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P1,P2,P3 OCR 21ST CENTURY SCIENCE Revision from BBC Bitesize I want to . Jump to P1 Jump to P2 Jump to P3 Start from beginning Created by green500 TES – PowerPoint PPT presentation

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  • Revision from BBC Bitesize

I want to. Jump to P1 Jump to P2 Jump to
P3 Start from beginning
Created by green500 TES
  • Earth, stars, galaxies and space
  • How the Earth is changing
  • Seismic waves

Earth, stars, galaxies and space
  • Earth, stars, galaxies and space
  • The Earth is one of the eight planets orbiting
    the Sun, and there are many other members of the
    Solar System including asteroids, moons and
    planets. Data provides the answers to many
    questions on this subject, but some questions
    remain unanswered.
  • The Earth and the Universe
  • The Universe is considered to be everything there
    is, though most of it is thought to be empty.
  • Much is now known about the Earth and the place
    of the Earth in the Universe, for example
  • the diameter of the Earth is 12,800km (7,953
  • the diameter of the Sun is 109 times that of the
  • the Earth is 150 million km (93 million miles)
    from the Sun
  • the distance to the nearest star is four light

Earth, stars, galaxies and space
  • The Solar System
  • The Earth is just one of the eight planets
    orbiting the Sun, which is a star. The orbits all
    lie in the same plane, and the planets all go
    round in the same direction.
  • There are many other members of our Solar System
  • asteroids are much smaller than planets, and
    orbit the Sun. Most of the asteroids are between
    the planets Mars and Jupiter, but some come close
    to the Earth
  • moons orbit planets. Most are tiny. Only a few
    are as large as our Moon, which is nearly a sixth
    of the diameter of the Earth
  • comets have different orbits to those of planets,
    spending much of their orbital time far from the
    Sun. Comets are similar in size to asteroids, but
    are made of dust and ice. The ice melts when the
    comet approaches the Sun, and forms the comets

The Sun
  • The Sun
  • Nearly all of the mass in our Solar System is in
    the Sun. The Sun is very large. Its diameter is
    109 times the Earth's. The Sun is the source of
    nearly all the energy we receive. For many years,
    it was a mystery as to where this came from and
    this baffled the leading scientists. It is now
    understood that the nuclear fusion is the energy
    source. In nuclear fusion, smaller nuclei come
    together and form larger nuclei. For example
    hydrogen nuclei are joined together to make
    helium nuclei. This releases enormous amounts of
  • hydrogen nucleus hydrogen nucleus   ?   helium
  • In stars larger than our Sun helium nuclei can be
    fused together to create larger atomic nuclei. As
    the Earth contains many of these larger atoms,
    like carbon, oxygen, iron, etc, scientists
    believe that our Solar System was made from the
    remains of an earlier star.

Stars form from massive clouds of dust and gas in
Gravity pulls the dust and gas together
How stars and planets are formed
  • How stars and planets are formed
  • As the gas falls together, it gets hot. A star
    forms when it is hot enough for anuclear fusion
    reaction to start. This releases energy, and
    keeps the star hot. The outward pressure from the
    expanding hot gases is balanced by the force of
    the star's gravity. This happened about 5 billion
    years ago. This is quite recent in the history of
    the Universe, which is currently believed to be
    14 billion years old.
  • Gravity pulls smaller amounts of dust and gas
    together, which form planets in orbit around the

Looking at the sky
  • Looking at the sky
  • The radiation that distant stars and galaxies
    produce gives us information about the distances
    to stars, and about how they are changing. In the
    future, this may allow us to find out if life
    exists on planets around some of these stars.
  • Everything we know about stars and galaxies has
    come from the light, and other radiations, that
    they give out. This has become more difficult to
    see from the Earths surface, as light pollution
    from towns and cities interferes with
    observations of the night sky.
  • Looking at the sky with the naked eye shows the
    Sun, Moon, stars, planets and a few cloudy
    patches called nebulae. When telescopes were
    invented and developed, astronomers could see
    that some of the nebulae were in fact groups of
    millions of stars. These are galaxies.
  • Parallax
  • Powerful telescopes allowed astronomers to answer
    a question that had baffled scientists since the
    astronomer Copernicus (1473-1543) first suggested
    that the Earth moved around the Sun. If the Earth
    moves, you would expect to see a different view
    of the stars at different times of the year, in
    the same way as the room you are in looks
    slightly different if you move your head to one
    side. That is to say everything seems to move in
    the opposite direction to your head, but the
    objects close to you seem to move more. This
    effect is called parallax. So if the Earth was
    moving, why did the stars always look the same?
  • The answer to the question was revealed by more
    powerful telescopes. These showed that nearby
    stars do seem to move from side to side and back
    every year when compared with very distant stars,
    but that the amount of movement is tiny.

Finding the distance of a star using parallax
The second nearest star to us is Proxima
Centauri. The Sun is the nearest. It seems to
move through an angle of 1.5 seconds between
January and June. As one second 1/60 of a
minute, and one minute 1/60 of a degree, this
tiny movement, which is less than a thousandth of
the diameter of the Moon, needed powerful
telescopes and accurate measurement to observe.
Light Pollution telescopes
  • In the last 200 years, it has become very
    difficult to make astronomical observations in
    industrialised countries such as the UK. This is
    not just because of cloudy weather or air
    pollution. It is due to the bright lights found
    in cities and towns, and on roads. This light
    pollution means that it is hard for many people
    to see more than a few of the very brightest
    stars at night.
  • Telescopes
  • Telescopes are now placed in the few remote, dark
    places left on our planet, or out in orbit around
    the Earth.
  • The Very Large Telescope is part of the Paranal
    Observatory that is built on top of the Cerro
    Paranalmountain, which is 2,635 m high, in the
    Atacama Desert in Chile.

More On Telescopes
  • Telescopes in space, such as the Hubble Space
    Telescope, can observe the whole sky. They are
    above light pollution and above dust and clouds
    in the atmosphere. However, they are difficult
    and expensive to launch and maintain. If anything
    goes wrong, only astronauts can fix them.

