Chapter 5 Energy
Module 5.1
SHE: CETO 6 and the Perth wave farm
1 Energy sources that are non-renewable will eventually run out or reach levels that can no
longer meet our energy needs. Non-renewable energy sources, such as oil and coal, are
also a source of environmental pollution and degradation. In order to continue to have
sources of energy available in the future, we need to develop technology to harness
renewable sources of energy. It is important that we invest in and continue to develop
renewable energy technology to ensure an environmentally responsible and sustainable
energy future.
2 Student answers will vary and may include:
• habitat protection—are there still ongoing threats to the habitat?
• wind
• solar
• hydroelectricity (from dam or river water)
• geothermal (thermal energy that is stored in the Earth, such as hot springs)
• bioenergy (fuel from biological material/biomass such as bioethanol from plant
material).
3 Student answers will vary and may include:
• wind—Australia has large areas of open, unutilised land that is ideal for wind farms
• sun—we have the highest levels of solar radiation per square kilometre and plenty of
open space for solar farms
• waves—we are surrounded by water and tides suitable for wave farms
• dams—we already have a well-established hydropower network
• geothermal—South Australia has large potential geothermal resource.
• biomass—burning sugarcane waste can be used to generate thermal energy to power
sugar mills and can also be converted into liquid or gas biofuel. Sugarcane is already
a widespread crop in Queensland and New South Wales.
Module review answers
Remembering
1 a gravitational potential energy: energy stored in an object when it is above the ground
b elastic potential energy: energy stored in a stretched or quashed spring
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c energy transformation: a change in energy from one type into another
2 a kinetic energy
b convection
c electrical energy
3 a kinetic energy = v in a moving object
b sound energy = i in vibrating air particles
c elastic potential energy = ii in a stretched or squashed spring
d gravitational potential energy = iii in objects positioned above the ground
e light energy = iv released from glow-worms
4 Heat can be transferred by conduction, convection and radiation.
Understanding
5 Three ways that heat can be transferred are:
• Conduction—heat energy is transferred through direct contact with an object of
different temperature. It travels from the hotter object to the cooler object.
Example: You touch a bath tap and it feels hot.
• Convection—energy is transferred through moving particles of a liquid or a gas.
Example: Heat from a ducted heating vent is circulated in a room.
• Radiation—Energy is transferred as radiation and can do so through empty space.
Example: You feel the Sun’s rays on your skin on a summer’s day.
6 a The law of conservation of energy states that energy can never be created or
destroyed, but it can be converted from one form into another.
b This means that energy cannot be produced from nothing and it cannot disappear. For
example, to make a light globe work, energy must be supplied from a source, such as
a household electricity supply. All of the energy supplied to the globe is then converted
into a form of energy, such as light or heat. The amount of energy that is put into the
globe is exactly the same as the amount of energy that comes out.
7 Petrol, kerosene and oil all possess chemical energy.
Applying
8 a Heat energy
b Kinetic energy
c Chemical energy
d Kinetic energy
e Chemical energy
f Gravitational potential energy
9 a Taylah heats the water by convection currents in the kettle.
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b Mein feels the radiant heat of the Sun.
c Emmaline feels the heat of the metal due to conduction.
10 a 3 megajoules = 3 × 1 000 000 J
= 3 000 000 J
b 7500 kilojoules = 7500 × 1000 J
= 7 500 000 J
11 a 2 500 000 joules ÷ 1 000 000 = 2.5 megajoules
b 5000 kilojoules = 5000 × 1000 J
= 5 000 000 J ÷ 1 000 000 = 5 MJ
12 The types of energy that caused the changes in ‘Making spiders’ are the chemical
potential energy of the ice-cream and lemonade.
13 Elastic potential energy → kinetic energy + heat energy + sound energy
14 Chemical energy from food can be used by your body to produce:
• growth (forming new molecules and storing energy)
• sound energy (talking, singing)
• kinetic energy (movement)
• heat energy (body warmth).
15 a ii
b i
c iv
d iii
Analysing
16 Note that it is assumed that all objects are on the ground except where specifically stated
otherwise.
a Chemical
b Elastic potential
c Chemical
d Gravitational
e Chemical
f Chemical
g Chemical
h Gravitational
i Chemical
j Elastic
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17 Similarities:
• Conduction and convection are methods of heat transfer
• Particles are needed for conduction and convection to occur
Differences:
• Convection is a type of heat transfer that occurs in liquids and gasses whereas
conduction occurs only in solids.
Evaluating
18 a i
heat energy
ii gravitational potential energy
iii kinetic energy
b Glass A, ball A and car A all have more energy than their pair.
c Each glass has the same amount of water, but glass A is hotter and so has more heat
energy. Ball A has more energy than ball B because it is higher and so has more
gravitational potential energy. Car A has more energy than car B because it is moving
faster and so has more kinetic energy.
