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OCR 21st Century Science P1 Answers COLLINS NEW GCSE SCIENCE © HarperCollinsPublishers Ltd 2011 Physics Module P1 Answers p1_01 Our solar system Student Book answers Q1 Dwarf planets are smaller than planets. Q2 Moons orbit planets; they are smaller than planets. Q3 Bar chart drawn using the data from the table on p. 205. Q4 Distances in the solar system are so large that numbers become difficult to interpret in kilometres. Q5 People would need to live in the spacecraft for at least twice this time (to reach the planet and return); it is dangerous and expensive; the manned rocket would probably take longer because it will be larger and heavier than an unmanned probe. Q6 Mars is closer so we have been able to send landers to it as well as use telescopes. Neptune is so far away that telescope images are not as detailed as those from Mars, and probes take a very long time to reach it and send signals back to us. Worksheet answers Activity 1 (Low demand) Moon and planet – moon is smaller; moon orbits a planet Sun and planet – Sun gives out heat and light, a planet reflects these; planet is much smaller than Sun; planet orbits the Sun Asteroid and planet – asteroid is smaller and lumpier than a planet (i.e. non-spherical); asteroids mainly orbit in a ‘belt’ between Mars and Jupiter Comet and planet – comet has very elongated orbit; smaller than planet Activity 3 (High demand) We cannot visit planets closer to the Sun than Earth because of the high temperatures, and cannot land on the four outer planets, because they do not have a solid surface. It is feasible to visit the Moon and, with a lot of preparation and great expense, Mars. Supplies of air, liquid water and food would need to be replenished regularly unless it were possible to generate or recycle supplies. p1_02 Observing stars Student Book answers Q1 Thousands of millions of galaxies. Q2 Thousands of millions of solar systems/stars. Q3 100 000 years Q4 A hypothesis is a sensible explanation of some data. As more data is collected, the hypothesis may be proven wrong. It only becomes a theory when it is tested repeatedly and data still supports the hypothesis. Q5 It takes time for light to travel from the star to us – so we only see this light a certain time after it has left the surface of the star. Q6 The more distant the galaxy, the longer its light takes to reach us, so we see the galaxy as it was longer ago. Worksheet answers Activity 1 (Low demand) Q1 Universe; galaxy; Milky Way; Sun Activity 2 (Standard demand) Q1 A: hypothesis; B: theory; C: hypothesis; D: data; E: data Q2 Data: star charts and recorded position of North Star. Hypothesis: North Star is fixed, other stars move around it. Theory: The Earth’s rotation about an axis pointing towards the North Star, which explains the observations. Activity 3 (High demand) Q1 10 billion years ago.

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  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Physics Module P1 Answers

    p1_01 Our solar system

    Student Book answers

    Q1 Dwarf planets are smaller than planets.

    Q2 Moons orbit planets; they are smaller than planets.

    Q3 Bar chart drawn using the data from the table on p. 205.

    Q4 Distances in the solar system are so large that numbers become difficult to interpret in kilometres.

    Q5 People would need to live in the spacecraft for at least twice this time (to reach the planet and return); it is

    dangerous and expensive; the manned rocket would probably take longer because it will be larger and heavier

    than an unmanned probe.

    Q6 Mars is closer so we have been able to send landers to it as well as use telescopes. Neptune is so far away

    that telescope images are not as detailed as those from Mars, and probes take a very long time to reach it and

    send signals back to us.

    Worksheet answers

    Activity 1 (Low demand)

    Moon and planet moon is smaller; moon orbits a planet

    Sun and planet Sun gives out heat and light, a planet reflects these; planet is much smaller than Sun; planet

    orbits the Sun

    Asteroid and planet asteroid is smaller and lumpier than a planet (i.e. non-spherical); asteroids mainly orbit in a

    belt between Mars and Jupiter

    Comet and planet comet has very elongated orbit; smaller than planet

    Activity 3 (High demand)

    We cannot visit planets closer to the Sun than Earth because of the high temperatures, and cannot land on the four

    outer planets, because they do not have a solid surface. It is feasible to visit the Moon and, with a lot of preparation

    and great expense, Mars. Supplies of air, liquid water and food would need to be replenished regularly unless it

    were possible to generate or recycle supplies.

    p1_02 Observing stars

    Student Book answers

    Q1 Thousands of millions of galaxies.

    Q2 Thousands of millions of solar systems/stars.

    Q3 100 000 years

    Q4 A hypothesis is a sensible explanation of some data. As more data is collected, the hypothesis may be proven

    wrong. It only becomes a theory when it is tested repeatedly and data still supports the hypothesis.

    Q5 It takes time for light to travel from the star to us so we only see this light a certain time after it has left the

    surface of the star.

    Q6 The more distant the galaxy, the longer its light takes to reach us, so we see the galaxy as it was longer ago.

    Worksheet answers Activity 1 (Low demand)

    Q1 Universe; galaxy; Milky Way; Sun

    Activity 2 (Standard demand)

    Q1 A: hypothesis; B: theory; C: hypothesis; D: data; E: data

    Q2 Data: star charts and recorded position of North Star.

    Hypothesis: North Star is fixed, other stars move around it.

    Theory: The Earths rotation about an axis pointing towards the North Star, which explains the observations.

    Activity 3 (High demand)

    Q1 10 billion years ago.

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Q2 It shows stars of all ages, up to about 10 billion years old.

    Q3 Any sensible method e.g. how many bright objects in a square cm on the photo, then multiply this by the area

    of the photo.

    Q4 Bright or large objects may be the closest ones (although there may be nearby small or dim objects).

    p1_03 Distances to stars

    Student Book answers

    Q1 Distances are too large to use kilometres.

    Q2 a) 4 million cm; b) 2800 million cm

    Figure 2: If the objects are similar types of star that can be assumed to have the same real brightness, the stars

    that seem brighter are closer.

    Q3 The atmosphere cannot interfere with light and other radiation reaching space-based telescopes.

    Q4 For stars of a similar type, brighter stars are closer and dimmer stars are further away.

    Q5 Apparent movement of nearby object relative to background objects when viewed from different positions.

    Q6 The angles of parallax are too small to measure accurately.

    Worksheet answers Activity 1 (Low demand)

    Note these distances are not exact the exercise is for students to practise ordering distances.

    1 mm thickness of 5 sheets of paper

    1 m height of a young child

    1 km about 1015 minutes walking distance

    1000 km distance from London to Inverness

    10 000 km diameter of the Earth

    10 million km diameter of the Sun

    100 million km distance from the Earth to the Sun

    10 million million km distance light travels in a year

    1 light-year diameter of the solar system

    100 thousand light-years distance across the Milky Way

    1 million light-years distance to next galaxy

    Activity 2 (Standard demand)

    Q1 The intensity is measured at the same distance to control variables.

    Q2 If the light meter were further away, the readings would be lower.

    Activity 3 (High demand)

    Q1 More

    Q2 Gets smaller

    Q3 Stars closer to the Sun have a larger parallax angle; distant stars have very small parallax angles, which are

    very difficult to measure accurately; also to be fainter and harder to distinguish from the background stars.

    Practical sheet answers

    Q1 Real brightness is the true brightness of the source; relative brightness is how bright it appears to an observer.

    Q2 Decreased as the voltage decreased.

    Q3 Decreased as the distance increased.

    p1_04 Fusion in stars

    Student Book answers

    Q1 Through nuclear fusion reactions.

    Q2 Helium

    Q3 Very high temperatures and pressures/densities.

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Q4 a) Through nuclear fusion reactions; b) In a supernova.

    Q5 It contains heavier elements than expected, like silicon and magnesium.

    Q6 Either: yes, the evidence is consistent with these ideas and they have not been proved wrong

    Or no, we have not studied enough stars yet to be sure.

    Worksheet answers Activity 1 (Low demand)

    Q1 a) Nuclear fusion reactions take place in stars; c) Nuclear fusion between two hydrogen nuclei forms a helium

    nucleus; e) New elements form in stars and during a supernova.

    Activity 2 (Standard demand)

    Q1 Working downwards 5, 4, 3, 2, 1

    Q2 a) For example, beryllium + beryllium oxygen

    b) helium + helium + helium carbon

    Activity 3 (High demand)

    Q1 Practical experiments: Aston, Cowan and Reines, Davis.

    Creative explanations: Einstein, Eddington, Bethe, Pauli.

    Q2 If we use the wrong calculations or theories, we will come to the wrong conclusions; as our knowledge and

    capabilities develop, we may be able to obtain new data which may not fit our explanations.

    Q3 Experiments provide evidence that theories are correct.

