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Descrição
FlashCards por Chima Power, atualizado more than 1 year ago
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Criado por Chima Power
mais de 9 anos atrás
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| Questão | Responda |
| Infrared radiation | Use special cameras to 'see' people in dark, which detect infrared radiation. The hotter the object the more infrared radiation it emits in a given time. If you use a glass prism which splits up rays of light and place thermometer just to side of red ray temperature will rise, even though our eyes cant detect it it's infrared radiation. |
| Electromagnetic spectrum | Radio waves, microwaves, infrared radiation and visible light parts of electromagnetic spectrum, also, ultraviolet rays and x-rays. Electromagnetic waves are electric and magnetic waves that travel through space. Rude men in Vegas Wear X-ray glasses |
| Energy from the sun | Sun emits all types of electromagnetic radiation though earth's atmosphere blocks most of this radiation that would harm us. Doesn't block infrared radiation from the sun, a solar furnaces uses a giant reflector that focuses sunlight temperature at focus can reach thousands of degrees, 5500 degrees Celsius. |
| Greenhouse effect | Earth's atmosphere acts like a greenhouse made of glass: - short wavelength infrared radiation (and light) from the Sun can pass through the glass to warm the objects inside the greenhouse - infrared radiation from warm objects trapped inside by glass as objects emit infrared radiation of longer wavelength that can't pass through glass. So greenhouse stays warm. Gases in atmosphere like carbon dioxide, methane and water vapor trap infrared radiation from the Earth. Which makes the Earth warmer than it would be if it had no atmosphere. Yet earth is becoming too warm, if polar ice caps melt will cause sea levels to rise reducing use of fossil fuels will help to reduce the production of 'greenhouse gases'. |
| Surfaces are best absorbers and reflectors of radiation | - Dark matt surfaces are better at emitting radiation than light, shiny surfaces A light shiny surface absorbs less radiation than dark, matt surfaces. A matt surface has a lot of cavities: - The radiation reflected from the matt surface hits the surface - The radiation reflected from the shiny surface travels away from the surface. So shiny surface absorb less and reflect more radiation than a matt surface: - Light shiny surfaces absorb less radiation than dark matt surfaces - Light shiny surfaces reflect more radiation than dark matt surfaces. |
| States of matter | Everything around us is made of three states - solids, liquids, gases. Solids have no flow, a fixed volume, a fixed shape, and a much higher density than gas. Liquids can flow, have a fixed volume, they take the shape of a container and have a much higher density than gas. Gases flow, fills a container, the volume can be changed and have low density compared with liquids and solids. |
| Changes of state | Substances can change from one state to another can make these changes by heating or cooling substances, ex. When water in kettle boiled water evaporates to form steam also called water vapor in gaseous form, when solid carbon dioxide/ dry ice warms up directly forms gas, when steam touches a cool substance and turns to water. |
| Kinetic theory of matter | Solids, liquids and gases consist of particles, when temperature of substance is increased the particles move faster. - Particles in solid held next to each other in fixed position which vibrate about a fixed position so solid keeps its shape. - Particles in liquid are in contact with each other which move about at random. So liquid doesn't have it's own shape and can flow. - Particles in gas move move about at random faster, are on average much further apart from each other than in a liquid so very low density. - Particles in solid, liquids and gases have different amounts of energy, particles in gas have more energy than those in liquid which have more energy than those in solid. |
| Conductors | Metals conduct energy better than non-metals, copper is a better conductor than steel, wood conducts better than gas |
| Conduction in metals | Metals contain free electrons, these move about at random inside the metal and hold positive metal ions together. These collide with each other and with positive ions - ions are charged particles. When metal rod heated at one end free electrons at hot end gain kinetic energy and move faster: - Electrons diffuse and collide with other free electrons and ions in cooler parts of the metal. - As result they transfer kinetic energy to these electrons and ions. By this process energy is transferred from the hot end of the rod to the lower end. In non metallic solid all electrons are held in the atoms, energy transfer only takes place because the atoms vibrate and shake each other which is less effective than energy transfer by electrons. Why metals are much better conductors than non-metals. |
| Convection | Convection occurs whenever fluids are heated, the hot fluids rise the cold fluids are drawn down to replace the fluid. |
| Using convection | Hot water at home: Many homes have hot water tank, hot water from boiler rises and flows into the tank where it rises to the top. Sea breeze: These keep you cool at the seaside, on sunny day ground heats up faster than the sea. So air above grounds up and rises, cooler air flow in as the sea breeze to take place of the rising warm air. |