Module 5.2
SHE: The development of aircraft design
1 The science behind the gliders was not perfected yet, so flyers of these machines were
at great risk of falling from a height.
2 The Flyer was a glider that was built with an engine.
3 Enclosing the body of an aircraft reduces the air resistance encountered when in flight.
4 Student answers will vary.
5 Student answers will vary.
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Module review answers
Remembering
1 a energy efficiency: a measure of how much useful energy output is produced from
energy output
b energy rating label: a sticker found on new appliances that indicate the energy
efficiency by an increasing number of stars
2 a heat energy
b LED lighting
c insulation
3 Kinetic energy.
4 Any new household refrigerator, freezer, television, washing machine, clothes dryer,
single-phase air conditioner and dishwasher sold in Australia
5 a Heat energy
b Heat and sound energy
Understanding
6 Any heat losses produced by a device will increase the input of energy needed to get
useful work done. (Unless the device is a heater.)
7 The energy rating label shown in the cooling label in Figure 5.2.4 shows 7 stars and the
heating rating has 8 stars. This tells a consumer that this appliance has a good level of
energy efficiency, but they should compare ratings of similar appliances to see if there is
a more efficient model in their price range.
8 Student answers will vary and may include the following examples.
• Floor insulation traps heat and saves on heating costs.
• The air conditioning system is very energy efficient and will use less energy than other
models.
• Eaves over the windows provide shading that reduces cooling costs.
• Pool blanket traps heat in the pool, reducing heating costs.
• Compact fluorescent globes are energy efficient compared to incandescent globes.
• Gas-boosted solar hot water system maximises the use of solar energy, which
reduces gas use.
• North-facing aspect allows more solar energy to be collected for heating water and
producing electricity, and makes the house warmer in winter which cuts heating costs.
9 Adding insulation to a house and sealing up gaps reduces the heat exchange between the
inside and the outside of the house. This makes the heating used (or cooling used) more
effective and saves energy.
10 Regenerative braking stores some of the car’s kinetic energy while braking and uses this
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to charge an electric motor. This means that less energy needs to be used to make the
car run, which increases its energy efficiency.
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Applying
11 a Friction is the force that is always produced when two surfaces move across each
other.
b The contact between the particles of one surface dragging over another will add
energy to this point of contact which makes the particles vibrate faster. This is heat.
c Energy is converted to heat as the parts of the pump slide over each other. This
reduces the energy efficiency or percentage useful energy output of the pump, making
it less efficient.
12 a Steam engine, diesel engine, jet turbine, petrol engine
b 30% or 30 MJ
c 75%
Analysing
13 Radiation
14 a The useful energy output is the kinetic energy produced.
b Percentage energy efficiency = (useful energy output ÷ energy input) × 100
= (1210 ÷ 6050) × 100
= 20%
This means that 20% of energy input is converted into a useful form of energy output.
15 a Sound energy produced = 2000 J – (900 J + 300 J) = 800 J
b Percentage energy efficiency = (useful energy output ÷ energy input) × 100
= (800 ÷ 2000) × 100
= 40%
16 When an object falls to the ground, all of its gravitational potential energy is converted
into kinetic energy until the moment it hits the ground. An apple falling from the top of an
apple tree has more gravitational potential energy than an apple falling from a lower part
of the tree. So the apple from the top of the tree will have more kinetic energy when it hits
the ground.
Evaluating
17 a Heat and sound energy
b The radiator contains a liquid that absorbs some of the unwanted heat energy that is
produced by the engine and transfers the heat energy to the air. This makes the
engine much less likely to overheat.
18 a Coal possess chemical potential energy.
b The useful output energy of the power plant is the kinetic energy required to turn the
turbines.
c Vast amounts of heat energy are produced when the coal is burnt. This heat energy is
not useful energy and reduces the energy efficiency of the power plant. In addition,
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there are a number of stages involved before the kinetic energy is produced by
heating water to form steam. Heat energy is produced at each stage, resulting in the
overall low level of energy efficiency.
d Of every 100 J of energy input into a typical coal-fired power plant, approximately 67 J
are converted to heat with only about 33 J converted into useful kinetic energy.
e 33 J
19 a Incandescent bulbs cost the least to buy.
b An LED will typically operate for 50 000 hours before it needs to be replaced.
c LED, CFL, incandescent
d LED lighting
20 A 100% efficient car would need very little fuel. It would be silent while being driven and
the engine would not get hot.
