Transcript Electric Field in Conductors - Ms. Gamm

Daily Work Organizer
Tuesday
Question of the Day: Why are objects
attracted to each other?
Do Now:
Turn to page 231 and write responses to the
questions about electricity. You may discuss
your ideas with your partner.
Agenda:
Cornell Notes
Homework:
Homework
(2) Reading Log 24: pg 235236
Due Friday:
New HW System
1. HW is stamped
2. You write the number on the top of
the assignment (#1) Reading Log 23
3. Staple all your HW in order to the
back of your Cornell notes at the end
of the chapter
Jobs
1 PowerPoint Master
2 Graded Work Gurus
1 Whiteboard Cleaner!
Tuesday Tutoring
Everyone is Welcome!
Mandatory if your grade is below a
C
If you can’t make, you must provide Ms.
Gamm with a written or oral explanation.
It’s what we see…
Static Electricity
The Point of Cornell Notes
If you don’t review, you would need to spend 40Without Review, only about 20% of
50 minutes re-learning each hour of material
information is remembered after initial
later
memorization
•
Within 24 hours spend 10 minutes
reviewing
•
A week later
spend 5 minutes
to "reactivate" the
same material
Write
Questions!
Write the
Summary
Charges
•Rubbing plastic or glass
makes them attract to
bits of paper or dust
•Same objects charged
the same way will repel
each other
•Some charged objects
attract each other
Charges
•All charged objects either
attract or repel each other
•This implies 2 types of
charges
•Benjamin Franklin
decided to call the charge
on rubbed glass positive
Electricity
•One of the first objects to hold this charge
was amber
•The Greek word for amber is elektron
•Electricity
•Electron
Charge
•To understand Charge, let’s look at the atom
•Protons (nucleus) are
positively charged
•(repels charged glass)
•The electrons are
negatively charged
•(attracts charged glass)
Charge
•Even though protons are much bigger (2,000 x’s
bigger than electron), the – and + charges are
the same size.
•If an atom has equal number of electrons and
protons the charge is zero.
____?
•3 electrons (blue) and 3
protons (red)
•Net charge is zero
(neutral charge)
Charge Rules
•In order to be charged, an object must have extra
protons or electrons
•The following facts help understand charges:
1. In solids, positive charges do not move
protons are fixed in place
Charge Rules
2. In solids, negative charges can move
• conductors: electrons move all about material
Charge Rules
2. In solids, negative charges can move
• conductors: electrons easily move about material
• insulators: electrons mostly move around atom
Charge Rules
3. In fluids, both
protons and
electrons can
move all around
Charge Rules
4. Objects want to be neutral.
• If given a path to the earth, electrons will flow
out until the object is neutral.
• This is called grounding.
v
Charge by Rubbing
•Every atom attracts electrons (e-) a certain amount
•When you rub two objects together the object that
attracts electrons more will steal e-
+
−
Charge by Rubbing
•This stealer becomes negative (more e-) and the
other object becomes positive (lost e-)
What will happen to the charge when the bars
separate?
46Electrons
Electrons
42Electrons
Electrons
Transferring Charge
•This stealer becomes negative (more e-) and the
other object becomes positive (lost e-)
•Only works if there is contact
Daily Work Organizer
Wednesday
Question of the Day:
How do electrons move?
Do Now:
1. Graph your Test Score on your Tracker
2. Answer and give an explanation to
questions #1 & 2 on pg 244.
Hint: Q and 2Q represent charge
Agenda:
Cornell Notes
Activity
Cornell Notes
Homework:
(3) Reading
Log 25: pg 248Homework
252
(4) Finish Activity pg 238-239
(5) Problems 1-3 Pg 246
1.
2. Where is the
Electrostatic
Electrostatic Force
greatest?
smallest?
Q = charge
Test Corrections due Monday
Retake: Monday 3:15 – 4:15
Warning
If you do not return your test to me
you get -10 points
All tests must be returned by Tuesday
Conduction
① A charged conductor touches a neutral conductor
Total Charge = protons - electrons
Conduction
① A charged conductor touches a neutral conductor
Q1 = ?
Q1 = 3 protons + 7 electrons = -4 charge
Q2 = ?
Q2 = 4 protons + 4 electrons = 0 charge
Conduction
① A charged conductor touches a neutral conductor
② The electrons spread out so that the charges on
both are equal
Q1 = Q2 = -2 charge
What will happen to the charge when the
conductors separate?
Conduction
① A charged conductor touches a neutral conductor
② The electrons spread out so that the charges on
both are equal
Q1 = Q2 = -2 charge
Visualizing Electric Charge pg
237
Neutral
Draw 3 units of charge
(protons & electrons)
In each bar
Induction pg 237
6 units of charge
(protons or electrons)
9 protons &
9 electrons total
Neutral
Conduction pg 238
6 units of charge
(protons or electrons)
What
happen
Total can
protons:
6+9 = 15
when
charged= 9
Total2electrons
objects touch?
Difference: 6 protons
Charge has to be evenly
9 protons
totalelectrons
distributed…
How many
should each object have?
Initially
Neutral
Charging by induction pg 239
6 units of charge
(protons or electrons)
Charged objects want to be
neutral…
9 protons
&
How many
electrons
9 electrons
totalshould
enter from the ground?
Neutral
Vocab
Charging by
Induction
Word
Picture that reminds you of definition
A method used to charge
an object without actually
touching the object to
any other charged object
Definition
Sentence using word
Word or words that remind you of definition
Vocab
Charging by
conduction
Word
Picture that reminds you of definition
Electrons are
transferred from one
material to another
through contact
Definition
Sentence using word
Word or words that remind you of definition
Induced Polarity
•How do charged objects
attract neutral objects?
