Welcome to Physics 202Welcome to Physics 202Today’s Topics

The Physics 202 TeamCourse Formality and Overview

Ch. 21.1-21.5: Electric Charge, Coulomb's Law

Text: Giancoli, Physics for Scientists and Engineers, 4th ed., Volume II.

Physics 202 Homepagehttp://www.physics.wisc.edu/undergrads/courses/spring08/202/

Meet the Physics 202 Team

Faculty (lectures):

☻Prof. Lisa Everett leverett@wisc.edu

Research: theoretical high energy physicsOffice hrs: M 4:35 or by appointment, 5215 CH, 262-4699

☻Prof. Bruce Mellado bmellado@wisc.edu

Research: experimental high energy physics Office hrs: by appointment, 4223 CH, 262-8894

Meet the Physics 202 Team

Teaching Assistants (labs, discussion):

☺ Pankoj Gindodia gindodia@wisc.edu☺ Shusaku Horibe horibe@wisc.edu☺ Trevor Irwin irwin@astro.wisc.edu☺ Robert Lindner rrlindner@wisc.edu☺ Jason McCuistion mccuistion@wisc.edu☺ Paul McGuirk mcguirk@wisc.edu☺ Valerie Plaus plaus@wisc.edu ☺ Yongyan Rao yrao2@wisc.edu☺ Jared Schmitthenner schmitthenne@wisc.edu☺ Koki Takasaki ktakasaki@wisc.edu

Office hours: in 2307 CH (starting Jan 28). Schedule: http://www.physics.wisc.edu/undergrads/courses/spring08/202/consult.htm

Physics 202 Course Composition

Lectures: TR 8:50 am (Lec. 1), 9:55 am (Lec. 2) Honors: F 8:50 am (w/ Physics 208)

Labs: mandatory! Each missing lab = - 0.5 grade pt. 10 labs total. grading: weekly lab quizzes, 2 lab reports

Discussion Sections: 2/week. grading: discussion quizzes (5 total during the semester), participation,…

Exams: 3 midterms + final (word problem format)

Homework: ~10 problems/week, web-based

Online homework system: MasteringPhysics http://www.masteringphysics.com tutorial + end-of-chapter problems (not aligned with our text yet)

Exams and Exam PolicyExam Dates

– Midterms: (5:30-7 PM, rooms TBA)• Exam 1: M Feb 18 • Exam 2: R Mar 13 • Exam 3: M Apr 14

– Final: M May 12 (5:05-7:05 PM, rooms TBA), Cumulative

If you have an academic conflict with the exam dates, inform the professors and your TA ASAP (at latest: 2 weeks before the exam period) so that we can accommodate you.

(Exam policy details on course website)

The challenges of Physics 202:Topics: electromagnetism, waves, optics. Many new concepts, less familiar/intuitive topics, more mathematical rigor

e.g. vector calculus (line integrals, surface integrals, gradients)

How to Succeed …

1. Do the required reading before lecture- the lectures assume you are familiar with the material

2. Keep up -- don’t get behind!!

3. Ask questions early if you don’t understand things- in lecture ask!! …also consult outside class: in discussion section and office hours.

4. Problem solving develops and tests your conceptual understanding -- as well as your computational skill- this is how you can demonstrate what you have learned…

Physics 201, 202 and 249

Light and Optics

Electromagnetism

Classical MechanicsLaws of motionForce, Energy,Momentum,…

Oscillation and Waves

Relativity

Atomic Structure

Sub-Sub-Atomic:Elementary Particles

Cosmology

Many-Atoms:Molecules, solids

Sub-Atomic:Nuclear Physics

ModernClassical

201

202 249

Quantum theory

Building blocks: Physics 201

• Mechanics: Motion and Force • Newton’s laws of motion (“Classical” view)

• Conservation laws: energy, momentum, angular momentum (“modern” view)

• Newton’s Law of Universal Gravitation.

We will build on these concepts in Physics 202! We expect that you know the following basic concepts:

uniformly accelerated motion, work-kinetic energy theorem, potential energy, static equilibrium, circular motion, simple harmonic motion, torque and rotational motion,…

Mechanics

Gravitation

Physics 202• Electromagnetism

– Electric force, field, and potential: stationary charges (electrostatics)

– Current, capacitance & resistance – Magnetic force and field: steady currents (magnetostatics)– Time-dependent fields: Maxwell’s equations– Electromagnetic waves, wave motion, superposition– DC and AC Circuits

• Light and Optics – Light as rays: Geometric optics, imaging– Light as electromagnetic waves, interference

Chapter 21: Electric Charge and Field

Today: Electric charges

Fundamental units of chargeConductors and insulators

Electrostatic force: Coulomb’s Law

Thursday: Electric Field

Calculating electric fields from charge distributionsMotion of charged particle in external electric field

Please read Ch. 21 before Thursday’s lecture

Electric Charge

Like signs repelOpposite signs attract

Charges do not have to be in contact to interact

Two types!

Properties of Electric Charge 2 types: positive or negative* SI Unit: Coulomb (C). 1 C= chg of 6.24x1018 protons Building blocks of matter:

Electric charge is quantized: q=Ne (e=1.602x10-19 C) Electric charge of isolated system is conserved

*neutral objects: no charge or equal amount of + and -

Charge (C) Mass (kg)

Electron -e=-1.602x10-19 9.11x10-31

Proton +e=+1.602x10-19 1.673x10-27

Neutron 0 1.675x10-27

Conductors v. Insulators

------ -++

+++ ++ +

+ +++

++++

Electroscope (next lab)

charge also by induction!

Conductors (metals…):

charges free to move

Insulators (glass, plastic, rubber…):

Consider how charge is carried on macroscopic objects.

In Physics 202, we are concerned with only 2 types:

charges NOT free to move

(phenomenon: polarization)

Neutral metal

+ + + + + + ++ + + + ++

+++

+- --

-

-

Positively charged rod (too few electrons)

+ + + + + + +

Less positively charged rod

+

+++

+

Positively charged metal

+ + + + + + ++ + + + +

+

+++

+- --

-

-

electron flow

Charging by conduction (touching)

Charging conductors by Induction

• Charging by induction requires no contact with the object inducing the charge

a) We start with a neutral metallic sphere

b) The rod does not touch the sphere. The electrons in the neutral sphere are redistributed

charged rubber rod

a) b)

Charging by Induction, 2

If the sphere is grounded:

electrons can leave the sphere through the ground wire

(earth: infinite storage conductor)

If ground wire is removed, there is still a net positive charge on the sphere -- a positive charge has been induced.

When the rod is removed, electrons will

redistribute in the sphere.

Coulomb’s LawElectric Force b/w 2 stationary point charges:

(Coulomb’s Law)

Coulomb Constant: k = 8.987x109Nm2/C2 = 1/(40)

0: permitivity of free space = 8.85x10-12 C2/Nm2

Attractive (opp sign charges), repulsive (like sign charges)

+ - +- ++ - -

F =kq1q2

r2

Four fundamental forces:

Strong > Electromagnetic > Weak >> Gravitation

Coulomb’s Law: Vector Form

rF21 =ke

q1q2

r2 r̂ =−rF12

2 charges: force on q2 by q1

12r̂

principle of linear superposition

>2 charges: force on charge i

rFi =

rF1i +

rF2i +

rF3i + ...

F12

F21

F12

F21

Examples (board): 21.13, 21.18, 21.20