Transcript File

A. Some positive charges in
the sweater will move
onto the balloon
B. Some negative charges in
the sweater will move
onto the balloon
Negatively
charged
balloon
Neutral
wall
A.
B.
C.
D.
Some positive charges
in the wall will move
towards the balloon
Some negative charges
in the wall will move
towards the balloon
Some positive charges
in the wall will go onto
the balloon
Some negative charges
on the balloon will go
to the wall
Negatively
charged
balloon
Negatively
charged
balloon
A.
The balloons will move towards
each other
B. The balloons will move away from
each other
C. The balloons will not move.
A.
Most electrons will go
into the knob and
down to the earth.
B. Some electrons will go
from the earth
through the knob and
into the man.
 All
matter is composed of atoms
 We call different kinds of atoms elements
 Elements form compounds
 Compounds have different properties,
including different electrical properties
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The nucleus of an atom is made of smaller
particles, such as:
◦ Positive particles called protons
◦ Neutral particles called neutrons
Outside the nucleus are negative particles
called electrons
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The makeup of an element will determine
how it is electrically charged (will it gain or
lose electrons?)
If an atom has the same number of electrons
and protons it is considered electrically
neutral (balance of charges)
An atom with unequal numbers of protons
and electrons can be considered “electrified”
or electrically charged
An ion is an atom or molecule that has
unequal numbers of protons and electrons
 An atom with more electrons than protons is
negatively charged
 An atom with more protons than electrons is
positively charged
 Remember, only electrons can move! Protons
are tightly bound within the nucleus

Like charges repel
 Unlike charges attract
 A neutral object will be attracted to
any charged object
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An electric force is due to electric charges
Electric force is a non-contact force . . .
Objects can experience the force without
coming into contact
Non-contact forces are often called “field”
forces (like the gravitational force)
The electrical force is stronger than the
gravitational force.
 Electrical charges collected on an object can
be lost to surroundings
 Gravitational forces can only be detected
when observing large bodies like the Earth or
sun
 The electrical force can be either attractive or
repulsive
 The gravitational force is only attractive
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The process of separating charges into
opposite sides within one object
One side of an object is positive and the
other side is negative
One charged object is required to induce
electron movement or electron
rearrangement
Polarization occurs when the molecules
within an object reorient based on a nearby
charged object
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Conductors are materials that allow electrons
to flow freely
Conductive materials will allow charge to
distribute across the entire surface of the
material
This occurs because of the repulsive nature of
electrons
Conductors can transfer charge to other
objects
Examples include metals(electrons can be
removed easily), salts, water, humans
Insulators are materials in which
charge will not move easily
 The charge does not distribute over
the object but rather stays in one
location
 Examples include glass, dry wood,
plastics, dry air
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An electroscope consists of a metal knob
connected by a metal stem to two thin
lightweight pieces of metal foil, called
“leaves.”
There are 3 ways we can charge objects:
◦ Friction
◦ Conduction
◦ Induction
Friction occurs when two objects are
rubbed together
 Electrons transfer from one object to
another
 Both objects are left with an imbalance
of charge, one positive and one is negative
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A charged object comes in contact with a
neutral object
Excess electrons transfer to the neutral object
If a negatively charged object touches
another object, the excess electrons transfer
to the neutral object
The neutral object becomes charged, and is
no longer neutral
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If a positively charged object touches a
neutral object, it takes electrons from the
neutral object
The positively charged object becomes
neutral, and the neutral object becomes
positively charged (it has lost electrons)
Process of charging an object without
touching it (bringing one charged
object near an neutral object)
 Electrons are NOT transferred!
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A ground is simply an object that
serves as a seemingly infinite reservoir
of electrons
 The ground is capable of transferring
electrons to or receiving electrons
from a charged object in order to
neutralize that object.
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Electric force is a vector quantity
The closer two charged objects are to one
another the larger the electric force
The further away two charged objects are
from one another the smaller the electric
force
Inverse relationship
 Direction
of the Electrical
Force:
◦Dependent upon whether the
objects are charged with like
charges or opposite charges
The charge of an atom can be
measured
 This charge is measured in Coulombs
(C)
 Each electron holds a negative charge
of -1.6 x 10-19 Coulombs
 Each proton holds a positive charge of
1.6 x 10-19 C.
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States that the that the electrical force
between two charged objects is
directly proportional to the product of
the quantity of charge on the objects
and inversely proportional to the
square of the separation distance
between the two objects
 Assume that any collection of charges
is located in the center of an object

