Physics P1

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  • Created by: liya
  • Created on: 14-01-13 19:41

What is Energy ?

Energy cannot be created or destroyed

Energy helps us do things

Energy is stored and transferred to its surroundings by infrared radiation.

All objects have energy

Energy is not physical stuff, it cannot exist as different forms.

However, there are different types in which energy is stored and transferred to its surroundings by infrared raditation.

 Energy is only useful when it can be converted from one form to another. 

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Emitting and absorbing

All objects emit and absorb infrared radiation 

Hot objects emit more than cooler ones

Bigger the difference in temperature and surroundings, energy is transferred faster.

 Black surfaces give out more infrared radiation than white ones

Dull surfaces give out more infrared radiation than shiny ones

Dark, matt surfaces  = good absorbers but bad reflectors

Shiny,light surfaces =  good emitters but bad absorbers

Object : Lots of energy = Quick and easy to do things

Object : Less energy = Not much can be done

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Kinetic Theory (Solids Liquids and Gases

Kinetic theory describes the energy of particles and the way that they move

Solid =Particles vibrating around a fixed shape - almost touching,Fixed volume,Regular pattern, strong attractive force between particles. Strong Intermolecular forces.

Liquid = Particles moving around, very close to one another,Takes space of container, fixed volume, attractive forces but not arranged in a regular way, Medium Intermolecular forces.

Gas = Particles moving rapidy, fills up space available, no attractive forces, no fixed shape or volume, weak/No  Intermolecular forces.

Bond in Particles 

Strongest = Solid

Weakest = Gases 

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Different forms of energy

  • Magnetic: Energy in magnets and electromagnets.
  • Kinetic: The energy in moving objects. Also called movement energy.
  • Heat: 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 or static electric charges.
  • Elastic potential: Stored energy in stretched or squashed objects.
  • Nuclear: Stored in the nuclei of atoms.
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Advantages and disadvantages of energy resources.

Coal/oil/gas: Reliable/Non renewable + Produces the greenhouse gas CO2

Nuclear: Reliable/Non renewable/high risk of accident like Chernobyl

Wind: Renewable + free/unsightly and noise and not reliable due to lack of wind

Falling water: Renewable + free/Only works in wet areas and risk of flooding

Waves: Renewable + free/can be harzadous to boats and isnt reliable

Tides: Renewable + free/ Only few esturies are suitable

Solar: Renewable + free + reliable in hot countries/Only generates small amount of electricity

Geothermal: Free + renewable/very expensive to build

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Electromagnetic spectrum

Electromagnetic radiations and magnetic disturbances: They travel as waves and move energy from place to place

All of the waves travel at the same speed.

  • Gamma rays have the shortest wavelength and highest frequency.
  • radio waves have the longest wavelength and lowest frequency.
  • Different wavelengths of electromagnetic radiation are reflected, absorbed or transmitted differently by different substances and types of surface.
  • They travel through space at a speed of 300 million metres per second.

Gamma rays X-rays Ultra violet visible light Infra-red Microwaves Radio waves.

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Electromagnetic spectrum Uses

Gamma rays: Gamma rays are used to sterilise cells/bacteria, however they can also cause cancer.

X-rays: They are used to produce shadow pictures of bones, however can also cause cancer.

Ultra violet: Used for tanning and can also cause cancer.

Visible light: Photography, but can cause blindness.

Infra-red: Used for remote controls, however can burn and damage skin.

Microwaves: Used for mobile phones but also kills healthy cells.

Radio waves: Used for communication and there are no other dangers assosiated with radio waves.

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Analogue and digital signals

communication signals are either analogue or digital.

  • An analogue signal varies continuously in amplitude.
  • Digital signals only have certain values, usually they are either high or their low. Low or high. There is no inbetween values in digital signals.

Analogue signal ( Analogue signal.

Digital signal ( signal.

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Different types of Radioactivity.

Alpha, Beta, Gamma.

  • Alpha α: is a helium nucleus. Its made up of 2 protons and 2 neutrons.
  • Beta β: Is a high speed electron from the nucleus It is given out (emitted) when a neutron changes to a proton and an electron.
  • Gamma γ: Radiation is a very short wave length electromagnetic radiation. (
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What is Red shift and Blue Shift?

If a source of waves is moving relative to an observer, the wavelength and frequency 'seen' by the observer will have changed (shifted) from the original produced by the source.

This effect can be heard with sound waves. E.g: It is easier to hear when its moving towards you (red shift) and when it moves further away the sound decreases (blue shift)

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The Big Bang

Red shift shows us that distant galaxies are moving away from us and the furthest ones are moving the fastest.

