Electricity

1
Electricity
Whether we have turned on a radio or heard a
massive clap of nearby thunder, electricity is a
common phenomena that we have all experienced.
One thing is certainthere is energy in
electricity. Electricity can be harnessed to do
work. We use it to make light, heat, sound.
Nature also displays the massive potential energy
of electricity in a bolt of lightning which can
superheat air molecules to the temperature of the
sun and produce an extremely loud noise.
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• Describing electricity is extremely difficult
  however. If it were simple, humanity would have
  been able to use electricity a lot earlier in our
  development. To compound the problem, there are
  a great many misconceptions about the nature of
  electricity that many people believe to be true
  but are not. Electricity Online lists some of
  these common misconceptions.
• Electricity is not a phenomenon composed of
  energy.
• Electricity is not made of electrons.
• Electrons do not "carry" energy.
• Electrons do not flow at the speed of light.
• Batteries and generators do not create
  electricity.

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Now we know what electricity is notso what is
it? Electricity is anything that happens as a
result of charge. But this definition seems to
just replace one problem with another. Now the
question is what is charge? In many ways this is
even a more difficult question. The reason is
that charge is a fundamental quantitylike length
or mass. Objects have a certain charge that is
given by its very nature. We cannot describe
charge using other properties of matter because
charge is a property by itself. We cannot
describe charge in terms of length or mass, in
the same way that we cannot describe mass in
terms of length or charge. They are separate.
Objects can change their charge just like they
can change their length or mass.
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Like all fundamental properties, charges have
certain characteristics. There are two opposite
types of charge which we have called positive and
negative charges. There is nothing positive or
negative about either charge. It is just an
arbitrary label that we gave them to develop the
mathematics describing charges. Charles-Augustin
de Coulomb was the scientist who described the
behavior of charges in what is now known as
Coulombs Law.
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• Coulombs law states the following 4 things.
• Like charges repel each other while opposite
  charges attract.

• Attraction or repulsion of charges occurs in a
  straight line between the charges.

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• The size of the force gets bigger the closer the
  charges are are smaller the further they are
  apart (inversely proportional to the square of
  the distance). So if the charges are half as far
  apart the force is 4 times greater.

• The size of the force is directly proportional to
  the size of the charge.

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It then follows that when there is a charge
differential (difference in charges from one
place to another) then there is the potential for
a force to be created. When forces are created,
work can be done. Charges move, change, and
influence each other. We call this electricity.
Electricity can help us make a display at the
festival of lights in Robson Square in Vancouver.
It can also transport us at tremendous speeds on
Japans bullet train.
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The smallest units of charge are found in the
atom. The electron carries smallest unit of
charge. All other charges are multiples of this
basic charge.
We measure charge in coulombs (named after the
scientist).
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Because this unit is the fundamental charge size
and because it is so small we call this number e.
The proton is another basic atomic unit that
carries a charge that is equal and opposite to an
electron. This is where we get that a proton has
a charge of 1e and an electron has a charge of
1e. The neutron is another sub-atomic particle
that has a neutral charge (0). Protons and
neutrons are relatively stationary compared to
electrons. So, it is the influences of charges
on moving electrons that creates electrical
phenomena.
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Static Electricity
Friction can transfer electrons from one object
to another. The swirling air and water in a
pocket of the atmosphere makes a lot of friction.
When electrons are collected in a cloud, a net
build up of negative charge develops. This built
up charge that sits on the object is called
Static charge. The mass of static negative
charge on the cloud can cause a charge separation
with the neutral ground.
These anvil shaped thunder clouds commonly
demonstrate this charge separation process.
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The electrons on the ground disperse away from
the cloud leaving a spot on the ground that is
positively charged. The situation is very
unstable. The electrons in the cloud are trying
to get away from each other and the positive
ground is attracting the electrons. However,
there is no easy path for the electrons to follow
to get to the ground.
The instability of the now oppositely charged
areas cause the electrons from the cloud to jump
to the ground in an electrical discharge which we
see as lightning. This is a common phenomena
around Edmonton Alberta.
