# Physics Unit 1

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• Created on: 26-12-12 14:50

There are different ways that heat can be transferred including conduction, convection, radiation, evaporation and condensation. All of these require particles except infrared radiation.

• Another word for 'heat'
• All objects emit infrared radiation
• Hotter objects emit more infrared radiation
• Infrared radiation is a electromagnetic wave
• Infrared radiation can travel at the speed of light
• Different coloured surfaces emit differently
• Different coloured surfaces absorb differently
• You can detect infrared radiation with a special camera called a thermogram
• There are no particles required.

Matt black surfaces are great emitters and absorbers. However, shiny and white surfaces aren't.

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## Kinetic Theory

The kinetic particle theory explains the properties of the different states of matter. The particles in solids, liquids and gases have different amounts of energy. They are arranged differently and move in different ways.

Solids:

Properties of solids:

• They have a fixed shape and cannot flow this is because The particles cannot move from place to place
• They cannot be compressed or squashed this is because the particles are close together and have no space to move into

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## Kinetic Theory (part 2)

Liquids and Gases:

Properties of liquids -

• They flow and take the shape of their container this is because the particles can move around each other
• They cannot be compressed or squashed this is because the particles are close together and have no space to move into

Properties of gases -

• They flow and completely fill their container this is because the particles can move quickly in all directions
• They can be compressed or squashed this is because the particles are far apart and have space to move into
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## Heat Transfer - Conduction

Heat energy can move through a substance by conduction. Metals are good conductors of heat but non-metals and gases are usually poor conductors of heat. Poor conductors of heat are called insulators. Heat energy is conducted from the hot end of an object to the cold end.

As the temperature increase the atoms start to move more vigorously causing it to bump into its neighbour and then causing it to bump into its neighbour. The free electrons help by going to the atoms on the far end and making them vibrate aswell and it speeds up the process.

Heat conduction in metals

The electrons in piece of metal can leave their atoms and move about in the metal as free electrons. The parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together and they vibrate continually. The hotter the metal, the more kinetic energy these vibrations have. This kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons. These move through the structure of the metal, colliding with ions as they go.

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## Heat Transfer (part 2) - Convection

Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection.

The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas. In this way, convection currents that transfer heat from place to place are set up.

What happens in convection:

• The particles gain energy
• The liquid expands this is because the particles in liquids and gases move faster when they are heated than they do when they are cold.
• The liquid becomes less dense
• The warmer liquid rises to the top
• Since the liquid at the top is cool the heated liquid cools down
• The liquid contracts
• The liquid becomes more dense
• The liquid falls back down

This becomes a cycle and is continued until the whole liquid/gas has heated up.

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## Evaporation and Condensation

Evaporation and condensation are changes of state, evaporation involves a liquid changing to a gas. Condensation involves a gas changing into a liquid.

Evaporation

• The particles absorb heat energy
• They start to move faster and start to vibrate causing some of the particles to escape
• The remaining liquid is then cooler

Condensation

• The particles lose heat energy
• They move more slowly
• They move much closer together
• The gas condenses into a liquid

Factor affecting the rate of condensation and evaporation

• the surface area of the liquid is increased
• the temprature is increased
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## Factors affecting heat transfer

You can change the rate at which heat is transferred by:

• Changing the surface area- if the object has a large surface area heat will be lost more rapidly.
• Change the material the object is on- if the object is placed on wood, heat will be lost more slowly because wood is an insulator. However, if you place if on metal, heat will be lost faster because wood is a conductor.
• Change the material of the object- if you want heat to be lost slowly, you can change the material of the object into an insulator such as wood or plastic.

Cooling fins

Cooling fins have a very high surface area so more heat is radiated away. Cooling fins can be found at:

• the back of fridges to increase the rate of which heat is lost
• microchips
• motor bike engines
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## Keeping warm or cool

Animals living in different environments have certain adaptations to make heat transfer increase or slow down.

Elephants have a high volume therefor it is difficult to lose heat. However, they have large flat ears (large surface area) so more heat will be lost via the ears.

Whales also have a large surface area. On the other hand they have a small surface area so heat is lost far less rapidly.

Small animals like mice have a large surface area compared to their volume. They lose heat to their surroundings very quickly and must eat a lot of food to replace the energy lost.

