Download Energy Resources and Energy Transfer

Energy Resources and Energy Transfer
This section is about energy and energy resources. It has these parts in it:
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Energy basics
Energy transfer diagrams
Temperature and heat
Transfer of thermal energy
Non-renewable energy resources
Renewable energy resources
Saving energy
Energy basics
Energy allows things to happen. If you leap around wildly, people often say
that you have lots of energy. Energy allows you to move around and keep
warm. It allows you to see and to hear. Energy cannot be created out of thin
air or destroyed - it can only be stored or transferred from place to place in
different ways. Let's look at some examples.
The vibrating drum and the plucked guitar string transfer energy to the air as
sound. This sound energy can be transferred to your eardrum as kinetic
energy (movement energy).
The battery transfers stored chemical energy as electrical energy in the
moving charges in the wires. The electrical energy is transferred to the
surroundings by the lamp as light energy and thermal energy (heat energy).
The rock on the mountain has stored energy because of its position above the
ground and the pull of gravity. This energy is called gravitational potential
energy. As the rock falls to the ground, the gravitational potential energy is
transferred as kinetic energy.
A cup of hot tea has heat energy in the form of kinetic energy from its
particles. Some of this energy is transferred to the particles in cold milk, which
you pour in to make the tea cooler.
When the explosive goes off, chemical energy stored in it is transferred to
the surroundings as thermal energy, sound energy and kinetic energy.
Energy transfer diagrams
Energy transfer diagrams show the locations of energy stores and energy
transfers. For example, consider the energy transfers in the simple electrical
circuit below.
We can show the transfers like this:
The battery is a store of chemical energy. The energy is transferred by
electricity to the lamp, which transfers the energy to the surroundings by light.
These are the useful energy transfers - we use electric lamps to light up our
rooms. But there are also energy transfers that are not useful to us. In the
example above, the lamp also transfers energy to the surroundings by
heating. If we include this energy transfer, the diagram looks like this:
Sankey diagrams
Sankey diagrams summarise all the energy transfers taking place in a
process. The thicker the line or arrow, the greater the amount of energy
involved. The Sankey diagram for the lamp (below) shows that it transfers
most of the energy by heating, rather than by light. Notice that the total
amount of energy transferred to the surroundings is the same as the amount
of electrical energy. We say that the energy has been conserved. Energy is
always conserved, it is never "lost" or "wasted", although some energy
transfers are useful and some are not.
Temperature and heat
Temperature and heat are not the same, although both are concerned with
thermal energy.
The temperature of an object is to do with how hot or cold it is, measured in
degrees Celsius. Note that the unit of temperature is written as oC, not oc or
oc.
A thermometer is used to measure the temperature of an object
The heat an object contains is the amount of its thermal energy, measured in
joules or J. Let's look at two examples to see the difference between
temperature and heat.
A swimming pool at 30°C is at a lower temperature than a cup of tea at 80°C.
But, the swimming pool contains more water, so it stores more thermal energy
or heat than the cup of tea.
To boil water, we must increase its temperature to 100°C. It takes longer to
boil a large beaker of water than to boil a small beaker of water, because the
large beaker contains more water and needs more thermal energy or heat to
reach 100°C.
The small beaker of water boils first
Transfer of thermal energy
Thermal energy can be transferred by:
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conduction
convection
radiation
Thermal energy can also be transferred when a liquid evaporates. The liquid
particles with the most energy leave the liquid and enter the surroundings.
This is why your skin feels cold if you lick the back of your hand and blow over
it gently. Conduction and convection also need moving particles to transfer
thermal energy.
Conduction
Thermal energy can move through a substance by conduction.
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Substances that allow thermal energy to move easily through them are
called conductors. Metals are good conductors of thermal energy.
Substances that do not allow thermal energy to move through them
easily are called insulators. Air and plastics are insulators.
When a substance is heated, its particles gain energy and vibrate more
vigorously. The particles bump into nearby particles and make them vibrate
more. This passes the thermal energy through the substance by conduction,
from the hot end to the cold end. This is why the handle of a metal spoon
soon gets hot, as well as its rounded part, when the spoon is put into a hot
drink.