Beyond Our Solar System
  • Beyond our Solar System
  • The Sun is 150 million km(93 million miles) from
    the Earth, but thats a tiny distance compared
    with the distance to other stars, or other
    galaxies. Larger units of distance are used for
    these measurements. One popular measurement is
    the light-year.
  • Light-years
  • A light-year is the distance light travels in a
    year. Light travels very fast (300,000 km/186,282
    miles per second), and takes only about eight
    minutes to reach us from the Sun. It takes over
    four years to reach us from the next nearest star
    (Proxima Centauri), and 100,000 years to cross
    the Milky Way galaxy. We say that the distance to
    the next nearest star is four lightyears, and the
    diameter of the Milky Way is 100,000 light years.
  • The most distant galaxies observed are about
    13,000 million light-years away. However,
    measuring distances to other stars, and to very
    distant galaxies, is not easy, so the data is

Measurement uncertainties
  • Measurement uncertainties
  • When initial distances to stars were being
    established more than one method was employed.
    After establishing distances of nearby stars
    using the parallax method, the 'brightness
    method' was used to approximate distances to
    further stars. Other methods were also used.
  • Each method had its own assumptions. For example,
    with the parallax method an assumption made is
    that during the total time in which the
    measurement is taking place, distance remains
    constant between the two stars.
  • As methods were reliant on each other, a certain
    level of uncertainty is found in the results.

A cluster of young stars in the Small Magellanc
Cloud dwarf galaxy
Ideas about Science
  • Ideas about science - developing explanations
  • Different explanations can be developed to
    illustrate the theory that the dinosaurs were
    destroyed by an asteroid impact.
  • Data and explanations
  • Data statements tell you facts, and may contain
    measurements. For example, look at these three
  • asteroids are small objects orbiting the Sun
  • some asteroids have orbits close to the Earth
  • the dinosaurs died out at about the same time as
    a large crater was made in Mexico.
  • Explanations seek to explain the data, and
    formulating an explanation requires imagination
    and creativity. One explanation is that an
    asteroid collision may have killed off the
    dinosaurs. The asteroid impact would have created
    dust that blocked out light and heat from the Sun.

  • Predictions
  • A good explanation will explain data, and link
    together things thatwere not thought to be
    related. It should also make predictions.
  • asteroids often contain the rare metal iridium -
  • a huge asteroid impact would send iridium dust
    throughout the world - prediction
  • sedimentary rocks from the time the dinosaurs
    died out contain iridium - data
  • when the asteroid crashed, the iridium came from
    the dust tha tblocked out the Sun - explanation.
  • Data and predictions can be used to test an
    explanation, but you have to be careful. When an
    observation agrees with the prediction, it makes
    you more confident in the explanation, but it
    does not prove that the explanation is true.
  • The opposite is also correct. When an observation
    disagrees with a prediction, it makes you less
    confident in the explanation, but it does not
    prove that the explanation is wrong. The data may
    be faulty.
  • The asteroid theory is not the only one about the
    death of the dinosaurs. Other are
  • there were huge volcanic eruptions in India at
    the time the dinosaurs died out - data
  • big volcanic eruptions cause dust clouds
    thatblock out the Sun - data
  • the big Indian eruptions could have killed out
    the dinosaurs by cooling the Earth - explanation.
  • Unanswered questions
  • Not all scientific questions have answers at this
    time. For some of the questions there is not
    enough data yet. An example of this is the
    question is there life on distant planets? For
    other questions, there may never be the data you
    need. An example of this is what happened before
    the Big Bang when the Universe was created?

  • Galaxies
  • Galaxies contain thousands of millions of stars.
    For many years, it was thought that our galaxy,
    which is the Milky Way, was the only one that
    existed, and that the blurry nebulae that could
    be seen were clouds of dust and gas in the Milky
  • Observations of many of these nebulae by
    astronomers such as Edwin Hubble showed they were
    in fact galaxies outside the Milky Way, and that
    distant galaxies are all moving away from us.
  • The beginning and end of the Universe
  • Hubbles observations led to the Big Bang
    explanation of the beginning of theUniverse, and
    set a date for this at 14,000 million years ago.
  • There are many questions left unanswered about
    the beginning and end of the Universe.
    Observations suggest it contains a lot of dark
    matter that cannot be seen, and this is not yet
    clearly understood.
  • Perhaps the Universe will continue to expand in
    the way it is at the moment. Perhaps gravity will
    eventually win and pull all the fleeing galaxies
    back together again. Better observations of very
    distant galaxies and a better understanding of
    the mysterious dark matter are needed before
    these will be understood.
  • Hubbles Law- Higher tier
  • The astronomer Edwin Hubble (1889-1953) measured
    the distance to many galaxies, and also the
    speeds with which they are moving away from us.
    He found a strong correlation between these

Some galaxies do not fit exactly on the line of
This correlation is summed up in Hubbles Law
which says that the speed at which a galaxy moves
away from us is proportional to its distance from
us. The causal link which explains this law is
that space itself is expanding. As the Universe
expands, galaxies that are already further apart
will increase in separation even more, and so
move away at higher speeds.
Age of the Universe
  • Age of the Universe
  • The development of powerful telescopes allowed
    astronomers to see distant galaxies. The light
    observed was shifted towards the red end of the
    spectrum. This phenomenon is known as red-shift.
    The degree to which light has been shifted
    indicates how fast the galaxies are moving away.
  • In general, the further away the galaxy is, the
    faster it is moving away from the Earth. The
    motions of the galaxies themselves suggest that
    space itself is expanding.
  • It is estimated that the Universe is
    approximately 13.7 billion years old. Evidence
    suggests that our Solar System formed around 4.5
    billion years ago, so it is around one-third the
    age of the Universe.
  • The eventual fate of the Universe is hard to
    predict due to the uncertainty in measuring such
    large distances and studying motion of distant
    objects. A better idea of the mass of the
    Universe would lead to better predictions.

