4 Energy
4
Energy
4.1
Forms of energy
1
Activities of living things and the working of machines need energy.
2
Different forms of energy:
heat energy
sound energy
light energy
kinetic energy
Energy
electrical energy
chemical energy
potential energy
4.2
1
Energy conversion
Energy can change from one form to another. For example,
torch
solar panel
toy car
potential energy stored in the spring
light energy given out by the torch
 kinetic energy of the spring toy
 kinetic energy of the toy car
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During an energy conversion, intermediate forms of energy may be involved between the
initial and the final forms of energy.
3
Energy converters can change energy from one form to another. Motors and generators are
common energy converters.
4
Motors change electrical energy to kinetic energy.
cells
pulley
switch
motor
weights
electrical energy
from the cells
5
motor

kinetic energy
of the pulley
kinetic energy
 of the rising
potential energy
 gained by the
weights
weights
Generators change kinetic energy to electrical energy.
light bulb
pulley
switch
generator
weights
potential energy
lost by the falling
weights

kinetic energy
of the pulley
and the
generator
generator

electrical
energy

light energy and
heat energy
given out by the
light bulb
6
Controlled energy conversions can provide us with useful forms of energy in a safe way.
7
If energy conversions get out of control, disasters may result.
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4.3
Common fuels
1
Fuel
Main uses
Town gas
For cooking and heating
Remarks
Does not give out black smoke
when burnt
Liquefied
For cooking and powering vehicles
petroleum gas
(LPG)
Does not give out black smoke
when burnt
Petrol and
diesel
For powering vehicles
Give out black smoke when
burnt
Kerosene
For cooking; high quality kerosene
Gives out black smoke when
for powering aeroplanes
burnt
Mainly for generating electricity
Gives out black smoke when
Coal
burnt
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2
3
Properties of good fuels:
a
easy to light;
b
clean when burnt;
c
safe to use;
d
give out a lot of heat energy when burnt;
e
easy to store and transport.
Safety precautions should be taken when using, transporting and storing fuels.
4.4
Generating electricity
1
Electricity is the most common energy source used at home today.
2
Steam engines are used to supply kinetic energy to drive a generator to generate electricity.
steam pipe
boiler containing water
fuel chamber
light bulb
steam turbine
generator
 Steam engine model
chemical
energy stored
in the fuels
3

heat energy and
kinetic energy
of the steam

kinetic energy
of the steam
turbine
generator

electrical
energy
The principle of generating electricity is to change kinetic energy to electrical energy using
a generator.
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pollution reduction system
generator

boiler
steam

to consumers

turbine
air
steam
water
coal

sea water condenser
cold sea water
hot sea water
The steps in the generation of electricity in a coal-fired power station:

Coal is crushed into fine powder so that it can be burnt more completely.

The coal powder is burnt in a boiler. A large amount of heat energy is given out to heat
the cold water in the tubes inside the boiler.

Water boils and changes to steam.

The steam turns the turbine.

The turbine drives the generator to generate electricity.
5 The energy conversions involved in generating electricity by burning fuels in a power station:
chemical energy
stored in the fuels
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
heat energy and
kinetic energy
of the steam
generator

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kinetic energy
of the turbine

electrical
energy
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4.5
Energy sources and us
1
Fossil fuels are non-renewable sources of energy. Burning fossil fuels gives out a large
amount of carbon dioxide and many air pollutants.
2
Effects of air pollutants include:
3
a
making us sick when breathed in;
b
forming acid rain;
c
leading to global warming.
We can reduce the use of fossil fuels and hence air pollution by saving energy and using
alternative energy sources.
Alternative energy source
a)
Energy conversions involved
Solar power
Solar panels:
light energy given out by the sun
 electrical energy
solar panel
Solar power stations:
heat energy given out by the sun
 heat energy and kinetic energy of steam
 kinetic energy of the turbine
 electrical energy generated by the
generator
 A solar power station in the United States
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potential energy of the water upstream
b) Hydroelectric power
water
upstream
 kinetic energy of the running water
generator
 kinetic energy of the turbine
 electrical energy generated by the
generator
turbine
c)
kinetic energy of the wind
Wind power
 kinetic energy of the turbine
turbine
wind
 electrical energy generated by the
generator
generator
d) Nuclear power
turbine
generator
heat energy given out when nuclear materials
undergo reactions
steam
 heat energy and kinetic energy of steam
 kinetic energy of the turbine
water
 electrical energy generated by the
generator
nuclear materials (e.g. uranium)
e)
potential energy of the water in reservoir
Tidal power
sea
reservoir
 kinetic energy of the running water
 kinetic energy of the turbine
 electrical energy generated by the
tide falls
generator
generator
turbine
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water
coal
4 Energy
f)
heat energy deep underground
Geothermal power
turbine
generator
 heat energy and kinetic energy of steam
 kinetic energy of the turbine
 electrical energy generated by the
steam
coming up
generator
water pumped
down
hot rocks deep underground
g)
Biofuels
chemical energy stored in plants
 heat energy and kinetic energy of steam
 kinetic energy of the turbine
 electrical energy generated by the
generator
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