Welcome to Physics 102 Electricity Magnetism Optics Atomic

Welcome to Physics 102! • • • Electricity + Magnetism Optics Atomic Physics Nuclear Physics Relativity Please turn cell phones off Physics 102: Lecture 1, Slide 1

Meet the Lecturer • Alan Nathan • Research a-nathan@uiuc. edu – Experimental Nuclear/Particle Physics – Physics of Baseball • see http: //webusers. npl. uiuc. edu/~a-nathan/pob • Office Hours: Monday 11 -12 – or drop in any time and I’ll talk with you if I am not otherwise tied up Physics 102: Lecture 1, Slide 2 04

Course Format • http: //online. physics. uiuc. edu/courses/phys 102/spring 08/ • Daily Planner – what you should be doing and when you should be doing it • Course Description • Lectures – posted just after the lecture is given 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

Course Format (Spiral Learning) • • Preflights 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 07

Grading Scale • • • 950 -1000 920 -949 900 -919 880 -899 860 -879 835 -859 Physics 102: Lecture 1, Slide 6 A+ A AB+ B B- • • 810 -834 780 -809 750 -779 720 -749 690 -719 610 -689 <610 C+ C CD+ D DF

Prelectures & Lecture • Do it! • Answer preflights 50/1000 points – 1 point for honest attempt at preflight. – 1 point for using clicker in lecture (75%) • 2 points/lecture x 25 lectures = 50 points Physics 102: Lecture 1, Slide 7 10

P 102 Lectures • Not everything you need! – – Lectures: Concepts, Connections, Motivation Textbook: Comprehensive Homework + Discussion: Calculations Lab: Hands-On • Taking Notes – Lecture notes are available at bookstore or online – Some key pieces for you to fill in Physics 102: Lecture 1, Slide 8 15

Content Physics 102 Physics 101 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: Protons – Negative Charge: electrons – Opposite charges attract. Like charges repel. • Atoms are neutral – Negatively charged electrons “orbit” r~10 -10 m – Positively charged central nucleus r~10 -15 m 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 • Conduction – Charged rod is brought near scope – Charged rod touches scope transferring some charge – Scope is left w/ same charge as rod • gold leaves repel fly apart Physics 102: Lecture 1, Slide 12 27

Electroscope • 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 13 27

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 2 separated a distance r: F = k q 1 q 2/r 2 k = 9 x 109 Nm 2/C 2 • Force on electron in Hydrogen atom 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 Physics 102: Lecture 1, Slide 16 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

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 20

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 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 2) Since + is closer, attractive force is strongest Physics 102: Lecture 1, Slide 22

ACT: 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? 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

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 25

Prior to next lecture…. • Read Sections 16. 1 -6 • Do your prelecture and preflight before 8: 00 AM on the day of lecture. See you Wednesday! Physics 102: Lecture 1, Slide 26