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Welcome to Physics 202
Today s Topics
 The Physics 202 Team
 Course Formality and Course Overview
 Q&A
  Ch 21: Electric Charges
Physics 202 Homepage
http://www.physics.wisc.edu/undergrads/courses/fall2011/202/index.html
(under construction, almost done)
Physics Department Homepage
http://www.physics.wisc.edu
The Physics 202 Team
 Faculty (lectures):
☻  Prof. Matthew Herndon, [email protected] 4279 Ch. 262-8509
☻  Prof. Gary Shiu, [email protected] 5279 CH. 265-3285
 Teaching Assistants (labs, discussions):
Daniel Crow
Scott Douglass
Yutao Gong
Taylor Klaus
Aaron Levine
Andrew Loveridge
Jason Milhone
Hojin Yoo
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[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Physics 202 Course Composition
  Text: EText: Tipler and Mosca, Physics for Scientists and Engineers,
6th ed
  Lectures: TR 1:20 pm (Lec. 1), 2:25 pm (Lec. 2) (you can attend either)
  Discussion Sessions: 2/week. (Grading: quizzes, attendance)
  Labs: Mandatory. Each missing lab = - 1 letter grade level (AàAB,ABàB...)
  Homework: ~10 problems/week online by Webassign.net
  Exams: (3 middle-terms + final)
  Office Hours. (Faculty: by appointments, TAs: as scheduled)
  Your home time: > 4 hours/week + homework.
 Honor credit: email announcement latter this week
  Grading:
 Homework:
200 pts
 Laboratory:
100 pts (plus missing lab penalty)
 Discussion:
100 pts
 Midterm 1:
100 pts
 Midterm 2:
100 pts
 Midterm 3:
100 pts
 Final Exam:
200 pts
(Final grades are based on curved component scores)
Lectures
  Style:
•  PPT + white board + demos
  Subjects:
•  Key concepts.
•  Interactive problem solving
  Lectures are NOT meant to be complete.
•  In addition to your own study of the subject
•  Do read materials BEFORE the lecture.
 Our lectures are designed with the assumption
that you’ve read the corresponding sections!
•  Review materials after the lectures.
  Lecture notes will be posted after each lecture
  Physics is about solving problems. In this case problems
relevant to engineers and scientists. There is no substitute
for experience solving problems.
Learning Physics: Preview + Lecture + Review +
Application to Problems
Exams and Exam Policy
  Exam Dates:
  Midterms (5:30-7:00 pm, rooms TBA)
•  Exam 1: Wednesday Oct 5th
•  Exam 2: Wednesday Nov 2nd
•  Exam 3: Wednesday Nov 30th
  Final: Tuesday Dec 20 (7:25-9:25 pm, rooms TBA), cumulative.
  If you have a conflict with above exam dates, inform your professors
asap, at least 2 weeks before the scheduled date. Alternative exam
arrangements are granted only for valid reasons.
  Valid excuses:
•  University Academic/athletic conflicts
•  Medical emergency
•  Legal obligations
Some Practical Issues
  Course Web:
http://www.physics.wisc.edu/undergrads/courses/fall2011/202/index.html
(under construction – nearly done)
  When sending us emails:
  Include word 202 somewhere in the subject line.
( phy202 , physics 202 , p202 , or simply 202 will do)
  Mentioning your section # is essential.
  Homework assignments are posted each Tuesday before
lecture and due by 11 pm of the following Monday.
  Lecture notes will be posted after each lecture on the same
day. Follow the links on course web.
  One discussion session, no labs this (first) Week
  Please all sign up for WebAssign. (www.webassign.net)
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202
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Physics 201 and 202
201
Cosmology
Light and Optics
Electro-Magnetism
Sub-Sub-Atomic:
Elementary Particles
Thermodynamics
Sub-Atomic:
Nuclear Physics
Heat, Temperature,
Pressure, Entropy,..