    Q4 The existing theories were inconsistent with the evidence of geology/fossils.

    Q5 For example, very likely it has evolved over time and many scientists have agreed with its findings.

    Or not likely there have been mistakes already and we are still finding new evidence; we cant test the ideas

    directly.

    p1_05 The expanding universe

    Student Book answers

    Q1 The wavelength of their light is longer.

    Q2 If the galaxy is moving towards or away from us, and if it is moving faster than other galaxies.

    Q3 Their light has a greater redshift.

    Q4 Almost all galaxies are moving away from the Milky Way, and the more distant galaxies are moving away faster.

    Q5 Scientists may find more data to support their ideas, making the theory more plausible; or they may find data

    that cannot be explained using the theory and have to adjust the explanation or rethink it.

    Worksheet answers

    Activity 1 (Low demand)

    Q1 a) short; b) long

    Q2 a) lower; b) shorter, higher; c) redder; d) shorter, bluer

    Activity 2 (Standard demand)

    Q1 A redshifted, moving away; B no shift, no movement relative to us; C redshifted, moving away; D blueshifted,

    moving towards

    Q2 A is moving fastest (greatest shift).

    Activity 3 (High demand)

    Q1 All dots move away from our galaxy dot.

    Q2 The dots moving away faster are those further away (students should be able to refer to their measurements).

    Q3 Similarities: the balloon and space are expanding; the dots and galaxies are all moving apart; the dots and

    galaxies move apart faster if their separation is greater.

    Differences: the balloon only has dots on its surface; the balloon is a specific shape; in reality some

    neighbouring galaxies are moving closer together, but no dots on the balloon are.

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    p1_06 The Big Bang

    Student Book answers

    Q1 Universe 14 billion years; Sun 5 billion years; Earth 4.5 billion years old.

    Q2 Several different pieces of evidence all point to the same age.

    Q3 It was evidence for the Big Bang theory; other theories of the start of the Universe could not account for cosmic

    background radiation.

    Q4 Many pieces of evidence all support the theory.

    Q5 It may continue expanding; expansion may slow down after which it would stay at a fixed size; it may reach a

    maximum size and then shrink back to a small size.

    Q6 Scientists are not sure what the mass of everything in the Universe is, so cannot be sure what the effect of

    gravity will be.

    Worksheet answers Activity 2 (Standard demand)

    Q1 a) Look at the style and compare with other buildings; find an age for the materials used to build it.

    b) Compare it with other trees of different ages of the same variety; count the rings in the bark.

    c) Check how fresh/stale it is; look at any packaging.

    Q2 a) The Earth: is older than fossils and rocks; is likely to be older than the Moon (it is likely that the Moon formed

    when something collided with Earth as it was forming, or just after it formed); is likely to be a similar age to

    meteorites (these probably formed at similar times); so a possible age is 4.5 million years.

    Activity 3 (High demand)

    Q1 A keep expanding; B reach fixed size; C shrink; D reach fixed size; E keep expanding; F shrink.

    Q2 Uncertainty in the size and shape of the Universe; uncertainty about whether or not the density is equal

    throughout the Universe.

    p1_07 Rocks on Earth

    Student Book answers

    Q1 Erosion, volcanic eruption, sedimentation, the surface of the earth pushing up.

    Q2 Fossils are a record of the types of plants and animals present in that place millions of years ago; they enable

    the rock to be dated and give an indication of what the Earths surface was like at that time.

    Q3 The sketch should show rock fragments breaking off a rock face and travelling in a river or glacier to be

    deposited on the sea bed.

    Q4 Rocks 4 thousand millions of years old can be found on Earth.

    Q5 We see new rocks form when volcanoes erupt; when rocks samples are dated, rocks of different ages may be

    found in the same mountain range, suggesting rock formation is a continuous process.

    Q6 We can study rock processes that occur today and we can study rock samples that formed millions of years

    ago. From this, we can work out which processes took place in which sequence.

    Worksheet answers

    Activity 1 (Low demand)

    Event Timescale

    earthquake day

    mudslide day

    volcano eruption months

    volcanic island appearing years

    erosion decades

    Event Timescale

    retreat of glacier hundreds of years

    formation of English Channel thousands of years

    fossilisation two million years

    formation of fold mountains several million years

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Activity 2 (Standard demand)

    Q1 New rocks forming: image A volcano (igneous); images C, D basin fills with layers of sediment (sedimentary).

    Rocks breaking down: images C, D mountains and basin edges eroding

    Q2 Students own sentences about erosion, transportation and sedimentation

    Q3 There needs to be further mountain building.

    Activity 3 (High demand)

    Q1 Fossil comparisons easy to compare samples; does not give a true age, cannot be used for older rocks.

    Comparing rock samples reasonably easy to use; does not give a true age.

    Radioactive dating very accurate; requires specific elements to be present.

    Q2 Radioactive dating of the oldest rock samples, including single crystals; assuming that Earth is approximately

    the same age as the Moon and meteorites.

    Q3 The Earth cannot be younger than its oldest rocks but we may still find older rocks; rocks are recycled on Earth

    so the oldest rocks may not be in an accessible form.

    Q4 Radioactive dating gives an accurate age and can date much older rocks than the other methods.

    p1_08 Continental drift

    Student Book answers

    Q1 South America and Africa; North America and Eurasia; Antarctica and Australia

    Q2 Cynognathus; Glossopteris

    Q3 Wegener could not explain how the continents moved; the movement was too slow to detect; the idea was very

    unexpected; Wegener was not a geologist.

    Q4 Yes; scientists need evidence to back up new hypotheses and need to question new ideas.

    Q5 Oceanic ridges form; they contain strips of rocks magnetised in opposite directions.

    Q6 The magnetised strips on the seabed show that new rock is constantly being formed in the oceanic ridges; so

    the seafloors are spreading and the continents are being pushed apart.

    Worksheet answers

    Activity 1 (Low demand)

    Q2 India; Australia

    Q3 For example, the shapes slotted into each other; the picture was partly on one piece and partly on another

    piece; the colours/lines matched.

    Q4 Decide which shapes had matching outlines; decide which had surface evidence that matched.

    Activity 2 (Standard demand)

    Wegener Geologist Explanation/evidence

    The continents are moving We cant see continents moving If the continents take millions of

    years to move, it would be hard to

    detect

    Continents may have moved

    because of tidal movement

    There is no evidence that tides are

    strong enough to move continents

    Tides cant move continents but

    processes inside the Earth could

    Continents are shaped like jigsaw

    puzzle pieces that could be joined

    together

    Continents have always been the

    same shape and dont fit exactly

    together

    We need more evidence to prove

    continents were once joined

    together

    Fossils that lived in cold climates

    can also be found in continents

    that have hot climates

    The cold climate was more

    widespread in the past

    Several continents were clustered

    near the South Pole and have now

    spread across the Earth

    Mountains made from the same

    rock types occur on separate

    continents

    Mountains formed in the same way

    all over the Earth as the Earth

    cooled and the crust wrinkled

    The same types of mountain are

    only found in some places on Earth

    The same animals occur on

    separate continents because the

    continents moved apart

    The same animals occur on

    separate continents because all

    continents were linked by land

    bridges that have now vanished

    There is no evidence of land

    bridges but they cant vanish

    completely

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Activity 3 (High demand)

    Q1 a) At the far ends of the paper/ far from the ridge.

    b) Where the paper emerges from the table/ by the ridge.

    Q2 The different times taken for the Earths magnetism to switch from North to South.

    Q3 The rock is spreading outwards in two directions from the ridge.

    Q4 The continents have been moving apart.

    p1_09 Tectonic plates

    Student Book answers

    Q1 Consists of several solid tectonic plates that fit together but can move relative to one another.

    Q2 They can slide past each other, move apart, move together, or one can slide under another.

    Q3 These events tend to occur at the boundaries of tectonic plates; the relative movement of the plates causes

    large forces.

    Q4 Plates moving apart allow magma to rise, forming ridges and eventually new mountains; plates moving together

    push rock upwards, forming mountains.

    Q5 See the High demand lesson notes above.

    Q6 Existing data can be explained using the theory of tectonic plates; successful predictions have been made

    using the theory.

    Worksheet answers

    Activity 1 (Low demand)

    Q1 The building could be damaged.

    Q2 There is no/ less movement of the ground under the buildings.

    Q3 The semi-liquid rock will escape through the gap.

    Q4 A gap is much less likely away from the boundary.

    Q5 At plate boundaries the tectonic plates push against each other, causing the land to lift.

    Activity 2 (Standard demand)

    Q1 a) Mountain ranges occur where plates are moving closer together.

    b) Volcanoes and mid-ocean ridges occur where plates are moving apart.

