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GCSE Physics
Energy resources and energy transfer
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This topic
•During this topic we will learn about energy transfers in a
range of different contexts and how insulation can reduce
energy transfers,
•We will learn and use the formula: Work done = Force x
Distance, we will also learn the formulas for kinetic and
gravitational energy,
•We will learn about power as the rate of transfer of
energy or the rate of doing work.
•We will learn about the advantages and disadvantages of
methods of large-scale electricity production using a
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variety of renewable and non-renewable resources.
Lesson 1 – Energy and transfers
Aims:
•To describe energy transfers involving the following
forms of energy: thermal (heat), light, electrical, sound,
kinetic, chemical, nuclear and potential (elastic and
gravitational),
•To understand that energy is conserved and to recall and
use the relationship: efficiency = useful energy output /
total energy output.
•To draw energy flow (sankey) diagrams for a variety of
situations.
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Energy types
There are many different types of energy.
All of these energies can be classified into
three groups:
•Potential or stored energy,
•Kinetic or movement energy,
•Radiation.
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Classification
Potential energy
Kinetic energy
Radiation
Gravitational
(GPE)
Moving objects
Radio waves
Chemical (CPE)
Micro waves
Elastic (EPE)
Hot objects
(thermal energy)
Sound
Nuclear (NPE)
Electricity
Visible light
Infra red
Ultra violet
X-rays
Gamma rays
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Energy is measured in Joules (J)
Joule was a brewer of beer
by trade but had a passion for
science. His experiments
were famous for their
attention to detail and the
quality of his analysis.
James Prescott Joule,
1818 - 1889
He spent years trying to
measure a temperature
difference between water at
the top and the bottom of a
waterfall. He even took his
thermometers when he went
on his honeymoon!
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Energy transfer diagram
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Sankey diagrams
A sankey diagram can
be used to show the
different energy
transfers that are taking
place.
Electric motor
In all transfers some
heat is lost to the
surroundings. It is hard
to get this heat back as
it is randomly spread
out.
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Toaster
The toaster gets hot
Changing
the bread
into toast
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Complete the input and useful output energies for the
devices in this table.
Device
Input
energy
Output
energy
kettle
solar cell
catapult
coal fire
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All energy transfers follow the law of conservation of energy:
Energy cannot be created or destroyed,
just changed in form.
 This means that energy never just ‘disappears’.
 The total amount of energy always stays the same,
i.e. the total input energy = total output energy.
 In most energy transfers, the energy is transferred to
several different forms, which may be useful or not useful.
 The energy that is transferred to unwanted forms of energy
is wasted.
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The efficiency of a device can be calculated using this
formula:
useful energy out
efficiency =
total energy in
Useful energy is measured in joules (J).
Total energy is measured in joules (J).
This means that efficiency does not have any units.
It is a number between 0 and 1 or a percentage.
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Efficiency is a measure of how good
a device is at changing energy from
one form to another.
All devices waste energy, so the
efficiency of a device is never 100%.
The more efficient a device
is the less energy is wasted.
Energy efficient light bulbs are more
efficient than normal light bulbs
because they w____ less energy.
More of the e_______ energy that
they are supplied with is converted
into l____ energy and not h___.
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Efficiency example 1
What is the efficiency of a speaker that is supplied
with 2530 J of energy and gives out 1010 J of
sound energy?
Efficiency = Useful energy out
Total energy in
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Efficiency example 2
What is the efficiency of a neon light bulb that that
is supplied with 35 J of electrical energy and gives
out 10 J of light energy?
Efficiency = Useful energy out
Total energy in
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Efficiency example 3
A guitar amp is 45 % efficient. Work out the total
energy in (energy input) if the electrical energy
given out is 200J?
Efficiency = Useful energy out
Energy input
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Efficiency Example 4
This filament bulb is
supplied with 100 J of
electrical energy which
it converts to 45 J of
light energy.
a) How much energy
is wasted?
b) In what form is the
energy wasted?
c) What is the efficiency
of the bulb?
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Efficiency Example 5
This radio is supplied
with 300J of electrical
energy which it converts
to 96J of sound energy.
a) How much energy
is wasted?
b) In what form is the
energy wasted?
c) What is the efficiency
of the radio?
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Efficiency Example 6
This television converts
2 000J of electrical
energy into useful energy
at an efficiency of 65%.
a) What useful energy does
a television produce?
b) How much useful
energy is produced?
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Summary – Energy transfers
•An energy arrow diagram can show how energy is
transferred from one type to another.
•When an energy arrow diagram is drawn to scale it is
called a ‘Sankey diagram’.