The universe is now expanding outwards, this suggests that it started with a massive expolsion at a very small initial point. This is knows as the big band theory.

Telescopes are used to collect the visible light coming from the stars, and so see them. Telescopes are also used to collect radiation from other parts of the electromagnetic spectrum such as x-rays, or radio waves.

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Electromagnetic radiation

  • Transmitted (passed straight through) an object.
  • Reflected back from the object.
  • Absorbed, this makes the object increase in heat or create an alternating current.

What happens to the waves depend on the wavelength, this is because different types of radiation react differently with different matter.

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Fossil Fuels

Process of burning fossil fuels

  • Coal is a store of chemical energy.
  • When heated it Boils water which is a store of heat energy.
  • The water evaporates into steam, which turns turbines.
  • A generator converts the kinetic energy in the turbine into Electrical energy.

Disadvantages of Fossil Fuels

  • Fossil fuels are non-renewable energy sources. Meaning they will eventually run out.
  • Fossil fuels release Carbon Dioxide when they burn. Adding to the greenhouse effect that is causing global warming.
  • Coal and oil also release Sulfur Dioxide gas which contributes to acid rain, which damages buildings.
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Nuclear Power

Process of Nuclear Power

  • Plutonium and Uranium are highly radioactive elements that are used in the process of Nuclear Fission.
  • Nuclear Fission is when the nucleus of an atom is separated into small parts called Nuclei.
  • This process releases extremely high amounts of thermal energy, which is used to boil water.
  • The steam then turns turbines.
  • A generator then turns the kinetic energy of the turbines into electrical energy.

Advantages and Disadvantages

  • Much more energy produced per kilo of fuel than any fossil fuel.
  • Products of Nuclear are extremely dangerous and need to be stored in a Lead lined container (usually dumped in the sea).
  • Nuclear power stations are extremely expensive to build and run. Even closing nuclear power stations is expensive. 
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Solar Panels

Solar Panels (or Photo-voltaic cells) are panels that have a chemical in them that turns light into electrical energy.

They are implemented into many machines, like the Parking Ticket Machine below. It can also be installed onto house roofs.

However because the cost of a solar panel is about the same are 20 years worth of electricity bills. You need to own one for 20 years before you start getting free electricity

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Payback Time

Payback Time

This is the time taken to recover from the up-front cost of an appliance.

Suppose you pay £2000 to buy and install a solar panel. You save £100 a year on electricity bills. It would take 20 years of payback time to recover from the £2000 cost of the solar panel.

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Energy can move through a substance. Metals are good conductors of thermal energy,whereas gases and non-metals are usually poor conductors of thermal energy.

When a metal is heated, ions vibrate around a fixed point. The more heat the more kinetic energy the ions have.

  • Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
  • This process is gradually continued through the solid and some of the kinetic energy or heat is passed all the way through.
  • Usually conduction is faster in denser solids, because the particles are closer together and so will collide more oftenand pass energy between them.
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Convection can only take place in liquids and gases, which are fluids.

When a liquid or gas is heated. When the particles get further apart and less dense, the particles will rise.

When the particles cool down, they become closer together and more dense. Causing them to fall. The process of convection is a continuous cycle.

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Heat Transfer - Radiation

All objects give out and take in thermal radiation, which is also called infrared radiation. The hotter an object is, the more infrared radiation it emits. Infrared radiation is a type of electromagnetic radiation that involves waves. Because it doesn't involve particles it can even work in space (vacuums).

The colour of a surface can effect the how much infrared radiation the surface will absorb and emit.

If you get two objects made of exactly the same materials and painted with the same shape, the thin, flat object will radiate heat faster. This is why radiators are thin, despite the fact that radiators are designed to create convection currents.

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Reducing Heat Loss

Heat is lost through houses in many ways. Below are a few examples of how.

  • through the roof
  • through windows
  • through gaps around doors
  • through walls
  • through the floor

Thermal Energy is transferred from homes by conduction through walls, the floor, roof and windows. But also by convection currents. When air is heated it the particles will expand and rise up and out through the roof.Here is how we can reduce heat loss in houses:

loft insulation will reduce heat loss through the roof                                                                              wall insulation will reduce heat loss through the walls                                                                  curtains and draught excluders will reduce heat loss through windows                                   Double-glazed windows mean that thermal energy cannot be conducted through the glass because of the thin layer of air in between the two window panes

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Energy Transfer

An energy transfer is when one form of energy is transferred into another form of energy.

In a simple circuit consisting of a light bulb and battery, chemical energy in the battery is transferred into electrical energy along the wires. Which is then transferred into light energy at the light bulb. There is also waste energy (unwanted forms of energy), in this case it is heat given of by the light bulb.A Sankey diagram is an accurate way of displaying energy transfer.