•By inducing a charge on
the neutral object.
•A neutral balloon has no
effect on wall’s e•The neutral wall has efound randomly around
nuclei of the atom
Induced Polarity
•Let’s charge the balloon
•Now the e- in the wall are
being repelled
•This leaves the exposed
wall acting positive
•Negative and positive
charges attract each other
What was wrong with this movie?
Electrostatic Force
•Electric Force is 1039 times larger than gravity
•Coulomb studied charge with charged metal balls
•Let’s look at how the amount of charge on each
ball and the distance effect the electrostatic force
Coulomb’s Law
•Electrical force is proportional (
FE µ Q1Q2
1
FE µ 2
d
µ) to both
Coulomb’s Law
•These lead to one equation called Coulomb’s Law:
kQ1Q2
FE =
2
d
FE ºElectric Force in Newtons (N)
Q1,Q2 ºcharge in Coulombs (C)
d º distance between centers
in meters (m)
k º 9.0 ´10
9 N× m 2
C2
Coulomb’s Law
•A Newton is about equal to ¼ pound
•A Coulomb is the amount of charge in 6.25 x 1018
electrons or protons
kQ1Q2
FE =
2
d
Example
Two charged spheres, one with 1x1012
extra electrons and one with 2x1012 extra
protons are separated by 50 cm. What
force do they exert on each other?
Given:
d = 50cm
(
1m
100 cm
Q1 = -1´10
(
(
)=
0.50 m
) = -1.6 ´10 C
) = 3.2 ´10 C
-7
12 1Coulomb
Q2 = 2 ´10
12
Want:
FE
18
6.25´10
1Coulomb
6.25´1018
-7
Example
solve for FE
kQ1Q2
FE =
2
d
FE =
(9 ´10
9 N ×m 2
C2
-7
-7
)(-1.67 ´10 C)(3.2 ´10 C)
(0.50 m)
2
FE = - 0.0019 N
- force is attractive
Time to practice
Go to pg. 235
Daily Work Organizer
Friday
Question of the Day:
What is an electric filed?
Do Now:
Answer questions 3, 4, 11 & 12 on pg 244
Agenda:
Labette
Cornell Notes
Activity
Homework:
(7) Reading Log
26: 255-256
Homework
(8) Problems Set 8
(9) Finish E-field activity 253
 Test Corrections!
Daily Work Organizer
Friday
Question of the Day:
What is an electric filed?
Do Now:
Answer questions 3, 4, 9, 11 & 12 on pg 244,
Agenda:
Labette
Cornell Notes
Activity
Homework:
(7) Reading
Log 26: 255-256
Homework
(8) Problems Set 8
 Test Corrections!
Answers
1.
2.
3.
4.
5.
6.
7.
A
C
A
C
E
A
B
8. A
9. D
10. B
11. A
12. A
13. B
If distance is doubled:
dfinal = 2dInital
FE initial = 12 N
1
FE µ 2
d
1
FE µ
(2d)2
1
FE µ 2
4d
#3
1 1
FE µ
2
4d
12
FE final µ N
4
Tutoring After School
Today, room 308
Static Electricity Test on
Tuesday
Why? Because I don’t want you that
have to study over Thanksgiving
Advice: Finish your Cornell notes over
the weekend
Labbette pg 240
Read pg 240
Complete Part 1 with your lab
group
The Electric Field
•All charged objects produce electric fields
•We know that a positive charge will repel another
positive charge and attract a negative one
•If we draw lines to represent this we would be
drawing an electric field
The Electric Field
Let’s look at the rules for drawing field lines:
① Field lines always point in the direction that a
positive test charge would move
The Electric Field
② Field lines always intersect charged objects at
right angles
The Electric Field
② Field lines always intersect charged objects at
right angles
The Electric Field
③ Field lines never intersect each other
The Electric Field
④ The closer that field lines are to each other, the
greater the electric field
The Electric Field
Example:
•Draw the electric Field Lines
Time to practice
Go to pg. 253
Electric Field in Conductors
•Imagine a charged circle
•Where can charges move to get farthest away?
Electric Field in Conductors
•Imagine a charged circle
•Where can charges move to get farthest away?
•To the edges!
•The excess charge on a conductor will always be
on the surface
Electric Field in Conductors
•How would the field effect a lone charge in the
middle?
Electric Potential
•Which is worse, 120 volts or
25,000 volts?
•depends
•Voltage is a potential for energy
per charge
E
and
E = Vq
V=
q
1 volt = 1 Joule of energy per 1 Coulomb of charge
1 Joule
1 volt =
Coulomb
Electric Potential
•What makes voltage dangerous is how fast the
charge flows out
•1 Joule is about the energy required to lift half a
glass of water 1 meter high
1 J!
1m
Electric Potential
•Basic outlet is 120 V
•The flow of an outlet is about 20
Coulombs/sec
•The energy released in 1 sec
would be:
E = Vq
E = (120V)(20C) = 2,400 J
Amount of energy to lift 75 gal of water 1 m high!
Electric Potential
•Van de Graff generator carries up to 400,000 V!
•But, it only flows 10 μCoulombs/sec
•The energy released in 1 sec would be:
E = Vq
5 J
-6
E = (4 ´10 C )(10 ´10 C) = 4 J
Amount of energy to lift 2 cups of water 1 m high
Time to practice
Go to pg. 253