How the Earth is changing
  • The theory of plate tectonics is now well
    established. Continental drift is happening as
    tectonic plates move, with earthquakes and
    volcanoes often occurring around their edges.
  • Evidence from rocks
  • Rocks provide evidence for changes in the Earth.
    In 1785 James Hutton presented his idea of a rock
    cycle to the Royal Society. He detailed ideas
    oferosion and sedimentation taking place over
    long periods of time, making massive changes to
    the Earths surface.
  • Geologists can use other evidence from the rocks
    themselves such as
  • looking at cross-cutting features (rock that cuts
    across another is younger)
  • using fossils (species existed/ became extinct
    during certain time periods)
  • deepness of the rock (younger rocks are usually
    on top of older ones).
  • This kind of evidence only shows that some rocks
    are older than others. To get a more accurate
    idea of the age of rocks radioactive dating is

Wegeners theory
  • Wegeners theory
  • Alfred Wegener (1880 - 1930)
  • Alfred Wegener proposed the theory of continental
    drift at the beginning of the 20th century. His
    idea was that the Earth's continents were once
    joined together, but gradually moved apart over
    millions of years. It offered an explanation of
    the existence of similar fossils and rocks on
    continents that are far apart from each other.
    But it took a long time for the idea to become
    accepted by other scientists.

Before Wegener
  • Before Wegener
  • Before Wegener developed his theory, it was
    thought that mountains formed because the Earth
    was cooling down, and in doing so contracted.
    This was believed to form wrinkles, or mountains,
    in the Earth's crust. If the idea was correct,
    however, mountains would be spread evenly over
    the Earth's surface. We know this is not the
    case. The heating effect of radioactive materials
    inside the Earth prevents it from cooling.
  • Wegener suggested that mountains were formed when
    the edge of a drifting continent collided with
    another, causing it to crumple and fold. For
    example, the Himalayas were formed when India
    came into contact with Asia.
  • This slideshow explains Wegener's theory.

Earth around 200 million years ago, at the time
of Pangaea
The single landmass began to crack and divide,
due to the slow currents of magna beneath it
The positions of the continents today
Wegeners evidence
  • Wegeners evidence for continental drift was
  • the same types of fossilised animals and plants
    are found in South America and Africa
  • the shape of the east coast of South America fits
    the west coast of Africa, like pieces in a jigsaw
  • matching rock formations and mountain chains are
    found in South America and Africa.

Ideas about science - the scientific community
  • Publishing and peer review
  • Scientists report their ideas to the scientific
    community. They present them at conferences and
    then write them up in journals or books.
  • At conferences, other scientists will listen and
    debate the new ideas. Before journals or books
    are published, other expert scientists read the
    new ideas and decide if they are sensible. This
    is called peer review.
  • Wegener presented his ideas at a conference in
    1912, and then published them in a book in 1915.
  • Repeating experiments
  • Scientists do not usually accept the results of
    experiments until someone else has repeated them
    to get the same results. It is hard to set up
    experiments in geology and astronomy, so new
    theories need support from different observations.

  • Different explanations
  • Data often allows more than one possible
    explanation, so different scientists can have
    different explanations for the same observations.
  • Wegeners ideas could certainly explain
    similar fossils turning up in different
    continents, but other geologists thought that
    there were once land bridges between
    continents, allowing animals to travel between
  • The different backgrounds of different scientists
    can affect their judgements, so they may have
    quite different explanations for the same data.
  • Wegener was trained as an astronomer and a
    meteorologist. Many geologists did not think that
    he had the right background to judge geological
  • Wagener's new explanation becomes accepted
  • The old geological theory explained mountains as
    wrinkles made by the Earth shrinking as it cools
  • There was no clear explanation of how continents
    could move about - a new scientific explanation
    often needs new supporting evidence to convince
    scientists that it is correct.
  • Then, in the 1950s, evidence from magnetism in
    the ocean floor showed that the seafloors were
    spreading by a few centimetres each year. This
    showed movement of large parts of the Earths
    crust, now called tectonic plates. This new
    evidence allowed Wagener's theory to be accepted.
  • A scientific explanation is rarely abandoned just
    because some data does not correspond to it, but
    it is safer to stick with a theory that has
    worked well in the past.

Seafloor spreading
  • Seafloor spreading
  • In the centres of many oceans, there are
    mid-ocean ridges. At these places, thetectonic
    plates are moving apart. Molten material, known
    as magma from inside the Earth oozes out and
    solidifies. This movement of the mantle is
    referred to as convection due to heating by the
    core of the Earth. This process is calledseafloor
    spreading. It results in seafloors spreading by a
    few centimetres each year.

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Inside the Earth
  • Inside the Earth
  • All our evidence for changes in the Earth comes
    from looking at rocks. Folds and fossils
    in sedimentary rocks, radioactive dating and the
    weathering of ancient craters show that the
    oldest rocks are about 4000 million years old.
    That means the Earth must be at least as old as
  • The only thing that we have been able to observe
    directly is the Earths crust, which is the very
    thin outer rocky layer.
  • Evidence from earthquakes shows that the Earth
    has a very dense core surrounded by a
    solid mantle.

Cross section showing structure of the Earth
The Earth is almost a sphere. These are its main
layers, starting with the outermost The crust,
which is relatively thin and rocky The mantle,
shown here as dark red, which has the properties
of a solid, but can flow very slowly The outer
core, shown as orange, which is made from liquid
nickel and iron The inner core, shown as yellow,
which is made from solid nickel and iron
The Earth's magnetic field - Higher tier
  • The Earth's magnetic field - Higher tier
  • The typical speed of seafloor spreading is slow
    about 10 cm per year. When themagma oozing out of
    mid-ocean ridges solidifies into rock, the rock
    records the direction of the Earths magnetic
    field. The Earths magnetic field changes with
    time, and sometimes even reverses its direction.
    These changes are recorded in the rocks. The same
    magnetic patterns are seen on both sides of the
    mid-ocean ridges.

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Plate tectonics - Higher tier
  • Plate tectonics - Higher tier
  • The Earths crust, together with the upper region
    of the mantle, consists of huge slabs of rock
    called tectonic plates. These fit together rather
    like the segments on the shell of a tortoise.