F = Force
k = constant, based on the medium the object
is immersed in (air)
For air, the value of k = 9.0 x 109 N·m2/C2
Q = charge of each object
d = distance separating the objects
Johnny’s soccer ball has a positive charge of
+6.0 x 10-6 C. Rachel’s soccer bag, with a
charge of +3.0 x 10 –6 C, is 3.0 m away.
a. Calculate the force on the soccer ball.
b. Calculate the force if Rachel’s bag had a
negative charge.
Q1 = 6.0 x 10-6 C
Q2 = +3.0 x 10 –6 C
d = 3.0 m
k = 9.0 x 109 N·m2/C2
𝐹=
F=
𝑘𝑄1 𝑄2
𝑑2
=
9.0 𝑥 109 (6.0 𝑥 10−6 )(3.0 𝑥 10−6 )
32
We can call the space around a
charged object the electric field
 This space affects other charges as
they come near the charged object
 An object that enters the electric field
will experience a force.
 The size of the force is based on the
amount of charge present and the
distance between objects
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 The
electric field is a vector
quantity
 It has a magnitude and a direction
 The direction of the field can be
measured using a positive test
charge (as a standard)
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http://phet.colorado.edu/sims/charges-and-fields/charges-andfields_en.html
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To show direction,
electric field lines are
drawn around the
charges within an
electric field
The electric field is
stronger where the
field lines are closer
together
Arrows move away
from a positive charge
(because a positive
charge repels the
positive test charge)
Arrows point toward
a negative charge
(because a negative
charge attracts the
positive test charge)
 Electric field lines
are also called lines
of force
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There is an electric field with a magnitude of
150 N/C. Determine the force on a dust
particle having a negative charge of 9.2x10-16
C.
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You have 7 problems to complete.
kQ1Q2
F=
2
d
F
E=
Q
Note: If you substitute “F” from the
Coulomb’s law equation into the “F” of the
electric field equation, you get the
following:
Review . . . Potential
energy is due to an
object’s position
 All energy is measured
in joules
 For an object to gain
gravitational potential
energy, work must be
done on the object Example: a book is lifted into

the air and gains gravitational
potential energy
The energy gained by an electric charge
when work is done on the charge is
called electric potential energy
 Work is done on the charge when it is
moved against an electric field
 Example: A negatively charged balloon is
pushed toward a Van de Graff generator
 Once the charge is released, the electric
potential energy becomes kinetic energy

Electric potential is a comparison of
the electric potential energy and the
number of charges present
 A balloon charged by rubbing it on
your hair does not have many charges
(only about 1 millionth of a Coulomb)
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Electric potential difference is referred
to as voltage (V)
A device used to measure electric charge is a
voltmeter.
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v = work
E=v
Charge
d
V = electric potential difference (“voltage”)
Work = f x d
Charge = in coulombs
E = electric field
D = distance
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Unit: volt (v) which is equal to j/c
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A high voltage transmitter
Allows us to enjoy television, automobiles,
and just about every other electronic device
Wireless electrical transmission
X-rays, radio, wireless telegraphy all
attributed to Nikola Tesla
http://www.youtube.com/watch?v=B7yqn89j
wZo
LIGHTNING
http://video.nationalgeographic.com/video/kids/force
s-of-nature-kids/lightning-101-kids/
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http://www.flickclip.com/flicks/sw
eethomealabama2.html
Lightning can travel up to 140,000
mph
Produce temperatures of 54,000°F
Can form fulgurites (sand into glass)
Transfers 15 C of electric charge
Charges are polarized within a cloud
 The top of the cloud becomes
positively charged
 The bottom of the cloud becomes
negatively charged
 The electric field induces a movement
of electrons from the cloud down
toward Earth
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The electric field causes ionization of the air
surrounding the cloud
This results in a conductive substance called
plasma
The lightning bolt begins as a step leader or
flow of electrons from the cloud toward the
ground
A positive streamer rises up from the ground
When the step leader and the streamer meet,
a conductive pathway allows the excess
electrons to move to the earth
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http://www.teachersdomain.org/asset/phy03
_vid_lightning/
Make a lightning strike
http://environment.nationalgeographic.com/
environment/natural-disasters/lightninginteractive/
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A lightning rod is a
protective measure for
tall buildings, farm
houses, etc.
Used to direct lightning
strikes to the ground
This allows the excess
electrons to flow into the
ground and not into the
house or building
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You are safe in a vehicle during a lightning
storm.
http://www.youtube.com/watch?v=C8xt9AP4
1-A
Electrical energy can be stored in a
device called a capacitor
 Capacitors are found in nearly all
electronic devices
◦ Televisions, camera flash, computer
 A capacitor must be charged
 A capacitor is discharged when a
conducting path is provided between
the plates

A
device that
stores charge
 Made of 2
conductors
separated by
an insulator
 The
charge stored will
SHOCK you if you are
in the conducting
pathway!!
 Found in many
electrical circuitscomputers,
televisions, camera
flashes