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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/
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Meet the Physics 202 Team
Faculty (lectures):
☻Prof. Lisa Everett [email protected]
Research: theoretical high energy physicsOffice hrs: M 4:35 or by appointment, 5215 CH, 262-4699
☻Prof. Bruce Mellado [email protected]
Research: experimental high energy physics Office hrs: by appointment, 4223 CH, 262-8894
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Meet the Physics 202 Team
Teaching Assistants (labs, discussion):
☺ Pankoj Gindodia [email protected]☺ Shusaku Horibe [email protected]☺ Trevor Irwin [email protected]☺ Robert Lindner [email protected]☺ Jason McCuistion [email protected]☺ Paul McGuirk [email protected]☺ Valerie Plaus [email protected] ☺ Yongyan Rao [email protected]☺ Jared Schmitthenner [email protected]☺ Koki Takasaki [email protected]
Office hours: in 2307 CH (starting Jan 28). Schedule: http://www.physics.wisc.edu/undergrads/courses/spring08/202/consult.htm
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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)
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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)
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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…
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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
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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
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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
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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
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Electric Charge
Like signs repelOpposite signs attract
Charges do not have to be in contact to interact
Two types!
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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
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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)
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Neutral metal
+ + + + + + ++ + + + ++
+++
+- --
-
-
Positively charged rod (too few electrons)
+ + + + + + +
Less positively charged rod
+
+++
+
Positively charged metal
+ + + + + + ++ + + + +
+
+++
+- --
-
-
electron flow
Charging by conduction (touching)
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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)
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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.
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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
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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