•In all energy transfers the total amount of energy
entering a system is equal to the total amount of energy
leaving the system. This is called the Law of
conservation of energy.
•Efficiency = Useful energy output / Total energy input.
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Lesson 3 – Work done
Aims:
•Understand that ‘work done’ is equal to
energy transferred.
•Be able to rearrange and use the formula
Work done = Force × Distance
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Force and direction

F

Fy

Fx
When we calculate the work done by the person
pushing the pram we are only interested in force Fx.
The work done is the distance travelled multiplied by
the force in the direction of the movement.
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Work done Example 1
A lady pushed a trolley with a force of 50 N
and the trolley moved through a horizontal
distance of 12 m. What is the work done by
the lady?
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Work done Example 2
Can you calculate the work done?
Weightlifter =
Lawnmower =
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More examples
•
How much work does it take to lift a 200 N
weight 2 m off the floor?
Work done =
• How much work does it take to hold a 200 N
weight 2 m off the floor?
Work done =
• How much work is done if you drop a 2.5 N
text book 3 metres?
Work done =
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More examples
How much force is required to move a box 4 m if 200 J
of work is done?
Force = Work ÷ Distance
How far will a cart be pushed if a force of 45 N is used
and 405 J of work are done?
Distance = Work ÷ Force
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Summary – Work done
•Sometimes when energy is transferred we use the term
‘work done’.
•Work is done when a force is applied and a distance
travelled in the direction of this force.
•Be able to rearrange and use the formula
Work done = Force × Distance
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Lesson 4 – Kinetic energy
Aims:
•Understand that kinetic energy is a measure of the
amount of energy of a moving object.
•Be able to rearrange and use the formula
KE = ½ m v2
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Kinetic energy is the energy an object has because
it is moving.
 The greater the mass of a moving object,
the greater its kinetic energy.
If the mass is doubled, the kinetic energy is doubled.
 The greater the velocity of a moving object,
the greater its kinetic energy.
If the velocity is doubled, the kinetic energy is quadrupled!
So, if the velocity of a car is slightly above the speed limit,
its kinetic energy is much greater than it would be at the
speed limit. This means it is more difficult to stop the car
and there is more chance of an accident.
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The kinetic energy (KE) of an object depends on its mass
and its velocity.
The equation for calculating kinetic energy is:
kinetic energy = ½ x mass x velocity2
KE = ½mv2
What are the units of kinetic energy, mass and velocity?
 Kinetic energy is measured in joules (J).
 Mass is measured in kilograms (kg).
 Velocity is measured in metres per second (ms-1).
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Sometimes it is necessary to rearrange the kinetic energy
equation in order to calculate the mass or the velocity of
a moving object.
KE = ½mv2
What are the rearranged versions of this equation for
calculating mass and velocity?
mass =
2KE
v2
velocity =

2KE
m
TIP: If you do not think you can rearrange the KE formula
during an exam, learn the rearranged formulae instead.
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Kinetic energy - Example 1
A car has a mass of 1500 kg
and is travelling at a velocity
of 10 ms-1.
What is the kinetic energy of
the car?
kinetic energy = ½ x mass x velocity2
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Kinetic energy – Example 2
Calculate the kinetic energy of an apple thrown at
9.0 m/s.
Estimated mass of an apple = 100 g = 0.100 kg
KE = ½ m v2
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Kinetic energy - Example 3
A train has a mass of 100 000 kg.
If its kinetic energy is 3 MJ,
what velocity is it travelling at?
3 MJ = 3 000 000 J
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Kinetic energy – Example 4
Calculate the mass of a balloon of water thrown at 10
m/s that has a kinetic energy of 50 J.
KE = ½ m v2
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Kinetic energy – Example 5
Calculate the speed of a shot put with kinetic energy 90 J,
if its mass is 5 kg.
KE = ½ m v2
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Summary – kinetic energy
•Kinetic energy is the energy of movement. Sound
waves, moving objects and electricity can be
thought of as kinetic energy.
•Kinetic energy can be calculated using the formula:
KE = ½ m v2
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Lesson 5 – GPE
Aims:
•Understand that Gravitational potential energy is the
amount of energy of an object due to its height above
the ground.
•Be able to rearrange and use the formula
GPE = m g h
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Potential energy
Potential energy is sometimes called stored energy.
In chemistry we study the energy given out or taken in
during a chemical reaction. Energy changes take place
when there are changes to the chemical potential energies
of the chemicals.
When we release a stretched elastic band it will fly across
the room as its elastic potential energy is changed in
kinetic energy.
