Download Electricity, Magnetism, and Light

Welcome to PHY212!
General Physics II:
Electricity, Magnetism, and Light
Prof. Mitch Soderberg
[email protected]
Lecture 1.1
Jan. 14, 2014
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Announcements
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Register for PHY222 (labs) if you haven’t already!!!
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PHY212 and PHY222 are separate courses.
PHY222 IS A REQUIRED CO-REQUISITE COURSE
PHY222 will NOT be meeting this week (Instructor: Sam Sampere)
Let’s review the course syllabus:
https://msoderbe.expressions.syr.edu/phy212-s14/files/2014/01/PHY212_Spring2014_Syllabus.pdf
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I will post course content in both Blackboard and on http://
msoderbe.expressions/syr.edu/phy212-s14 . I will put lecture
slides and recordings on the expressions site, usually the same
day of the lecture.
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Homework and Recitations
•You should have received your first HW assignments today.
‣HW0 is a questionnaire. Complete by your Friday recitation, and you get a 100%.
‣HW1 has your Mastering Physics assignment for the week.
•You will work in groups of 3 or 4 during recitation (a.k.a. workshops) on selected problems. One group member will present
their solution to the whole section. All problems assigned during
recitation are fair game for quizzes/exams.
•Read the relevant textbook sections before recitation.
•Your recitation grade is based on attendance and participation.
•TAs will discuss further details with you when you start
tomorrow!
•Show up for your recitations prepared - Bring calculator,
textbook, paper, pencil, etc... (Note: WF 9:30-10:25AM M010
section is not held in the Physics building!).
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Lecture 1.1 :
Introduction to Electric Charge
Lecture Outline:
Motivation
Model of Electric Charge
Insulators and Conductors
Textbook Reading:
Ch. 25.1 - 25.3
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Motivation
The study of Electricity and Magnetism in modern form has
been around for over 100 years. Perfect example of how
studying something esoteric can revolutionize the word.
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Motivation
Why are Electricity and Magnetism important?
•Our natural world is awash in electric and magnetic phenomena.
•Understanding this phenomena, and developing theories of it that
can be applied in other domains, is the bread and butter of many
scientists.
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Motivation
Why are Electricity and Magnetism important?
Applications of Electricity and Magnetism are too vast
to enumerate...all of you probably have at least one
electronic device on you right now!
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Motivation
Why are Electricity and Magnetism important?
The theoretical underpinnings of electromagnetism are quite
beautiful, and helped lead scientists down the path to our
present-day understanding of “modern physics”.
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Motivation
What are the overall goals for this course?
Magnets?
Maxwell’s Equations
1.To develop a basic understanding of the laws of electromagnetism.
2.To develop the ability to apply these new concepts to physical situations.
3.To develop an appreciation for the role that electromagnetism plays both
in our modern society and in the universe.
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CLICKERS!
I will be using data obtained from your
answers to clicker questions to:
1. Determine how well you are following the subject matter.
2. Keep you awake. If you answer (most) clicker questions, and
you answer them (mostly) correctly, final grade is boosted.
Maximum of 2% boost to final course grade if you do well.
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CLICKERS!
1. Register your clickers using Blackboard: https://
answers.syr.edu/display/blackboard01/Registering+a
+TurningPoint+Clicker+in+Blackboard
2. We will be using channel 41 for clicker polls. At beginning of
lecture, press: “Ch+4+1+Ch” on your clicker.
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Clicker Question #1
Who do you think will win the Superbowl?
A
B
C
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D
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Clicker Question #1
Who do you think will win the Superbowl?
A
B
C
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D
E
Model of Electric Charge
We discover electric charge at a young age
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Model of Electric Charge
As scientists, we want to understand what’s going on, so we experiment:
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Model of Electric Charge
As scientists, we want to understand what’s going on, so we experiment:
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Model of Electric Charge
As scientists, we want to understand what’s going on, so we experiment:
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Model of Electric Charge
As scientists, we want to understand what’s going on, so we experiment:
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Model of Electric Charge
If we did a systematic study of electric charge
and its properties, we would find:
1.Friction/rubbing can sometimes charge an object.
2.There are only two kinds of charge.
3.Two objects of like charge (plastic/plastic or glass/
glass) repel each other. Two objects of unlike charge
(plastic/glass) attract each other.
4.The magnitude of the force increases as the quantity
of charge increases, and decreases as the distance
between the charges increase.
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Model of Electric Charge
Electric Charge is a property of matter.
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e = fundamental unit of electric charge (not defined yet).
Protons are TIGHTLY bound in nucleus – they don’t go anywhere.
Electrons are more loosely bound.
Object Charge (q) = Npe - Nee = (Np-Ne)e
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Model of Electric Charge
http://www.xkcd.com
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Model of Electric Charge
Electric Charge is conserved.
• The algebraic sum (taking the + or – sign
into account) of all electric charges in any
closed system is constant.
• Electrons and protons are not created out of
nothing, or destroyed into nothing.
• Neutral objects have no net charge.
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Clicker Question #2
Before charging, both
rods have identical mass.
After charging:
A) plastic (on the left) has more mass
B) glass (on the right) has more mass
C) both have identical mass
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Clicker Question #2
Before charging, both
rods have identical mass.
After charging:
A) plastic (on the left) has more mass
B) glass (on the right) has more mass
C) both have identical mass
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Insulators and Conductors
• Conductor – electrons move
easily from one part of material
to another (examples: copper
wire, many metals, graphite,...)
• Insulator – electrons are
relatively fixed in place, can be
moved with effort (examples:
rubber, glass, plastics, air,...)
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Insulators and Conductors
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Clicker Question #3
What happens when a
charged object is brought near
an isolated neutral conductor
(such as a soda can)?
A) Nothing
B) Soda can is attracted to object
C) Soda can is repelled from object
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Clicker Question #3
What happens when a
charged object is brought near
an isolated neutral conductor
(such as a soda can)?
A) Nothing
B) Soda can is attracted to object
C) Soda can is repelled from object
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Insulators and Conductors
Excess charges within a conductor quickly arrange
themselves to achieve electrostatic equilibrium.
The neutral conductor becomes polarized.
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Insulators and Conductors
How do neutral insulators respond when a
charged object is brought nearby?
Charge does not easily move around in an insulator, so this
must be different than what happens for conductors.
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Insulators and Conductors
The individual atoms within an insulator become
polarized when a charged object is brought
nearby , forming an electric dipole.
Since the charged object pulls more on the
opposite-sign end than it pushes on the samesign end, there is an overall attractive force.
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Reminders
•Show up prepared for recitation session tomorrow.
•If you haven’t already, begin reading Ch. 25. You
should read the whole chapter before Thu.
•Complete and turn in HW0 at your Friday
recitation.
•Please come see me if you have any issues/
questions. Office hours: Tue. 3-5pm in Room 315.
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