Transcript Electricity Powerpoint

What is an electric
charge?
An electric charge is
the electrical
property of matter
that creates a force
between objects.
•
the attracting or
repelling
behavior of a
material.
What is an electric
charge?
To create this
charge,
electrons must
move from one
atom to
another.
What is an electric
charge?
All matter is made up
of atoms.
Atoms are made up of
smaller particles
called protons,
neutrons and
electrons.
Why do objects become charged?

An imbalance of its
protons and electrons
occurs
 Protons positive,
found in the
nucleus
 Neutrons neutral,
found in the
nucleus
 Electrons negative,
orbits the nucleus
Conservation of Charge
Electrons are bound
more tightly to
some atoms and
molecules than
others.
When an electron is
transferred, it
creates an ion.
Conservation of Charge
A charged atom is an ion.

positive ion – atom
loses electrons

negative ion – atom
gains electrons
Charge is always
conserved – never
created or destroyed!
Conductors and Insulators
ELECTRICAL CONDUCTORS
Conductors allow electrons
to flow
 Conductivity depends
upon how tightly the
atom holds on to its
electrons.
 loose electrons in a
material conduct the
electric charge through
(metals).
Examples of conductors:
Metal, graphite, etc.

ELECTRICAL CONDUCTORS
In solid conductors, the
electrons carry the charge
through the circuit because
they are loosely held.
In fluids, like those in a car
battery, positive and
negative ions and electrons
may compose the flow of
electric charge.
ELECTRICAL INSULATORS
Insulators DO NOT conduct
electricity well!! They provide
RESISTANCE to the flow of
electrons.
RESISTANCE IS CAUSED BY
INTERNAL FRICTION
Examples of Insulators: Glass,
wood, rubber, etc.
SEMICONDUCTORS
Semiconductor –
material made to
behave sometimes
as insulators and
sometimes as
conductors
(germanium and
silicon).
Electric Fields
An electric field surrounds
every electric charge and
exerts the force that causes
other electric charges to be
repelled or attracted.
Electric fields are represented
by arrows that show how
the electric field would
make a positive charge
move.
Charges Exert Forces
Charges Exert Forces
Unlike charges attract
each other (positive
and negative)
Like charges repel each
other (positive to
positive or negative
to negative)
Charges Exert Forces
Just like gravity, the
amount of
electrical force
exerted on an
object is related to
the following:
1. Distance from the
charged object
2. Strength of the
charge on the
charged object
How can objects become
charged?
1) Charging by Contact –
Two objects are rubbed
against each other and
electrons are
transferred.
PROTONS NEVER
MOVE from one
atom to another.
How can objects become
charged?
OR, A charged object touches a neutral object,
transferring electrons –
PROTONS NEVER MOVE from one atom to
another
How can objects become
charged?
Charging by Induction
(charging at a
distance) – A
charged object is
held near a neutral
object and causes an
overall charge.
Charge Polarization
When charges
rearrange in an atom,
one side becomes
slightly more positive
and the other side
becomes slightly more
negative. The atom is
electrically polarized.
Ex – charged comb
attracting bits of paper
or charged balloon
sticking to the wall.
ELECTRIC CURRENT
What is current electricity?
Current Electricity - Flow of electrons
What causes electrons to flow?
When an electric force is applied, it
causes a potential difference or
difference in voltage between the
ends of a conductor.
When there is no potential difference,
the flow of charge stops.
Direct Current and Alternating
Current
Direct Current – flow of charge always
flows in one direction. Batteries use
DC to flow from the negative terminal
to the positive terminal.
Alternating Current – electrons move
back and forth about relatively fixed
positions. Power utilities use AC. AC
allows low-cost, high voltage energy
transmission across great distances,
with safe low-voltage use by the
consumer.
Potential difference or
voltage difference
causes electrons to flow
in one net direction.
This voltage difference
provides the “push” or
the “pressure” to move
in a given direction,
and the SI unit is
Voltage (volts)
Voltage Sources
Voltage sources: dry
cell batteries, wet
cell batteries, leadacid batteries and
generators.
They supply the
energy or the
“push” to allow the
charges to move.
Voltage Sources
Dry Cell Batteries
 Consists of two
electrodes surrounded
by an electrolyte.
 In the dry cell shown
here, one electrode is
the carbon rod and the
other is the zinc
container.
Voltage Sources
Wet Cell Batteries
 Contains two
connected plates made
of different metals in a
conducting solution.
Voltage Sources
Lead-Acid Batteries
 Most car batteries are
lead-acid batteries.
 Contains six wet cells
made of lead and lead
dioxide plates in a
sulfuric acid solution.
Voltage Sources
In dry and wet cell
batteries, a chemical
reaction occurs
releasing energy inside
the cell which is then
converted to electrical
energy.
Generators, like the
alternators in vehicles,
convert mechanical
energy to electrical
energy.
Resistance
Resistance is the
tendency of a
material to
oppose the flow
of electrons,
changing
electrical energy
into thermal
energy and light.
Resistance
Almost all materials
have some
electrical
resistance.
Conductors have
less resistance
than insulators.
The SI unit for resistance is
Resistance
Temperature, Length,
and thickness affect
the amount of
resistance of a
material.
Resistance increases
as temperature
increases.
Resistance
Resistance
increases as wire
becomes longer
or as the gauge
(diameter)
becomes thinner.
Electric current is the flow of electric
charge and is measured in amperes
(amps).
Amperes can be thought of as the
volume of current running through a
circuit.
Current in a Simple Circuit
A simple circuit
contains:
1)A voltage source
2)A resistor (such
as a light bulb)
3)Conductors that
connect the
device to the
voltage source.
Current in a Simple Circuit
Voltage, current,
and resistance in
a simple circuit
are related.
This relationship is
known as Ohm’s
law.
Current in a Simple Circuit
Ohm’s Law can be
written as:
V=IR
V= Voltage
I= Amperage
(Current)
R= Resistance
Electrical Power
Electrical Power is
the rate at which
electrical energy is
converted into
another form of
energy, and can be
written as:
P=IV
P=power
I=Ampere
V= Voltage
ELECTRICAL ENERGY
SERIES AND PARALLEL
CIRCUITS
What is a series
circuit?
A series circuit
has only one
path for current.
SERIES AND PARALLEL
CIRCUITS
What is a parallel
circuit?
A parallel circuit
has multiple paths
for current.
SERIES AND PARALLEL
CIRCUITS
For a circuit to allow
the flow of
electrons, it must be
closed which means
that it makes a
complete loop back
to the power source.
SERIES AND PARALLEL
CIRCUITS
If it is open, the
path that
electrons can
follow is broken
and the resistor
will not work.
SERIES AND PARALLEL
CIRCUITS
If there is a short circuit, the
resistor will not work, even
though there is a complete
path.
The reason is because
electricity will always follow
the path of least resistance
and will therefore not travel
through the resistor.
SCHEMATIC DIAGRAMS
Schematic
Diagrams are
used to
represent
circuits.
FUSES AND CIRCUIT BREAKERS
How do fuses work?
Fuses melt to prevent
circuit overloads.
 A fuse is a ribbon of
wire with a low
melting point
How do circuit
breakers work?
Circuit breakers open
circuits with high
current.
 Made of a magnet or
bimetallic strip