    Activity 3 (High demand)

    These points should be highlighted: plates moving apart change magma into igneous rocks in the ocean; plates

    moving together change sedimentary rocks into metamorphic rocks; or magma into igneous rocks (mountain

    forming and volcanoes near subduction zones).

    p1_10 Earthquake waves

    Student Book answers

    Q2 P-waves and S-waves.

    Q3 P-waves reach detectors before S-waves.

    Q4 S-waves cannot travel through the liquid outer core.

    Q5 a) Longitudinal waves vibrate along the direction in which the wave travels; transverse waves vibrate at right

    angles to the direction of the wave; both longitudinal and transverse waves transfer energy.

    b) Just solids

    Q6 A shadow region for S-waves indicates liquid regions inside the Earth; a shadow region for P-waves indicates

    an abrupt change in density inside the Earth; the time taken for waves to reach certain places varies, indicating

    regions of different densities inside the Earth.

    Worksheet answers

    Activity 1 (Low demand)

    Q1, 2 See Student Book p. 224

    Q3 a) Similarities: the skin is thin; there is a central core; the flesh is similar to the mantle.

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Differences: there is no semi-liquid material inside the apple; there are not four distinct layers inside the apple;

    the structure of the core is different in the apple; the relative thicknesses do not correspond.

    b) Similarities: the shell is a hard, thin layer; the yolk and white are semi-liquid like the mantle and outer core.

    Differences: different shape; there is no solid core in the egg; there is an air pocket in the egg.

    Activity 2 (Standard demand)

    Q1 Station B; it detected the waves first.

    Q2 Station F; it took longest to detect the waves.

    Q3 P-waves travel faster than S-waves, and both types of wave reached these detectors.

    Q4 S-waves cant travel through the liquid outer core to reach these detectors.

    Q5 The earthquake was close to detector B, about midway between detectors A and C.

    p1_11 What a wave is

    Student Book answers

    Q1 A series of regular disturbances that carries energy in the direction in which the wave travels.

    Q2 See Fig. 3 in Student Book p.226.

    Q3 0.2 m/s

    Q4 a) Left-hand diagram; left-hand diagram; b) larger amplitude means louder sounds.

    Q5 a) Left-hand diagram; left-hand diagram; b) longer wavelength means lower pitch.

    Q6 Amplitude = 7.5 units, wavelength 0.2 m.

    Worksheet answers

    Activity 2 (Standard demand)

    Q3 When the loudness increases/decreases, the amplitude increases/decreases.

    Q4 The wavelength.

    Q5 When the pitch increases/decreases, the wavelength decreases/increases.

    Q6 The amplitude.

    Activity 3 (High demand)

    Q1 Eleven

    Q2 a) Almost four; b) 4 0.2 = 0.8 seconds; c) 60/0.8 = 75 beats per minute

    Q3 The peaks should be the taller than the first patients, with peaks reaching 4.0 mV and about 4 squares apart on

    the time axis.

    Q4 The peaks should be the same height as the first patients (reaching just over 3 mV), but closer together with

    three squares between the peaks.

    Q5 Oscilloscopes are useful because they record what is actually happening, and will show an immediate change if

    the patients condition changes.

    Practical sheet answers Q3 The speed of the wave should increase as the depth increases.

    p1_12 The wave equation

    Student Book answers

    Q1 400 waves per second

    Q2 4 Hz

    Q3 1500 m/s

    Q4 The wavelength will get larger as the frequency decreases (0.165 m rising to 1.65 m).

    Q5 2 m

    Q6 275 Hz

    Q7 The frequency of blue light is higher than the frequency of red light ; wavelength is inversely proportional to

    frequency as all light travels at the same speed in air.

  • OCR 21st Century Science P1 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Worksheet answers

    Activity 1 (Low demand)

    a) Frequency 2 Hz, wavelength 0.1 m

    b) Frequency 0.17 Hz, wavelength 2 m

    c) Frequency 0.33 Hz, wavelength 4 m

    d) Frequency 25 000 million Hz, wavelength 0.012 m

    Activity 2 (Standard demand)

    Q1 The wavelength halves.

    Q2 Higher attaining students should quote numbers in their answer.

    Activity 3 (High demand)

    Q1 a)180 m/s

    b) 150 000 m/s

    Q2 a) 30 m/s

    b) 120 000 m/s

    c) 15 m

    Q3 a) 480 000 m/s

    b) 75 000 m/s

    c) 6 kHz

    Q4 a) 750 Hz

    b) 0.625 m

    c) 9900 m/s

    d) 166 667 m/s

    e) 5 400 000 m/s

    f) 0.17 m.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Physics Module P2 Answers

    p2_01 Electromagnetic radiation

    Student Book answers

    Q1 Star, lit candle

    Q2 Glass from a windscreen, tracing paper, lens from sunglasses, cardboard

    Q3 Light from the Sun a source of light is transmitted through the window and falls on the page. Black print

    absorbs the light, the white paper reflects almost all the light, and the coloured sections reflect some of the light.

    The reflected light enters our eyes. The eye is a detector and responds to the light.

    Q4 They have a high frequency and so a high energy that can damage cells when absorbed.

    Q5 A massless packet of electromagnetic energy (and the amount of energy depends on the frequency of the

    electromagnetic wave).

    Q6 Blue; its photons carry more energy, and photon energy depends on the frequency.

    Worksheet answers Activity 1 (Low demand)

    Q1 a) Sun; b) a mirror; c) dark walls; d) the image sensor in a camera; e) clear windows

    Q2 The windows reflect more light than the walls.

    Q3 Dark-coloured walls make a photograph dark because they reflect less light / light-coloured walls make a

    photograph brighter because they reflect more light.

    Q4 Clouds absorb some of the Suns light so it is dimmer, but they transmit some light so we can still see.

    Activity 2 (Standard demand)

    Q1 Radio/microwave/infrared/visible/ultraviolet/X-rays/gamma rays

    Q2 As frequency increases, so does the energy of the wave.

    Q3 X-rays are very energetic and can damage cells.

    Q4 For example: radio: TV broadcasts; microwaves: mobile phone communications, satellite communications

    including satnav; infrared: TV remote control, toaster; visible: optical fibre communications; ultraviolet: sterilising

    water; X-rays: airport security; gamma rays: medical imaging, treating cancer.

    Activity 3 (High demand)

    Q1 Both carry energy; both travel at the same speed; photons in a beam of radiation have the same frequency as

    the waves frequency; neither has mass.

    Q2 The wave is continuous, whereas photons are discrete packets of energy

    Q3 The wave properties of light give everyday effects that have been observed for thousands of years. The

    observations that led to the photon model were observed only in the 1890s, and were seen only using scientific

    equipment for that purpose.

    p2_02 Radiation intensity

    Student Book answers

    Q1 No photons arriving from the Sun.

    Q2 The number of photons and the energy of each photon/frequency of the electromagnetic wave.

    Q3 The candle emits fewer photons than the spotlight; the frequency of light from a candle (yellow) is lower than

    the frequency of blue light and so the photons carry less energy; the intensity is less at greater distances.

    Q4 The Sun is very much closer to Earth than Cygni is; intensity depends on distance.

    Q5 Three times lower.

    Q6 The area that the light spreads over increases 9 times (3 3), so the light is 9 times less intense.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Worksheet answers

    Activity 1 (Low demand)

    Change made to the lighting Change to the

    number of photons

    Change to the energy

    of each photon

    A spotlight is made brighter but stays

    the same colour

    More photons No change

    A spotlight is made dimmer but stays

    the same colour

    Fewer photons No change

    A spotlight colour changes from red to

    green, but stays the same brightness

    No change More energy

    A spotlight colour changes from blue to

    green and gets dimmer

    Fewer photons Less energy

    A spotlight colour changes from blue to

    green and gets brighter

    More photons Less energy

    A spotlight colour changes from yellow

    to red and gets dimmer

    Fewer photons Less energy

    Activity 2 (Standard demand)

    Q1 Ultraviolet radiation

    Q2 Ultraviolet radiation

    Q3 B

    Q4 Earth; it is nearer the Sun.

    Q5 Less well; fewer solar photons arrive.

    Activity 3 (High demand)

    Q1 a) 60 J; b) 60 J

    c) The energy transferred from the lamp does not change it is the intensity that depends on distance from the

    lamp.

    Q2 a) Winter 3600 J; summer 4800 J

    b) The solar panels provide significantly less energy per second in winter; people usually need more heating

    and hot water in winter.