Electricity is generated in a nuclear power station when
nuclear fission releases the nuclear potential energy of
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uranium atoms.
Any object in a gravitational field has gravitational potential
energy due to its position in that field.
The Moon has gravitational
potential energy due to the
gravitational field of the Earth.
The Earth has gravitational
potential energy due to the
gravitational field of the Sun.
The gravitational potential energy depends on the
distance between the two objects.
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The gravitational potential
energy of an object on Earth
depends on its weight and
its height above the Earth’s
surface.
When a bungee jumper
starts to fall they start to
lose gravitational potential
energy.
As the elastic cord pulls the
bungee jumper back up,
they gain gravitational
potential energy.
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Calculating GPE
The gravitational potential energy (GPE) of an object
depends on its weight and its height.
The equation for calculating GPE is:
GPE = weight x height
What are the units of GPE, weight and height?
 GPE is measured in joules (J).
 Weight is measured in newtons (N).
 Height is measured in metres (m).
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GPE – Example 1
A seagull with a weight of
30 N flies at a height of
10 m above the ground.
How much gravitational
potential energy does the
seagull have?
GPE of seagull = weight x height
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The weight of an object is its mass multiplied by the strength
of the gravitational field acting on the object.
This can be substituted into the GPE equation to give:
GPE = weight x height
gravitational
GPE = mass x field strength x height
What are the units involved?
 GPE is measured in joules (J).
 Mass is measured in kilograms (kg).
 Gravitational field strength is measured in newtons per
kilogram (Nkg-1).
 Height is measured in metres (m).
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GPE
If this mass m is held at a
height h then it has
gravitational potential
energy. It is equal to its
weight, mg, times its height
above the ground:
m
h
GPE = m  g  h
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When an object falls or is raised, it is useful to calculate the
change in gravitational potential energy (GPE).
To do this, the change in height is used in the GPE equation:
GPE = weight x height
change in GPE = weight x change in height
What are the units involved?
 Change in GPE is measured in joules (J).
 Weight is measured in newtons (N).
 Change in height is measured in metres (m).
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GPE – Example 2
A parachutist of weight 600 N
jumps from a plane, which is
2000 m above the ground.
How much gravitational
potential energy will the
parachutist have lost when
she reaches the ground?
GPE = weight x height
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Increasing GPE
m
GPE = m g h
If the object starts from
rest, its initial kinetic
energy is zero.
m
As the object falls,
gravitational potential
energy is converted into
kinetic energy.
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Potential and Kinetic energy
•When a body falls from a height, its
gravitational potential energy is changed into
kinetic energy during the fall.
•As the body gains speed, more and more of
its gravitational potential energy is changed
into kinetic energy.
G.P.E.
•Just before the body strikes the ground, all
its gravitational potential energy is changed
into kinetic energy.
G.P.E+
K.E.
•The total amount of energy at the beginning
and the end is the same.
K.E.
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Jordan jumps
Michael Jordan does a vertical
leap of 1.0 m and dunks
successfully.
What was his original take-off
velocity if all his kinetic energy
was transferred to gravitational
potential energy ?
m  g  h = ½  m  v2
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Sledge example page
1
What is the total energy of the boy (m = 50 kg) at the top
of the hill? (gravitational field strength = 10 N / kg)
•GPE = m g h
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Sledge example page
2
What is the work done to pull the boy to the top of the hill?
•Work done = Change in energy
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Sledge example page 3
What is the total energy, gravitational potential and
kinetic, on top of the 15 m bump?
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Sledge example page 4
What is the kinetic energy of the boy at the bottom of the hill?
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Sledge example page 5
What is the speed of the boy at the bottom of the hill?
KE = ½ m v2
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Summary - GPE
•Gravitational potential energy is equal to the energy
given to an object by lifting it away from the surface of
the Earth.
•GPE can be calculated using the following formula:
GPE = m g h
or
GPE = Weight x height
•g is the gravitational field strength of the Earth and
equal to 9.8 N/kg. It is also sometimes called the
acceleration due to gravity and equal to 9.8 m/s/s.
•Your weight on the Earth is W = m g
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Lesson 6 – Power
Aims:
•Describe power as the rate of transfer of energy or
the rate of doing work.
•Be able to rearrange and use the formula
Power = Work done / time
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The units of power are Watts
James Watt was born the son of a
shopkeeper and carpenter in
Scotland. Watt is best known for
improving the steam engine. Crude
steam engines were used before
Watt’s time, but they used large
amounts of coal and produced very
little power. Watt designed a steam
engine that was much better and
more practical.
