Unit 6 textbook answers
Useful energy
What do you know?
Page 126
1 a Choose any three from: sound energy, light energy, heat energy, electrical energy, chemical
energy, kinetic energy (energy of movement), potential energy, nuclear energy
b Forms of energy are identified by where they come from (solar, geothermal, wind, etc.) or how
they are experienced or measured on instruments.
2 Temperature is measured with a thermometer.
Sound energy is detected by the ears.
Solar energy comes from the Sun.
Geothermal energy comes from within the Earth.
3 Light energy can be seen or measured with our eyes, and sound energy can be heard or
measured with our ears.
4 A qualitative measurement of heat would describe it, e.g. hot, cold, cooler, etc. A quantitative
measurement would give a value, e.g. 500 kilojoules.
5 a i 1 000 000 J
ii 4200 J
b i 5 000 000 cal
ii 21 000 Kj
What do you know?
Page 131
1 Energy transfer is the process in which the same form of energy moves from place to place.
Examples are sound moving from a speaker to a listener, light moving from the Sun to the
Earth, and heat travelling along a metal rod.
2 Radiation (heat transfer across space), as when heat travels from the Sun to the Earth.
Conduction (heat transfer through a solid object), as when heat travels along a metal rod.
Convection (heat transfer by fluid movement), as when heat is carried by air currents.
3 Heating vents are usually in the floor because heat rises and forms convection currents,
which helps to distribute heat through the house.
4 Answers will vary. Explanation should state that when energy is transformed or transferred,
the total energy at the end will be the same as that at the beginning, and/or that energy is
neither created nor destroyed in the process.
5 When the temperature difference is greatest (at the windows)
What do you know?
Page 133
1 Renewable energy is energy that is unlikely to disappear or run out over time.
Non-renewable energy will eventually run out and cannot be replaced.
2 Oil, natural gas and coal are called fossil fuels because they are produced from living things, and are now
a bit like ‘fossils.’ They cannot be replaced and so are called non-renewable resources.
4 Answers will vary, but should centre around the fact that the Earth’s energy resources are limited, and
these are ways of saving non-renewable energy resources (petrol) or using less of our limited renewable
energy resources (electric lights).
5 Primary energy is the total amount of energy available to us from a basic resource.
What do you know?
Page 135
1 This is because many energy applications involve heat, and things
such as producing electrical energy or driving engines involve the
combustion of fossil fuels.
2 When anything burns, it releases energy in the form of heat.
3 Assuming the amount is proportional to the mass of the body to
be kept at that temperature,
then (a) 10 MJ, (b) 6 M, (c) 4 MJ.
4 A heavier person would use slightly less than that because the ratio
of volume to surface area would be less, and proportionately a little
less heat would be lost, so a little less energy, proportionately,
would be required. The reverse applies to persons of smaller mass.
Active people need more energy than non-active people.
Young people need more energy during puberty.
In cold environments, we need more energy to keep the inner chemical
energy conversions to heat going.
What do you know?
Page 133
1 Renewable energy is energy that is unlikely to disappear or run out over time.
Non-renewable energy will eventually run out and cannot be replaced.
2 Oil, natural gas and coal are called fossil fuels because they are produced from living things, and are now
a bit like ‘fossils.’ They cannot be replaced and so are called non-renewable resources.
3 Energy source
Renewable or non- Percentage
renewable
Oil
Non-renewable
35%
Coal
Non-renewable
25%
Gas
Non-renewable
20%
Biomass
Renewable
15%
Nuclear
Non-renewable
3%
Hydro
Renewable
2%
4 A heavier person would use slightly less than that because the ratio of volume to surface area would be
less, and proportionately a little less heat would be lost, so a little less energy, proportionately, would be
required. The reverse applies to persons of smaller mass.
Active people need more energy than non-active people.
Young people need more energy during puberty.
In cold environments, we need more energy to keep the inner chemical energy conversions to heat going.
What do you know?
Page 139
1 Geothermal energy is the energy in the Earth’s molten core. Water heated from cracks in
the seabed forms hydrothermal vents, which supply energy to heat-loving thermophiles
such as giant worms and bacteria.
2 Chemical energy is converted to heat energy, which is dissipated.
3
4 Since animals consume solar energy by eating plants (and each other), they cause more
waste heat to leave the system.
5 Plants get their energy from the Sun. Humans eat plants such as grains, vegetables
and fruits and convert them to energy. So do the animals that some humans eat.
Without solar energy, no plants would grow and humans would not be able to eat
plants or other animals.
6 It is a unit of energy, since it is the energy produced by 1000 watts of power over one hour.
Unit review
1 Forms of energy are defined by their source, e.g. solar energy is that which comes from the Sun.
2 Any example as long as the qualitative measurement is descriptive (e.g. loud) and the quantitative
measurement has a numerical value, e.g. a sound of 20 decibels.
3 As a chemical reacts, heat is produced. This is a transfer of chemical energy into heat energy.
4a
4 a Energy
Percentage
source
Oil
35%
Coal
25%
Gas
20%
Biomass
15%
Nuclear
3%
Hydro
2%
6 A renewable resource is unlikely to disappear or run out over time. A non-renewable resource cannot be
replaced. Once it is used, it is gone.
7 Student answers will vary, but heat (measured by skin), light (measured by eyes) and sound (measured
by ears) are obvious answers.
8 Unit
joule, J
kilojoule,
cal
kcal
kJ
Value
3 600 000
3600
857 142
857
9 Data
Weight of evaporating basin plus unburnt marshmallow: A (grams)
Weight of evaporating basin plus burnt marshmallow: B (grams)
Temperature of water before heating: X (°C)
Temperature of water after heating: Y (°C)
Calculations
Weight of marshmallow that burnt: W = A – B (grams)
Temperature rise: R = Y – X (°C)
Energy in kilojoules from the marshmallow:
42 R E W
Note that the formula assumes that all the heat from the marshmallow goes into the water.
10 Diagrams will vary, but should show a sequence of atoms moving round, atoms bumping into each
other, atoms joining together, the joined atoms releasing energy in the form of heat.
11 Fossil fuels are the remains of plants, which have used energy from the Sun, or animals that have eaten
plants or other animals. In every case, the original source of energy was the Sun.
12 a Animals and plants consume solar energy. Animals consume more solar energy by eating plants.
Together they cause waste heat to leave the system.
b No, the energy is transformed to other forms, e.g. heat, sound, movement.
13 Answers will vary.
14 Answers will vary.
15 Answers will vary.