Creating
21 a electrical energy → sound energy + heat energy
b chemical energy → light energy + heat energy + sound energy
c gravitational potential energy → kinetic energy + sound energy + heat energy
22 a elastic potential energy → kinetic energy + heat energy
b light energy → electrical energy→ kinetic energy + heat energy + sound energy
c chemical energy → electrical energy → kinetic energy + sound energy + heat energy
23 Student answers will vary.
24 kinetic energy (from wind) → electrical energy → kinetic energy (of fan inside vacuum
cleaner) + heat energy + sound energy
25 Gravitational potential energy (of water on the wheel) → kinetic energy (as water falls) →
kinetic energy of machinery (such as that to grind flour)
Module 5.3
Module review answers
Remembering
1 a wave motion: the transfer of energy without an overall transfer of matter
b acoustics: the science of sound
2 a frequency
b decibel scale
3 a metre (m)
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b Hertz (Hz)
4 a Folds of skin vibrate in your vocal cords
b The skin of the drum vibrates when it is hit.
c The lips of a trumpet player vibrate.
5 a 80 dB
b 105 dB
c 30 dB
Understanding
6 Ripples in a pond spread outward from a source in all direction. Sound also spreads from
a vibrating source in all directions.
7 The vibration of the bell makes the air particles immediately next to the bell vibrate.
These vibrating air particles make air particles adjacent to them vibrate. This series of
vibrating air particles is a sound wave. If you are close enough to the source of the sound,
the sound waves will reach your ears.
8 Sound can be described as kinetic energy because it is the vibration, or movement of air
particles back and forth.
9 Sound is the vibration of particles. Empty space has no particles that can be set into
vibration and sound cannot be transmitted.
10 Some sound is transmitted as vibrations through plaster walls in a house because they
are relatively thin and lightweight compared to the thickness and density of the brick
walls of a garage.
11 High-pitched sounds: person screaming, ambulance siren
Low-pitched sounds: jackhammer, bass guitar
Applying
12 a Jet take-off, 12-gauge shotgun
b Lawn mower, rock concert, chainsaw, jet take-off, 12-gauge shotgun
13 Bats at night send out sounds that are reflected off their prey. Their large sensitive ears
can pick up the echoes and follow their prey until they catch it.
14 a Absorb sound
b Reflect sound
c Diffuse sound
Evaluating
15 The reed is a thin strip of a material such as bamboo that is designed to vibrate to
produce the source of sound in the clarinet.
16 a Ticking clock
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b The sound wave of a ticking clock consists of air particles vibrating faster than those
the sound wave of a lawn mower because it has higher pitch.
17 a True
b Sound is the vibration of particles. Empty space has no particles that can be set into
vibration and sound cannot be transmitted.
18 The kinetic energy of the vibrating particles of a sound wave will eventually be
transferred as heat to its surroundings.
19 Student answers will vary and may include the following.
• Install carpet or mats on the floor.
• I Replace the wooden chairs with cushioned chairs with fabric.
• I Install felt boards on the walls.
• I Install ceiling tiles on the roof to absorb sound.
20 The five student answers will vary and may include any of the following.
• I Sound travels faster through air at higher temperature.
• I Sound travels much more slowly through air than through water.
• I Sound can travel through copper, glass and diamond.
• I Sound travels faster through glass than copper.
• I Sound travels at a very high speed through diamond, around three times the speed it
travels in glass.
Module 5.4
SHE: Lighting the world
1 Red, green and blue
2 White LEDs are far more energy efficient than previous lighting.
3 25%
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4 Student answers will vary. Example: People will be able to lessen reliance on potentially
dangerous fuels such as kerosene to power lamps to see in the dark.
5 Persistence, resilience, and ability to review and improve
6 Student answers will vary. Example:-New technologies will be needed to cater for clean
energy solutions.
Module review answers
Remembering
1 a reflection: the bouncing of light off a flat surface
b visible spectrum: the range of colours of light visible to the human eye—red, orange,
yellow, green, blue, indigo and violet light
c concave: an inward directed curve
2 a electromagnetic spectrum
b plane mirror
c refraction
3 300 million metres per second.
4 a TV or radio waves
b Gamma rays, X-rays or ultra-violet light
5 Dispersion
6 Light can be transmitted through the substance, reflected from the surface or absorbed
into the substance.
Understanding
7 Red, orange, yellow, green, blue, indigo, violet
8 Light from the sun reflects off a tree and into our eyes in order for us to see the tree.
Applying
9 Josie: 50 cm inside the mirror
Pot plant: 30 cm inside the mirror
Soccer ball: 20 cm inside the mirror
10 a Radiation
b Radio waves
c Microwaves
d Atom-X-rays
11 a Convex mirror
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b Convex mirror
c Concave mirror
Analysing
12 a No
b Light reaches us from the Sun. In travelling to Earth, it has crossed 150 million
kilometres of empty space.