James Watt, 1736 - 1819
Power is measured in Watts
Inventor of the Steam Engine
1 Watt = 1 Joule/second
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Power example 1
What is the power of a machine that can do 640 J
of work in 4.00 s?
Power = Work done  Time
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Power example 2
How long does it take for a 150 W motor to do
1350 J of work?
Power = Work done  Time
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Power example 3
How much work is done by a 1500 W blender in
90 s?
Power = Work done  Time
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Power example 4
A 57 N force is exerted through a distance of 2.5 m for
3.0 s. How much work was done and how much power
was used?
Work done = Force  Distance
Power = Work done  Time
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Power example 5
A builder carried a pile of bricks of total mass 30 kg
up a staircase of height 3 m. If he took 5 minutes to
do the job, what is his power?
Change in GPE = Work Done
Power = Work done  Time
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Summary - Power
•Power is the rate at which energy is transferred or the
rate at which work is done.
•We can calculate the power of an object using the
following formula’s:
•Power = Energy transferred / Time
•Power = Work Done / Time
•Power is measured in Watts, Watts have the symbol W.
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Lesson 7 – Electricity and fossil
fuels
Aims:
•Be able to describe the advantages and disadvantages
of methods of large-scale electricity production using
a variety of renewable and non-renewable resources.
•Understand energy transfer chains illustrating the
environmental implications of fossil fuels.
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Steam, heat and work
•Power stations that use coal, oil, gas and nuclear fuels all
rely on the properties of steam to generate electricity.
•When water turns to steam it increases its volume by
approximately 1500 times.
•This increase in volume in an enclosed space creates a lot
of pressure. It is this pressure that can be used to turn the
turbine blades.
•The pressure of the steam can still be thought of as heat
as the particles are moving randomly. The motion of the
turbine is work as it has an ordered direction of rotation.
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Turbine
The turbine has
many sets of
blades at opposing
angles to each
other.
The blades must
be able to
withstand the
1000 C steam
that passes
through, most
metals will melt.
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Turbine generator
Like all steam turbine generators, the force of steam is used to spin
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the turbine blades which spin the generator, producing electricity.
Cooling towers
These are cooling
towers, steam turns
back to water.
Cooling towers heat the
atmosphere but do not
cause pollution. 69
Fossil fuel power stations
Fossil fuel power stations convert c______ energy into
e______ energy.
Oil and coal fired power stations work in a very similar way.
The fuel is burnt and the heat boils water to make high
pressure superheated steam, which is used to turn a turbine.
Natural gas fired power stations do not use steam.
The natural gas is burnt, which produces hot gases
that turn the turbine directly.
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Power station energy transfers
Fossil fuels, like coal, are used to generate electricity in a
power station.
Chemical
energy in
fuel
Burn
fuel
Heat
energy
Turbine
Kinetic
energy
Generator
Electrical
energy
Coal is used to turn water into steam at high pressure. The
steam can turn the blades of the turbine, like the wind
turning the blades of a windmill. The turbine spins coils
inside of magnets in the generator that creates the electricity
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for use in our homes.
Fossil fuels
What is a fuel?
What is a fossil fuel?
Name three fossil fuels:
1. ___________
2. ___________
3. ___________
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Fossil fuels
Today, coal provides 55% of the U.S. electricity supply and the
U.S. imports more than half of the oil it consumes. The burning of
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fossil fuels cannot be sustained.
How coal formed
Millions of years ago trees died and fell
to the bottom of swamps.
Over time they became
covered by mud and rock.
…the trees became
fossilized, forming coal.
Over millions of years, due to high
temperatures and pressure…
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Millions of years ago plankton died and
fell to the bottom of seas and oceans.
Over time they became
covered by mud and rock.
…the plankton became oil
and natural gas.
Over millions of years, due to high
temperatures and pressure…
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What damage ?
Damage to the environment can come in many
forms including:
•The greenhouse effect,
•Acid rain,
•Depletion of resources,
•Mining and quarrying.
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Global Temperatures - 150 years
The year 2000 was the 6th warmest on record
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The big three
CO2 (Carbon Dioxide)
• 25 billion tons produced on earth each year.
• Earth can absorb 15 billion tons.
• 10 billion ton excess each year.
CH4 (methane)
• Has increased since 1977.
• In less amount than CO2 .
• 20 – 30 times better at trapping heat.
CFC’s (ChloroFloroCarbons) (also causes ozone hole)
• Smaller amount produced than others.
• Has increased since 1977.
• 20,000 times better at trapping heat.
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Carbon in, carbon out.