| How convection works | Takes place in fluids and due to circulation (convection) currents within the fluid. Circulatiion currents caused because fluids rise when heated as heating makes them less dense then fall when cool down as cooling makes them more dense. Convection currents transfer energy from the hotter part to the cooler parts. Most fluids expand when heated, as particles move about more taking up more space. Therefore density decreases as the same mass of fluid now occupies a bigger volume. So heating part of the liquid makes them less dense hence rises. |
| Evaporation | Evaporation of water occurs if leave saucer in room water in saucer gradually disappears, water molecules escape from the surface of the water and enter air in the room. In well ventilated room water in air molecules are unlikely to re-enter water, they continue to leave water until all water evaporated. |
| Condensation | Mirror - film of water, lots of water molecules in air, some hit mirror, cool down and stay there water vapour in air condenses on mirror. |
| Cooling by evaporation | If have injection, nurse might numb skin by dabbing it with liquid that easily evaporates. As liquid evaporates skin becomes too cold to feel pain as fastest moving molecules those with the greatest thermal evaporate. - Weak attractive forces exist between molecules in liquid. - Faster molecules with more kinetic energy break away from the attraction of other molecules and escape into liquid. - After leave the liquid is cooler because average kinetic energy of remaining molecules in the liquid have decreased. |
| Factors affecting rate of evaporation | Evaporation of liquid increased by: - increasing surface area of liquid - increasing temperature of liquid - Creating a draught of air across the liquid's surface |
| Factors affecting rate of condenstation | Rate of condensation of a vapour on a surface: Increasing the surface area Reducing the surface temperature |
| Cooling by design | Things can go wrong if don't control energy transfer: - Cooling system of car engine transfers energy from engine to radiator, radiator shaped so has large surface area this increases the rate of energy transfer through convection in air and radiation. - Motorcycle engine is shaped with fins on outside surface, fins increase the surface area of engine in contcat with air so engine transfers energy to the surrounding faster than without fins. - Most cars have cooling fan that switches on when engine is too hot, this increases the flow of air over the surface of the radiator. |
| Vacuum flask | If outdoors in cool environment, hot drink form flask keeps you warm in summer same flask keeps your drink cold. Liquid you drink is a double-walled glass container. - Vacuum between walls of container cuts out energy transfer by conduction and convection between walls - Glass poor conductor so there's less energy transfer by conduction through glass. - Glass surfaces are silvery to reduce radiation from outer walls. - Spring supporting double-walled container is made of plastic which is a good insulator. - Plastic cap stops cooling by evaporation as it stops vapour loss from flask, energy transfer by conduction is cut down as cap is made of plastic. Although these do not completely stop energy transfer, it occurs at low rate due to radiation from silvery surfaces and conduction by plastics and glass, liquid slowly transfers energy to surroundings so eventually cools. |
| Factors affecting rate of energy transfer | bigger temperature difference between object and surroundings faster the rate energy is transferred. Design factors: - Material object is in contact with - Object's shape - Object's surface area Object mass and material important, as they affect how quickly its temperature changes( hence rate of energy transfer to and from it) when loses or gains energy. |
| Specific heat capacity | When substance heated temperature rise depends on: - Amount of energy supplied to it - mass of substance - what substance is The specific heat capacity of a substance is the energy needed or energy transferred to 1kg of substance to raise it by 1 degree celsius. For a known change of temperature of a known mass of substance: E=m*c* (-) E- energy transferred in joules, J m- mass in kilograms, kg c-specific heat capacity J/kgC (-) Temperature change in degrees celsuis |
| Storage heaters | Use electricity at night (off-peak) to heat special bricks or concrete blocks in the heater. Energy transfer from the bricks keep the room warm. Bricks have a high specific heat capacity so store lots of energy, warm up slowly when heater element is on and cool down slowly when it turns off. Electricity consumed at off-peak times is sometimes charged for at a cheaper rate so storage heaters are designed to be cost effective. |
| Reducing rate of energy transfer at home | Home heating bills can be expensive, we can reduce the rate of energy transfer at home and reduce our home heating bills. Loft insulation: Such as fiberglass reduce rate of energy transfer through roof, fiberglass is a good insulator. Air between the fibres also help to reduce rate of energy transfer by conduction. - Cavity wall insulation: Reduces energy loss through outer wall of house, 'cavity' of outer wall is space between two layers of brick that make up wall. Insulation is pumped into the cavity, it's better insulator than air it replaces. Traps air in small pockets reducing convection currents. - Aluminum foil: Between radiator panel and wall reflects radiation away from wall. - Double-glazed windows: Have two glass panes with dry air or vacuum between planes, dry air is a good insulator so reduces the rate of energy transfer by convection. