Transcript STATIC ELECTRICITY

STATIC
ELECTRICITY
How Would you define
Static Electricity?
Electric Charge
• BASIC to all
matter
• Different
materials have
different
affinities for
electrons.
Basic Facts About Atoms
• Every atom has a positively charged nucleus
surrounded by negatively charged electrons.
• The electrons of all atoms are identical.
Each has the same quantity of negative
charge and mass.
• Protons have exactly the same magnitude
charge of an electron but is opposite in its
sign.
When charged particles
come near one another,
they give rise to two
different forces. A force
can pull objects together
or it can push objects
apart.
Law of Electric Charge
• 1:Like charges repel one
another
• 2: Unlike charges attract one
another
Why do
balloons stick to
the wall after
being rubbed on
hair or fur?
How Can This Happen?
Static Electricity
• The buildup of electric charges
on an object
• The electric charges build up
because electrons have moved
from one object to another.
Three Ways of Creating a Charge
• Rubbing two objects
together-FRICTION-TRIBOELECTRIC
• Conduction–
transferring a charge
by TOUCHING
• Induction-- Inducing
a charge-NOT
TOUCHING
Friction
• Transfer of
electrons by
rubbing.
Rubbing Separates charges on
Objects
• One object loses electrons while the other
object gains these electrons.
• The object that loses electrons has an
overall positive charge.
• ONLY THE ELECTRONS MOVE!!!
A van der
Graff
Generator
rubs electrons
off a rubber
band. These
electrons are
transferred to
the dome.
Van de Graff Generator
CHARGING BY
CONDUCTION
Charging a neutral body by
touching with a charged
body
Conduction
• Conduction
transfers the
electrons to
another object
through actual
contact.
What Is Happening?
Conservation of Charge
• It is important to
note that when
we charge
something, no
electrons are
created or
destroyed.
Charging by
INDUCTION
Charging an object by
NOT Transferring Charges.
What are the charges doing?
Electric Fields
• Charged Particles have
fields around them
• As the distance from a
charged particle
increases, the strength
of the electric field
decreases.
Coulomb’s Law
q1q2
F = k ———
d2
Electric Discharge
• The rapid discharge of
electrons.
• Examples:
– Spark that jumps
between your finger
and a doorknob
– lightning
VOLTAGE
• Also known as POTENTIAL
DIFFERENCE
• Voltage “acts” like a force in
electrical circuits.
VOLTAGE
• Electrical
Potential
difference or
energy per
charge is
called a volt
Separation of Charges
• Look at the
picture: establish
a relationship
between Energy,
Voltage and
Distance for two
charge plates..
Electricity
may be
defined as
the energy
associated
with
electrons
DANGER!!! STATIC
CHARGES
• 200 years ago, young
boys called powder
monkeys ran below
the decks of warships
to bring sacks of
gunpowder to the
cannons above. It was
the ship law that this
task be done barefoot.
DANGER!! STATIC
ELECTRICITY
• Always touch
something metallic
before grabbing the
pump handle if you
think you have built
up a static
charge….
DANGER!!! STATIC
Never pump
gas without
discharging
the static
charge first
1 Coulomb
6.25 X
18
10
electrons
Coulomb’s Law
• The amount of force the a tiny sphere with a
charge q1 exerts on a second sphere of q2 is
inversely proportional to the square of the
distance.
• If I double the distance the force decreases
to one fourth of the original force
• The Force between the spheres is directly
proportional to the charge.
Coulomb’s Law
q1q2
F = k ———
d2
• F=force
• k=9 X 109 N*m2/C2
• q1= 1st charge in
Coulombs
• q2= second charge
• d= distance in meters
Electric Field
• All charges create an
area in all directions
around it that an
electric charge can be
detected.
Electric Fields
• Electric Field strength measured in N/C
E= F/q
Electric Field Lines
• Radiate from the
positive charge to the
negative charge.
• Defined by the path of
a positive test charge.
Electric Field Lines
Determined from + test charge
Electric Field lines
• Show forces around a point charge that go
from positive to negative.