Put in : Electrical energy :100J

Wasted : Heat energy :90J

Useful : Light energy :10 J

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Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred. A bit like a Mexican wave!

  • Some waves can only be transferred through a medium (a solid, liquid or gas). Seismic waves and Sound Waves are two examples.
  • Other waves can travel through a medium, but they do not have to. These are all part of the Electromagnetic spectrum and include Visible Light, Infrared Waves and Microwaves.

Light travels as waves. Waves can be described by their amplitudewavelength andfrequency. The speed of a wave can be calculated from its frequency and wavelength.

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Waves .1

  • Amplitude is the distance from the peak of a wave to the point of origin. Amplitude is the the loudness of the wave, and is measured in Decibels.
  • Wavelength is the distance between one peak and the next. It is measured in millimeters, nanometers or even picometers.
  • Frequency is the pitch of a sound. Frequency is how many waves are produced per second. It is measured in Hertz/Hz. The more waves per second, the higher the pitch.
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Electromagnetic Spectrum Equations

The electromagnetic waves are electric and magnetic disturbances that transfer energy from one place to another.


wave speed  =  frequency  x  wavelength

        V           =        F         x          λ

      (m/s)               (Hz)                 (m)

This simple word equation can be rearranged to work out the frequency and the wavelength.

F  =  V  /  λ      and      λ  =  V  /  F   

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Transverse and Longitudinal Waves

Transverse Waves

Vibrations are perpendicular to movement.

Longitudinal Waves

Vibrations are along the direction of movement. 

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Geothermal Energy

Geothermal energy is energy produced from volcanic magma or hot rocks under the earths crust. The hot rocks or magma heat water into steam, this steam then turns turbines. Generators then turn this kinetic energy into electrical energy.

  • The steam and hot water is sent up to the surface through pipes.
  • Any cold water at the end of the process is pumped back down into the earth, where it will eventually be heated and re-used.

Advantages and Disadvantages

  • Geothermal energy is a renewable energy resource and there are no fuel costs.
  • No harmful gases or substances are produced in the process.
  • Most parts of the world do not have suitable areas where geothermal energy can be exploited.
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Non-Renewable & Renewable Energy

Renewable Energy

  • Renewable energy sources are not in limited supply and will not run out. They include production methods such as Wind Energy, Solar Energy, Tidal Energy, Hydroelectric Energy and Nuclear Power.
  • Nuclear power is extremely costly and can cost millions to build, run and destroy a Nuclear power station. It also results in the creation of radioactive substances which are expensive to dispose of.

Non-Renewable Energy

  • Non-Renewable energy sources are in limited supply and will eventually run out. They include Coal, Oil and Gas.
  • Non-Renewable energy sources usually pollute the atmosphere will harmful gases such as Sulphar Dioxide and Carbon Dioxide.
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The National Grid

The National Grid

England, Wales and Scotland is divided into 27 areas. Each area has its own name. Each block has its own electricity transmission system. An electricity transmission system consists of overhead lines and underground cables that carry electricity to buildings.


Step-up and step-down transformers are used to increase or decrease electricity.

Power from power stations is stepped-up for traveling along power lines. It is stepped-down for factories and industrial buildings, and stepped-down even more for use in homes.

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Specific Heat Capacity

The specific heat capacity of a substance is the energy needed or heat transferred to raise the temperature of 1kg of a substance by 1C.

The unit of specific heat capacity is joules per kilogram per C.

specific heat cap.  =  heat transferred (joules)  /  mass (kg)  x  temp. change (C)

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This is the energy per second that passes through one square meter of material when the temperature difference across it is 1C.

For example, replacing a single glazed window with a double glazed window that has a U-Value four times smaller then the energy loss will be four times smaller.

Lower U-Value = More Effective the Insulator

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  • Condensation is when gas turns to liquid.
  • When a gas cools, the particles in the gas slow down and lose kinetic energy.
  • The attractive forces between the particles pull them closer together.
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  • Evaporation is when particles escape from a liquid.
  • Particles can evaporate from a liquid at temperatures that are much lower than the liquids boiling point.
  • The fastest particles are most likely to evaporate from the liquid
  • The cooling effect can be really useful. As the water from the sweat on your skin evaporates, it cools you down.
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energy efficiency at home

  • payback time = intial cost divided by annual saving
  • The most effective methods of insulation are ones that give you the biggest annual saving 
  • Eventually, the money you've saved on heating bills will equal the intial cost of putting in the insulation
  • The most cost-effective methods tend to be cheapest
  • They are cost-effective becuase they have a short payback time - this means the money you save covers the amount you paid really quickly.
  • Heat transfers faster through materials with high U-values, so better the insulator the lower the U-value.
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Energy transfer

Different types of energy can be transferred from one type to another. Energy transfer diagrams show each type of energy, whether it is stored or not, and the processes taking place as it is transferred. Sankey diagrams also show the relative amounts of each type of energy. This energy transfer diagram shows the useful energy transfer in a car engine. You can see that a car engine transfers chemical energy, which is stored in the fuel, into kinetic energy in the engine and wheels.

