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THE EARTH IN THE UNIVERSE INCLUDING:

1. Earth, stars, galaxies and space

2. How the Earth is changing

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

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 comet’s tail.

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.

Stars form from massive clouds of dust and gas in space

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 star.

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 Earth’s 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

that’s 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.

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 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.

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?

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 Hubble’s 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.

Hubble’s 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.

Some galaxies do not fit exactly on the line of correlation

This correlation is summed up in Hubble’s 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 Earth’s 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.

Wegener’s theory Wegener’s 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

Wegener’s evidence Wegener’s evidence for continental drift was that:

1. the same types of fossilised animals and plants are found in South America and Africa

2. the shape of the east coast of South America fits the west coast of Africa, like pieces in a jigsaw puzzle

3. 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.

MORE Different explanations Data often allows more than one possible explanation, so different scientists can have

different explanations for the same observations. Wegener’s 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 Earth’s 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.

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 Earth’s 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 rockyThe mantle, shown here as dark red, which has the properties of a solid, but

can flow very slowlyThe outer core, shown as orange, which is made from liquid nickel and ironThe 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 Earth’s magnetic field. The Earth’s 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.

Plate tectonics - Higher tier Plate tectonics - Higher tier The Earth’s 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.

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.

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.

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.

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 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.

Radiation Life – P2Radiation Life – P2INCLUDING:INCLUDING:

• Electromagnetic radiationElectromagnetic radiationBenefits and risksBenefits and risks Global warming Global warmingWaves and communicationWaves 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. It’s the

part we can see.

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 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.

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 machines gamma rays, which are produced by some

radioactive materials.

MORE 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.

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 Earth’s surface. Gamma rays, X-rays, most of the ultraviolet and some of the infrared are absorbed by the atmosphere and do not reach the Earth’s surface.

Infrared Infrared from the Sun reaches the Earth’s 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 Earth’s 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.

•Light from the sun reaching earth

MicrowavesThe atmosphere transmits microwaves, and these can be used to communicate with satellites.

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.

MORE 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.

MORE 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.

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.

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 can’t 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.

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 Earth’s 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.

Greenhouse effect

The Sun’s rays enter the Earth’s atmosphere

Heat is emitted back from the Earth’s 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 Earth’s atmosphere. The Earth becomes hotter as a result.

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 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.

MORE 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.

Diagrams

MORE 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.

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 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

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.

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.

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 Earth’s atmosphere and can be used to transmit information to and from satellites in orbit.

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 Earth’s 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 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.

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.

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.

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 minute’s 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.

P3 – SUSTAINABLE ENERGYP3 – SUSTAINABLE ENERGY 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 sourcesA 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.

Fossil fuelsFossil 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 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 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 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.

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 circuit.

On magnet in the magnet goes in and the dial turns to the + sign

MORE 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.

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.

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

Hazards from radioactive materials

Hazards from radioactive materials Radioactive materials in the environment, whether

natural or artificial, expose people to risks. This can happen in two ways: The radiation from the material can damage the

cells of the person directly. This is damage by irradiation.

Some of the radioactive material can be swallowed or breathed in. While inside the body, the radiation it emits can cause damage. This is damage bycontamination.

Ideas about science - risk Ideas about science - risk Scientific or technological developments often introduce new risks: The development of radioactive materials in the early 20th century led

to the deaths of many workers. As the materials were new, no one realised they could be dangerous.

Risk can sometimes be assessed by measuring its chance of occurring in a large sample:

The safe dose that people may receive has been based on the rate of cancer in workers exposed to radiation over many years.

It is important to be able to assess the size of risks in any activity. No activity is completely safe:

The likelihood of dying from a nuclear accident has been calculated, and it is very low. Cycling is much more dangerous.

For most risky activities, there are benefits as well as risks: A gamma scan gives doctors valuable information to help cure a

patient. This benefit outweighs the slight risk from the gamma radiation itself.

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?

If the radiation dose someone has received is known, the chance of them getting a cancer is also known.

What is the consequence of that outcome? Cancers are serious conditions but, if diagnosed early, treatment

is now very successful for most types. This makes the consequence less severe.

The idea is that you may decide to avoid any activity if serious harm could arise. For example, people who are worried about working with radioactive materials may turn down a job in any situation where radioactive materials are used.

Perceived and real risk The real risk may be very different from the perceived risk ie

the risk that you think is there. Nuclear radiation is invisible, and sounds threatening to many

people. This makes the risk seem worse than something you can see, and which is more familiar.

Many people do not realise that nuclear radiation has always been part of our environment.

People are afraid that irradiated food is itself radioactive, even though this is not true.

Sometimes risk should be regulated by governments and other public bodies. This usually applies to an organisation that is responsible for its employees. In some situations decisions my be made by the organisation or public body that may cause controversy.

National GridNational Grid There are issues around the distribution of electricity

through the country as well as with the generation of it.

