P1,P2,P3 OCR 21ST CENTURY SCIENCE

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P1,P2,P3OCR 21ST CENTURY SCIENCE

• Revision from BBC Bitesize

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P1

• THE EARTH IN THE UNIVERSE
• INCLUDING
• Earth, stars, galaxies and space
• How the Earth is changing
• Seismic waves

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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
  miles)
• the diameter of the Sun is 109 times that of the
  Earths
• the Earth is 150 million km (93 million miles)
  from the Sun
• the distance to the nearest star is four light
  years.

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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
  tail.

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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
  energy.
• hydrogen nucleus hydrogen nucleus   ?   helium
  nuclei
• 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.

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Stars form from massive clouds of dust and gas in
space
Gravity pulls the dust and gas together
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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
  star.

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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.

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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.
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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.

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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.

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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
  uncertain.

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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
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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
  statements
• 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.

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Predictions

• 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 -
  data
• 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?

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Galaxies

• 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
  Way.
• 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
  factors.

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Some galaxies do not fit exactly on the line of
correlation
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.
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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.

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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
  used.

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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.

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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.

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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
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Wegeners evidence

• Wegeners evidence for continental drift was
  that
• 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
  puzzle
• matching rock formations and mountain chains are
  found in South America and Africa.

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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.

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MORE

• 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
  them.
• 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
  theories.
• Wagener's new explanation becomes accepted
• The old geological theory explained mountains as
  wrinkles made by the Earth shrinking as it cools
  down.
• 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.

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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
  this.
• 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.

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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
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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.
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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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MORE

• 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
  chain.
• 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
  earthquake.
• 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.

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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
  Earth.
• 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.

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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.

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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
  equation
• 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.

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Radiation Life P2INCLUDING

• Electromagnetic radiationBenefits and risks
  Global warmingWaves and communication

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• 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
  see.

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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.

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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
  photons
• 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.

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• 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.
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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
  machines
• gamma rays, which are produced by some
  radioactive materials.

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• 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.

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Atmosphere

• 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
  transmitted.
• 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.

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• 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
satellites.

• Light from the sun reaching earth

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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.

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• 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
  ionising.

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• Ultraviolet
• Umbrellas can be useful in the sun as well as the
  rain
• 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.

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• 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
  safe.
• 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
  people.
• 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.

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• 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
  months.
• The real risk may be very different from
  the perceived risk ie the risk that you think is
  there.
• 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
  controversial.

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• 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
  explanation.
• 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
result.
Greenhouse effect
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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.

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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
  air
• photosynthesis by plants
• dissolving in the oceans.
• Processes that return carbon dioxide from the
  air
• 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.

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• 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
  respiration.

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Diagrams
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• 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
  sources
• burning large areas of forests to clear land,
  which means that there is less photosynthesis
  removing carbon dioxide from the air.

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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.

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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
  questions
• 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
  years
• 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.

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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
  others.
• 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.

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Microwaves

• 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
  orbit.

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• 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.

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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
  sound.
• 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
  distances.
• You should be able to explain why digital
  signals maintain their quality better than
  analogue signals.

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Noise

• 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.

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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
  computers.

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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.

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P3 SUSTAINABLE ENERGY
INCLUDING Using energy Generating
electricity Choosing energy sources
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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.

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Primary and secondary sources

• A primary source of energy is one that occurs
  naturally.
• 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.

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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.

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Power

• 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).

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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)

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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.

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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.

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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.
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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.

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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

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Note that only about a third of the energy stored
in the fuel was transferred as electrical energy
to customers.
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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.

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Electricity

• 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

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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
  by
• wind turbines
• hydroelectric turbines
• wave and tidal turbines
• When electricity is generated using wave, wind,
  tidal or hydroelectric power (HEP) there are two
  steps
• 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.

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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.
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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
  circuit.

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On magnet in the magnet goes in and the dial
turns to the sign
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• 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 stationsNuclear 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.
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Ionising radiation and living cells

• The radiations from radioactive materials
  alpha, beta and gamma radiation are all
  ionising radiations which can damage living
  cells.
• 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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