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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 though 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
R= Resistance
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 an
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
Electrical Power
Electrical Power is the
rate at which
electrical energy is
converted into
another form of
energy, and can be
written as:
P=IR
P=power
I=Ampere
R=Resistance