Although the mantle below the tectonic plates is
solid, it does move. This movement is very, very
slow a few centimetres every year. This means
that the continents have changed their positions
over millions of years.
Movement of tectonic plates - Higher tier
  • Movement of tectonic plates - Higher tier
  • Volcanoes, mountains and earthquakes occur at the
    edges of tectonic plates - their creation depends
    on the direction the plates are moving.
  • Volcanoes
  • If the plates are moving apart, as at mid-ocean
    ridges, volcanoes are produced as molten magma is
    allowed to escape. This happens in Iceland.
  • Mountains
  • If the plates are moving towards each other, the
    edges of the plates crumple, and one plate
    dives under the other. This is
    called subduction. It produces mountains, like
    the Himalayas. The friction of the movement can
    also melt rocks and produce volcanoes.
  • This is also part of the rock cycle, because the
    plate that dives under the other one becomes part
    of the mantle and emerges much later from
    volcanoes and in seafloor spreading.

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  • There are two other ways in which mountains can
    be formed. At destructive margins mountain chains
    can be formed as plates push against each other.
    If an ocean closes completely then continents can
    collide. This occurs slowly but the collision
    would still result in the formation of a mountain
  • Earthquakes
  • If the plates are moving sideways, stresses build
    up at the plate boundary. When the stress reaches
    some critical value, the plates slip suddenly,
    causing an earthquake. It is hard to predict when
    such an event may happen.

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Detecting wave motions
  • Detecting wave motions
  • A seismometer detects the vibrations of an
  • The vibrations of an earthquake are detected
    using a seismometer that records the results in
    the form of a seismogram.
  • The vibrations that are detected from the site of
    an earthquake are known as seismic waves.

Seismic waves
  • Vibrations from an earthquake are categorised as
    P or S waves. They travel through the Earth in
    different ways and at different speeds. They can
    be detected and analysed.
  • P and S waves
  • A wave is a vibration that transfers energy from
    one place to another without transferring matter
    (solid, liquid or gas). Light and sound both
    travel in this way.
  • Energy released during an earthquake travels in
    the form of waves around the Earth. Two types of
    seismic wave exist, P- and S-waves. They are
    different in the way that they travel through the
  • P-waves (P stands for primary) arrive at the
    detector first. They are longitudinal waves which
    mean the vibrations are along the same direction
    as the direction of travel. Other examples of
    longitudinal waves include sound waves and waves
    in a stretched spring.

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Amplitude, wavelength and frequency
  • Amplitude, wavelength and frequency
  • You should understand what is meant by the
    amplitude, wavelength and frequency of a wave.
  • Amplitude
  • As waves travel, they set up patterns of
    disturbance. The amplitude of a wave is its
    maximum disturbance from its undisturbed
    position. Take care the amplitude is not the
    distance between the top and bottom of a wave. It
    is the distance from the middle to the top.

Wavelength and Frequency
  • Wavelength
  • The wavelength of a wave is the distance between
    a point on one wave and the same point on the
    next wave. It is often easiest to measure this
    from the crest of one wave to the crest of the
    next wave, but it doesn't matter where as long as
    it is the same point in each wave.
  • Frequency
  • The frequency of a wave is the number of waves
    produced by a source each second. It is also the
    number of waves that pass a certain point each
    second. The unit of frequency is the hertz (Hz).
    It is common for kilohertz (kHz), megahertz (MHz)
    and gigahertz (GHz) to be used when waves have
    very high frequencies. For example, most people
    cannot hear a high-pitched sound above 20kHz,
    radio stations broadcast radio waves with
    frequencies of about 100MHz, while most wireless
    computer networks operate at 2.4GHz.

Wave Speed
  • Wave speed
  • Wave speed is the velocity at which each wave
    crest moves and is measured in metres per second
    (m/s). The wave speed only depends on the
    material the wave is travelling through. The
    distance travelled by a wave is calculated using
    this equation
  • Distance speed x time
  • The speed of a wave - its wave speed (metres per
    second, m/s)- is related to its frequency (hertz,
    Hz) and wavelength (metre, m), according to this
  • wave speed frequency x wavelength
  • For example, a wave with a frequency of 100Hz and
    a wavelength of 2m travels at 100 x 2 200m/s.
  • The speed of a wave does not usually depend on
    its frequency or its amplitude.

Radiation Life P2 INCLUDING
  • Electromagnetic radiation Benefits and risks
    Global warming Waves and communication

  • Light is one of the family of radiations called
    the electromagnetic spectrum. Some types of
    electromagnetic radiation are used to transmit
    information such as computer data, telephone
    calls and TV signals.
  • The electromagnetic spectrum
  • Refraction from a prism
  • The pattern produced when white light shines
    through a prism is called the visible spectrum.
  • The prism separates the mixture of colours in
    white light into the different colours red,
    orange, yellow, green, indigo and violet.
  • In fact, visible light is only part of the
    electromagnetic spectrum. Its the part we can

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Photons and ionisation
  • Photons and ionisation
  • Electromagnetic radiation comes in tiny packets
    called photons.
  • The photons deliver different quantities of
    energy, with radio photons delivering the
    smallest amount, and gamma photons delivering the
    greatest amount of energy.
  • A higher frequency of electromagnetic radiation
    means more energy is transferred by each photon.
  • If the photons have enough energy, they can break
    molecules into bits called ions. This is called
    ionisation. These types of radiation are
    called ionising radiation. This radiation can
    remove electrons from atoms in its path.
  • In the electromagnetic spectrum only the three
    types of radiation, which have the photons with
    most energy, are ionising. These
    are ultraviolet, X-rays andgamma rays.
  • Damaging to health - Higher tier
  • The ions produced when ionising radiation breaks
    up molecules can take part in other chemical
    reactions. If these chemical reactions are in
    cells of your body, the cells can die or become
    cancerous. This is the reason that ionising
    radiation can be damaging to health.

Energy and intensity
  • Energy and intensity
  • The intensity of electromagnetic radiation is the
    energy arriving at a square metre of surface each
    second. This depends on two things the energy in
    each photon, and the number of photons arriving
    each second.
  • To have the same intensity, a beam of red light
    would need ten times as many photons as a beam of
    ultraviolet, and a beam of microwaves would need
    a million times as many.
  • Energy of 1 ultraviolet photon      Energy of 10
    red photons      Energy of 1,000,000 microwave
  • Absorption of radiation - Higher tier
  • All forms of electromagnetic radiation deliver
    energy. This will heat the material that absorbs
    the radiation. The amount of heating depends on
    the intensity of the radiation, and also
    the length of time the radiation is absorbed for.

