Transcript ELECTRICITY

Basic Electricity Info...
All electricity is
energy that results
from the
movement of
electrons.
All matter is made up of
positive and negative
charges
The negatives charges
(electrons) can
move freely and this
movement creates…
ELECTRICITY!
Electric current is the movement or flow of electrons.
CIRCUIT is the PATH the electricity travels on.
• Most of the time, the + and
– charges cancel each other
out.
• Most matter is neutral
Static Electricity
• Static electricity is the
buildup of charges on
an object
• The word static means
not moving
How can electric charges build up on an
object?
• Friction
• Conduction
• Induction
When charges on an object are rearranged without
physical contact, it has been charged by induction.
Conductors
• A conductor is a material through which electric
charges move easily
Examples of conductors:
Metals such as copper, aluminum, gold, silver
Insulators
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• An insulator is material through which electric charges cannot
move easily
• Examples: plastic, rubber, wood, glass and sand
Static Discharge
The loss of static
electricity as charges
move off an object is
called static
discharge
Lightning!
A giant electric spark,
called lightning, is
the result of static
discharge created in
a cloud.
Only some lightning
reaches Earth
and it can be VERY
dangerous and can
cause property damage.
• The wind rubs together the
water molecules and
particles of matter in the
clouds
• This friction causes static
electricity to build up in the
cloud
• The electrons collect in
the lower part of the
cloud
• They induce positive
charges from the
ground below.
Who is this?
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Clues:
Inventor
Lightning rod
Ben Franklin
A lightning rod conducts an
electric charge from the
cloud directly to the
ground.
Electricity ~ Mouse and
Cheese Analogy
The negative charges (mice) will
do work in order to get to the
positive charges (cheese).
Electricity ~ Mouse and
Cheese Analogy
• The mouse wants to get to the cheese, but
there is no path.
The Mouse Cheese Circuit
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• The mouse (electron) will gladly do work to get
to the cheese (proton)
The Mouse Cheese Battery
• This is the
mouse-cheese
version of a D
cell and an AA
cell
• Which is which?
The Mouse Cheese Battery
• Both the D cell and
the AA cell produce
1.5 volts.
• What is the
difference?
• Answer: The D cell
will last longer
Real Batteries
• Both the D cell and the AA cell
produce 1.5 volts.
• What is the difference?
• Answer: The D cell will last
longer
Electrochemical Cells
• Electricity can be generated
by a chemical reaction
• An electrochemical cell
changes chemical energy into
electrical energy
Electric Current Measurement
• Each month your family
receives an electric bill.
• How does Con Ed
determine how much
money you owe?
CURRENT ~ is the
rate of flow of
charges
Voltage -causes
current to flow
through an
electric current
VOLTAGE ~ The
amount of work that
each charge will do as
it goes through the
circuit.
RESISTANCE ~ the opposition to the flow of charge. Any
appliance that asks the charge -- to do work will slow the
charge down
A wire’s resistance depends on:
• The kind of material it is made of
• The length
• The temperature
What do you think are the TOP FIVE Power
RATINGS for Common Appliances?
1.
2.
3.
4.
5.
NAME this SCIENTIST!
Who invented the
light bulb?
Thomas Edison
How does a light bulb
work?
Electrons flow through a
wire and heats up the
chemicals in the
filament.
Light Bulbs
When the electrons reach the
filament, its resistance is
so great that the electric
energy is converted into
heat and light energy.
Current
• The symbol for current is
the capital letter I
• The unit measure for
current is amperes or
amps
• Current is measured with
an ammeter
Resistance
• The symbol for
resistance is R
• Resistance is
measured in units
called ohms
Voltage
• Voltage is measured in
volts
• The symbol for volt is V
• Voltage is measured
with a voltmeter
Electroscope
An electroscope is an
instrument used to
detect an electric
charge
Ohm’s Law
• Ohm’s Law
states that the
current in a
circuit is equal
to the voltage
divided by the
resistance
Ohm’s Law
• Where:
V is the Voltage
measured in volts
I is the Current
measured in
amperes
R is the resistance
measured in
Ohms
Sample Problem
• A nine volt battery supplies power to a cordless
curling iron with a resistance of 18 ohms. How
much current is flowing through the curling
iron?
Solution
• 1.) Since
V(Voltage) and
R(Resistance) are
known, solve for
I(Current) by
dividing both sides
of the equation by
R.
Solution
2. The R's on
the right hand
side of the
equation
cancel.
Solution
• 3.) I is then
left in terms
of V and R
Solution
• 4.) Substitute
in the values
for V(Voltage)
and
R(Resistance).
5.) Solve for I (Current)
Why can a bird
sit on a power line?
When a bird sits on a
power line, both feet
are on the line.
There is no potential
difference between
the feet.
If one leg is on the ground
and the other one is on
the power line, then
there are potential
difference between these
two legs.
Therefore, there is a flow of charge
and eventually the chicken will be
fried…get it?
Sample Problem
• A 110 volt wall outlet supplies power to a
strobe light with a resistance of 2200
ohms. How much current is flowing
through the strobe light?
Sample Problem
• Answer:
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