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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 into the surroundings and spreads out so much that it becomes very difficult to do anything useful with it. 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 energy instead of light energy.

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). The efficiency of a device will always be less than 100%.

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Electricity is supplied to consumers through the National Grid at a very high voltage to reduce energy losses during transmission. Transformers are used to increase or decrease the voltage of the supply. Electricity is charged in units. One unit is equivalent to one kilowatt of electricity used for one hour.

Power stations are built in order to generate electricity. There are four main stages: the fuel is burned to boil water to make steam, the steam makes a turbine spin, the spinning turbine turns a generator which produces electricity, the electricity goes to the transformers to produce the correct voltage. The energy needed to boil the water comes from fossil fuels or nuclear fuels. Renewable energy resources such as wind and wave power may drive the generators directly.

A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer changes a high-voltage supply into a low-voltage one, or vice versa. A transformer that increases the voltage is called a step-up transformer. A transformer that decreases the voltage is called a step-down transformer.

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How waves travel

Light travels as waves. Waves can be described by their amplitude,wavelength and frequency. The speed of a wave can be calculated from its frequency and wavelength. Waves are vibrations that transfer energy from place to place without matter (solid, liquid or gas) being transferred. Think of a Mexican wave in a football crowd. The wave moves around the stadium, while each spectator stays in their seat only moving up then down when it's their turn.

Some waves must travel through a substance. The substance is known asthe medium, and it can be solid, liquid or gas. Sound waves and seismic waves are like this. They must travel through a medium. 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 don't have to. Visible light, infrared rays, microwaves and other types ofelectromagnetic radiation are like this. They can travel through empty space. Electrical and magnetic fields vibrate as the waves travel.

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Gamma radiation

Gamma waves have a very high frequency. Gamma radiation cannot be seen or felt. It mostly passes through skin and soft tissue, but some of it is absorbed by cells. Gamma radiation is used, among other things, to sterilise surgical instruments, kill harmful bacteria in food and kill cancer cells (note that lower doses of gamma radiation could lead to cells becoming cancerous).

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X-rays have a lower frequency than gamma radiation. Like gamma rays, they cannot be seen or felt. X-rays mostly pass through skin and soft tissue, but they do not easily pass through bone or metal.

X-rays are used to produce photographs of bones to check for damage such as fractures. They are also used in industry to check metal components and welds for cracks or other damage.

Lower doses of X-rays can cause cells to become cancerous, so precautions are taken in hospitals to limit the dose received by patients and staff when X-ray photographs are taken. 

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infrared radiation

Infrared radiation is absorbed by the skin and we feel it as heat. It is used in heaters, toasters and grills. It is also used for television remote controls and in optical fibre communications.

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Microwave radiation has lower frequencies and longer wavelengths than visible light. Microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking. Water in the food absorbs the microwave radiation, which causes the water to heat up and cook the food. The water in living cells can also absorb microwave radiation. As a result, they can be killed or damaged by the heat released.

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. Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit.

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Television and radio

Radio waves have lower frequencies and longer wavelengths than microwaves. They are used to transmit television and radio programmes. Television uses higher frequencies than radio.

A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals. For low frequency radio waves diffraction can allow them 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 reach receivers that are not in the line of sight because of the curvature of the Earth's surface.

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Origins of the Universe

The foremost theory of the origin of the universe is the Big Bang theory. It suggests that the universe began several billion years ago in an explosion that caused it to expand, and to continue expanding. Some of the evidence for the Big Bang comes from studying the red shift of light received from distant galaxies. Telescopes allow us to observe the universe.

Scientists have gathered a lot of evidence and information about the universe. They have used their observations to develop a theory called the Big Bang. 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, and it is still expanding today. This explosion is called the Big Bang, and happened about 13.6 billion years ago (that's 13,600,000,000 years using the scientific definition of 1 billion = 1,000 million).

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

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Evidence from Big Bang

There are two key pieces of evidence for Big Bang theory. These are red shift and theCosmic Microwave Background radiation.