    Q3 The satellite is (slightly) closer to the Sun when it is in daylight; the satellite is above the Earths atmosphere,

    which absorbs some radiation.

    p2_03 Ionisation

    Student Book answers

    Q1 Ions are charged and atoms are not; ions are charged and molecules are not.

    Q2 a) Positive; b) negative

    Q3 An atom absorbs an X-ray photon. An electron is knocked out of the atom. A positive ion is formed.

    Q4 The photons of radio waves do not carry enough energy to cause ionisation; gamma photons do.

    Q5 Ionisation in the body is a problem because it changes molecules in cells and so changes processes in cells,

    e.g. causing cancer, or even the death of the cell.

    Q6 Gamma radiation; it is the most energetic form.

    Worksheet answers

    Activity 1 (Low demand)

    Q1 Helium atom; iodine ion; carbon dioxide molecule; magnesium ion; oxygen molecule.

    Q2 Atoms can absorb energy from photons of electromagnetic waves. If the photon has enough energy, an

    electron is knocked out of the atom. The atom becomes an ion. This process is called ionisation.

    When a lithium atom loses an electron, it becomes a positively charged ion.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    When a chlorine atom gains an electron, it becomes a negatively charged ion.

    Activity 2 (Standard demand)

    Q1

    electromagnetic radiation passes through the substance

    photons of a radio wave, of

    microwave radiation, of infrared and

    of visible light has too little energy

    photons of high-frequency

    ultraviolet, X-rays or gamma rays

    can have enough energy

    they cant ionise molecules they can ionise molecules

    photons are absorbed by molecules

    electrons are

    knocked out of

    molecules

    molecules are

    left as positively

    charged ions

    Q2 Sketches should include:

    radio photons shown with longer wavelength than X-ray photons;

    the same number of radio photons enter and leave the gas (none are absorbed), but fewer (or no) X-ray

    photons emerge from the gas;

    atoms remain as atoms after radio waves pass, but atoms become ions and electrons after X-rays absorbed.

    Activity 3 (High demand)

    (These are only a selection of possible answers. Answers should include as much detail as possible.)

    Gamma: yes; e.g. kills cells; can cause cancer; ionises DNA; photons from stars ionise gases and can interfere

    with our atmosphere

    X-ray: yes; e.g. can kill cells; can cause cancer such as leukaemia; ionises DNA; photons from stars ionise gases

    and can interfere with our atmosphere

    Ultraviolet: yes (high frequency/energy only); e.g. high-energy ultraviolet can damage DNA and ionise nitrogen and

    oxygen in the atmosphere

    Visible, infrared, microwave: no

    p2_04 Effects of ionising radiation

    Student Book answers

    Q1 The gamma rays can penetrate to these cells and ionise molecules.

    Q2 X-rays are less energetic than gamma rays.

    Q3 They absorb X-rays and gamma rays.

    Q4 X-rays and gamma rays can penetrate the body and form images of organs and tissues.

    Q5 More willing to accept risks (of side effects) for a short time and if there is a known problem.

    Q6 People are more familiar with travelling by car; they also feel more in control.

    Worksheet answers

    Activity 1 (Low demand)

    Q1 Advantage: can diagnose conditions without operating; disadvantage: very slight increased cancer risk.

    Q2 Lead apron; short exposure time to X-rays; low dose of X-rays (compared to CT scan)

    Q3 Radiographer is repeatedly exposed to X-rays in his/her work; accumulated time of exposure increases the risk.

    Q4 Advantage: provides very detailed 3D image; disadvantage: increased cancer risk.

    Q5 X-rays are absorbed by cells, damaging them by ionising their molecules

    Activity 2 (Standard demand)

    The leaflet should include these points:

    the radiographer is at higher risk than the general public because they are exposed for longer periods of time

    and any damage caused by exposure is cumulative

    the radiographer is at risk when the equipment is switched on and X-rays are being produced, and if they are

    near the beam (and exposed to high levels of radiation)

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    the main principles of protection are to limit the time of exposure, to keep a safe distance away (e.g. in another

    room), and/or to stay behind shielding, which absorbs the radiation

    the extra risk of harm is very small if precautions are followed, as the additional exposure is very small.

    p2_05 Microwaves

    Student Book answers

    Q1 Radiation is absorbed and heats the cell till it is damaged or killed.

    Q2 Time of exposure; intensity of radiation.

    Q3 To avoid people being exposed to more radiation than necessary.

    Q4 How many calls you make a day; how many years you use the phone for; whether you text or call; the strength

    of the signal.

    Q5 No clear evidence has emerged of a change in risk, over many years of studying large samples of people who

    use mobile phones; the level of microwave radiation at the base of masts is tiny.

    Q6 Either yes, with a good reason e.g. young childrens cells are more susceptible to damage

    or no, with a good reason e.g. the risk is very low and the benefits for the community may be very great.

    Worksheet answers Activity 1 (Low demand)

    Less; less; less; smaller; longer

    Activity 2 (Standard demand)

    These points should be covered:

    Food containers should be non-metal because microwaves reflect off metals (so the food wont cook properly

    and there may be sparks).

    A more powerful microwave oven means shorter heating times because the energy is transferred more quickly.

    Larger quantities of food need longer heating times, because more energy must be absorbed.

    It is the water molecules that absorb microwaves, so dry food needs to have water added.

    After heating, food and containers may be very hot in places.

    Microwaves may escape.

    Activity 3 (High demand)

    Q1 Advantages: communication with friends/family/colleagues; communication in emergencies; checking

    information; entertainment (games, apps etc.); use as camera.

    Short-term disadvantages: bullying; expense; mugging/injury/other crime risk; increased risk of car crash.

    Long-term disadvantages: possible cancer risk; possible infertility risk; increased risk of benign tumours.

    Q2 People are happy to take a risk if they feel they are in control (choosing to use the phone) or if it is a very

    familiar setting, or if there is a clear short-term advantage.

    Q3 People are less willing to accept a risk if they have no control (many people cannot move house easily) and if

    the risk to them seems higher than for the general population.

    Q4 People tend to overestimate an unfamiliar risk (cancer from microwave radiation); if a hazard takes a long time

    to have an effect, but has a long-term impact on the population, it is sensible to investigate this thoroughly to

    limit potential risk; governments may be mindful of possible future damages claims if they do not act now, and it

    turns out there is real problem.

    p2_06 Ozone

    Student Book answers

    Q1 Ultraviolet

    Q2 Absorbs ultraviolet radiation, so less ultraviolet reaches Earth.

    Q3 It is not possible to reduce all risks (exposure to ultraviolet radiation is not the only cause of skin cancer); nor

    can we limit exposure to the sun to zero without suffering other health risks.

    Q4 By studying the health records of thousands of people living in regions affected most by changes in the ozone

    layer.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Q5 Ozone is produced if high-energy ultraviolet radiation is absorbed; but ozone splits into oxygen if low-energy

    ultraviolet radiation is absorbed.

    Q6 It is re-emitted as infrared radiation.

    Worksheet answers

    Activity 2 (Standard demand)

    Health benefit of exposure to a small amount of ultraviolet radiation: formation of vitamin D; no risk with exposure to

    small amount of UV so no control needed except of time of exposure.

    Harm caused by exposure to strong ultraviolet radiation for a few hours: sunburn; reduce exposure time between

    11am and 3pm in summer; wear sun cream and sun hat; keep inside or covered up or in shade when the sunlight

    is very intense.

    Harm caused by exposure to strong ultraviolet radiation over many years: skin cancer; people who work outside or

    visit hot countries without taking adequate precautions are at high risk and should limit exposure; wear protective

    clothing and use sunscreen routinely.

    Activity 3 (High demand)

    Q1 High-frequency ultraviolet radiation: absorbed by oxygen; ozone and infrared radiation produced.

    Lo- frequency ultraviolet radiation: absorbed by ozone; oxygen molecules, oxygen atoms and infrared radiation

    produced.

    Q2 Additional information depends on students research e.g. nitrogen oxide and ozone react to form nitrogen

    dioxide (e.g. at ground level near traffic); chlorine can react and convert ozone to oxygen (which is damaging as

    it does not absorb ultraviolet radiation effectively).

    Ozone completely absorbs UV-C (the highest-energy ultraviolet radiation) UV-B is less--energetic ultraviolet

    radiation, which is still harmful to humans and is mainly absorbed by the ozone layer. Where the ozone layer is

    thinner (the ozone hole), more UV-B passes through to Earth and there is a higher incidences of skin cancer

    etc.

