Welcome to Physics 102 Electricity Magnetism at the

Welcome to Physics 102! • Electricity + Magnetism (at the heart of most processes around us: …in atoms & molecules; living cells) • • Optics Atomic Physics Nuclear Physics Relativity http: //www. communicationcurrents. com Please turn cell phones off Physics 102: Lecture 1, Slide 1

Meet the Lecturer • ____ • Research: @illinois. edu _____________________________________ • Office Hours: ___________ Physics 102: Lecture 1, Slide 2

Course Website • http: //online. physics. uiuc. edu/courses/phys 102/spring 11/ • Daily Planner – what you should be doing and when you should be doing it • Course Description • Required Materials – Be sure to register your I-Clicker prior to lecture • Lectures – posted after the lecture is given • First Discussion: _____ • First Lab: _____ • Exam dates: _____ Physics 102: Lecture 1, Slide 3

Course Philosophy • • • Read about it (textbook and prelecture) Untangle it (lectures) Play with it (labs) Challenge yourself (homework) Close the loop (discussion/quiz) The order is important! Physics 102: Lecture 1, Slide 4

Grading • • Preflights & Lectures Homework Lab (Prelab due at start of lab) Discussion 50 100 150 – Take-home quizzes; drop lowest 1 • Hour Exams (3 x 100) • Final Exam 300 250 1000 Physics 102: Lecture 1, Slide 5

Prelectures & ACTS • Do it! • Answer preflights 50/1000 points – 1 point for honest attempt at preflight. – 1 point for using clicker in lecture (ACTS) • 2 points/lecture x 25 lectures = 50 points • Note that there are 28 lectures, so you have some free ones • Register I-Clicker before lecture Physics 102: Lecture 1, Slide 6

! e t si Content e r Physics 102 P Physics 101 i u q Macroscopic • • • Kinematics Forces Energy Fluids Waves (Sound) Physics 102: Lecture 1, Slide 7 Microscopic • Electricity+Magnetism • Circuits • Optics • Modern • Atomic • Nuclear • Relativity

Physics 102: Lecture 01 Electric charge & Coulomb’s Law Physics 102: Lecture 1, Slide 8

Origin of Charge • Charge is an intrinsic property of matter • Two types: – Positive Charge: e. g. protons – Negative Charge: e. g. electrons – Opposite charges attract. Like charges repel. – The electric force is what holds stuff together • Atoms are neutral – Negatively charged electrons “orbit” around positively charged central nucleus Physics 102: Lecture 1, Slide 9

Conductors and Insulators Q: How do electrons behave in a perfect conductor? Q: How do electrons behave in a perfect insulator? Most things are in between perfect conductor / insulator Physics 102: Lecture 1, Slide 10

Electroscope (+demo) • Conduction – Charged rod is brought near scope – Charged rod touches scope transferring some charge – Scope is left w/ same charge as rod +++ + + ++ ++ Physics 102: Lecture 1, Slide 11 ++ ++ + charge + ++ + + + +++ ++ + – + – –– + +++ + charge

Electroscope (+demo) • Induction – Charged rod is brought near scope – Scope is briefly grounded allowing charge to flow on (or off) scope – Scope is left w/ opposite charge as rod +++ + – + – –– + +++ + – – – + ++ + + – – – – -- --- – --- -- +++ - charge Physics 102: Lecture 1, Slide 12

ACTS • A negatively charged rod is used to charge an electroscope by induction. What is the resulting net charge on the electroscope? A) positive B) zero C) negative • If the conducting electroscope were replaced by an insulating ball and then charged by induction as above, what would be the net charge on the ball. A) positive Physics 102: Lecture 1, Slide 13 B) zero C) negative

Coulomb’s Law • Force between charges q 1 and q 2 separated a distance r: de u it n ag “Coulomb constant” M Or: D on i ct e ir “Permittivity of free space” Opposite charges attract, like charges repel Physics 102: Lecture 1, Slide 14

Coulomb’s Law • What is the magnitude of the force on the proton due to the electron in hydrogen? F = k q 1 q 2/r 2 Qp=1. 6 x 10 -19 C k = 9 x 109 Nm 2/C 2 Qe = -1. 6 x 10 -19 C + r = 1 x 10 -10 m n ag M de u it Physics 102: Lecture 1, Slide 15

ACT: Coulomb’s Law • What is the direction of the force on the proton due to the electron? (A) Left (B) Right qp=1. 6 x 10 -19 C (C) Zero qe = -1. 6 x 10 -19 C + r = 1 x 10 -10 m • What is the direction of the force on the electron due to the proton? Physics 102: Lecture 1, Slide 16

Electric dipole A positive and negative charge of equal magnitude separated by a (usually small) distance Ex: water –Q 2 d- = O H d+ Physics 102: Lecture 1, Slide 17 H d+ – = +Q +

ACT An electric dipole is placed near a large negative charge. What is the net force on the two connected charges? A) Left – Physics 102: Lecture 1, Slide 18 B) Zero + C) Right -

ACT: Induced Dipole • An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released? 1) Nothing – 2) Attracted to charged sphere. 3) Repelled from charged sphere. Physics 102: Lecture 1, Slide 19

Induced Dipole • An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released? – Physics 102: Lecture 1, Slide 20 + – + –

Demo: Induced Dipole • An uncharged conducting sphere is hung between a charged sphere and a grounded sphere and held midway between the two. What happens when the uncharged sphere is released? – Physics 102: Lecture 1, Slide 21

Summary of Today’s Lecture • The concept of charge • Conductors and insulators • Coulomb’s Law for the force between charges – Much more on Coulomb’s Law in next lecture • Electric dipoles (permanent & induced) Physics 102: Lecture 1, Slide 22