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13 a Opaque
b Translucent
c Translucent
d Transparent
14 a Refraction is the bending of light due to its change in speed when it enters a new
medium. Reflection is the bouncing of light off a surface which occurs at the same
angle that the light hits the surface.
b A lens is a specifically shaped piece of glass or plastic that is designed to bend light. A
mirror is a very smooth, hard surface from which light is reflected.
c A concave mirror is a mirror that curves inwards. This mirror can be used to magnify
an object when held close to the object but produces small images for objects
positioned farther away. A convex mirror bulges outwards. It produces a smaller, wide
angled image of any object. A plane mirror is flat. It produces an image that is laterally
inverted (back to front) from an object.
15 Student answers will vary but may include:
• a pencil appearing bent in a glass of water
• a fish in a fish tank appearing distorted or legs looking short in a swimming pool.
Evaluating
16 The metal tray is a very smooth, polished surface. Fernando sees a reflection of himself
in the tray because light is reflected in a regular manner due to the smoothness of the
tray. The woolen sock has many ridges and as a result light scatters off the sock at many
angles and does not form an image.
17 a Concave mirror
b Only a concave mirror will magnify an object.
18 a Concave mirror
b Parallel rays of light from distant stars or objects hit the mirror and are reflected
inwards, concentrating at point called the focal point of the mirror. Light at this point
can be used to create an image of the night sky.
19 a An image seen in a plane mirror cannot be captured on a screen.
b It is not possible to focus a beam of light at any point behind a plane mirror as the light
has reflected away from the mirror itself. The image is not produced by actual rays of
light meeting but is an illusion.
20 a Convex lens
b Light from the top of the object being viewed is refracted downwards as it passes
through the convex lens and this part of the object is viewed at the bottom in the
image. Similarly, light from the base of the object passes through the lens and is
refracted upwards, forming the top of the image.
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Chapter review answers
Remembering
1 Potential energy.
2 Gravitational potential energy, chemical energy, nuclear energy and elastic potential
energy
3 Photosynthesis
4 A solar (or photovoltaic) cell
Understanding
5 Visible light lies between the ultra-violet and infrared parts of the electromagnetic
spectrum.
6 Student answers will vary but may include: moving car, a person jogging, a ball in motion.
7 Student answers will vary but may include: cooking an egg in a frying pan, being warmed
by a hot water bottle, a spoon becoming warm when sitting in a hot cup of tea.
8 a Sound travels faster on a warm day.
b Particles vibrate faster on a warm day so sound will be transferred more rapidly on a
warm day than a cooler day.
9 Student answers will vary but may include: a sound wave makes an ear drum vibrate,
which is kinetic energy.
10 Light refracts as it enters and leaves different media due to the change in speed as light
travels from one material into another.
Applying
11 Student answers will vary but may include:
• kinetic—push something over, such as a bowling ball knocking a pin down
• light—produce electricity using a solar cell
• heat—cook an egg in a frying pan
• electrical—make an alarm clock ring.
12 100 000 J
13 Similarities:
• Both travel as a wave.
• Both transfer energy.
• Both have a wavelength and frequency.
Differences:
• Light travels much faster than sound.
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• Sound needs a medium to travel through whereas light does not.
Analysing
14 Manufacturers could change the way the device was tested or misrepresent the test
results to make the device appear more energy efficient than it really is.
Evaluating
15 a SudZ machine
b SudZ machine
c Although the difference in energy use between the two washing machines may be
small for one wash, the difference in energy use between the two machines will be
large over the total life of the washing machines.
16 a Convex lens
b If a convex lens is held close to an object, it acts as a magnifying glass. A concave
lens makes a smaller image of the object.
17 When light travels from air into glass, it undergoes many more interactions with particles
in the glass than in air. Light itself travels at the same speed, the speed of light, but these
interactions slow its overall progression through the glass.
18 a Student answers will vary.
b Student answers will vary.
Creating
19 See the following figure.
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Inquiry Skills
Research
Answers are students’ own.
Thinking scientifically answers
1 B
2 D
3 The sound energy input is 1300 J. The machine is only 65% efficient
so only (0.65 x 1300) = 845 J will be output.
The energy output is:
•
120 J of gravitational potential energy;
•
(90 x 3) = 270 J of kinetic energy;
•
230 J of heat energy
This adds to 620 J energy.
The remaining (845-620) = 225 J of energy must have been released as heat of the three
pebbles.
This means that each pebble had heat energy of (225/3) = 75 J.
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