The electricity we use in our homes is distributed through the National Grid. All power stations are connected to the National Grid, who own and maintain the high-voltage electricity distribution through the UK.

Often electricity is needed far from where the power station is. As the current flows along wires to where it is needed, it heats the wires meaning energy is lost.

Reducing energy losses To reduce the energy lost when distributing

electricity, a high voltage is used. The mains supply voltage in our homes is 230 volts. Large currents would be needed to distribute electricity at 230 volts. This would heat wires and so the loss of energy would be large.

So, the National Grid distributes electricity at a much higher voltage. This means a lower current is needed and so less energy is lost due to heating.

Choosing energy sources A number of different energy sources

exist. Some of these are renewable and some are not. All of us have difficult choices to make when using energy, though it is clear that a mix of sources will need to be used.

Different kinds of energy sources p.t.o

Renewable energy sources Our renewable energy resources will never run out.

Their supply is not limited. There are no fuel costs either. And they typically generate far less pollution than fossil fuels.

Renewable energy resources include: wind energy water energy, such as wave machines, tidal

barrages and hydroelectric power geothermal energy solar energy biomass energy, for example energy released from

wood

However, there are some negatives to generating renewable energy. For example, wind farms are noisy and may spoil the view of people who live near them. The amount of electricity generated depends on the strength of the wind. Also, if there is no wind, there is no electricity.

Non-renewable energy sources There is a limited supply of non-renewable energy resources,

which will eventually run out. They include: fossil fuels, such as coal, oil and natural gas nuclear fuels, such as uranium Fossil fuels release carbon dioxide when they burn, which

adds to the greenhouse effect and increases global warming. Of the three fossil fuels, coal produces the most carbon dioxide, for a given amount of energy released, while natural gas generates the least.

The fuel for nuclear power stations is relatively cheap. But the power stations themselves are expensive to build. It is also very expensive to dismantle old nuclear power stations or store radioactive waste, which is a dangerous health hazard.

Nuclear power stations The main nuclear fuels are uranium and plutonium, both of which

are radioactive metals. Nuclear fuels are not burned to release energy. Instead, heat is released from changes in the nucleus.

Just as with power stations burning fossil fuels, the heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which drive generators to produce electricity.

Advantages Unlike fossil fuels, nuclear fuels do not produce carbon dioxide. Disadvantages Like fossil fuels, nuclear fuels are non-renewable energy

resources. And if there is an accident, large amounts of radioactive material could be released into the environment. In addition, nuclear waste remains radioactive and is hazardous to health for thousands of years. It must be stored safely.

Evaluating energy sources When evaluating energy sources you must consider: where the energy source is used (at home, in the work place or

at a national level) factors that affect the choice of energy source (economics,

environmental impact, waste produced including carbon dioxide) the advantages and disadvantages of the energy source All of us have choices to make on the use of energy. Some

would argue that we should not use less energy so we can maintain a good standard of living. Others would argue that reducing the amount of energy we use is essential.

There are a numbers of steps that could be taken to address problems faced by the energy industry. An important point we know for sure is that we need a mix of energy sources to meet the United Kingdom’s energy demands

Ideas about science - making decisions Scientific applications give people things that they value, but may have undesirable

impacts on the environment. Our society uses more and more energy every year, but the carbon dioxide

produced by most power stations is believed to be causing serious damage to the climate.

Natural resources should be used in a sustainable way. The use of renewable energy sources would guarantee energy for the future. At the

moment, renewable energy sources cannot provide enough energy. There are official regulations and laws which control scientific research and

applications. The nuclear industry is regularly inspected to ensure that standards of safety are

maintained. Some applications of science have ethical implications. One point of view is that the

right decision is the one which gives the best outcome for most people. Another point of view is that certain actions are never justified because they are wrong.

Disposal of nuclear waste raises ethical problems: Some people say that we must have nuclear power, or we will not be able to

combat global warming and still produce enough energy. Others say that it is unethical to produce waste that will still be dangerous in many

thousands of years’ time.

Weighing up the arguments - higher tier

Before deciding on a course of action, it is important to ask if it is feasible. Can it be done? Then it is possible to consider if it ought to done.

If nuclear waste could be sent down into the Earth’s mantle, it would take millions of years to resurface. Unfortunately, there doesn’t seem to be any way to do this. It is not feasible.

Nuclear waste could be sent into space in rockets so that it falls harmlessly into the Sun. Unfortunately, this would be far too expensive, and any accident on take-off would spread dangerous waste over a large area. It ought not to be done.

In different social and economic contexts, different decisions might be taken.

Many developing countries insist that they need to burn fossil fuels in their power stations, even if it produces global warming. They need this to allow them to catch up with the standard of living that we enjoy.

END OF P1,P2,P3END OF P1,P2,P3

This covers the basis of the needed revision. Teaching and learning this will help you

achieve A*/A Careful learning will make everything on the

exam paper to your level of ability. This PowerPoint is for OCR 21ST CENTURY

PHYSICS P1,P2,P3