In general, similar animals have different ear sizes depending on the climate in which they live. The arctic fox has much smaller ears than the fennec fox, which lives in the desert. The arctic fox must conserve its heat energy in the cold climate, while the fennec fox must avoid overheating in the hot climate.

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## U values

Insulating buildings

U values is basically the rate of heat being transferred through a material.

If you have a high u value, a lot of heat energy is being transferred.

If you have a low u value, a little heat energy is being transferred.

In terms of insulating buildings, having a high u value is bad and a having a low u value is good.

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## Specific Heat Capacity

Specific heat capacity

• the amount of energy required to raise the temperature of 1kg of a substance by 1°C.

energy = mass x specific heat capacity x temprature change.

Example

A concrete block is warmed up by 10°C. The mass of the block is 10kg. The specific heat capacity is 800j/kg°C. Calculate the energy transferred to the block.

energy = mass x specific heat capacity x temprature change.

energy =  10  x  800  x  10

80000 joules (800 kg)

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## Heat energy and efficiency

Forms of energy                - Most Kids Hate Learning GCSE Energy Names.

• magnetic- energy in magnets and electromagnets
• kinetic (movement energy)- the energy in moving objects – also called movement energy
• heat (thermal energy)- also called thermal energy
• light - also called radiant energy
• gravitational potential- stored energy in raised objects
• chemical- stored energy in fuel, foods and batteries
• sound- energy released by vibrating objects
• electrical- energy in moving charges or static electric charges
• elastic potential- stored energy in stretched or squashed objects
• nuclear- stored in the nuclei of atoms

Energy can be transferred usefully, stored or dissipated. It cannot be created or destroyed.

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## Efficiency

Calculating Efficiency

The efficiency of a device such as a lamp can be calculated:

efficiency = useful energy out ÷ total energy in (for a decimal efficiency)

efficiency = (useful energy out ÷ total energy in) × 100 (for a percentage efficiency)

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## Payback times

Payback time is how long it takes for something you changed in the house to pay for itself over time.

• Loft insulation- stops heat being lost from the roof
• Cavity wall insulation- stops heat escaping from the walls (between the double thickness of the wall they put an insulating material which then prevents heat loss)
• Double glazing- two layers of glass with a vacuum in the middle which stops heat loss through convection
• Draft excluders- stops cool air from entering the house and or warm air to escape.

Led lighting produces much more or the same amount of light as a normal bulb but with much less electricity.

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## Electrical Appliances

We can calculate the amount of electrical energy transferred by an appliance and how much it costs to run. This is useful for comparing the advantages and disadvantages of using different electrical appliances for a particular purpose.

Electrical energy calculations

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 1 kWh.

E = P × t

• E is the energy transferred in kilowatt-hours, kWh
• P is the power in kilowatts, kW
• T is the time in hours, 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 1,000.

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## Cost of electricity

Electricity meters measure the number of units of electricity used in a home or other building. The more units used, the greater the cost. The cost of the electricity used is calculated using this equation:

total cost = number of units × 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.

Remember that the number of units used can be calculated using this equation:

units (kWh) = power (kW) × time (h) … so …

total cost = power (kW) × time (h) × cost per unit

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## Generating Electricity

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## Generating Electricity

Electricity is a very convenient form of energy that can be generated using different energy resources. Some of these resources are renewable and some are non-renewable. Each resource has advantages and disadvantages.

Fossil Fuels

The fossil fuels are coal, oil and natural gas. They were formed from the remains of living organisms millions of years ago and they release heat energy when they are burned. They are non-renewable.

About three-quarters of the electricity generated in the UK comes from power stations fuelled by fossil fuels. The diagram on the previous card shows an energy transfer diagram for the generation of electricity from a fossil fuel such as coal.

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## Fossil Fuels

Fossil fuels are non-renewable energy resources: their supply is limited and they will eventually run out. Fossil fuels do not renew themselves, while fuels such as wood can be renewed endlessly.

Coal and oil release sulfur dioxide gas when they burn, which causes breathing problems for living creatures and contributes to acid rain.

Fossil fuels release carbon dioxide when they burn, which adds to the greenhouse effect and increases global warming. Of the three fossil fuels, for a given amount of energy released, coal produces the most carbon dioxide and natural gas produces the least.