    UV-A is the least-energetic ultraviolet radiation, but is still damaging to humans. It is not absorbed by the ozone

    layer, but contributes less to the harmful effects than UV-B.

    p2_07 The greenhouse effect

    Student Book answer

    Q1 The Earths atmosphere absorbs infrared radiation from the Earth and warms up; it re-radiates infrared and

    warms up the Earth.

    Q2 a) The atmosphere reflects some radiation from the Sun back into space, reducing the amount reaching Earth.

    b) The atmosphere absorbs radiation from the Earth and re-radiates it back to Earth, and also reflects some

    radiation from Earth back to Earth, reducing the amount of radiation leaving Earth.

    Q3 Ice cube; it is coldest.

    Q4 Less

    Q5 Depends on cloud cover, pressure and temperature.

    Q6 The growth of people does not cause the number of exams they take (nor the other way round). However, they

    are linked because teenagers normally have a growth spurt and also take GCSEs, A-levels and other exams.

    Worksheet answers

    Activity 1 (Low demand)

    a) reflects; b) transmits; c) absorbs; d) reflects; e) absorbs; f) transmits

    Activity 2 (Standard demand)

    Possible answers: a) Clues 1, 6; b) 2, 4; c) 3, 4; d) 3, 7, 8

    Activity 3 (High demand)

    Q1 All factors are correlated they all increase at the same time. Encourage students to look carefully at data, to

    say if the correlation is close (e.g. the factors increase at the same rate).

    Q2 There is more than one correct answer for these. For example:

    a) Burning fossil fuels releases carbon dioxide directly into the atmosphere, so this could be a direct causal link.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    b) Economic growth means people burn more fossil fuels to keep warm/drive more/ buy more things built in

    factories powered using fossil fuels etc. and this causes more carbon dioxide to be released directly into the

    atmosphere.

    c) If everybody needs to burn fossil fuels to keep warm/cook/move around, more people means more carbon

    dioxide emissions released directly into the atmosphere.

    Q3 For example, erupting volcanoes; deforestation; warming oceans.

    p2_08 Carbon cycling

    Student Book answers

    Q1 Photosynthesis; growth of plants

    Q2 Respiration; burning fossil fuels

    Q3 We are burning fossil fuels in large quantities; and cutting down trees (deforestation).

    Q4 Stayed the same; but the proportion existing as carbon dioxide in the air has increased.

    Q5 When one thing changes there will be an increase or decrease in the other thing.

    Q6 Yes; morning time is when the sun rises and as it rises the intensity of its radiation falling on the Earth

    increases, so increasing the temperature. Other factors that affect this correlation are specific weather events

    that take place.

    Worksheet answers

    Activity 1 (Low demand)

    Releases carbon into the atmosphere: respiration by animals; respiration by plants; burning fossil fuels; forest fires;

    volcanic eruptions

    Removes carbon from the atmosphere: photosynthesis by phytoplankton in oceans; photosynthesis by plants on

    land; diffusion of carbon dioxide into the surface of oceans; gases absorbed by oceans; fossilisation of animal and

    plant remains.

    Activity 2 (Standard demand)

    The carbon cycle 500 years ago should include: photosynthesis (on land and in oceans), respiration (on land and in

    oceans), fossilisation, burning, dissolving (into the oceans).

    The modern-day carbon cycle should also include burning of fossil fuels, deforestation, increased respiration (due

    to population growth and farming methods).

    Q1 a) Burning fossil fuels, deforestation, (also increased respiration).

    b) Possibly less photosynthesis due to deforestation and changes in land use, but this may be offset in other

    ways.

    Q2 a) Burning fossil fuels; respiration

    b) Photosynthesis; dissolving

    Q3 Students should identify that processes that release carbon dioxide into the atmosphere now take place to a

    greater extent than before, so the concentration of carbon dioxide in the atmosphere has been increasing.

    Activity 3 (High demand)

    Q1 a) All of these things are correlated; they have all increased during the last 100 years.

    b) Possible reasons: increased population leading to increased deforestation to clear land; increased burning of

    fossil fuels.

    Q2 It is harder to claim a cause than a correlation because a direct link needs to be found, and other possible

    causes discounted. While we can confidently say that burning more fossil fuels causes an increase in carbon

    dioxide emissions, it is harder to say that burning more fossil fuels causes global temperatures to increase

    because there is no direct link, and also because there have been increases in global temperatures in the past,

    due to other causes.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    p2_09 Global warming

    Student Book answers

    Q1 Global warming has occurred at the same time as increasing levels of greenhouse gases; it is believed that the

    increase in greenhouse gases in the atmosphere is causing an increase in global surface temperature directly.

    Q2 Increasing average worldwide temperature; climate change and more severe weather events; melting polar ice

    caps; melting glaciers; rise in sea levels.

    Q3 Additional water in the oceans from melting glaciers on land; water in the oceans may expand as it warms.

    Q4 If something is done now, we may be able to limit the effects and impact of global warming.

    Q5 Educate people about the future effects of not changing certain behaviours; they can monitor the effects of the

    green taxes on our choices and inform people of any positive effects.

    Q6 Benefits: we can link different data and test different assumptions to predict the future impact of global warming

    Problems: there are so many factors affecting the climate that simplifications and assumptions need to be made

    when testing models.

    Worksheet answers Activity 1 (Low demand)

    Q1 Scientists believe the increase in levels of greenhouse gases in the atmosphere is causing global warming.

    Q2 The effects of global warming include smaller glaciers, rising sea levels, and more extreme weather patterns.

    Q3 Sea levels will rise because glaciers (ice sheets on land) will melt (so more water will find its way into the sea).

    Q4 e.g. A cold winter in the UK is a localised and short-term weather event that cannot be used as evidence of a

    global trend.

    Q5 e.g. Global warming happens naturally on some other planets, but is partly caused by the actions of humans on

    Earth.

    Activity 2 (Standard demand)

    Answers depend on students research. Students may emphasise different aspects of the same problems or may

    describe different groups/areas vulnerable to an effect. Examples:

    a) People living in regions where famine and drought are regular occurrences but are becoming hotter and drier.

    b) People living in regions where rainfall is increasing and severe storms are more frequent.

    c) People living on low-lying islands, or in coastal/delta regions.

    Activity 3 (High demand)

    Students are likely to find that solutions acceptable to everyone are very hard to identify; controlling global warming

    itself is a long-term process that can only happen if all countries comply; reducing the effects of climate change

    may be a more localised problem but steps taken may not be adequate; the costs of such action are likely to

    impact some groups of people disproportionately.

    p2_10 Electromagnetic waves for communication

    Student Book answers

    Q1 Radio waves; microwaves; infrared radiation; visible light.

    Q2 Carry infrared or visible light signals very long distances without the radiation being absorbed.

    Q3 Cannot travel long distances in air so would not reach the satellite.

    Q4 The carrier wave frequency.

    Q5 So they can broadcast at the same time without interfering with one another.

    Q6 Still match the shape of the sound signal it is transmitting; the carrier waves (shown in blue) would have a

    longer wavelength.

    Worksheet answers

    Activity 1 (Low demand)

    Q1 Radio waves; microwaves; infrared; visible.

    Q2 Lower frequency and energy.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Activity 2 (Standard demand)

    Q1 Radio waves: radio, terrestrial TV

    Microwaves: mobile phone, satnav, satellite TV

    Infrared: remote control, cable TV, land line telephone, automatic sensor

    Visible: warning light

    Q2 Radio waves and microwaves.

    Activity 3 (High demand)

    Students diagrams should show the waves before modulation, after modulation and after decoding (along the lines

    of Figure 3 on Student Book p. 255) and with clear annotation.

    Practical sheet answers Independent variable thickness of material; dependent variable if the infrared is absorbed or not; control

    variables type of material; distance from TV; the remote controller used; how the readings are taken.

    Possible method: Point the remote control straight at the TV from a distance of 2 m. Check that the TV can receive

    the signal. Put a 2 cm thick sample of the material directly in front of the remote control. The two should be very

    close and the signal must travel through the material. Check if the TV receives the signal. Increase the sample

    thickness by 2 cm each time until the signal is no longer received. Repeat with another material.

    p2_11 Digital signals

    Student Book answers

    Q1 Digital signals only have two discrete values: 0 and 1; analogue signals can have any value.

    Q2 When the buzzer is turned on, the signal has a value of 1; when it is off, the signal has a value of 0; turning the

    buzzer on and off creates a digital signal.

    Q3 When the digital signal changes, the carrier wave is turned on or off.

    Q4 To change the digital signal back into a copy of the original analogue sound or image.

    Q5 It interferes with signals so that they become distorted or unclear.

    Q6 Checks if the received signal has a value close to the allowed range of values; if not, that part of the signal is

    rejected as noise.