• The total amount of carbon on our planet remains quite
stable. When coal was formed, over millions of years,
trees were taking carbon from the air which ended up in
coal, oil and gas after the trees had died.
• When we burn fossil fuels we release this carbon goes
into the air.
• Carbon dioxide is a greenhouse gas that keeps our
planet warm. Unfortunately when the amount of carbon
increases the Earth becomes hotter, which may have
severe effects on our environment.
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Acid Rain
Coal is not a pure
hydrocarbon it
also contains small
amounts of other
substances. One
of these is sulphur.
Sulphur dioxide
gas is given out
when coal is burnt.
The poisonous sulphur gases rise into the air and returns to
earth as acid rain (sulphuric acid). This can damage trees
as shown above, kill wildlife on both land and in lakes. 80
The effect on buildings
Acid rain can have a devastating effect on historic building made
from carbonate materials such as limestone. The picture on the left
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was taken in 1908, the one on the right was taken in 1968.
Reducing acid rain
Acid rain is mostly caused by sulfur dioxide
(which forms sulfuric acid), but carbon dioxide
also contributes (by forming carbonic acid).
How can acid rain be reduced?
1. Burn fewer fossil fuels – generate electricity in other ways.
2. Remove sulfur from oil and natural gas before it is burnt.
3. Scrub waste gases to remove sulfur dioxide.
4. Use expensive coal that contains little sulfur.
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Production and consumption
Combustion
(95%)
Mining, Transport
& Handling
(5%)
It is not only the burning of fuels that damages the
environment. Energy is required to mine and quarry
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coal for power stations.
Pros and cons of fossil fuels
Advantages
Disadvantages
Although there are problems burning fossil fuels in power
stations there are also advantages:
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Summary – Electricity and Fossil fuels
•Fuel is burnt to produce heat,
•Water is turned to steam at high pressure,
•The steam drives a turbine,
•The turbine drives a generator to create electricity.
•Coal, oil and gas are fossil fuels formed over millions of
years from dead plants and animals.
•Burning fossil fuels releases carbon dioxide and sulphur
dioxide. Acid rain can damage forests, lakes and
buildings. Carbon dioxide contributes to global warming
that will cause widespread environmental change.
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Lesson 8 – Geothermal energy
Aims:
•Understand a range of energy transfer chains
illustrating the environmental implications of
generating electricity, including geothermal resources.
86
Old faithful Geyser
•Natural hot springs
and geysers have
been used by native
people for thousands
of years.
•Washing, bathing
and cooking were
common practises
before the industrial
revolution.
87
What is Geothermal power ?
• Geothermal power is energy that is taken
from the hot parts of the Earth’s crust. Geo
= earth, Thermal = heat.
• In many cases water is pumped down into
the Earth where it is heated and returns to
the surface. Steam from this water can be
used to drive turbines and generate
electricity.
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Structure of the Earth
89
Internal temperature of the Earth
90
Geothermal reservoir
When the rising hot water and steam is trapped in
permeable and porous rocks under a layer of
impermeable rock, it can form a geothermal reservoir.91
A basic geothermal generator
92
Geothermal emissions
93
California calling
© David Parsons/NREL
The largest geothermal power plant is in California
94
and has an output of 750 megawatts.
Advantages of geothermal
• Geothermal energy will last for many thousands of
years and can therefore be considered renewable.
• It is a relatively clean source of energy.
– 1/10 of carbon dioxide compared with fossil
fuels.
• Fewer environmental problems than fossil fuels.
• Once operating the running costs are low
compared to other sources of energy.
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Disadvantages of geothermal
• Physical effects due to fluid withdrawal including
possible volcanic activity and earthquakes.
• Some noise pollution.
• Other chemicals, within the heated water, can come to
the surface of the Earth and cause pollution.
• Many sites are found in reservoir areas and areas of
natural beauty.
• Areas suitable for geothermal generation are often in
tourist areas.
• Social impact on in small rural societies.
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Summary – Geothermal energy
•In some places of the Earth steam rises from the
ground. In others water can be pumped down into
the ground and returns as steam.
•The steam can be used to drive a turbine/generator
and create electricity.
•Geothermal energy does not originate from the Sun.
It does not contribute to global warming and does
create significant amounts of pollution.
97
Lesson 8 – Nuclear energy
Aims:
•Understand a range of energy transfer chains
illustrating the environmental implications of
generating electricity, including nuclear energy.
98
Why nuclear ?
•Why would anyone choose to use nuclear
power to generate electricity?
Independence – Many countries do not not
natural sources of coal, oil and gas and want to
be independent.
Weapons – Nuclear power plants can be used to
generate isotopes useful for creating weapons.
