Welcome to Physics 102! Please turn cell phones off 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 ychemla@illinois.edu Research: Biophysics see http://www.illinois.edu/~ychemla Office Hours: Monday 11-12, Loomis 161 Physics 102: Lecture 1, Slide 2

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, 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 website Physics 102: Lecture 1, Slide 3

Course Website http://online.physics.uiuc.edu/courses/phys102/spring11/ 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 Go over Daily Planner, Course Description, Lectures Physics 102: Lecture 1, Slide 4

Course Philosophy Read about it (textbook and prelecture) Untangle it (lectures) Play with it (labs) Challenge yourself (homework) Close the loop (discussion/quiz) Lectures M,W HW due 8 AM Tuesday the following week Disc Tues-Wed, the week following the lecture Quiz: due two days after Disc The order is important! Physics 102: Lecture 1, Slide 5

Grading Preflights & Lectures 50 Homework 100 Lab (Prelab due at start of lab) 150 Discussion 150 Take-home quizzes; drop lowest 1 Hour Exams (3 x 100) 300 Final Exam 250 1000 Key to doing well is keeping up with the volume of work. Stuff comes very fast in this course. Lots of new concepts. You need to work hard and often to keep up. Physics 102: Lecture 1, Slide 6

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 7

ACT: iClicker test Let’s switch to “BB” frequency: hold the power button for 2 seconds (blue light flashes) push B twice (green light confirmation) Let’s take a poll. What is your major? A) pre-med B) biology (MCB or IB), non pre-med C) other D) undecided iClicker registration problems? Contact me Physics 102: Lecture 1, Slide 8

Content Physics 102 Physics 101 Macroscopic Microscopic Prerequisite! Physics 102 Physics 101 Macroscopic Microscopic Electricity+Magnetism Circuits Optics Modern Atomic Nuclear Relativity Kinematics Forces Energy Fluids Waves (Sound) There’s a rumor that physics 102 is harder than physics 101….. Physics 102: Lecture 1, Slide 9

Electric charge & Coulomb’s Law Physics 102: Lecture 01 Electric charge & Coulomb’s Law Physics 102: Lecture 1, Slide 10

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 Start by asking if electric force is so large, why don’t we ever feel it? Copper and wood both made of atoms, both have positive and negative charges, but are electrically very different. Why? Physics 102: Lecture 1, Slide 11

Conductors and Insulators Q: How do electrons behave in a perfect conductor? Q: How do electrons behave in a perfect insulator? Copper and wood both made of atoms, both have positive and negative charges, but are electrically very different. Why? Most things are in between perfect conductor / insulator Physics 102: Lecture 1, Slide 12

Electroscope (+demo) Conduction Charged rod is brought near scope Charged rod touches scope transferring some charge Scope is left w/ same charge as rod – + + + + + + + + + + + + + + + charge + + + + + + + + + + + + + + charge Do the demo first, then show the visualization. Comment on how electroscope works. It’s like VandeGraaff and hair standing on end. Physics 102: Lecture 1, Slide 13

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 Do the demo first, then show the visualization. Comment on how electroscope works. It’s like VandeGraaff and hair standing on end. Physics 102: Lecture 1, Slide 14

ACTS A) positive B) zero C) negative A) positive B) zero C) negative Set your iClicker Frequency to “BB” 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 Physics 102: Lecture 1, Slide 15

Coulomb’s Law Force between charges q1 and q2 separated a distance r: “Coulomb constant” Magnitude “Permittivity of free space” Or: Magnitude – take absolute value sign for charges, only positive sign Direction Opposite charges attract, like charges repel Physics 102: Lecture 1, Slide 16

Example Coulomb’s Law What is the magnitude of the force on the proton due to the electron in hydrogen? F = k q1q2/r2 k = 9x109 Nm2/C2 + - r = 1x10-10 m Qp=1.6x10-19 C Qe = -1.6x10-19 C Calculate force on electron due to proton Magnitude Physics 102: Lecture 1, Slide 17

ACT: Coulomb’s Law Set your iClicker Frequency to “BB” What is the direction of the force on the proton due to the electron? (A) Left (B) Right (C) Zero What is the direction of the force on the electron due to the proton? + - r = 1x10-10 m qp=1.6x10-19 C qe = -1.6x10-19 C F Physics 102: Lecture 1, Slide 18

Electric dipole –Q H O = = +Q A positive and negative charge of equal magnitude separated by a (usually small) distance Ex: water –Q H O d+ 2d- – = = + Dipole of water is permanent +Q Physics 102: Lecture 1, Slide 19

ACT Set your iClicker Frequency to “BB” An electric dipole is 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) This is why water is attracted to ions & why it aligns with respect to ions (depending on charge). Negative charge is repelled (force to right) Positive charge is closer so force to left is larger. Physics 102: Lecture 1, Slide 20

ACT: Induced Dipole 1) Nothing 2) Attracted to charged sphere. – Set your iClicker Frequency to “BB” 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

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 – Explains why non-polar molecules will also be attracted to ions via induced dipole 2) A dipole is induced in the uncharged sphere 3) Since + is closer, attractive force is strongest Physics 102: Lecture 1, Slide 22

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? – The do VdG demo 1121 Physics 102: Lecture 1, Slide 23

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 24

Prior to next lecture…. Do your prelecture and preflight before 6:00 AM on the day of lecture. Physics 102: Lecture 1, Slide 25