Transcript Chapter 7 Notes

Chapter 7
Electricity
Section 1
Electricity
Structure of Atoms
Atoms contain the following…
Particle
Charge
Location
Proton
+1
Nucleus
Neutron
0
Nucleus
Electron
-1
Outside the
nucleus
Positive and Negative Charges
In most atoms, the negative charge cancels
out the positive charge. These atoms are
said to be electrically neutral.
Static Electricity

The accumulation
of excess electrical
charge on an
object.
Ex:
 Walking on carpet.
Electrons are transferred
from the carpet to your
shoes.
 Lightning is a very large
static charge
Charges Exert Forces
The force on the atoms
depends on…
Opposite charges attract
The distance
between the atoms.
2. The amount of
charge on the
atoms.
1.
Like charges repel
Electric Fields
• An electric field surrounds every electric
charge and exerts the force that causes other
electric charges to be attracted or repelled.
• Any charge that is placed in an electric field
will be pushed or pulled by the field.
Earth’s Electric Field
Law of Conservation of Charge

A charge can be transferred from object to
object, but cannot be created or
destroyed.
Static Charge
Charging Objects By Contact

Charges can be
transferred by
rubbing or touching
objects.
Ex: Rubbing your
shoes on carpet or
rubbing your hair with
a balloon.
Charging By Induction
(Charging at a distance)
Charged objects brought near a neutral
object will cause electrons to rearrange
their positions on the neutral object.
Charging at a Distance

The balloon on the
left is electrically
neutral.

The balloon on the
right is negatively
charged and
produces a positively
charged area on the
sleeve by repelling
electrons.
Lightning
• Lightning is a large static discharge.
• A static discharge is a transfer of charge
between two objects because of a buildup
of static electricity.
Lightning
• Eventually, enough charge builds up to cause
a static discharge between the cloud and the
ground.
• As the electric charges
move through the air,
they collide with atoms
and molecules. These
collisions cause the
atoms and molecules
in air to emit light.
Thunder
• Lightning also generates powerful sound
waves.
• The electrical energy in a lightning bolt rips
electrons off atoms in the atmosphere and
produces great amounts of heat.
• The heat causes air in the bolt's path to
expand rapidly, producing sound waves that
you hear as thunder.
Grounding

Connecting an object to Earth.

Providing a path for a charge to reach the
Earth prevents an excess charge from
building up.
Electroscope

A device used to
detect an electric
charge.
Section 2
Electric Current
Electric Current

The net movement of electrons in a single direction.

Flows from higher voltage to lower voltage.

Measured in Amperes. (amps)
Voltage Difference

The differences in
electrical charges.

Measured in Volts.
Circuits
A closed path that the electric current
follows.
A battery can provide the voltage difference
needed to keep current flowing.
Resistance

Resistance is the tendency for a material
to oppose the flow of electrons, changing
electrical energy into thermal energy
and light.
 Resistance is measured in ohms
Ohm’s Law
Current (in amps) = voltage difference (in volts)
resistance (in ohms)
I=V
R
Section 3
Electrical Energy
Circuits
There are 2 types of circuits:
Series and Parallel
Series Circuit
 Have
only one
loop to flow
through.
EX: flashlights, some
holiday lights.
Parallel Circuits



Contain two or more
branches for the current
to move through.
The current can flow
through both or either of
the branches.
Advantage: When one
branch opens the current
continues to flow through
the other branches.
Household Circuits

A combination of
parallel circuits
connected in a
network.
Protection From Overheating
Fuses: Contain a small
piece of metal that
melts when it
becomes overheated,
breaking the circuit
and stopping flow of
current.
Circuit Breaker

A circuit breaker
contains a piece of
metal that bends
when the current in it
is so large that it gets
hot.