  • Electromagnetic radiation
  • An object which gives out electromagnetic
    radiation is called a source of radiation.
  • Something which is affected by the radiation is
    a detector.
  • Lower intensity of radiation
  • Further from the source, the detector receives a
    lower intensity of radiation.

As the photons spread out from the source, they
are more thinly spread out when they reach the
detector. The intensity may also decrease with
distance due to partial absorption by the medium
it travels through.
Ionising radiation
  • Ionising radiation
  • Ionising radiation can break molecules into
    smaller fragments. These charged particles are
    called ions. As a result, ionising radiation
    damages substances and materials, including those
    in the cells of living things. The ions
    themselves can take part in chemical reactions,
    spreading the damage.
  • Ionising radiation includes
  • ultraviolet radiation, which is found in sunlight
  • x-rays, which are used in medical imaging
  • gamma rays, which are produced by some
    radioactive materials.

  • Non-ionising radiation
  • Not all types of electromagnetic radiation are
    ionising. Radio waves, light and microwaves are
    among them.
  • Microwaves
  • Microwaves are used to heat materials such as
    food. The molecules in the material absorb the
    energy delivered by the microwaves. This makes
    them vibrate faster, so the material heats up.
  • The heating effect increases if
  • the intensity of the microwave beam is increased
  • the microwave beam is directed onto the material
    for longer.
  • So you need to cook food for longer in a less
    powerful microwave oven. This is why they have
    power ratings, and food labels recommend
    different cooking times depending on this.

  • Radiation that is not absorbed by the atmosphere
    reaches the Earth's surface and warms it, leading
    to the greenhouse effect. Some radiation, such as
    ultraviolet, exposes our skin to harmful rays and
    puts us at risk of developing skin cancer.
  • The atmosphere
  • Some radiation of the electromagnetic spectrum is
    absorbed by the atmosphere, but some is
  • Light, some infrared, some ultraviolet,
    and microwaves, pass through the atmosphere and
    reaches the Earths surface. Gamma rays, X-rays,
    most of the ultraviolet and some of
    the infrared are absorbed by the atmosphere and
    do not reach the Earths surface.

  • Infrared
  • Infrared from the Sun reaches the Earths surface
    and warms it.
  • The warm Earth emits some infrared radiation, and
    some of this is absorbed by gases in the
    atmosphere. This is called the greenhouse effect.
    If there was no greenhouse effect, the Earth
    would be too cold for life as we know it.
  • Photosynthesis
  • Light from the Sun reaching the Earths surface
    provides the energy for plants to produce food
    by photosynthesis.
  • Photosynthesis replaces carbon dioxide in the
    atmosphere with oxygen. This reverses the process
    of respiration.

Microwaves The atmosphere transmits microwaves,
and these can be used to communicate with
  • Light from the sun reaching earth

Radiation and cell damage
  • Radiation and cell damage
  • Any radiation absorbed by living cells can damage
    them by heating them. However, ionising
    radiations are more likely to damage living
    cells. This is because photons of ionising
    radiation deliver much more energy. They can
    easily kill cells, and can also cause cancer by
    damaging the DNA in the nucleus of a cell.
  • Effects of microwaves
  • Microwaves in the environment may be harmful, but
    there is no agreement on this. They are not
    ionising, and so cannot cause cancer in the way
    that ultraviolet, X-rays orgamma rays do.
  • Microwave ovens work because the food contains
    water molecules which are made to vibrate by the
    microwaves. This means that food absorbs
    microwaves and gets hot. The microwaves cannot
    escape from the oven, because the metal case and
    the metal grid on the door reflect microwaves
    back into the oven.

  • Some people think that mobile phones, which
    transmit and receive microwaves, may be a health
    risk. This is not accepted by everyone, as the
    intensity of the microwaves is too low to damage
    tissues by heating, and microwaves are not

  • Ultraviolet
  • Umbrellas can be useful in the sun as well as the
  • One health risk which is definitely present in
    our environment is ultraviolet, in sunlight. Not
    much of the ultraviolet reaching the Earth gets
    to us, because the ozone layer high up in the
    atmosphere absorbs most of it. In the summer, it
    is wise to use sunscreens and clothing to absorb
    ultraviolet, and prevent it reaching the
    sensitive cells of the skin.
  • The ozone layer - Higher tier
  • Ozone molecule formation
  • The ozone layer absorbs ultraviolet because
    ultraviolet ionises the ozone, which then changes
    to oxygen. This chemical change is reversible,
    and the oxygen changes back to ozone.

  • Ideas about science - risk
  • Scientific or technological developments often
    introduce new risks.
  • Chemicals used in aerosol spray cans and fridges
    gradually made their way up to the ozone layer
    when released into the atmosphere, and removed
    some of it. This has increased the intensity of
    the ultraviolet radiation reaching the Earth.
    These chemicals are not used any more, and the
    ozone layer is gradually returning to normal.
    However, this will take a number of yers more.
  • It is important to be able to assess the size of
    risk in any activity. No activity is completely
  • The consequence of too much ultraviolet skin
    cancer often does not appear until much later
    in life, so it doesn't seem a real risk to young
  • It is difficult to assess how much ultraviolet
    you are receiving when you are sunbathing. If you
    feel hot, that is because of the infrared, not
    the ultraviolet
  • Weather forecasts now inform you of the intensity
    of ultraviolet radiation.
  • Benefits
  • For most risky activities, there are benefits as
    well as risks
  • sunbathing produces a sun tan, which many people
    find more attractive
  • some ultraviolet is good for you, as it produces
    vitamin D in the skin.
  • Read on if you are taking the higher tier paper.

