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 • Yann Chemla • Research: ychemla@illinois. edu Biophysics • see http: //www. illinois. edu/~ychemla • Office Hours: Monday 12 -1, Loomis 161 Physics 102: Lecture 1, Slide 2 04

When emailing me: • Email must be sent from UIUC account (no Gmail, Yahoo, etc. ) • Subject line should begin with “Physics 102 question: ” • Message should contain: student’s full name, net. ID, 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 website Physics 102: Lecture 1, Slide 3

Course Website • http: //online. physics. uiuc. edu/courses/phys 102/spring 10/ • 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: See website • First Lab: See website • Exam dates: See website Physics 102: Lecture 1, Slide 4

i. Clicker registration problems? Need i. Clicker ID? • Go to Illini bookstore • Find i. Clicker system near coat check • “Vote” and LCD panel reveals your ID Other problems contact me Physics 102: Lecture 1, Slide 5

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 6

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 7 07

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 8 10

! 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 9 Microscopic • Electricity+Magnetism • Circuits • Optics • Modern • Atomic • Nuclear • Relativity 18

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 10 20

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 11 23

Electroscope (+demo) • Conduction – Charged rod is brought near scope – Charged rod touches scope transferring some charge – Scope is left w/ same charge as rod • 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 Physics 102: Lecture 1, Slide 12

Draw: Electroscope conduction & induction Physics 102: Lecture 1, Slide 13

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 B) zero C) negative 32 Physics 102: Lecture 1, Slide 14

Coulomb’s Law • Magnitude of the force between charges q 1 and q separated a distance r: 2 e n d o i u it ect n ag dir M d an F = k q 1 q 2/r 2 k = 9 x 109 Nm 2/C 2 • Force on electron in Hydrogen atom ! lve o S Qp=1. 6 x 10 -19 C Qe = -1. 6 x 10 -19 C + r = 1 x 10 -10 m Physics 102: Lecture 1, Slide 15 34

Coulomb’s Law 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 de ion u t t ni rec g i a M dd an Physics 102: Lecture 1, Slide 16 Solution: F= 2. 3 x 10 -8 N 35

ACT: Coulomb’s Law • What is the direction of the force on the proton due to the electron? (A) Left (B) Right (C) Zero • What is the magnitude of the force on the proton due to the electron? qp=1. 6 x 10 -19 C F= 2. 3 x 10 -8 N + F qe = -1. 6 x 10 -19 C - r = 1 x 10 -10 m Physics 102: Lecture 1, Slide 17 38

ACT A positive and negative charge with equal magnitude are connected by a rigid rod, and placed near a large negative charge. What is the net force on the two connected charges? A) Left B) Zero C) Right Positive charge is attracted (force to left) Negative charge is repelled (force to right) Positive charge is closer so force to left is larger. Physics 102: Lecture 1, Slide 18 + 43

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 45

Draw what happens: Physics 102: Lecture 1, Slide 20

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 21

ACT: Induced Dipole • An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released? 1) Negative charge attracts + repels - Physics 102: Lecture 1, Slide 22

ACT: Induced Dipole • An uncharged conducting sphere is hung next to a charged sphere. What happens when the uncharged sphere is released? 1) Negative charge attracts + repels 2) Since + is closer, attractive force is strongest Physics 102: Lecture 1, Slide 23

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 24

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 25

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 Physics 102: Lecture 1, Slide 26

Prior to next lecture…. • Do your prelecture and preflight before 6: 00 AM on the day of lecture. Physics 102: Lecture 1, Slide 27