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Static Electricity

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Static Electricity Chapter 16 and 24 – PowerPoint PPT presentation

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Title: Static Electricity


1
Static Electricity
  • Chapter 16 and 24

2
Review The 4 Fundamental Forces
Strong Force The force that is involved in
holding the nucleus of an atom together
Electromagnetic Force The force that exists
between charged particles
Weak Force The force involved in nuclear decay
Gravity The force that exists between any two
objects that have mass.
3
Static Electricity
  • Better known as Electrostatics comes from the
    roots electro and statics.
  • Electro is Greek for amber, a petrified tree
    resin which when rubbed will attract other
    objects. When it was discovered that the movement
    of a sub-atomic particle was responsible for this
    attraction, the particles were called electrons
    the force was called electric.
  • Stati is Greek for standing or place.
  • Thus, electrostatics is the study of electrical
    forces at rest.

4
What do the forces do?
  • First they are not like gravity
  • The electrical forces can either attract or repel
    one another.
  • Ben Franklin named the two types of forces
    positive and negative.

5
Structure of the Atom
Helium Atom
Electron
Proton
  • Negative Charge
  • Charge -1.6x10-19 C
  • Positive Charge
  • Charge 1.6x10-19 C

6
Charge Interaction Like Charges
Like charges REPEL each other
7
Charge Interaction Unlike Charges
Opposite Charges Attract
8
Coulombs Law
The force between two electrically charged
particles (q) is proportional to the product of
their charges divided by the square of the
distances between them. K is the universal
electrostatic constant. It is equal to 9.0 x 109
Nm2/C2.
Which is stronger, gravitational forces or
electric forces?
Problem Assume that you have two objects, one
with a mass of 10 kg and the other with a mass of
15 kg, each with a charge of 3.0 x 10-2 C and
separated by a distance of 2 meters. Compare the
electrical and gravitational forces, which is
greater?
9
Ions
Most atoms have an equal amount of protons and
electrons. Because of this they are neutral
(they have no NET charge)
If an atom has too few or too many electrons, it
will have either a net positive charge or a net
negative charge. These are called IONS.
?Ions are NEVER created by moving or trading
protons. The only part of an atom that moves
from place to place is an electron.
10
Charged Atoms
Neutral Atom
Positive Ion
Lost an electron so it has a net positive charge
11
Charged Atoms
Neutral Atom
Negative Ion
Gained an electron so it has a net negative charge
12
Insulators and Conductors
In a conductor, electrons are NOT tightly bound
to their atoms. These are called CONDUCTION
(free) ELECTRONS. - Therefore, it is easy to
make charges move in and out of a conductor.
This is the same reason we use conductors for
wires. Charges (electrons) will flow easily
through them. - In a conductor, electrons will
spread out so they are as far apart from each
other as possible - Metals, water with dissolved
materials in it
13
Insulators and Conductors
In an insulator, electrons ARE tightly bound to
their atoms. - Therefore, it is not easy to make
charges move in and out of an insulator. In
fact, even if an insulator is charged (maybe by
friction) the charge will stay in one place and
not spread out. - Glass, rubber, plastic, wood,
pure water
14
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15
How to Charge and Object
  • Friction Charging two objects by rubbing them
    together.
  • One takes electrons from the other so one becomes
    positive and one becomes negative

Conduction (Contact) Since charges like to
spread out, touching a charged object to a
neutral or differently charged object will
transfer charge.
  • Induction Bringing a charged object near a
    neutral object to induce a dipole in the neutral
    object.
  • NO TRANSFER OF CHARGE!!!!!

16
Induction
Before
17
Induction
Induce an Electric Dipole
Also called polarization
The negative charges move away from the negative
sphere. REMEMER, the protons dont move!
18
Induction
Induced charge in both blocks when we separate
them
Positive Block
Negative Block
19
Law of Conservation of Electric Charge
  • In a closed system, the net amount of charge
    produced in any process is zero
  • The strength of charged particles is measured in
    coulombs. An electron and a proton have the same
    magnitude of charge, just opposite signs. The
    magnitude of the charge of either of these two
    particles is
  • 1.602x1019 coulombs So, we can say that an
    electron has a charge of 1.602x1019Coulombs,
    and a proton has a charge of 1.602x1019Coulombs
    .

20
A little more on the conservation of charge
  • How much energy required to tear away electrons
    varies from substance to substance.
  • Rubber holds electrons more firmly than fur. When
    rubber and fur are rubbed together, electrons
    transfer from the fur to the rubber rod.
  • The rubber has excess electrons and is negatively
    charged.
  • A glass or plastic rod rubbed with pure silk will
    transfer its electrons to the silk. Giving the
    silk a negative charge.
  • The electrons are not created or destroyed, they
    are simply transferred from one object to
    another.

21
Neutral Objects
Using your knowledge about induction and dipoles,
how do you think Neutral Objects are affected by
charged objects?
They Attract! Neutral objects are attracted to
charged objects
22
Charge Distribution
How does charge distribute itself on an object?
  • Charges spread out as much as they can.
  • In order to be in equilibrium, charges will bunch
    up at corners. (they gather so the net force in
    the center of a conductor is zero)

23
Charge distribution on a car
What should you do if a broken power lands on top
of your car?
24
Shielding
  • Static charge occupies only the outer surface of
    a conductor inside the conductor the electric
    field is zero.

25
Electric Fields
  • The space around every electrical charge
  • Has both magnitude and direction, a vector
    quantity
  • Exploring Electrical Fields

26
Electrical Potential Energy
  • The work required to push a charged particle
    against the electric field of a charged object
    increases the particles electrical potential
    energy.
  • Work done is equal to the energy
    gained.
  • Similar to how a masss PE depends on its
    location within the Earths gravitational force
    field

27
Electric Potential
  • Electrical potential is the electrical potential
    energy per charge.
  • Electric potential electrical potential
    energy/charge
  • Other terms for Electric
    Potential
  • Voltage
  • EMF (electromotive force)
  • 1 volt 1 joule/coulomb

28
Lightning
Lightning on Science Joy Wagon
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