Lecture01bd - Welcome to Physics 102! Electricity +...

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Unformatted text preview: 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 Prof. Brian DeMarco bdemarco@illinois.edu Research: Ultracold Quantum Gases see http://www.illinois.edu/~bdemarco Office Hours: Mondays 11 am, Loomis 329 Physics 102: Lecture 1, Slide 2 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 website The course directors reserve the right to penalize your HW score if you ask questions via email that are answered on the website Physics 102: Lecture 1, Slide 3 Course Website http://online.physics.uiuc.edu/courses/phys102/spring12/ 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: 1/17 (yesterday!) First Lab: 1/25 Exam dates: 2/20, 3/25, 4/23 7 pm Physics 102: Lecture 1, Slide 4 Course Philosophy Read about it (textbook) Untangle it (lectures) Play with it (labs) Challenge yourself (homework) Close the loop (discussion/quiz) The order is important! Physics 102: Lecture 1, Slide 5 Content There will be changes to 102 this semester! Based on student feedback & MCAT Topics not covered: phasors, mutual inductance, Brewster's angle, quantum atom Your coursepacks will not match lectures and discussions exactly...that's OK! Physics 102: Lecture 1, Slide 6 Grading CheckPoints & Lectures Homework Lab (Prelab due at start of lab) Discussion in-class quizzes; drop lowest 1 50 150 150 100 300 250 1000 Hour Exams (3 x 100) Final Exam Physics 102: Lecture 1, Slide 7 CheckPoints & ACTS Answer CheckPoints 50/1000 points 1 point for attempt at Checkpoint. ACTS: use iClicker in class 1 point for answering the questions 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: gradebook Physics 102: Lecture 1, Slide 8 ACT: iClicker test Change your frequency to BB at the beginning of every lecture 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? Check registration in the Gradebook first. Physics 102: Lecture 1, Slide 9 Content Physics 102 Physics 101 Macroscopic Kinematics Forces Energy Fluids Waves (Sound) Microscopic Electricity+Magnetism Circuits Optics Modern Atomic Nuclear Relativity Physics 102: Lecture 1, Slide 10 Physics 102: Lecture 01 Electric charge & Coulomb's Law Physics 102: Lecture 1, Slide 11 Origin of Charge Charge is an intrinsic property of matter Two types: proton electron Positive Charge Negative Charge Opposite charges attract, like charges repel. The electric force is what holds stuff together electron "orbits" the positive nucleus Physics 102: Lecture 1, Slide 12 + + - - - + - Atoms are neutral + 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 13 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 Physics 102: Lecture 1, Slide 14 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 15 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 16 B) zero C) negative Coulomb's Law Force between charges q1 and q2 separated a distance r: "Coulomb constant" 1 2 = 2 = 9 109 2 / 2 "Permittivity of free space" 1 1 2 Or: = 2 0 = 8.85 10-12 2 /2 40 Opposite charges attract, like charges repel Physics 102: Lecture 1, Slide 17 Coulomb's Law What is the magnitude of the force on the proton due to the electron in hydrogen? F = k q1q2/r2 Qp=1.6x10-19 C k = 9x109 Nm2/C2 Qe = -1.6x10-19 C + r = 1x10-10 m - 2 1.6 10-19 1.6 10-19 = 9 109 2 1 10-10 2 Physics 102: Lecture 1, Slide 18 = 2.3 10-8 ACT: Coulomb's Law What is the direction of the force on the proton due to the electron? (A) Left (B) Right (C) Zero qp=1.6x10-19 C + F qe = -1.6x10-19 C - r = 1x10-10 m What is the direction of the force on the electron due to the proton? Physics 102: Lecture 1, Slide 19 Electric dipole A positive and negative charge of equal magnitude separated by a (usually small) distance Ex: water d- Q H = d+ = O H d+ + +Q Physics 102: Lecture 1, Slide 20 ACT 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) Negative charge is repelled (force to right) Positive charge is closer so force to left is larger. 1 2 = 2 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) Nothing 2) Attracted to charged sphere. 3) Repelled from charged sphere. Physics 102: Lecture 1, Slide 22 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) A dipole is induced in the uncharged sphere 3) Since + is closer, attractive force is strongest 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 1 2 = 2 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 CheckPoint before 8:00 AM on the day of lecture. Physics 102: Lecture 1, Slide 25 ...
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