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The negative clouds can also influence the charge
of another cloud causing a cloud-cloud
discharge. Air normally doesnt let charge flow
through it.
Therefore, when the charge differential is great
and a discharge occurs, heat is produced from the
airs attempts to stop the movement of charge.
This massive heating causes the light and sound
we notice as lightning and thunder.
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This same process on a much smaller scale
explains why you get a shock if you rub your feet
on carpet and then come close to touching a metal
door knob. When you touch the door knob, the
electrons have a relatively easy path to get to
the ground so they discharge from your body.
Making a path for the electrons to get to the
ground is called grounding. But, why would
electrons attempt to get to the ground?
The reason is that electrons all carry negative
charge, hence they repel one another. The ground
offers electrons the greatest area to spread out
and stay as far away from each other as possible.
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Other common static phenomena include rubbing a
balloon in your hair and sticking it to a wall.
The electrons from your hair are transferred to
the balloon. When the balloon is brought close
to the wall, the negative charge makes a
temporary positive spot on the wall. The two are
attracted to each other and the balloon sticks.
Pet hair is very hard to clean off of fuzzy
fabrics because it seems to cling to the
fabric. A little water interupts the charge
separation and the hair pulls off more easily.
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A Van De Graaff generator is a device that
collects static charge on a metal sphere. The
friction of the rubber band brushes electrons
to the sphere.
If you grab the sphere the electrons travel to
your hair. Each strand of hair is then
negatively charged and repel each other making
your hair stand on end.
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Electric Current
Static electricity is not really all that common.
Electrons dont usually like to gather in large
stationary groups. When they do they create an
unstable situation. The unpredictability of
static electricity also makes it less useful to
us. Electrical current is a much more common and
useful phenomena. It is a steady flow of charged
particles. Some materials allow charged
particles to pass through more easily than
others. These materials are called conductors.
Metals are good conductors of electric current.
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The path that electric current travels is called
a circuit. A Wire made of conductive material,
carries the electric current. A complete circuit
is require for current to flow.
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Positive holes flow
Negative electrons flow
Electrons flowing in this case to the right and
the holes left behind flow to the left. It is a
kind of paradox. The electrons need holes to
flow into and the holes need the electrons to
leave in order to exist. Hence, the circuit
needs to be completed in order for electric
current to flow.
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Current is measured in amperes (or amps). An amp
measures the rate of the flow of charge. One
ampere is defined as one coulomb of charge
passing through a given point in one second. 6 ?
1018 electrons per second 1 ampere Most common
household appliances require few amps to work.
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This galvanometer measures small amounts of
electric current. An ammeter will measure larger
amounts of current.
This digital ammeter is connected to a battery, a
switch, and a light. The circuit is complete so
the current should flow.
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However, the speed that the current flows is not
the same as the potential energy that can be
done. The electrical potential energy is a
result of the difference in charge. In a
battery, chemicals force electrons to move to one
end making a negative and positive terminal of
the battery. This is the role of batteries of
all shapes and sizes.
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If the battery is then connected to a circuit,
there is a difference in the charges at different
spots in the circuit line. The term potential
difference describes the energy per coulomb of
charge of one point in a circuit compared to
another point in the circuit. We commonly call
potential difference voltage. A volt is the unit
of potential difference and is given as the
joules (Unit of work) per coulomb. Voltage is
measured with a voltmeter.
22
A battery will create a steady voltage in a
circuit called direct current. A battery is a
device that converts chemical energy into direct
current. A solution with a dissolved salt called
an electrolyte and two metal called electrodes
are connected as the diagram shows.
The chemical reaction drives the flow of
electrons through the wire in the circuit.
Different substances will produce different
voltages.
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A primary cell is a battery that uses the
chemicals to produce electric current. Once the
chemicals are use up, the cell is dead.
This lead acid battery is a secondary cell.
Electricity can be used to restore the chemicals
and recharge the batterys potential energy.
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Making and Transferring Electricity
Magnetism and magnetic force is actually a result
of moving charges. So electric current produces
magnetic forces. Electricity and magnetism are
actually two aspects of the same
phenomenaelectromagnetism.