    Worksheet answers Activity 1 (Low demand)

    Q1 Analogue; digital; analogue; digital

    Q2 Digital readings have only two values: 1 or 0 (on or off); no in-between values.

    Q3 The detector needs only to judge whether the digital signal is on or off and for how long; it doesnt need to

    measure in-between values.

    Activity 2 (Standard demand)

    Q1 It is continually and rapidly changing.

    Q2 The electromagnetic wave can have two values only (on, 1, and off, 0).

    Q3 Changes the electromagnetic pulses back into a copy of the original sound signal.

    Q4 The digital signal cannot carry all the information from the original signal; the analogue signal may change

    between each measurement.

    Activity 3 (High demand)

    Q1 An unwanted signal mixed in with the original signal; due to interference with other transmissions or picking up

    random signals.

    Q2 Noise can cause an analogue recording to have hiss; if the volume is turned up, the hiss level increases too;

    the analogue image is likely to be lacking clarity with less contrast and more smudges and marks that are not

    part of the original image.

    Q3 Digital signals are either on or off, so an unwanted signal is easier to spot and remove; analogue signals can

    have any value so it is harder to spot an unusual value and remove it.

  • OCR 21st Century Science P2 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    p2_12 Storing digital information

    Student Book answers

    Q1 The amount of digital information in the form of binary digits (1 byte = 8 digits).

    Q2 7 bytes; one byte per letter).

    Q3 When more data is stored, the quality of an image improves.

    Q4 We can store more data on devices than previously.

    Q5 Can be processed by computer and changed into different forms, e.g. sound, text; it can be stored and sent

    between different devices.

    Q6 Can be shared by users and transmitted (e.g. by email) and used on different computers for different purposes.

    Worksheet answers Activity 1 (Low demand)

    Q1 A: 384; B: 96

    Q2 A: 384; B: 96

    Q3 A; the picture on the smallest grid size

    Q4 Higher-quality images use more pixels.

    Activity 2 (Standard demand)

    Generally the software can edit files in these formats MP3, WMA, WAV, OGG, Windows Media.

    The software can record new files from different input devices such as microphone, sound card etc; it can edit

    the file (cut, paste, copy, delete, mix, etc.) and can apply different effects (e.g. delay, fade, etc.); it can save

    files onto different devices (e.g. CDs).

    People who could use this include DJs, radio and TV sound engineers, music technicians, etc.

    Activity 3 (High demand)

    The report should include points like these:

    Viewers bigger range of programmes; better quality; more interactivity; but may need to upgrade equipment

    and retune; may not receive a strong signal.

    Broadcasters opportunity to broadcast more programmes; can broadcast several simultaneous events, e.g.

    sports events.

    Manufacturers and retailers more sales as people need to upgrade; some stock becomes obsolete.

    The country as a whole enables the UK to compete internationally in the field.

    Overall beneficial for the majority of people, but some people will be forced to invest in costly new equipment

    and some may have a weaker signal than before.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Physics Module P3 Answers

    p3_01 Energy sources

    Student Book answers

    Q1 A primary energy source is used in the form it is found; a secondary energy source is produced from a primary

    energy source .

    Q2 We now use electricity and more forms of transport; reserves of natural gas have been found; we have the

    technologies to extract energy from nuclear fuel; etc.

    Q3 Fossil fuels take millions of years to produce; we are using them quicker than they are forming.

    Q4 They emit carbon dioxide, a greenhouse gas.

    Q5 a) Mining destroys the local habitat and produces waste.

    b) Burning fossil fuels produces pollutants.

    c) Flue ash is produced in large quantities and contains harmful substances.

    Q6 Our use of fossil fuels has increased dramatically in the last century.

    Worksheet answers Activity 1 (Low demand)

    Q1 Primary: coal, solar energy, uranium, waves, wind power, wood

    Secondary: battery, mains electricity, ethanol, steam power

    Q2 Energy sources that do not need processing (apart from extraction and refining) are primary energy sources.

    Secondary energy resources have been processed (e.g. changed into a different product).

    Activity 2 (Standard demand)

    Q1

    Use of energy 1890 Now

    Travel e.g. walking, horses; trains e.g. cars, buses, planes

    Heating and cooking e.g. coal, wood e.g. electricity, gas

    Products e.g. goods made locally or at home e.g. goods manufactured in

    factories; many goods travel

    across the world; many items

    have short lifetimes

    Leisure and communication e.g. games/music at home,

    communication by letter or in

    person

    e.g. travel, TVs, computers, mobile

    phones

    Q2 We are using electricity for activities that we used to do in person. We are travelling further and more often, and

    using modes of transport not in common use 100 years ago. We are producing fewer goods locally and in the

    home; most goods are factory made, sold in packaging and travel long distances; they are relatively cheap so

    we tend to replace items rather than mend them, etc.

    Activity 3 (High demand)

    Credit any relevant and correct information, clearly presented. For example:

    Advantages: reliable; found in many countries; straightforward to use

    Disadvantages: damage from mining; waste products to dispose of; emissions that contribute to acid rain and

    global warming; oil spills

    Ways of reducing the impact: develop new mining techniques; improve methods of refining ore; find uses, e.g. in

    the building industry, for waste products; develop safer transportation methods, e.g. better designed boats or more

    pipelines; scrub/clean the coal to remove impurities before burning it; use carbon storage techniques to capture

    carbon dioxide rather than releasing it to the atmosphere; use more gas and less coal.

    p3_02 Power

    Student Book answers

    Q1 a) 120 J; b) 480 J

    Q2 438 kWh

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Q3 920 W

    Q4 4.8 W

    Q5 10 A in America; 4.78 A in the UK; the current is larger in America so there is a bigger risk of overheating.

    Q6 The kettles may have different powers.

    Worksheet answers Activity 2 (Standard demand)

    Q1 Increasing the power increases the current used.

    Activity 3 (High demand)

    Q1 a) 0.1 kWh

    b) 0.43 A

    c) The rate of energy transfer by the 100 W bulb is 5 times that of the 20 W bulb.

    Q2 a) 0.3 kWh

    b) 5.2 A

    c) 10 minutes (possibly very slightly less because there is less time for energy to be wasted in transfer to the

    surroundings)

    Q3 a) 0.475 kW

    b) 33.6 kWh used by the fridge in one week (0.2 kW 24 hours 7) and 2.85 kWh (0.95 kW 3) used by the

    washing machine, so the fridge uses more energy.

    p3_03 Ionisation

    Student Book answers

    Q1 An electric current.

    Q2 Some energy is changed in any energy transfer into non-useful forms of energy (e.g. heat), which spread to the

    surroundings.

    Q3 Depending on the action the energy is used for, it can be used in very small amounts or very large amounts.

    Q4 Units; equivalent to kWh (kilowatt-hours).

    Q5 a) 1000 units; b) 1600 pence; c) 16

    Q6 a) 7.5 kWh; 120p or 1.20

    b) 0.25 kWh; 4p

    c) 0.36 kWh; 5.76p

    Worksheet answers Activity 1 (Low demand)

    For example:

    Equipment Useful energy transfer

    From electrical energy to

    Non-useful energy transfer

    From electrical energy to

    hairdryer / fan

    heater

    the air as heat the surroundings as sound

    radio the ears as sound the surroundings as heat

    lamp the surroundings as light the surroundings as heat

    TV / computer

    screen

    the eyes (and ears) as light (and sound) the surroundings as heat

    In the non-useful transfers, energy is transferred to surroundings often as heat.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    p2_04 Energy diagrams

    Student Book answers

    Q1 29%

    Q2 Fridge-freezer and lighting.

    Q3 a) Laptop, fridge, LCD TV, hand blender, washing machine.

    b) The fridge is on all the time.

    Q4 Total energy input is 100 J; total energy output is 100 J; the energy input is the same as the energy output

    energy is conserved.

    Q5 a) On the Sankey diagram the input arrow splits into two output arrows one (to the right, light) is the width

    of the input arrow, and one (downwards, heat) is the width of the input arrow.

    b) The width of the light energy arrow is wider; showing more of the energy is transferred as light.

    Worksheet answers Activity 1 (Low demand)

    Q1 800 kWh in August; 1200 kWh in February.

    Q3 The bar chart is better for comparing changes in how energy is used in each month.

    Q4 The stacked bar chart is better for comparing the total energy used in each month.

    Activity 2 (Standard demand)

    A 75% gravitational energy and 25% thermal energy.

    B 25% light, 25% sound and 50% heat energy.

    C 30% kinetic, 60% heat and 10% sound energy.