Efficiency – When first created it was thought
that nuclear power would be very cheap.
99
Nuclear
reactor animation
Hot coolant out
Control rod
Fuel rod
Cold coolant in
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Generating electricity
•Controlled nuclear fission reactions produce heat in the
form of the kinetic energy of the particles involved.
• Coolant fluid is passes around the fuel rods absorbing
heat and reaching very high temperatures.
•The coolant fluid passes this energy to a separate
source of water, which is turned into steam at very high
pressure.
•This steam drives a turbine, which in turn drives a
generator converting kinetic energy into electrical
energy.
101
Advantages of nuclear power
• Independent of fossil fuels.
• Less emissions of sulphur and nitrogen dioxide.
• Some reduction in carbon dioxide emissions.
•Independence of imported fuel prices.
•A source of weapons grade plutonium.
102
Disadvantages of nuclear power
•A high cost of building and decommissioning the
power plant.
• High running costs makes electricity expensive.
•Potential nuclear disasters are rare but possible.
•Storage of nuclear waste a very long term problem.
•The cost of safely storing nuclear waste is high. The
US Congress has been told that radioactive cleanup
and decontamination at military nuclear facilities in
the US will cost over $200 billion.
103
Nuclear waste
•Nuclear waste comes in several forms.
•The used fuel rods contain some uranium that has not
decayed as well as other isotopes made from the
uranium that are dangerous.
•All the other components of the power station e.g.
moderator, control rods and coolant fluid become
contaminated.
•Many other parts of a nuclear power station must be
stored when it is dismantled.
•It has only been 3000 years since the Egyptian Empire.
•Some high level radioactive waste will take over
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20,000 years to decay.
Nuclear fuel rod storage
Used nuclear fuel
rods, called spent
rods, are stored in
water.
Water keeps the
rods cool as the
number of nuclear
reactions gradually
decreases.
After some time
they can be cut up
105
and processed.
High level waste disposal
106
Although there are problems in the use of nuclear power,
there are also advantages:
Advantages
Disadvantages
Cheap to run
Conserves fossil fuels
No sulfur dioxide
emissions
No carbon dioxide
emissions
Safe under
normal conditions
Little fuel used means
less transport needed
Expensive to build
Expensive to decommission
Radioactive waste
Links with cancer
Non-renewable
Risk of disaster
107
Summary – Nuclear power
•The controlled fission of Uranium 236 can be used to
generate electricity.
•The fission releases energy as heat that can be used to
turn water in to steam.
•Nuclear waste products can remain radioactive for long
periods of time. These waste products need to be
carefully stored for long periods of time in a secure site.
•Accidents at nuclear power stations can cause wide
spread death and contamination.
108
Lesson 8 – Solar energy
Aims:
•Understand a range of energy transfer chains
illustrating the environmental implications of
generating electricity, including solar energy.
109
Solar energy systems
There are two main types of solar energy, both of
which are renewable sources of power.
The basic type is found in solar panels that absorb
energy form the Sun to heat water that can be used
for domestic use or to generate steam for
electricity.
The second type consists of solar cells, sometimes
called photovoltaic cells. These cells directly
convert energy from the Sun in electrical energy.
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Solar panel cross section
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Some solar
power stations
use a series of
mirrors called
heliostats to
reflect light onto
a boiler.
© Sandia National Laboratory/NREL
This solar power station in California consists of
about 1800 heliostats, with an electrical output of
10 megawatts.
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Solar furnace
•Water within
the tower is
turned to steam
at high pressure.
The steam drives a turbine which in turn drives
the generator and makes electricity.
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Solar power stations are
most effectively located in
areas with high light
intensity.
This test design is located in
Arizona where the sunlight
is intense and the air
temperature is high.
The mirrors must track the
Sun as it moves across the
sky to be efficient as
possible,
© Bill Timmerman/NREL
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Solar cells (or photocells) turn light energy from the Sun
directly into direct current electricity.
Manufacturing solar cells is very expensive and requires the
use of highly toxic materials. However, once the solar cell is
built it produces no pollution and requires little maintenance.
This makes solar cells
ideal for use in remote
locations where
maintenance is difficult
and other sources of
electricity would be
expensive.
© NASA/NREL
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Solar cells suffer from a low efficiency. This is because only
light with enough energy causes an electron to be released
which is only about 25% of all sunlight.
The amount of electricity a solar panel can produce depends
on two factors: its surface area and the light intensity.
Producing enough
electricity to power a
town would require a
very large area of solar
panels but covering the
roof of a house can
meet the annual
electricity needs of the
household.