An electromagnet can be created by wrapping a
wire around an iron core (like a nail) and
connecting the wire to a power source. A
magnetic field is created. Making more wraps or
increasing the current will make the magnet
stronger. Wrapping the wire the other direction
will reverse the poles of the magnet.
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So electricity can create magnetism. But can
magnetism create electricity? The answer is yes.
Moving a wire coil over a magnet or moving the
magnet over a coil produces a current. This is
called electromagnetic induction. Once again,
putting more coils in the wire or moving the wire
more quickly will increase the current produced.
Movement in opposite directions will produce
currents in opposite directions. Without motion,
or if the motion of the magnet is parallel to the
wire, there is no current.
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An alternating current (AC) generator uses a wire
coil that rotates between the poles of a magnet.
When the coil rotates half a turn, the coils are
in the opposite orientation so the current
reverses direction. The current cycles in waves
from one direction to the opposite.
In North America, current changes direction 120
times a second. This means 60 complete cycles in
60 seconds. We call this 60 cycle AC or 60
Hertz. So, a Hz is a measure of how long it
takes for AC to cycle. Alternating current is
very useful. It travels long distances very
easily compared to direct current produced from
batteries.
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A DC generator is called a dynamo. The
connection to the wires is alternated with each
half cycle. This is done by a split-ring
commutator that insulates and reconnects the
wires to the correct sources as the coil rotates.
This way the current produced is all the same
direction (direct current) even though the flow
of electricity is not steady.
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As the ring turns the relative connection to the
coil alternates. So instead of the current
alternating, the connection does. The current is
interrupted each time the insulators hit the
brushes.
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An AC motor converts the electric energy to
kinetic (moving) energy. These are common
devices. The rotor rotates a coiled wire.
Stators are stationary electromagnets. The power
is fed into the coil and motion is produced from
the opposing and alternating magnetic forces.
The AC motor does the opposite of an AC generator.
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The DC motor uses a split-ring communtator to
alternate the polarity of the electromagnet and
turn the machine. Thus the DC motor undoes the
DC generator.
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Why would we use AC if we can do all the same
things with DC? AC is easy to produce but more
importantly it is much easier to transport.
Because of the alternating polarity of AC, the
magnetic fields generated alternate as well. A
simple device, called a transformer, uses this
alternation to dial up voltage to send the AC
long distances, and then dial down to come into
your home.
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Electricity flows in wires. Wires carry
electricity to our homes and to the electrical
appliances that have become a part of our
everyday life. We have already seen how
electricity flows in a wirenegative charge
flowing one way and positive holes flowing the
other. When a complete wire path is created for
the flow of electricity we call the path a
circuit. A circuit made completely out of wire is
not very interesting. Usually, a circuit is
interrupted by devices that control to flow of
electricity or converts the electrical energy
from one form of energy to another form of
energy. A device that converts electrical energy
from one form to another is called a load.
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A load like a light bulb will take some of the
energy from the electrons and slow them down,
converting the electrical energy to heat and
light.
This electric motor will convert the electrical
energy into kinetic (motion) energy.
This speaker converts electrical energy into
sound energy.
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It would be extremely difficult to draw a circuit
with all of the devices hooked up. Therefore, we
have made a standard way to draw circuit
diagrams. Here are a few of the common symbols
we use and what they mean.
Wire Carries electric current.
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Joined Wire Wires that cross and are connected
offering a second path. Wires are usually joined
with connectors.
Not Joined Wire Wires that cross and are not
connected.
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Cell A single electrochemical cell (technically
a battery is more than one cell).
These lemons are acting as an electrochemical
cell.
Battery Electrochemical cells that convert
chemical energy to DC.
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DC Power Source A dynamo or some other producer
of DC.
This dynamo is used on a bicycle to work a
headlight.
AC Power Source A generator producing AC.
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Fuse A safety device that is broken when the
current is too great.
This car fuse box (left) holds fuses that burn
when the current is too great. The breaker box
(right) flips a switch and can be flipped back.
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Transformer Device that dials up or dials down
voltage.
Ground A path for electrons to go to the earth.