Carbon Capture

Carbon capture and storage is a way to prevent carbon dioxide building up in the atmosphere. It is a rapidly evolving technology that involves separating carbon dioxide from waste gases. The carbon dioxide is then stored underground, for example in old oil fields or gas fields such as those found under the North Sea.

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## Nuclear Fuels

The main nuclear fuels are uranium and plutonium. These are radioactive (a substance that emits radiaton) metals.Nuclear fuels are not burnt to release energy. Instead, nuclear fission reactions (where the nuclei in atoms are split) in the fuels release heat energy.

The rest of the process of generating electricity is then identical to the process using fossil fuels. The heat energy is used to boil water. The kinetic energy in the expanding steam spins turbines, which then drive generators to produce electricity.

Unlike fossil fuels, nuclear fuels do not produce carbon dioxide or sulfur dioxide.

Fossil fuels, nuclear fuels are non-renewable energy resources. 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.

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## Wind Energy

The wind is produced as a result of giant convection currents in the Earth's atmosphere, which are driven by heat energy from the sun. This means that the kinetic energy in wind is a renewable energy resource: as long as the sun exists, the wind will too.

Wind turbines

Wind turbines use the wind to drive turbines directly. They have huge blades mounted on a tall tower. The blades are connected to a 'nacelle', or housing, which contains gears linked to a generator. As the wind blows, it transfers some of its kinetic energy to the blades, which turn and drive the generator. Several wind turbines may be grouped together in windy locations to form wind farms.

Wind is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced.

Wind farms are noisy and may spoil the view for people living near them. The amount of electricity generated depends on the strength of the wind. If there is no wind, there is no electricity.

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## Water energy

Like the wind, water can be used to drive turbines directly. There are several ways that water can be used, including waves, tides and falling water in hydroelectric power schemes.

Wave

The water in the sea rises and falls because of waves on the surface. Wave machines use the kinetic energy in this movement to drive electricity generators.

Tides

Huge amounts of water move in and out of river mouths each day because of the tides. A tidal barrage is a barrier built over a river estuary to make use of the kinetic energy in the moving water. The barrage contains electricity generators, which are driven by the water rushing through tubes in the barrage.

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## Water energy

Hydroelectric power

Like tidal barrages, hydroelectric power (HEP) stations use the kinetic energy in moving water. But the water comes from behind a dam built across a river valley. The water high up behind the dam contains gravitational potential energy.This is transferred to kinetic energy as the water rushes down through tubes inside the dam. The moving water drives electrical generators, which may be built inside the dam.

Water power in its various forms is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced. Tidal barrages and hydroelectric power stations are very reliable and can be easily switched on.

It has been difficult to scale up the designs for wave machines to produce large amounts of electricity. Tidal barrages destroy the habitat of estuary species, including wading birds. Hydroelectricity dams flood farmland and push people from their homes. The rotting vegetation underwater releases methane, which is a greenhouse gas.

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## Geothermal energy

Hot water and steam from deep underground can be used to drive turbines: this is called geothermal energy.

Volcanic areas

Several types of rock contain radioactive substances such as uranium. Radioactive decay of these substances releases heat energy, which warms up the rocks. In volcanic areas, the rocks may heat water so that it rises to the surface naturally as hot water and steam. Here the steam can be used to driveturbines and electricity generators.

Hot rocks

In some places, the rocks are hot, but no hot water or steam rises to the surface. In this situation, deep wells can be drilled down to the hot rocks and cold water pumped down. The water runs through fractures in the rocks and is heated up. It returns to the surface as hot water and steam, where its energy can be used to drive turbines and electricity generators. The diagram below shows how this works.

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## Geothermal energy

Geothermal energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced.

Most parts of the world do not have suitable areas where geothermal energy can be exploited.

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## Solar energy

Solar cells are devices that convert light energy directly into electrical energy. Do not confuse solar cells with solar panels, which use heat energy from the Sun to heat up water.

Solar energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced. Solar cells provide electricity in remote locations, such as roadside signs.

Disdvantages

Solar cells are expensive and inefficient, so the cost of their electricity is high. Solar cells do not work at night.

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## Resources compared

Power stations

Power stations fuelled by fossil fuels or nuclear fuels are reliable sources of energy, meaning they can provide power whenever it is needed. However, their start-up times vary according to the type of fuel used.

