Today’s Topics

 Text: Physics for Scientists and Engineers -- Tipler and Mosca 6, Vol II

 The Physics 202 Team

 Course Formality and Overview

 Electric Charge, Coulomb's Law Physics 202 Homepage

http://www.physics.wisc.edu/undergrads/courses/spring10/202/

Physics for Scientists and Engineers -- Tipler and Mosca 6, Vol II

DO NOT BUY HARD COPY OF TEXTBOOK FROM THE BOOKSTORE. Access Webassign + ebook (with link to buy hard copy of text (volume 2) for $25) by going to: http://webassign.net You will get email instructions for logging into webassign.

Meet the Physics 202 Team  Faculty (instructors):

☻ Prof. Susan Coppersmith snc@physics.wisc.edu

Research: condensed matter Office hrs: by appointment, 5334 CH, 262-8358

☻ 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):

Office hours: in 2307 CH (starting Jan 25). Schedule: http://www.physics.wisc.edu/undergrads/courses/spring09/202/consult.htm

Physics 202 Course Composition  Lectures: TR 8:50 am (Lec. 1), 9:55 am (Lec. 2)

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

 Start on January 25th

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

 Start on January 19th

 Exams: 3 midterms + final (word problem format)

 Homework: ~7-10 problems/week, web-based Online homework system: Webassisn http://www.webassign.net/ tutorial + end-of-chapter problems

Exams and Exam Policy Exam Dates

–  Midterms: (5:30-7 PM, rooms TBA) •  Exam 1: Wednesday Feb 17 •  Exam 2: Wednesday March 17 •  Exam 3: Wednesday April 21

–  Final: Monday May 10 (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)

Physics 201, 202 and 249

Light and Optics

Electromagnetism

Classical Mechanics Laws of motion Force, Energy, Momentum,…

Oscillation and Waves

Relativity

Atomic Structure

Sub-Sub-Atomic: Elementary Particles

Cosmology

Many-Atoms: Molecules, solids

Sub-Atomic: Nuclear Physics

Modern Classical

201

202 249

Quantum theory

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 charge  Conductors and insulators

 Electrostatic force: Coulomb’s Law

Next Thursday:  Electric Field

 Calculating electric fields from charge distributions  Motion of charged particle in external electric field

  Please read Ch. 21 before Thursday’s lecture

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

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)

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

(Coulomb’s Law)

Coulomb Constant: k = 8.987x109Nm2/C2 = 1/(4πε0) ε0: permitivity of free space = 8.85x10-12 C2/Nm2

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

+ - + - + + - -

F =kq1q2r2

 Four fundamental forces: Strong > Electromagnetic > Weak >> Gravitation

Coulomb’s Law: Vector Form 2 charges: force on q2 by q1

12r̂

principle of linear superposition

>2 charges: force on charge i

F21

F12

F21 F12

€

F i =

F 1i +

F 2i +

F 3i + ...

€

F 12 = k q1q2

r 2 r 12 = −

F 21