    Activity 3 (High demand)

    Q1 Light energy arrow 1 cm thick to right; heat energy arrow 3 cm thick downwards.

    Q2 Kinetic energy arrow 2 cm to right; heat energy arrow 1.6 cm downwards; sound energy arrow

    0.4 cm downwards.

    Q3 Kinetic energy arrow 1.6 cm to right; sound energy arrow 0.8 cm to right; heat energy arrow 1.6 cm downwards.

    p3_05 Efficiency

    Student Book answers

    Q1 5% or 0.05

    Q2 0.8

    Q3 30%

    Q4 Any sensible suggestions e.g. walk to school; turn off lights; dont leave equipment on standby.

    Q5 More efficient goods use less energy; users pay lower electricity/fuel bills.

    Q6 Recycling methods developed; use of renewable fuels for transport; use of renewable resources to generate

    electricity.

    Q7 Less land is used to grow or produce raw materials; less land for landfill sites; more land can be used for food

    production or housing; less energy used in processing raw materials; less waste.

    Worksheet answers Activity 1 (Low demand)

    Q1 kettle (0.93, 93%); iron (0.90, 90%); diode lamp (0.80, 80%); fan (0.75; 75%); washing machine (0.70, 70%);

    lamp (0.04, 4%)

    Q2 Some energy is always transferred to the surroundings.

    Activity 2 (Standard demand)

    a) An Energy Performance Certificate indicates how efficiently a house or flat uses energy and what its

    environmental impact is; one is needed when a house or flat is to be sold or rented.

    b) The efficiency rating and the environmental impact rating (based on CO2 emissions) now, and the potential

    ratings if energy-saving measures are put in place.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    c) Results are prepared after a survey of the building and its heating system etc.

    d) The certificate includes recommendations that can be used to target specific measures (e.g. more insulation or

    double glazing).

    e) It isnt always practical or affordable to put these measures in place, especially in older homes.

    Activity 3 (High demand)

    The content of the leaflet/poster depends on the choice made by the student. Look for a clear description of the

    problem being solved, and how the new scientific developments have reduced the impact on the environment.

    p3_06 Generators

    Student Book answers

    Q1 In power stations.

    Q2 A generator has a magnet and coil of wire, one of which spins relative to the other.

    Q3 Electromagnets can be much stronger than permanent magnets.

    Q4 To provide energy to make turbines spin.

    Q5 To provide more energy for more generators.

    Q6 The electricity produced at any power station can be used anywhere, reliably and safely.

    Worksheet answers Activity 1 (Low demand)

    Q1 By spinning the generator more quickly.

    Q2 By spinning the generator more quickly.

    Q3 Depending on the generator may be the coil or the magnet .

    Activity 2 (Standard demand)

    Q1 Coal, biomass, gas.

    Q2 The electromagnet in the middle spins and is surrounded by stationary copper bars in which the current flows.

    Q3 More is used when a larger voltage is produced.

    Activity 3 (High demand)

    The outcomes depend on what students find. Regulation is needed for several reasons safety and consistency;

    coordination; affordability; accountability in case of disruptions to supply, etc. Students should identify a number

    of benefits and explain why regulation is helpful in each case.

    p3_07 How power stations work

    Student Book answer

    Q1 To spin the turbine.

    Q2 To spin the generator.

    Q3 Furnace, set of pipes, turbine, generator.

    Q4 Falling water spins the turbine in a hydroelectric power station, rather than steam.

    Q5

    Q6 a) They both have boilers, turbines, generators.

    b) Nuclear reactor (with fuel rods and moderator), concrete shielding, water pressuriser.

    Worksheet answers Activity 1 (Low demand)

    Primary fuels heat water in a power station The water changes to steam The steam is sent through pipes to

    spin a turbine The turbine is connected to a generator The generator spins to generate electricity

    falling water spins turbine spins generator

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Activity 2 (Standard demand)

    Here are possible responses. The parts can be seen labelled in the Student Book.

    Boiler: This is where steam is

    produced from water

    Cooling tower: Its job is

    to remove excess heat

    Pipes: Their job is direct steam to spin

    the turbine

    Generator: Its job is to generate

    electricity

    Turbine: Its job is to

    spin the generator

    Furnace: This is where coal is burnt

    Outflow: Its job is to release water

    after it passes through the turbine

    Dam: Its job is to trap

    water in the reservoir

    Pipes: Their job is to direct and control

    the water that spins the turbine

    Generator: Its job is to generate

    electricity

    Turbine: Its job is to

    spin the generator

    Reservoir: Its job is to store water

    Activity 3 (High demand)

    Q1

    Reactor: safely contains fuel rods

    and control rods

    Fuel rods: produce

    heat (from nuclear

    fission)

    Control rods: control the amount of heat

    being produced

    Boiler: where steam is produced

    from water

    Turbine: spins the

    generator

    Generator: generates electricity

    Q2 a) Possible responses:

    Identical features: all make a generator turn; all produce electricity from a generator; all feed electricity into

    National Grid power lines.

    Similar features: all are large installations that have a negative impact on the environment; all are hazardous.

    Different features: coal-fired power stations burn large quantities of coal to release heat; they produce ash and

    soot; they release greenhouse gases and chemicals that cause acid rain; gas-fired power stations burn large

    quantities of gas that arrive through pipelines; they produce greenhouse gases and chemicals causing acid

    rain; hydroelectric power stations need large quantities of water to fall from a higher level; they can be turned

    on and off much more quickly; nuclear power stations use two different sets of pipes so that the water that

    produces steam does not circulate in the reactor (reduces the chance of contamination); they have concrete

    shielding to reduce the chance of radiation being released; the water pressuriser allows the water to be heated

    to super-high temperatures; the moderator and coolant are used to control the temperatures in the reactor.

    b) Coal-fired advantageous when coal is cheap and plentiful; if there is no suitable landscape for building

    hydroelectric scheme.

    Gas-fired advantageous where gas supplies are cheap and reliable; can be chosen in preference to coal due to

    the increased efficiency and reduced pollution; used where landscape not suitable for hydroelectricity.

    Hydroelectric advantageous where coal or gas is expensive; there is a desire to reduce carbon emissions; the

    landscape is suitable to build dams or utilise mountain lakes.

    Nuclear advantageous where coal or gas is expensive; where there is easy access to nuclear fuels; a desire to

    reduce carbon emissions; no suitable landscape for building hydroelectric scheme; a location away from

    populated areas so risks are reduced.

    p3_08 Waste from power stations

    Student Book answers

    Q1 Radioactive waste emits harmful radiation.

    Q2 Some waste has a higher level of radioactivity than other waste; so needs to be stored away from people.

    Q3 Contamination is when the radioactive substance mixes with a material; irradiation is when the material is in the

    path of ionising radiation coming from the radioactive substance.

    Q4 Contamination is reduced by storing radioactive waste as solid substances; contamination and irradiation are

    reduced by using shielding.

    Q5 For example, flying off on holiday.

    Q6 It is important to estimate risks correctly so we take suitable precautions.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Worksheet answers Activity 1 (Low demand)

    Most radioactive waste is thrown out with household rubbish false

    Over time, radioactive waste becomes less radioactive true

    It is safe to store radioactive waste in warehouses false

    Some radioactive waste is recycled and reused true

    Radioactive was emits ionising radiation true

    All radioactive waste is highly dangerous false

    Activity 2 (Standard demand)

    Q1 a) Putting diesel into a car that runs on petrol contamination. Ideas to reduce: warning signs to reduce human

    error; different size/shaped nozzles to prevent contamination; on realising error dont run the engine, to reduce

    chance of fuels mixing.

    b) Exposure to sunlight irradiation. Ideas to reduce: stay out of the sun as much as possible to reduce

    exposure time; cover up with clothes and wear a hat and sunglasses to shield.

    c) Standing near a bonfire contamination (with smoke). Ideas to reduce: stand upwind not downwind of the

    fire to reduce contamination; stay indoors to shield; wash hair, clothing etc. afterwards to decontaminate.

    Also irradiation from the bonfire. Ideas to reduce: move further away to reduce intensity; stand behind

    something to shield; stay indoors to shield or move indoors to reduce exposure time.

    Q2 It is harder to control or remove contamination; it is mixed in with other substances; irradiation can be controlled

    by distance or shielding.

    Activity 3 (High demand)

    In decreasing order of risk (figures in brackets give the lifetime chance of dying from these causes):

    smoking 10 cigarettes per day (1 in 200); influenza (1 in 500); road accident (1 in 8000); playing football (1 in

    25 000); accident at home (1 in 26 000); accident at work (1 in 43 000); hit by lightning / radiation from nuclear

    power station (1 in 10 000 000).

    p3_09 Renewable energy sources

    Student Book answers

    Q1 Renewable energy resources will not run out.