  • Making a judgement - Higher tier
  • To make a judgement about a possible bad outcome
    you need to consider two factors
  • What is the chance of the outcome happening?
  • What is the consequence of that outcome?
  • The precautionary principle
  • The precautionary principle tells you to avoid
    any activity if serious harm could arise.
  • parents may insist that their children are not
    allowed out on the beach at all in the summer
  • The real risk may be very different from
    the perceived risk ie the risk that you think is
  • you cant see ultraviolet, and the word
    radiation sounds frightening to many people.
    This makes the risk seem worse than something you
    can see, and which is more familiar
  • Some parents may assume that summers are no
    different from when they were young, so there is
    no danger to their children
  • Other parents may be very alarmed by stories of
    increases in skin cancer, and not let their
    children out in sunny weather at all
  • Sometimes risk should be regulated by governments
    and other public bodies. This usually applies to
    an organisation which is responsible for its
    employees. In some situations this may be

  • Types of radiation from the electromagnetic
    spectrum make life on Earth possible, but some
    have hazards associated with them. These hazards
    need to be carefully considered, and the evidence
    weighed up in order to reach a scientific
  • Greenhouse gases
  • Some gases in the Earths atmosphere
    absorb infrared radiation. One of these is carbon
    dioxide. Even though carbon dioxide is only about
    0.04 per cent of the atmosphere, it is a very
    important greenhouse gas because it absorbs
    infrared well.

The Suns rays enter the Earths atmosphere Heat
is emitted back from the Earths surface at a
lower principal frequency than that emitted by
the Sun Some heat passes back out into space But
some heat is absorbed by carbon dioxide, a
greenhouse gas, and becomes trapped within the
Earths atmosphere. The Earth becomes hotter as a
Greenhouse effect
Water vapour and methane
  • Water vapour and methane
  • Other greenhouse gases are water vapour, and also
    methane. Even though methane is present in trace
    (tiny) amounts only, it is a very efficient
    absorber of infrared.

The carbon cycle
  • The carbon cycle
  • The amount of carbon dioxide in the atmosphere is
    controlled by the carbon cycle.
  • Processes that remove carbon dioxide from the
  • photosynthesis by plants
  • dissolving in the oceans.
  • Processes that return carbon dioxide from the
  • respiration by plants, animals and microbes
  • combustion ie burning wood and fossil fuels such
    as coal, oil and gas
  • thermal decomposition of limestone, for example,
    in the manufacture of iron, steel and cement.

  • Cellulose
  • All cells contain carbon, because they all
    contain proteins, fats and carbohydrates. For
    example, plant cell walls are made of cellulose,
    a carbohydrate.
  • Decomposers
  • Decomposers, such as microbes and fungi, play an
    important role in the carbon cycle. They break
    down the remains of dead plants and animals and,
    in doing so, release carbon dioxide through

  • For thousands of years, the processes in the
    carbon cycle were constant, so the percentage of
    carbon dioxide in the atmosphere did not change.
    Over the past 200 years, the percentage of carbon
    dioxide in the atmosphere has increased steadily
    because humans are
  • burning more and more fossil fuels as energy
  • burning large areas of forests to clear land,
    which means that there is less photosynthesis
    removing carbon dioxide from the air.

Global warming
  • Global warming
  • Although the changes have been gradual, most -
    but not all - scientists agree that the climate
    is getting gradually warmer. This is
    called global warming.
  • Most - but not all - scientists lay the blame for
    this on human activities increasing the amount of
    carbon dioxide in the atmosphere.
  • Global warming could cause
  • climate change
  • extreme weather conditions in some areas.
  • Climate change may make it impossible to grow
    certain food crops in some regions. Melting polar
    ice, and the thermal expansion of sea water,
    could cause rising sea levels and the flooding of
    low-lying land. Extreme weather events become
    more likely due to increased convection
    accompanied by more water vapour being present in
    the hotter atmosphere.
  • Computer climate models - Higher tier
  • One piece of evidence that supports the view of
    scientists who blame human activities for global
    warming has been provided by 'supercomputers'.
    Computer generated climate models, based on
    different amounts of carbon dioxide in the
    atmosphere, produce the same changes as have been
    observed in the real world.

Ideas about science correlation and cause
  • Ideas about science correlation and cause
  • The ideas of correlation and cause are
    illustrated with the evidence for global warming.
  • Any process can be thought of in terms of factors
    that may affect an outcome.
  • in global warming, one factor is the amount of
    carbon dioxide in the atmosphere. The outcome is
    the mean temperature of the atmosphere.
  • Establishing a correlation
  • To establish a correlation between a factor and
    an outcome, convincingevidence is needed. This
    usually means that enough data must be collected,
    and that different samples should match.
  • Compare these two graphs and consider these
  • are the changes reported significantly large?
  • are they properly matched in terms of the times
    over which they are reported?
  • do these two graphs match well enough? P.T.O

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  • Other factors
  • A correlation between a factor and an outcome
    does not mean that the factor causes the outcome.
    They could both be caused by some other factor.
  • For emample Children with bigger feet (factor)
    are, on average, better readers (outcome).
  • There is another factor which affects both of
    these things age. Older children usually have
    bigger feet, and older children are usually
    better readers!
  • To investigate the relationship between a factor
    and an outcome, it is important to control all
    other factors that may affect the outcome.
  • Other factors affecting global warming
  • Another factor that may affect the mean
    temperature of the atmosphere is the amount of
    energy given out by the Sun. Most scientists
    agree that this has not changed in the past 200
  • There are some scientists who agree that global
    warming is taking place, but do not agree that
    carbon dioxide levels are to blame.
  • Scientific explanation - Higher tier
  • Once experiments have shown that there is a
    definite correlation between a factor and an
    outcome, it is still not enough to prove that the
    factor causes the outcome.
  • For this to be proven, there must be
    some scientific explanation of how the
    relationship can happen.
  • for carbon dioxide and global warming, the
    explanation is that carbon dioxide is a
    greenhouse gas. It absorbs infrared given off by
    the warm Earth, and this infrared cannot then
    escape into space. This keeps the Earth warmer
    than it would be if the carbon dioxide did not
    absorb so much infrared.