Oscillation and Waves
Classical Mechanics
Many-Atoms:
Molecules, solids
Atomic Structure
Laws of motion
Force, Energy,
Momentum,…
Quantum Theory
Classical
Modern
Relativity
Before Physics 202
Mechanics Gravitation
Waves
Thermodynamics
  Mechanics: Motion and Force
  Fundamental Laws:
•  Newton s laws of motion (Classical view)
•  Energy/Momentum/Angular Momentum conservation
(modern view)
  Gravitation: One of the four fundamental forces
  Fundamental Law: Newton s Law of Universal Gravitation.
  Waves: Coherent phenomena over space and time
  Fundamental Law: Superposition Principle
  Thermodynamics: Statistical behavior of large quantity
  Fundamental Laws:
•  Laws of Probability (average, entropy,…)
•  + Laws of Physics.
Physics 202
Electro-Magnetism
Light &Optics
  Electro-Magnetism:
  Electric force, electric charge, electric fields àCh. 21,22
  Electric potential à Ch. 23
  Current, capacitance & resistance à Ch. 24, 25
  Magnetic fields and magnetic force à Ch. 26, 27, 28
  DC and AC Circuits à Ch. 29
  Electromagnetic waves à Ch. 15, 30
  Light and Optics
  Physics of light
•  Electromagnetic waves à Ch. 30
•  Properties of light à Ch. 31
•  Lights as rays: Geometric optics, imaging à Ch. 32
•  Lights as (electromagnetic) waves, interference àCh. 33
Demo: Two Types of Electric Charges
Opposite signs attract Like signs repel
Properties of Electric Charges
 
 
 
 
2+1 types: positive, negative (+neutral).
Unit: Coulomb (C). 1 C= charge of 6.24x1018 -electrons, +protons.
Electric charge is quantized: q=±Ne, e=1.602x10-19 C
Building blocks of matters:
Charge (C)
Electron
Proton
Neutron
-e-=-1.602x10-19
e=+1.602x10-19
0
Mass (kg)
9.11x10-31
1.673x10-27
1.675x10-27
  Electric charge is conserved: charges can be moved around, but
the total charge remains the same.
  For very deep thinkers: Why electrons and protons have the same
electric charge?
What Are Happening in Previous Demo
  Initially both the rod and the fur are neutral
  Neutral ßà the object carries equal amount of negative
(electron) and positive (protons) charges.
  When the rod is rubbed against the fur, electrons are separated
from the protons and transferred from one objects to another.
The result is that the rod (and the fur) now have un-equal
mount of charges à they are charged (charge by friction)
  rubber rods tend to acquire more electron à negative
  glass/acrylic rods tends to lose electron à positive
  Attraction/repel behavior can be explained by the rules:
  Like sign charges repel each other
  Opposite sign charges attract each other.
One More Demo:
Electroscope, Charge by Induction
+++
+ ++++
- - - --
+
+
++
Remember:
Like signs attract,
opposite signs repel
++
+
+
Conductivity of matter:
  Conductors (metals): electrons are free to move (protons do not move)
  Insulators (glass, plastic, most fabric): charges can not move (or at least
fairly difficult to move them)
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  Semi-conductors : charges have limited mobility, future topics
A Repeated Message
Lectures supplement but do not substitute for reading
and solving problems!
Learning Physics: Preview + Lecture +
Review + Application to Problems
Before Thursday (Read Ch. 23)
  Review:
  Electric charge is an intrinsic property of matter.
  There are two types of charges: positive and negative.
  A particle (an object) can have three charge states:
•  positive, negative, neutral
  Electric forces exist between two charged particles
•  Like sign changes repel one another
•  Opposite sign charges attract one another.
  Preview:
  Electric forces are quantified by Coulomb s Law
  A charged particle creates an electric field around it.
  Electric field exerts electric forces on charged particles.
  General ideas on how to calculate electric field….
Electric Force And Coulomb s Law
 Electric forces exist between two charged particles
 The direction of electric force depends on the signs of
the charges:
  forces between opposite sign charges are attractive
  forces between like sign charges are repulsive
+
-
-
+
+
+
-
-
 The magnitude of the electric forces for point charges
q1 q2
F12 = F21 = ke 2
r
(Coulomb s Law)
Coulomb Constant: ke = 8.987x109Nm2/C2 = 1/(4πε0)
ε0: permitivity of free space (Ch. 26)