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Heater A device that converts electrical energy
to heat mostly and light.
Lamp Converts electrical energy to light and
heat.
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Motor Device that converts electrical energy to
kinetic energy (motion).
Speaker Device that converts electrical energy
to sound.
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Switch Opens and closes the circuit. Controls
electrons to flow or not flow.
Two Way Switch Decides the path the current
flows.
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Resistor A device that restricts the flow of
electricity.
Charged particles moving through the resistor are
slowed down. Resistance is measured in ohms (O).
This resistor gives 100ohms of resistance and
helps protect delectate speaker components.
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Variable Resistor A device that restricts the
flow of electricity in varied amounts. Sometimes
called a rheostat.
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Voltmeter Measures the potential difference (V)
of a particular spot in the circuit.
Ammeter Measures the speed of the current (A)
of a particular spot in the circuit.
Galvanometer Measures the speed of the current
(mA) of a particular spot in the circuit.
Usually used for small amounts of current.
Ohmmeter Measures the resistance of current (O)
of a device.
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The loads in a circuit offer resistance to the
flow of current. Ohms law relates the voltage
(V) to the current (I) and resistance (R).
To find the resistance, we need 1) the potential
difference across a load, 2) the current in the
circuit, and 3) the equation solved for
resistance.
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A series circuit has one way the current can
flow. No other routes can be taken. Each load
is placed one after the other down the line in
series.
These lights would not be very bright since all
three offer resistance to the current in the line.
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A parallel circuit has more than one way for the
current to flow. The current has a choice of
routes to take. Each load is placed on a
parallel line in the circuit.
All of these lights would be just as bright as
one light in series since the resistance in each
individual branch is only as large as one light.
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In your home, wire is usually drawn in a bundle
of wires called cable. There are 3 wires that
are used. Two are called live wires.
They are a white insulated neutral wire and a
black insulated hot wire. The third wire is
either uninsulated copper or green insulated
ground wire (green ground). The potential
difference from white to black in North America
is 120V for normal outlets and 220V for items
that require more power like ovens and dryers.
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A home circuit is basically a combination of
series circuits connected in parallel circuits.
When there is a surge in any line the breaker
pops cutting the power to that line and
avoiding a build up of heat in the wire.
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Microchips are now a common part of our lives.
On a microchip are microcircuits. Instead of
using large switches, microcircuits us
transistors.
Voltage through the transistor will control the
current in tiny microscopic wires.
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Electrical Energy and Power
A fundamental law of physics states that energy
cannot be created or destroyed. Electrical
generators DO NOT create energy. They produce
electricity. To do this they need to convert
energy from one form to electrical potential
energy. In the case of generators, kinetic
energy (motion) is used to produce electric
current. An electric motor takes the electrical
potential energy in the current and creates
motion. In this way, generators and motors do
opposite jobs. Batteries take chemical energy
and produce DC. There are many ways to produce
electricity. The one we pick depends on many
factors and requires at least a basic
understanding of all of the processes.
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The efficiency of any device is its the ability
to convert one form of energy into another
useable form. None of the energy is actually
lost but it may be converted into an energy
form that is non-usable. We usually calculate
the efficiency with a percentage.
Energy is measured in Joules. A joule is defined
as the energy needed to exert one newton of force
over a one meter distance. A newton is
approximately the force exerted by the mass of a
small apple. So, one Joule of energy is about
the energy required to lift a small apple one
meter high.
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In electricity, energy can be calculated using
the voltage and charge since voltage is energy
per coulomb. We get the following equation.
The number of joules used in a second is the
number of watts used. We call the amount of work
in watts power. From this we get the following
equation.
From this we also get the following formula to
calculate power in electric current.
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Here is a summary of our formulas.
Energy Charge ? Voltage
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The need for power in our society is obvious. In
2001 Canada used a total 504.4 billion KWh (1 KWh
3.6 MJ) which makes us the greatest per person
consumer of electricity in North America and
number 3 on the world list. Our usage of power
is actually visible from space during the
blackout of 2003. How can we make all our power?