Waves and communication
  • Information such as computer data can be
    transmitted in a number of ways, including via
    waves and also analogue and digital signals. Some
    methods of transmission have advantages over
  • Transmitting information
  • Infrared light, microwaves and radio waves are
    all used to transmit information such as computer
    data, telephone calls and TV signals.
  • Infrared light
  • Information such as computer data and telephone
    calls can be converted into infrared signals and
    transmitted by optical fibres. Optical fibres are
    able to carry more information than an ordinary
    cable of the same thickness. In addition the
    signals they carry do not weaken so much over
    long distances. Television remote controls use
    infrared light to transmit coded signals to the
    television set in order to, for example, change
    channels or adjust the volume.

  • Microwave radiation can be used to transmit
    signals such as mobile phone calls. Microwave
    transmitters and receivers on buildings and masts
    communicate with the mobile telephones which are
    in their range.
  • Certain microwave radiation wavelengths pass
    through the Earths atmosphere and can be used to
    transmit information to and from satellites in

  • Radio waves
  • Radio waves are used to transmit television and
    radio programmes. Longer wavelength radio waves
    are reflected from an electrically charged layer
    of the upper atmosphere. This means they can
    reach receivers that are not in the line of sight
    because of the curvature of the Earths surface.

Carrying analogue and digital information
  • Carrying analogue and digital information
  • Analogue and digital
  • Before a sound or piece of information is
    transmitted, it is encoded in the transmitter in
    one of the ways described below - analogue or
    digital. The receiver must then decode the signal
    to produce a copy of the original information or
  • Analogue signals vary continuously in amplitude,
    frequency or both.
  • Digital signals are a series of pulses with two
    states - on (shown by the symbol 1) or off
    (shown by the symbol 0). Digital signals carry
    more information per second than analogue signals
    and they maintain their quality better over long
  • You should be able to explain why digital
    signals maintain their quality better than
    analogue signals.

  • Noise
  • All signals become weaker as they travel long
    distances. They may also pick up random extra
    signals. This is called noise, and it is heard as
    crackles and hiss on radio programmes. Noise may
    also cause an internet connection to drop, or
    slow down as the modem tries to compensate.
  • An important advantage of digital signals over
    analogue signals is that if the original signal
    has been affected by noise it can be recovered
    more easily. In analogue signals, when the signal
    is amplified to return to its original height,
    noise gets amplified as well.

Analogue vs. digital - Higher tier
  • Analogue vs. digital - Higher tier
  • Analogue signals
  • Noise adds extra random information to analogue
    signals. Each time the signal is amplified the
    noise is also amplified. Gradually, the signal
    becomes less and less like the original signal.
    Eventually, it may be impossible to make out the
    music in a radio broadcast from the background
    noise, for example.
  • Digital signals
  • Noise also adds extra random information to
    digital signals. However, this noise is usually
    lower in amplitude than the 'on' states of the
    digital signal. As a result, the electronics in
    the amplifiers can ignore the noise and it does
    not get passed along. This means that
    the quality of the signal is maintained. This is
    one reason why television and radio broadcasters
    are gradually changing from analogue to digital
    transmissions. They can also squeeze in more
    programmes because digital signals can carry more
    information per second than analogue signals.
    Another advantage of digital signals is that
    information can be stored and processed by

Coding and storing information
  • Coding
  • Coding involves converting information from one
    form to another. All types of information can be
    coded into a digital signal.
  • Digital signals are a series of pulses consisting
    of just two states, ON (1) or OFF (0). There are
    no values in between. The sound is converted into
    a digital code of 0s and 1s, and this coded
    information controls the short bursts of waves
    produced by a source.
  • When waves are received, the pulses
    are decoded to produce a copy of the original
    sound or image.
  • Amount of information
  • The amount of information needed to store an
    image or sound is measured in bytes (B).
  • A megabyte is larger than a byte, and a gigabyte
    is larger than a megabyte.
  • To store one minutes worth of music it would
    take about 1 megabyte, to store an average two
    hour movie it would take 1.5 gigabytes.
  • In general, the more information that is stored
    about an image or sound, the higher the quality.

INCLUDING Using energy Generating
electricity Choosing energy sources
Using energy
  • The world we live in uses a lot of energy. There
    are a number of different energy sources that
    could be used. The energy supplied in household
    electricity is measured in kilowatt hours (kWh).
    Energy is transferred from the power source to
    components in an electric circuit. Energy
    transfer in electrical appliances is always less
    than 100 per cent efficient.
  • Energy sources
  • The global demand for energy is continually
    increasing. Our population is growing even though
    we already have more people on the planet than
    ever before.
  • As well as this, modern lifestyles demand
    transport and communications technology, which
    also require more energy.
  • This raises issues about the availability of
    energy sources and the environmental effects of
    using them.

Primary and secondary sources
  • A primary source of energy is one that occurs
  • Fossil fuels (coal, oil and gas), biofuels, wind,
    waves, solar radiation and nuclear fuels are all
    primary sources of energy.
  • A secondary energy source is one that is made
    using a primary resource. Electricity is
    secondary resource, and can be generated by a
    number of different primary sources.

Fossil fuels
  • Fossil fuels
  • Fossil fuels are formed over millions of years by
    the decay of dead organisms. When they are burned
    they produce a number of pollutants. A major
    pollutant formed is carbon dioxide, which
    contributes to global warming and climate change.

  • Power
  • When an electric current flows in a circuit,
    energy is transferred from the power supply to
    the components in the circuit. The bigger the
    voltage, the more energy transferred.
  • Energy is measured in joules, J.
  • The rate of energy transfer is called the power.
  • Power is measured in watts, W.
  • The equation
  • The equation below shows the relationship between
    power (watt, W), voltage (volt, V) and current
    (ampere, A).
  • power voltage x current
  • If the voltage is 12V and the current is 5A, the
    power is 12 x 5 60W.
  • This means that 60J of energy is transferred per
    second. (1 watt 1 joule per second).
  • Remember that 1,000W is 1kW (kilowatt).