This list shows the type of fuel in order of start of time going from short to long:

1. gas-fired station (shortest start-up time)
2. oil-fired station
3. coal-fired station
4. nuclear power station (longest start-up time).

Nuclear power stations and coal-fired power stations usually provide 'base load' electricity - they are run all the time because they take the longest time to start up. Oil-fired and gas-fired power stations are often used to provide extra electricity at peak times, because they take the least time to start up.

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 and to store their radioactive waste, which is a dangerous health hazard.

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## Resources compared

Renewable resources

Renewable resources of fuel do not cost anything, but the equipment used to generate the power may be expensive to build. Certain resources are reliable, including tidal barrages and hydroelectric power. Others are less reliable, including wind and solar energy.

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## The national grid

Transformers

Electricity is transferred from power stations to consumers through the wires and cables of the National Grid. When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. To reduce these losses, the National Grid transmits electricity at a low current. This needs a high voltage.

Transformers are used in the National Grid. A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer that:

• increases the voltage is called a step-up transformer
• decreases the voltage is called a step-down transformer.

Power stations produce electricity at 25,000 V. Step-up transformers change the voltage to the very values needed to transmit electricity through the National Grid power lines. Electricity is sent through these at 400,000 V, 275,000 V or 132,000 V. This reduces energy losses during transmission but the voltages would be dangerous in homes. Step-down transformers are used locally to reduce the voltage to safe levels. The voltage of household electricity is about 230 V.

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## Main features of the national grid

Electricity from a power station goes to:

1. step-up transformers
2. high voltage transmission lines
3. step-down transformers
4. consumers, for example homes, factories and shops.

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## Waves

Waves can be described by their amplitude, wavelength and frequency. The speed of a wave can be calculated from its frequency and wavelength.

What are waves?

Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred.

Some waves must travel through a substance. The substance is known as the medium and it can be solid, liquid or gas. Sound waves and seismic wavesare like this. They must travel through a medium, and it is the medium that vibrates as the waves travel through.

Other waves do not need to travel through a substance. They may be able to travel through a medium, but they do not have to. Visible light, infrared rays, microwaves and other types of electromagnetic radiation are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.

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## Longitudinal and transverse waves

Transverse waves

In transverse waves, the oscillations (vibrations) are at right angles to the direction of travel and energy transfer

Light and other types of electromagnetic radiation are transverse waves. All types of electromagnetic waves travel at the same speed through a vacuum, such as through space.

Longitudinal waves

In longitudinal waves, the oscillations are along the same direction as the direction of travel and energy transfer.

Sound waves and waves in a stretched spring are longitudinal waves. P waves (relatively fast moving longitudinal seismic waves that travel through liquids and solids) are also longitudinal waves.

Longitudinal waves show area of compression and rarefaction. In the animation, the areas of compression are where the parts of the spring are close together, while the areas of rarefaction are where they are far apart.

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## Amplitude, wavelength and frequency

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.

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).

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## Wave speed

The speed of a wave is related to its frequency and wavelength, according to this equation:

v = f × λ

• v is the wave speed in metres per second, m/s
• f is the frequency in hertz, Hz
• λ (lambda) is the wavelength in metres, m.

All waves obey this wave equation. For example, a wave with a frequency of 100 Hz and a wavelength of 2 m travels at 100 × 2 = 200 m/s.

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## Refraction and diffraction

Sound waves and light waves change speed when they pass across the boundary between two substances with different densities, such as air and glass. This causes them to change direction and this effect is called refraction.

There is one special case you need to know. Refraction doesn't happen if the waves cross the boundary at an angle of 90° (called the normal) - in that case they carry straight on.

Diffraction

When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is called diffraction.

The extent of the spreading depends on how the width of the gap compares to the wavelength of the waves. Significant diffraction only happens when the wavelength is of the same order of magnitude as the gap. For example:

• a gap similar to the wavelength causes a lot of spreading with no sharp shadow, eg sound through a doorway
• a gap much larger than the wavelength causes little spreading and a sharp shadow, eg light through a doorway.
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## Reflection

Sound waves and light waves reflect from surfaces. When waves reflect, they obey the law of reflection:

the angle of incidence equals the angle of reflection

• The normal is a line drawn at right angles to the reflector
• The angle of incidence is between the incident (incoming) ray and the normal
• The angle of reflection is between the reflected ray and the normal.