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One obvious problem with solar cells is that they do not
produce electricity at night.
If more electricity is produced during the day than is used,
the excess can be used to charge a battery which can then
provide power during the night.
© Warren Gretz/NREL
Scientists are working
to develop improved
solar cells which
require less polluting
chemicals in their
manufacture, cost less
to produce and are
more efficient than the
current technology.
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Solar cells are very useful
for remote locations where
supplying mains electricity
would be expensive.
This solar-powered street
light is in a remote part of
mid-Wales with no mains
electricity supply close by.
The use of solar power in
this way removes the need
to lay electricity cables to the
light, which is another
benefit to the environment.
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Solar cells are very useful
where the light intensity is
highest.
These solar panels are in
a remote part of Morocco
where they are used by a
local utility company.
© Courtesy of BP Solarex/NREL
Solar cells are also useful
where low amounts of power
are needed.
Calculators only require a small
amount of electricity, so most
calculators now use solar cells
in place of batteries .
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Advantages of solar cells
•Running costs are low.
•No carbon dioxide emissions to add to the
Greenhouse Effect
•No sulphur dioxide emissions to cause acid rain.
•A renewable and almost unlimited source of
energy.
•A good source of energy in extreme conditions i.e.
space, deserts etc.
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Disadvantages of solar cells
•The initial cost of solar cells can be very high.
•The output is dependent on weather conditions
and the time of day.
•Many solar panels are needed to produce that of a
power station.
•Large areas of land are required for large scale
generation of electricity
•A warm reliable biome would be needed.
•Solar cells have relatively low efficiencies.
121
Summary – Solar power
•Solar panels can be used to heat water that can
be used as a cheap supply for home heating.
•Solar furnaces focus the Sun’s energy to turn
water into steam and then to generate electricity.
•Solar cells can directly transfer the light energy
from the Sun into electrical energy.
•Solar energy is renewable and does not create
any significant pollution.
122
Lesson 8 – Water energy
Aims:
•Understand a range of energy transfer chains
illustrating the environmental implications of
generating electricity, including water energy.
123
Energy from water
•Energy from water is derived in one of two ways.
• Gravitational forces from the Moon and Sun cause
the tides, this movement of water can be harnessed
by using wave power generation.
• The Sun powers the water cycle which increases
the gravitational potential energy of water.
124
The power of flowing water has been used for
hundreds of years to operate machinery. This
power can also be used to generate electricity.
125
Energy from the water cycle
•The heat of the
Sun evaporates
water which rises
into the
atmosphere. This
water returns to
higher parts of the
Earth during
rainfall.
•When moving along rivers the GPE of rain water can be
harnessed by hydroelectric power stations. This form of water
energy is the most common current form of alternative electricity
126
generation.
Hydroelectric power stations
• Hydroelectric power stations provide 5 to 10% of
the worlds electricity.
• The evaporation of water by the Sun increases the
GPE of the water droplets, this is the original
source of energy for hydroelectric power stations.
• Big lagoons, lakes or reservoirs are necessary to
provide a constant source of energy to be
converted to electrical power.
• Hydroelectric power stations can only be found in
certain areas where the rainfall, river flow and
geographical regions are correct.
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Energy Transfers
Stored water in the reservoir is used to generate electricity in a
hydroelectric power station.
Gravitational
Potential
Energy
Kinetic
Energy
(water)
Kinetic
Energy
(turbine)
Electrical
Energy
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How it works
• Water stored in the reservoir has a high
gravitational potential energy.
• The water is allowed to fall under gravitational
force.
• The water’s gravitational potential energy is
converted into kinetic energy.
• The kinetic energy drives the turbines of the power
station.
• The turbine drives the generators.
• Inside the generator kinetic energy is converted into
electrical energy.
129
Advantages of hydroelectric
•Hydroelectric power is a renewable source of energy, as long
as the Sun evaporates water we will have a source of power.
•It is a relatively clean source of energy emitting almost no
greenhouse gases and no contributions to other gas emissions.
•Once operating the running costs are low compared to other
sources of energy.
•It is a reliable and quick response system of generating
electricity.
•Excess power can be exported to other countries to generate
wealth.
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Disadvantages of hydroelectric
•A large area of land will need to be flooded when the dam is
constructed leading to loss of plant and animal species.
•Any change to the flow of a large river causes problems to
crops and fishing as well as increasing land erosion by the
wind; waterfalls disappear.
•The initial cost of building a hydroelectric power station is
high.
•Future problems if the reservoir fills up with silt and sand.
•The large area of land required makes their placement very
difficult to change. Risky near volcanoes.
