message should contain:your full name, NetID, discussion section, TA name Questions about physics:Do not use email, use office hours (see course website) Before emailing:Verify information is not already on the course websiteThe course directors reserve the right to penalize your HW scoreif you ask questions via email that are answered on the websitePhys. 102, Lecture 1, Slide 4

Course Website http://courses.physics.illinois.edu/phys102/ Course Description / Excused Absences First Discussion: First Lab: Exam dates: Required Materials:Be sure to register your i clicker prior to lecturePhys. 102, Lecture 1, Slide 5

Course Philosophy Think about it (pre-lecture & checkpoint) Untangle it (lectures) Play with it (labs) Challenge yourself (homework) Close the loop (discussion/quiz)The order is important!Phys. 102, Lecture 1, Slide 6

Phys 102 – Lecture 1Electric charge & Coulomb’s lawPhys. 102, Lecture 1, Slide 7

4 Fundamental forces of NaturePhys. 101Phys. 102Gravitational force (solar system, galaxies)Electromagnetic force (atoms, molecules)Strong force (atomic nuclei)Weak force (radioactive decay) Gravitationalweakest Weak ElectromagneticStrongstrongestPhys. 102, Lecture 1, Slide 8

Electric chargeCharge is an intrinsic property of matter, like mass EM force - electric chargePositive & negative chargeOpposite charges attract, like chargesrepel– Gravity - massMass always positiveGravity always attractive – –DEMOPhys. 102, Lecture 1, Slide 9

Units of electric charge Symbol: q or Q Unit: [Coulomb] [C] Electron: –e –1.6 x 10–19 CProton: e 1.6 x 10–19 C– How much charge is 1 C?Imagine you could separate H and OH– ions in pure water (pH 7.0)H OH–H H OH–OH–H H OH–OH–H OH–Phys. 102, Lecture 1, Slide 10

Conductors & insulatorsQ: How do electrons behavein a perfect conductor?––Q: How do electrons behavein a perfect insulator?––– ––––– –––– – – –––– – Most things are in betweenperfect conductor / insulatorPhys. 102, Lecture 1, Slide 11

ACT: ConductorsElectrons are placed on a neutral conducting sphere. Which of thefollowing diagrams correctly depicts how the charges are distributed?A. At the bottomB. Spread uniformlyC. On the ��–––––––DEMOPhys. 102, Lecture 1, Slide 12

Conservation of chargeCharges are physical entities (ex: electrons, protons)Cannot be created or destroyed –The net charge in a closedsystem is conservedHowever, charges (often electrons) can be transferredfrom one object to anotherPhys. 102, Lecture 1, Slide 13

Demo: electroscope Charging by conductionCharged rod is brought near scopeCharged rod touches scope transferring some chargeScope is left with same charge as rod––––––––––––Conducting sphere –– – ––Insulating cage – Gold leaves–Phys. 102, Lecture 1, Slide 14

Demo: electroscope Charging by inductionCharged rod is brought near scope (but does NOT touch)Scope is briefly grounded allowing charge to flow on (or off)Scope is left with opposite charge as rod––––––––––– ––– – –Ground wire– –– – –Phys. 102, Lecture 1, Slide 15

ACTs: ElectroscopeA positively charged rod is used to charge an electroscope byinduction. What is the resulting net charge on the electroscope?A. positiveB. zeroC. negativeIf the conducting electroscope were replaced by an insulatingball and then charged by induction as above, what would be thenet charge on the ball?A. positiveB. zeroC. negativePhys. 102, Lecture 1, Slide 16

Coulomb’s Law(1785)Force between charges q1 and q2 separated adistance r:kkqq1q1 2q2F 22rr1 q1 q2Or: F 24πε0 r“Coulomb constant”k 9 109 N m 2 C2“Permittivity of free space”ε0 8.85 10 12 C2 N m 2Opposite charges attract, like charges repelPhys. 102, Lecture 1, Slide 17

Coulomb’s LawWhat is the magnitude of the force on the proton dueto the electron in hydrogen?Protonqp 1.6 x 10–19 C –Electronqe –1.6 x 10–19 Cr 0.53 x 10–10 mCompare to gravitational force between them (Phys. 101)Phys. 102, Lecture 1, Slide 18

ACT: Coulomb’s LawWhat is the direction of the force on the proton due to theelectron in the hydrogen atom?protonA. Left –B. RightelectronC. ZeroWhat is the direction of the force on the electron due tothe proton?Phys. 102, Lecture 1, Slide 19

ACT: Coulomb’s LawTwo charges q1 1 μC and q2 10 μC are placed near eachother. Which of the following diagrams correctly depicts the forcesacting on the charges?q1 1 μCA.B.C.q2 10 μC

Summary of Today’s Lecture Electric charge Conservation of charge Conductors and insulators Coulomb’s Law for the force between chargeskq1q2F 2rMuch more on Coulomb’s Law in next lecturePhys. 102, Lecture 1, Slide 21

Atomic & Nuclear Physics Phys. 102, Lecture 1, Slide 1. Course content Kinematics Forces Energy Fluids Waves (Sound) Electricity & circuits Magnetism & induction Optics Modern Physics Physics 101 Physics 102 Macroscopic Microscopic

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