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. It happens with any wave source that moves relative to an observer. This happens with light too. 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.

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Optical fibre

the light ray enters the fibre at one end and is reflected out at the other end ( 

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Sending information

Optical fibres can carry information coded in light or infrared signals. Optical fibres can carry more information than an ordinary cable of the same diameter. Analogue signals vary continuously in amplitudefrequency or both. Digital signals are a series of pulses with two states – on or off. Digital signals carry more information per second than analogue signals, and they maintain their quality better over long distances. An optical fibre is a thin rod of high-quality glass. Very little light is absorbed by the glass. Light getting in at one end undergoes repeated total internal reflection, even when the fibre is bent, and emerges at the other end.

Information such as computer data and telephone calls can be converted into electrical signals. These can be carried through cables, or transmitted as microwaves or radio waves. However, the information can also be converted into either visible light signals or infrared signals, and transmitted by optical fibres. Optical fibres can carry more information than an ordinary cable of the same thickness. The signals in optical fibres do not weaken as much over long distances as the signals in ordinary cables.

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Ultraviolet radiation

Ultraviolet radiation is found naturally in sunlight. We cannot see or feel ultraviolet radiation, but our skin responds to it by turning darker. This happens in an attempt to reduce the amount of ultraviolet radiation that reaches deeper skin tissues. Darker skins absorb more ultraviolet light, so less ultraviolet radiation reaches the deeper tissues. This is important because ultraviolet radiation can cause normal cells to become cancerous.

Ultraviolet radiation is used in sun beds, security pens and fluorescent lights (coatings inside the tube or bulb absorb the ultraviolet light and re-emit it as visible light).

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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 have huge blades mounted on a tall tower. The blades are connected to a nacelle or housing that 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 however 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

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. 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. Like tidal barrages, hydroelectric power 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 turned on quickly. 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

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 drive turbines and electricity generators. This type of geothermal power station exists in places such as Iceland, California and Italy.

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.

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. You may have seen small solar cells in calculators. Larger arrays of solar cells are used to power road signs in remote areas, and even larger arrays are used to power satellites in orbit around Earth.

Solar panels do not generate electricity, but rather they heat up water. They are often located on the roofs of buildings where they can receive heat energy from the sun. Cold water is pumped up to the solar panel, there it heats up and is transferred to a storage tank. A pump pushes cold water from the storage tank through pipes in the solar panel. The water is heated by heat energy from the sun and returns to the tank. In some systems, a conventional boiler may be used to increase the temperature of the water.

Solar energy is a renewable energy resource and there are no fuel costs. No harmful polluting gases are produced however solar cells are expensive and inefficient, so the cost of their electricity is high, solar panels may only produce very hot water in very sunny climates, and in cooler areas may need to be supplemented with a conventional boiler and although warm water can be produced even on cloudy days and neither works at night.

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The cost of using electricity

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 transferred (kWh) = power (kW) × time (h) 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. ime is measured in hours here, instead of the more usual seconds. To convert from seconds to hours you must divide by 3600. For example, 1800s = 1800 ÷ 3600 = 0.5 hours.

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.

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The perpendicular line to the mirror is called the normal.

The angle of incidence is the angle between the incident ray and the normal.

The angle of reflection is the angle between the reflected ray and the normal.

Measurements show that for any light ray reflected by a mirror:

- The angle of incidence = angle of reflection

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there are many different types of mirror. a plane mirror will show you an exact MIRROR IMAGE of yourself. some mirrors bend outwards - convex mirrors so you will be tall and thin whereas a concave mirror - folds inwards will make you look FAT

an image seen in a mirror is caused by a reflection of light

A VIRTUAL IMAGE is wen light rays that reflect from the mirror into your eye appear to come from the image

A REAL IMAGE (cinema) is when light rays all focus onto the screen


  • there will be no change in direction if the light ray is along the normal
  • as the light ray travels from air to glass it bends towards the normal, so the angle of refractionr is smaller than the angle of incidence i
  • as the light ray travels from glass to air, it bends away from the normal so angle r is larger than angle i.
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Plane mirrors

The image in a plane mirror is:

  • the same size as the object
  • upright and virtual
  • the same distance behind the mirror as the object in front.
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Normal and Virtual Images

The difference between Normal and Virtual Images is very easy to understand.

You need to ensure that you are perfectly clear on the difference.

REAL Can be formed on a screen.
The rays of light that form the image, actually pass through it.

VIRTUAL Cannot be formed on a screen.
The rays that form the image, only appear to pass through it.

The names of the two images basically say it all. Real is normal and virtual is imaginary in a way - the rays do not really pass through the image, the only appear to.

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