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The Roosevelt dam
•Originally completed
in 1911, although
recent improvements
have been made.
•It delivers 36 MW of
power.
•Its reservoir covers
19200 acres.
•It is located 76 miles
north east of Phoenix,
Arizona.
132
How has the use of water power changed over time?
133
The rise and fall of waves is a
renewable source of energy.
Effective sites for harnessing
wave energy need to have
strong waves most of the time,
to ensure that enough
electricity will be produced.
The “Limpet” (land-installed
marine-powered energy
transformer) on Islay, Scotland,
is the world’s first commercial
wave energy device. Its low
profile is designed so that it
does not effect coastal views.
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Tidal Barrage
Tidal power involves
building a dam across a
river estuary.
Water can only flow in and
out of the estuary through
turbines in the dam, which
harness the tidal energy.
Tidal power is able to provide a lot of electricity, however
building a tidal barrage is very expensive.
When a tidal barrage is built, it results in some of the estuary
being flooded. This can mean the loss of important habits for
135
wading birds.
Tidal power
A huge dam (called a
"barrage") is built across
a river estuary. When the
tide goes in and out, the
water flows through
tunnels in the dam.
The ebb and flow of the
tides can be used to turn
a turbine. Large lock
gates, like the ones used
on canals, allow ships to
pass.
136
Effective use of tidal power
Tidal power provides a regular source of electricity. Exactly
when this electricity will be produced is governed by the tides,
which depend on the Moon.
Monthly variations in the
tidal range will also affect
how much electricity can
be produced.
The passage of ships past
the tidal barrier and the
effect on wildlife also
complicate the construction
of tidal barrage schemes.
137
Advantages of tidal power
•Once you've built the dam, tidal power is free.
•It produces no greenhouse gases or other waste.
•It needs no fuel.
•It produces electricity reliably.
•Not expensive to maintain.
•Tides are totally predictable.
138
Disadvantages of tidal power
•Very expensive to build.
•Affects a very wide area - the environment is
changed for many miles upstream and downstream.
Many birds rely on the tide uncovering the mud flats
so that they can feed.
•Only provides power for around 10 hours each day,
when the tide is actually moving in or out.
•There are very few suitable sites for tidal power
stations.
139
Summary – Water power
•The water cycle gives rain water gravitational
potential energy that can be changed into electrical
energy in hydroelectric power stations. It is
renewable energy but does cause localised
environmental damage when dams are constructed.
•Wave energy can be used to generate electricity but
is not yet widely available.
140
Lesson 8 – Wind energy
Aims:
•Understand a range of energy transfer chains
illustrating the environmental implications of
generating electricity, including wind energy.
141
Energy from the wind
•Wind is a renewable
energy resource.
•The Sun heats our
atmosphere causing
changes in temperature
and pressure. The
pressure differences
cause the winds.
•As long as the Sun heats
our atmosphere we will
have wind energy.
142
An old science
•Wind power has
been used for
thousands of years.
Early farmers used
windmills to grind
corn.
•Since the industrial
revolution steam
engines, petrol
engines and
electricity have took
over from wind.
•We can now generate electricity from the wind.
143
Generation of electricity
•The kinetic energy of the
wind is converted into
rotational work when the
turbine blades spin.
•The moving turbine drives
the generator. The generator
converts kinetic energy into
electrical energy.
•When the wind is strong the
blades automatically twist a
small amount to prevent
damage to the turbine and
generator.
144
Palm Springs, California
A large number of wind turbines grouped together is called a wind
farm. The turbines are arranged in special patterns.
145
Advantages of wind power
•Wind power is renewable- it will last as long as
the Sun shines.
•Particularly useful in remote areas without an
electricity supply.
•Wind power is a clean source of energy – there
are no emissions of carbon dioxide, sulphur
dioxide and nitrogen oxides.
•Government initiatives often provide funds to
promote wind power.
146
Disadvantages of wind power
•A large land area is required to get sufficient energy to
power a city. In many highly populated countries this land
is expensive.
•Not all areas have a constant source of wind to generate
electrical energy.
•Only approximately 5 MW of power is produced per
turbine so many are needed to produce the same amount of
energy as a power station.
•A large number of wind turbines can make sensitive
environmental areas look unattractive.
•Turbines can be noisy stopping them being used in urban
areas.
147
Summary – Wind energy
•The winds are caused by the heating of the
atmosphere by the Sun.
•The movement of the wind can be used to turn fan
blades, this in turn can be used to generate
electricity.
•Wind energy is renewable and does not create any
wide spread pollution but can be an eye sore and is
dependant on the weather.
148