Semester 2:
Unit 1
Electrostatics
Spring 2015
Agenda 1/20/15
Welcome!
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Seating Chart
Name Game
Info Sheets
Introduction to Electrostatics Activity
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What do you know about this stuff?
Seating Chart
Arrange yourselves in alphabetical order
ACROSS each ROW.
You have 2 minutes
GO!!
Agenda 1/21/15
Double Period
Collect Signed Syllabi
Complete Intro to Electrostatics Lab
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Think about:
What causes charge?
In what ways can charge build up?
Discuss findings from activity
Notes on types of charging
Begin Types of charging lab
HW: Complete analysis and conclusion of lab
Let’s talk
What are the parts of an atom?
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Which part moves most easily?
What is a conductor?
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Examples?
What is an insulator?
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Examples?
Big Question:
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What makes something a conductor or an
insulator?
Methods of Charging
Chapter 19
Conductors vs. Insulators
Conductor: allows charge flow easily
Metals
Insulator: doesn’t allow charge flow easily
Glass, dry wood, cloth, air,
most plastics
Like Charges & Unlike Charges
Charge moves due to motion of electrons
Electrons are negatively charged
When two materials +, repel
When two materials -, repel
When one material + and one material -,
attract
Charging by Conduction
Redistribution of charge by direct touching
together of two objects
Made easier/quicker if both are electrical
conductors
Originally uncharged material gets same
charge concentration as originally charged
material if contact between the two exists
for a long period of time
Charging by Conduction
Charging by Friction
When two initially uncharged materials
make contact, the better conductor grabs
the electrons from the better insulator
In the process, both become charged
Substance w/more electrons becomes
negative; other becomes positive
Charging by Friction
High affinity
for electrons
(conductors)
Low affinity
for electrons
(Insulators)
Charging by Induction
Charge accumulates on originally
uncharged material due to a charged
material being placed nearby the
uncharged material at the same time as a
ground is established.
Induction Example: Grounding
Induction Example: Contact
Induction Example: + Charge
Induction by Polarization
Polarized: the + and – charges are not
evenly distributed in a material (+ pole and
– pole)
When the charged material is an insulator
(non-conducting), polarization occurs in
the conductor and the two materials are
attracted
Cellophane on plastic, balloon on shirt
Induction by Polarization
Agenda 1/22/15
Complete Types of Charging Lab
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At least 2 Problem Solving Activities
Show off Physics Skills
Lab Exit Slip
Forces and Free Body Diagram Intro
HW: FBD Practice 1
Agenda 1/23/15 Physics Phriday
Discuss Types of Charging Analysis
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Turn in lab
Intro to Free Body Diagrams
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Practice
Coulomb’s Law Lab
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Netbook activity
HW: Complete Coulomb’s Law Lab Analysis
Before we start
On a separate sheet of paper:
Tell me the 4 types of charging
AND
Draw an example of each type
Agenda 1/26/15
Complete Coulomb’s Law Lab
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Graphing Hints
Build Coulomb’s Law
Practice problems with C.L.
HW: Finish Write-Up for C.L. Lab
Graphing Hints
Indirect
Relationship
F=x
F = -x
Inverse
Square
F =1/x2
Inverse
Relationship
F = 1/x
Agenda 1/27/15
Discuss Coulomb’s Law Lab
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Determine the flaw in the program
Complete Lab
Notes on Coulomb’s Law
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Practice Problems for CL
HW: Finish Write-Up for C.L. Lab
Coulomb’s Law
FE = k|q1||q2| / r2
k = Coulomb’s Constant = 9.0 x 109 Nm2/C2
q1 & q2: Charges in coulombs (C)
r = distance from center of one charge to center of
the opposite charge (m)
If charges opposite, then attractive
If charges like, then repulsive force
Equal force upon both objects (Newton’s 3rd Law)
Opposites Attract, Likes Repel
Inverse Square Law
Like with
sound
intensity, there
is an inversesquare
relationship
between force
and distance
of separation
Fundamental Charge
When an atom ionizes to +1 or -1 in chemistry,
how much charge does this represent in
coulombs?
+1 in chem = 1.60 x 10-19 C = e
1.60 x 10-19 C is smallest quantified charge
Proton = 1.60 x 10-19C, electron = -1.60 x 10-19C
Also called elementary charge
Net Charge
The net charge equals the (number of
extra or deficient electrons) x ( +/- 1.60 x
10-19 C)
q = Ne
If you have a substance with 5 extra
electrons, then q = (5) (-1.6 x 10-19 C)
= -8.0 x 10-19 C
Net Charge
What is the net charge in Coulombs of a...
Fe atom?
Fe2+ ion?
Fe3+ ion?
Charge amounts are always simple whole
number multiples of the fundamental
charge!
Coulomb’s Law in an Atom
What is the average electric force between
a proton and an electron in a hydrogen
atom? (average distance of separation
between p+ and e- is 5.3 x 10-11 m)
Answer is 39 orders of magnitude greater
than gravitational attraction between the
two!
Agenda 1/28/15
Doubles
Turn in Coulomb’s Law Lab
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Final Questions
Lab Exit Slip next period
Practice Net Charge and CL
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Practice Problems for CL
Practice Net Charge
Review Everything up to now
HW: Study for Quiz Tomorrow
Agenda 1/29/15
Discuss the Review Worksheet
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Types of Charging
Coulomb’s Law
Review Activity for types of charging
Brief Review Quiz
HW: None for tonight
Agenda 1/30/15
Review Electrostatics Quiz
Amount of Electrons on a Balloon Lab
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q = Ne
More Force Practice…maybe
HW: Write up the balloon lab
Agenda 2/4/15
Pass Back A LOT!!
Collect Balloon Lab from the rest
Electric Field PhETs
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Field of Dreams and Field Hockey
Notes of E-Fields and Diagrams
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Practice Problems
HW: Complete E-Field WS
Electric Fields
Vector quantity
Relates the force exerted on a positive test
charge to the size of the test charge
Changes with location
Unit:
N/C
E = Coulomb’s force on q’
q’
E = FE
q’
Example Problem
What is the strength and direction of the
electric field 0.250m to the right of a 1.00C
electric charge?
What is the strength of the field .250m to
the left of the same charge?
.250m above the same charge?
Electric Field Lines
Arrows show the force direction acting
upon a positive test charge
The more field lines per area, the more
intense the electric field is.
Notice that arrows flow
out of the positive
charge.
Electric field lines:
Multiple Charges
Charges of
opposite sign
display a
watermelon or
footballshaped field
line structure
between
them.
Again, arrows
flow out of +
and into -
Electric field lines:
Multiple Charges
Charges of
same sign
display a
diamondshaped
field line
structure
between
them.
Electric field lines:
Multiple Charges
Show field lines
entering or leaving
each charge in the
ratio of the relative
magnitudes of the
charges.
•Above, red charge (+) has 12 lines leaving, blue
charge (-) has 6 lines entering, so red charge must have
double the magnitude that the blue charge possesses.
Electric field lines:
Multiple Charges
More powerful
charge tends to
dominate the
less powerful
one and change
the basic
watermelon/
diamond shape.
Electric Field Lines:
Charged Conductors
Two oppositelycharged
conducting
plates have
field lines
roughly linear
between them
and rounded off
their edges.
Rules Recap for Drawing EField Lines
1. Don’t have field lines cross.
2. Have the same ratio of lines
entering/exiting charges as the ratio of the
magnitude of the charges
3. Have at least 3 lines entering/exiting all
charges
4. Best amount of field lines per charge is
from 4-12 lines.
Two
Charge
Examples