    Q2 Wind; hydroelectric; tidal; wave.

    Q3 Benefit: renewable; can generate large amounts of electricity quickly.

    Problem: cause flooding; costly to build; dams must be maintained; greenhouse gases are emitted in the initial

    stages.

    Q4 Large batteries could store surplus energy produced.

    Q5 Only a small number of sites can generate useful amounts of energy from waves; the technology is still being

    developed.

    Q6 Credit well thought-out answers with explanations. For example:

    a) Using wind turbines reduces greenhouse gas emissions, but the supply of electricity is expensive and

    unreliable. We need a reliable source of electricity, so the benefits of using only wind turbines do not outweigh

    the additional cost of the electricity generated, or the problems of unreliable supply. Wind turbines are probably

    best used to top up other forms of electricity generation.

    b) Using hydroelectric schemes reduces greenhouse gas emissions once established, but they are expensive

    to build and flood large areas; this is probably acceptable because the electricity is generated in large quantities

    and reliably.

    Worksheet answers Activity 2 (Standard demand)

    Students reports should include points such as the following.

    Solar energy: e.g. on satellites; produces energy directly; no pollution; can be used in remote areas; expensive per

    unit produced; no use at night.

    Hydroelectricity: in mountainous regions; reliable source of large amounts of energy; floods large areas; dams need

    maintaining.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Wind power: in coastal and hilly areas; can be sited in many areas; no pollution; weather dependent; dilute energy

    source.

    Wave energy: on coastline; no pollution; can be used in remote areas; only small amounts of energy produced;

    weather dependent; technology still being developed.

    Tidal: in large estuaries; reliably produces large amounts of energy; only suitable in some areas; high cost of

    construction; effect on shipping and wildlife.

    Activity 3 (High demand)

    Points that could be included: larger offshore wind farms generate more electricity than onshore farms but there are

    problems transporting the electricity onshore; offshore wind farms are more expensive to construct and maintain,

    and the effects of the sea on the turbines means they may have a shorter lifespan; these factors will affect the cost

    of electricity for customers.

    p3_10 The National Grid

    Student Book answers

    Q1 Carries electricity from power stations to users.

    Q2 Does not pollute at the point of use; can be transmitted long distances; can be used in many ways.

    Q3 By transmitting electricity at low current and high voltage.

    Q4 230 V is high enough to provide enough power for most of our needs in the home, without providing an

    unacceptably high risk of electrocution; 120 V has a lower risk of electrocution, but it does not provide as much

    power unless the current in the equipment is higher and this increases the fire risk.

    Q5 Some energy is wasted when transmitting the electricity; Sankey diagrams show the average proportions of

    energy transferred in these types of power station; different types of power station input electricity to the Grid.

    Q6 Useful output is 80 kJ; efficiency is 80% (0.8).

    Worksheet answers Activity 3 (High demand)

    Q1 It shows that the power station uses 40 kJ from fuels to produce 15 kJ of electrical energy, so 25 kJ is

    transferred to the surroundings; the National Grid delivers 13.5 kJ while 1.5 kJ is transferred to the

    surroundings from the transmission lines; the delivered energy is split between industrial and non-industrial use,

    6 kJ and 7.5 kJ respectively.

    Q2 Efficiency of power station = 15/40 = 0.375 or 37.5%

    Q3 Efficiency of transmission lines = 13.5/15 = 0.9 or 90%

    Q4 Burn the fuel more efficiently, e.g. use gas power stations that use the heat from burning gases as well as

    steam; allow sensible suggestions such as only generating the electricity that is needed as surplus electricity

    cannot be stored; in the transmission lines, transmit electricity at even higher voltage to reduce current further.

    p3_11 Choosing the best energy source

    Student Book answers

    Q1 Biofuel

    Q2 Reduces greenhouse gas emissions and other forms of pollution; reduces deaths due to their extraction;

    reduces damage to environment.

    Q3 Nuclear power stations are very expensive to build; would not be worth it on a small scale in a remote place.

    Q4 Fossil fuels generate electricity at a relatively low cost per kWh.

    Q5 Hydroelectric schemes produce electricity very efficiently.

    Q6 Wind turbines need replacing more often than coal-fired power stations; many are needed to give a sizeable

    output; but even a large number of them are cheaper to build than a power station; wind is free.

    Coal-fired power stations produce large amounts of electricity per power station relatively cheaply for decades;

    but we must pay for the fuel;, and at the end of their life they are very expensive to replace.

    Wind turbines may be as cost-effective over a long timescale.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Worksheet answers Activity 1 (Low demand)

    Advantage Fossil

    fuels

    Nuclear

    fuels

    Wind

    power

    Energy

    from water

    Solar

    energy

    Large amounts of electricity are generated / / /

    No greenhouse gases are released / / / /

    The energy source is free when used / / /

    The energy source will not run out / / /

    Disadvantage

    The energy source is weather-dependent / /

    Extracting the fuels is dangerous /

    Only some sites are suitable / /

    Using the fuel produces greenhouse gases /

    Extracting and using the fuel causes pollution / /

    The waste is radioactive /

    Causes large-scale flooding /

    Activity 2 (Standard demand)

    Situation 1: wind turbines; other possible options are solar, waves, biofuel generator; reasons are that wind blows

    almost constantly; wind turbines can be easily installed in small areas; there is too little sunshine for high output

    from solar power; wave and biofuel generators are not well developed yet.

    Situation 2: fossil fuel; other possible options are nuclear; wind, biofuel; reasons are that a large amount of

    electricity is needed, and transport links for fuel deliveries is good; the region is too heavily populated for

    nuclear power to be accepted as a safe option; the region is not hilly enough for reliable wind power; biofuel

    generators are not well developed.

    p3_12 Dealing with future energy demand

    Student Book answers

    Q1 Will reduce emissions across the world and so reduce the increase in global warming.

    Q2 Businesses can produce items that work more efficiently, use less energy during development/production, use

    greener methods of transportation, recycle waste, etc.

    Q3 Developing countries have the potential to emit high levels of carbon dioxide even if they are not currently doing

    so; industrialised nations have produced huge emission levels in the past even if they are now cutting

    emissions; this is a global problem that affects everyone.

    Q4 These three countries emit the most carbon dioxide, but the per person emissions (and so average standard of

    living) vary greatly. Also, many countries benefit from imported goods made in China and India, so they would

    be being made unfairly responsible for emissions related to this production and transport.

    Q5 Benefits include less reliance on supplies from one part of the world, or sources that may run out; introducing

    methods causing less environmental damage at an affordable price; keeping supplies reliable, etc.

    Q6 New power stations can take years to come into production once commissioned, but then have a life span of

    decades. Global warming is likely to have serious consequences in the future, unless we reduce it significantly

    now.

    Worksheet answers Activity 1 (Low demand)

    Q1 If everyone at home makes even small changes like turning off unnecessary lights and unused equipment,

    these differences add up across the country.

    Q2 If all shops make changes such as using energy-efficient lights, turning off lights at night and keeping shop

    doors closed, the energy saved and so the reduction in emissions would add up.

    Q3 If factories find more efficient ways of using energy, e.g. using energy-efficient machinery, they can save large

    amounts of energy that makes a really big difference.

  • OCR 21st Century Science P3 Answers

    COLLINS NEW GCSE SCIENCE HarperCollinsPublishers Ltd 2011

    Q4 If cars (even fast ones) are designed with very efficient engines, then they use less fuel and produce less

    emissions.

    Activity 2 (Standard demand)

    There are no right or wrong answers responses should stimulate debate, and students should be able to explain

    why they chose each response. These are some ideas students may consider:

    Q1 Is this a global or a local problem?

    Q2 How fair is a fixed reduction on developed vs developing countries, or countries with changing populations?

    Q3 Should countries reduce emissions per person, or overall?

    Q4 Is it acceptable for one country to retain conveniences, even if other countries cannot achieve these? Should

    countries that caused the problems in the past pay for choices of preceding generations?

    Q5 Should people in less developed countries catch up with developed countries on living standards using cheaper

    older technologies, or should developed countries subsidise more efficient machinery in developing countries?

    Activity 3 (High demand)

    Responses should consider some of these factors: if energy sources contribute to greenhouse gas emissions; how

    reliable their mix of sources would be; if the UK has easy access to these energy sources, their affordability and

    reliability of future supplies; how suited their choices are for the UKs landscape, climate and natural resources.

    Any mix should add up to 100%.