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Most of our power is produced in plants like this
thermo-electric plant where we burn a fossil fuel
to make AC.
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These power plants burn coal to generate heat,
create steam, and move the turbine.
The majority of the smoke from the stacks are
steam and carbon dioxide. Sulfur and nitrogen
compounds are also produced.
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Burning fossil fuels creates a lot of CO2(g) that
is released into the atmosphere as well as the
acid rain components SO2(g) and NO2(g). As well,
mining for coal (Albertas primary fuel source
for making electricity) can be very harmful to
the environment. Mining is also potentially
dangerous. Extracting, refining, and
transporting oil also has its pitfalls.
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A light bulb will create resistance in electric
current to superheat a thin filament in a bulb
that glows producing light and heat. We can also
reverse the process and use light to create
electrical energy. Many of us have used solar
calculators. The solar panel at the top collects
light and produces a weak electric current.
Solar panels on a house roof can make electricity
for the house during daylight hours. Batteries
are charged so that the house has electricity
available at night.
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There are two main types of solar power plants.
This one is a photovoltaic plant. Each panel is
a larger version of the panel on your calculator.
Electricity is created directly.
This plant uses large curved mirrors that
concentrate the suns light and heat to superheat
special liquids. The heated liquids then produce
steam and turn a turbine. These plants are
called solar thermal plants.
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Solar generators are very expensive and require
large sections of land. Battery technology has
also not improved to the point where we can use
solar power effectively at non-sunny times.
Solar energy does allow us another way to not
need as much electricity. A passive solar
design includes many windows to allow light and
heat to offset the needs of the building. Long
overhangs also shade the building from the high
and hot midday sun.
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This wind farm in Alberta, near Pincher Creek, is
used to create electricity. The turning of the
blades spins the turbine in this case creating
the needed motion for the electric generator.
Wind powered turbines require wind to work and
also require vast areas of land and dont produce
very much power.
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This CANDU nuclear power plant in Pickering
Ontario provides a great amount of electrical
energy. There are in fact 8 nuclear reactors
here producing 540 MW of power each.
Nuclear power is created through a process called
fission. This is where uranium (or plutonium) is
atomically altered to make other elements.
The atomic particles that break off from the
process are very energetic and release a lot of
energy. Nuclear energy is ten million times more
efficient than burning coal (by mass).
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The CANDU reactor has rods that can be added and
taken out while the reactor core is operating.
Many computerized and manual controls help
prevent a reaction from continuing too fast which
generates too much heat causing a melt down.
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Normal uranium is a mixture of two isotopes of
uraniumU-238 and enriched U-235. U-235 is more
radioactive and used more often in reactors. The
CANDU reactors are different because they use
normal uranium in their reactors and nuclear fuel
is constantly added and wastes taken out.
Nuclear wastes (plutonium) can then be recovered
and re-used as fuel. To this point, much of the
waste is not recovered. There is a great
political debate over the safety of nuclear
energy considering the potential destructive
capability of a nuclear plant. You can find
strong views supporting and opposing nuclear
power.
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Hydroelectric dams use the movement of water to
turn a turbine. There is little pollution made
but holding back the water causes flooding.
Flooding alters the marine and land ecosystems
drastically. As well, hydro dams must be near
large bodies of moving water.
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Geothermal energy uses naturally heated
underground water from geysers. Emissions are
around 50 times less than that of a fossil fuel
burning plant.
This steam plant uses very hot steam that
naturally occurs to turn the turbine and generate
electricity.
This binary plant uses less hot water to heat a
hydrocarbon with a low boiling point.
Just like hydroelectric power, geothermal power
is restricted to certain locations.
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There are environmental and economic pros and
cons to each source of power. Each province
generates its power in different ways. Alberta
and Saskatchewan use mostly fossil fuels.
Ontario uses mostly nuclear. Quebec,
Newfoundland and Labrador, and BC use mostly
hydroelectric. Overall, about 60 of Canadas
power is generated through hydroelectric
dams. Fossil fuels are considered non-renewable
resources and will be depleted some day. It is
therefore necessary for use to continue to look
at different and innovative ways to produce and
conserve electricity.