Energy Transfer
  • You should be able to calculate the cost of using
    an electrical appliance when given enough
    information about it.
  • The unit kilowatt-hours, kWh
  • The amount of electrical energy transferred to an
    appliance depends on its power and the length of
    time it is switched on. The amount of mains
    electrical energy transferred is measured
    in kilowatt-hours, kWh. One unit is 1kWh.
  • The equation below shows the relationship between
    energy transferred, power and time
  • energy transfered (kilowatt-hour, kWh)
     power (kilowatt, kW) x time (hour, h)
  • Note that power is measured in kilowatts here,
    instead of the more usual watts. To convert from
    W to kW you must divide by 1000. For example,
    2000W 2000 1000 2kW.
  • Also note that time is measured in hours here,
    instead of the more usual seconds. To convert
    from seconds to hours you must divide by 3600
    (this is the number of seconds in 1 hour). For
    example, 1800s 0.5 hours (1800 3600)

The cost of electricity
  • The cost of electricity
  • Electricity meters measure the number of units of
    electricity used in a home or other building.
    Units (kilowatt-hours) are used instead of joules
    because a joule is too small a unit of energy.
  • The more units used, the greater the cost. The
    cost of the electricity used is calculated using
    this equation
  • total cost number of units x cost per unit
  • For example, if 5 units of electricity are used
    at a cost of 8p per unit, the total cost will be
    5 8 40p.

Efficiency of energy transfer
  • 'Wasted' energy
  • Energy cannot be created or destroyed. It can
    only be transferred from one form to another, or
    moved. Energy that is "wasted", like the heat
    energy from an electric lamp, does not disappear.
    Instead, it is transferred to its surroundings
    and spreads out so much that it becomes difficult
    to do anything useful with it.
  • Electric lamps
  • Ordinary electric lamps contain a thin metal
    filament that glows when electricity passes
    through it. However, most of the electrical
    energy is transferred as heat rather than light
    energy. This is the Sankey diagram for a
    typical filament lamp.

Modern energy-saving lamps work in a different
way. They transfer a greater proportion of
electrical energy as light energy. This is the
Sankey diagram for a typical energy-saving lamp.
Sankey diagram for a typical energy-saving
lamp From the diagram, you can see that much
less electrical energy is transferred or 'wasted'
as heat energy when using an energy-saving lamp.
Calculating efficiency
  • Calculating efficiency
  • The efficiency of a device such as a lamp can be
    calculated using this equation
  • efficiency (useful energy transferred energy
    supplied) 100
  • The efficiency of the filament lamp is 10 100
    100 10. This means that 10 of the electrical
    energy supplied is transferred as light energy.
    90 is transferred as heat energy.
  • The efficiency of the energy-saving lamp is 75
    100 100 75. This means that 75 of the
    electrical energy supplied is transferred as
    light energy. 25 is transferred as heat energy.
  • Note that the efficiency of a device will always
    be less than 100.

Efficiency of power stations
  • The energy produced by burning fuel is
    transferred as heat and stored in water as steam.
    The energy in steam is transferred to movement in
    a turbine, then to electrical energy in the
    turbine. Energy is lost to the environment at
    each stage. Here is a Sankey diagram to show
    these losses

Note that only about a third of the energy stored
in the fuel was transferred as electrical energy
to customers.
Generating electricity
  • Electricity is a convenient source of energy and
    can be generated in a number of different ways.
    You will need to weigh up the advantages and
    disadvantages of other ways of producing energy,
    such as the use of nuclear power stations.

  • Electricity
  • Coal, oil and natural gas are primary energy
    sources. Electricity is a secondary energy source
    because we use primary energy sources to produce
    it. These primary sources can be non-renewable or
    renewable. Electricity itself is neither
    non-renewable nor renewable.
  • Electricity is convenient because
  • it is transmitted easily over distance, through
    electricity cables
  • it can be used in many ways, for example electric
    lamps, heaters, motors etc

Generating electricity
  • Generators are the devices that transfer kinetic
    energy into electrical energy. Mains electricity
    is produced by generators.
  • Turning generators directly
  • Generators can be turned directly, for example
  • wind turbines
  • hydroelectric turbines
  • wave and tidal turbines
  • When electricity is generated using wave, wind,
    tidal or hydroelectric power (HEP) there are two
  • The turbine turns a generator.
  • Electricity is produced.
  • Turning generators indirectly
  • Generators can be turned indirectly using fossil
    or nuclear fuels. The heat from the fuel boils
    water to make steam, which expands and pushes
    against the blades of a turbine. The spinning
    turbine then turns the generator.

These are the steps by which electricity is
generated from fossil fuels Heat is released
from a primary energy source fuel and boils the
water to make steam . The steam turns the
turbine. The turbine turns a generator and
electricity is produced. The electricity goes to
the transformers to produce the correct voltage.
Generating a current
  • Generating a current
  • Generators work using a process
    called electromagnetic induction.
  • One way of generating a current is to move a
    magnet into or out of a coil. This movement
    causes a voltage to be induced across the ends of
    the coil. If the coil is part of a complete
    circuit then a current will be induced in the

On magnet in the magnet goes in and the dial
turns to the sign
  • If this is done over and over again,
    an alternating current (a.c.) is generated. An
    alternating current is an electric current that
    reverses direction many times a second.
  • It is not practical to generate large amounts of
    electricity by passing a magnet in and out of a
    coil of wire. Instead, generators induce a
    current by spinning a coil of wire inside a
    magnetic field, or by spinning a magnet inside a
    coil of wire.
  • Some bicycles use a small generator. It uses the
    movement of the wheel to produce a current.

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Nuclear power stations Nuclear power stations use
fuel containing uranium.
These are the steps by which electricity is
generated by nuclear power Uranium atoms split
releasing energy so fuel becomes hot. This heats
the water turning it into steam. The steam turns
the turbine. The turbine turns a generator and
electricity is produced. The electricity goes to
the transformers to produce the correct
voltage. The fuel used eventually becomes solid
nuclear waste. This waste is radioactive and
emits ionising radiation.
Ionising radiation and living cells
  • The radiations from radioactive materials
    alpha, beta and gamma radiation are all
    ionising radiations which can damage living
  • This happens because ionising radiation can break
    molecules into bits called ions. These ions can
    then take part in other chemical reactions in the
    living cells.
  • This may result in the living cells dying, or
    becoming cancerous.

Radiation warning symbol
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