Smooth surfaces produce strong echoes when sound waves hit them, and they can act as mirrors when light waves hit them. The waves are reflected uniformly and light can form images The waves can:

• appear to come from a point behind the mirror, for example a looking glass
• be focused to a point, for example sunlight reflected off a concave telescope mirror.

Rough surfaces scatter sound and light in all directions. However, each tiny bit of the surface still follows the rule that the angle of incidence equals the angle of reflection.

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## Ray diagrams

In a ray diagram, the mirror is drawn a straight line with thick hatchings to show which side has the reflective coating. The light rays are drawn as solid straight lines, each with an arrowhead to show the direction of travel. Light rays that appear to come from behind the mirror are shown as dashed straight lines.

Make sure that the incident rays (the solid lines) obey the law of reflection: the angle of incidence equals the angle of reflection. Extend two lines behind the mirror. They cross where the image appears to come from.

The image in a plane mirror is:

• virtual (it cannot be touched or projected onto a screen)
• upright (if you stand in front of a mirror, you look the right way up)
• laterally inverted (if you stand in front of a mirror, your left side seems to be on the right in the reflection).
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## Sound and light

Sound waves are longitudinal waves that must pass through a medium. Echoes are reflections of sounds. Light and other forms of electromagnetic radiation travel as transverse waves. These waves can travel through a vacuum, and they all travel at the same speed in a vacuum.

Sound

Sound waves are longitudinal waves. Their vibrations occur in the same direction as the direction of travel. Sound waves can only travel through a solid, liquid or gas.

Vibrations

When an object or substance vibrates, it produces sound:

• the greater the amplitude, the louder the sound
• the greater the frequency, the higher the pitch.
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## The electromagnetic spectrum

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A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. Diffraction allows low-frequency radio waves to be received behind hills, although repeater stations are often used to improve the quality of the signals.The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the ionosphere. This means that they can still reach receivers that are not in the line of sight because of the curvature of the Earth's surface.

Microwaves

Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range. 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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## Visible light and infrared

Visible light

Visible light is the light we can see. It allows us to communicate with one another through books, hand signals and video, for example. The use of visible light needs the transmitter and receiver to be in the line of sight. But it is more secure against eavesdroppers than radio waves.

Cameras let us record still pictures and movies, and photography is an important use of visible light. Very bright light can damage our eyes – you should never look directly into the Sun.

Infrared

We cannot see infrared radiation, but we can feel it as heat energy. High intensity infrared is used in heaters, toasters and grills, and it can cause burns. Infrared sensors can detect heat from the body. They are used in security lights and burglar alarms.

Infrared radiation is also used to transmit information from place to place, including:

• remote controls for television sets and DVD players
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## Origins of the universe

Current evidence suggests that the universe is expanding and that matter and space expanded violently and rapidly from a very small initial ‘point’. This has also led to the theory that the universe began with a ‘big bang’.

The big bang theory

Scientists have gathered a lot of evidence and information about the universe, and have used observations to develop the Big Bang Theory. The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion (called the Big Bang), and it is still expanding today. The Big Bang happened about 13.7 billion years ago (that's 13,700,000,000 years using the scientific definition of 1 billion = 1,000 million).

Astronomers have even detected a cosmic microwave background radiation, CMBR, that is thought to be the heat left over from the original explosion.

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## The doppler effect

You may have noticed that when an ambulance or police car goes past, its siren is high-pitched as it comes towards you, then becomes low-pitched as it goes away. This effect, where there is a change in frequency and wavelength, is called the Doppler effect.

When a source moves towards an observer, the observed wavelength decreases and the frequency increases.

When a source moves away from an observer, the observed wavelength increases and the frequency decreases.

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## Red-shift

When an object moves away from an observer, its light is affected by the Doppler effect.

Spectra from distant galaxies

Our Sun contains helium. We know this because there are black lines in the spectrum of the light from the Sun where helium has absorbed light. These lines form the absorption spectrum for helium.

When we look at the spectrum of a distant star, we still see an absorption spectrum. However, the pattern of lines has moved towards the red end of the spectrum.

The positions of the lines have changed because of the Doppler effect. Their wavelengths have increased (and their frequencies have decreased).

Astronomers have found that the further from us a star is, the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it's moving away.

Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else.

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