Convection
The particles in liquids and gases can move from place to place. Convection
happens when particles with a lot of thermal energy in a liquid or gas move,
and take the place of particles with less thermal energy. Thermal energy is
transferred from hot places to cold places by convection.
Radiation
All objects transfer thermal energy by radiation called infrared radiation. The
hotter an object is, the more radiation it gives off. No particles are involved in
radiation, unlike conduction and convection. This means that thermal energy
transfer by radiation can even work in space, but conduction and convection
cannot.
Radiation is why we can feel the heat of the Sun, even though it is millions of
kilometres away in space. The police use infrared cameras to track down
criminals in the dark.
Non-renewable energy resources
Energy resources provide us with energy. There are different types of energy
resource, including fuels such as coal or food, and stores of energy such as
batteries or the wind. We can divide energy resources into two categories,
non-renewable and renewable.
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Non-renewable energy resources cannot be replaced once they are all
used up.
Renewable energy resources can be replaced, and will not run out.
Non-renewable: fossil fuels
The fossil fuels are coal, oil and natural gas. They formed millions of years
ago from the remains of living things. Coal was formed from plants, and oil
and natural gas from sea creatures. When the living things died, they were
gradually buried by layers of rock. The buried remains were put under
pressure and chemical reactions heated them up. They gradually changed
into the fossil fuels. You can find out more about this here Fossil fuels .
Coal is a fossil fuel
The fossil fuels are non-renewable energy resources. Once we have used
them all up, they will take millions of years to replace, if they can be replaced
at all.
The energy stored in the fossil fuels originally came from sunlight. Plants used
light energy from the Sun for photosynthesis to make their chemicals. This
stored chemical energy was transferred to stored chemical energy in animals
that ate the plants. When the remains of the plants and animals became fossil
fuels, their chemical energy was stored in the fuels. The energy is transferred
to the surroundings as thermal energy and light energy when the fuels burn.
Renewable energy resources
Renewable energy resources can be replaced, and will not run out. Take
care: it is not true to say that they can be re-used.
Renewable: biomass
Biomass fuels are fuels from living things such as trees. Wood is a biomass
fuel. As long as we continue to plant new trees to replace those cut down, we
will always have wood to burn. Just as with the fossil fuels, the energy stored
in biomass fuels ultimately came from the Sun.
Renewable: wind power
Wind is caused by huge convection currents in the Earth's atmosphere, driven
by heat energy from the Sun. The moving air has huge amounts of kinetic
energy, and this can be transferred into electrical energy using wind turbines.
Wind turbines cannot work if there is no wind, or if the wind speed is high
enough to damage them.
A wind turbine
Renewable: water power
Moving water has kinetic energy. This can be transferred into useful energy in
different ways. For example:
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wave machines use the up and down movement of waves to turn
electricity generators
tidal barrages are built across the mouths of rivers. As water moves in
or out of the river mouth when the tide turns, the kinetic energy in the
water is used to turn electricity generators.
Hydroelectric power (HEP) schemes store water high up in dams. The water
has stored gravitational potential energy. As the water rushes through pipes,
this stored energy is transferred to kinetic energy, which turns electricity
generators.
An energy transfer diagram for an HEP scheme
Saving energy
Electricity can be generated in many ways, including:
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in power stations using fossil fuels or biomass fuel
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using wind turbines
using hydroelectric power schemes
using wave power or tidal power
using solar cells.
Most of the UK's electricity is generated in power stations using fossil fuels.
Thermal energy released from the burning fuel is used to boil water to make
steam, which expands and turns turbines. These drive the generators to
produce electricity.
As the fossil fuels are non-renewable energy resources, and they produce
pollution when they burn, we are aiming to produce more of our electricity
using renewable energy resources. This will reduce the rate at which the fossil
fuels are used up.
We can also reduce the rate at which the fossil fuels are used up by saving
energy. For example, we can walk to school instead of getting a lift in a car.
We can turn down the heating a bit and we can turn off the lights when we
leave the room.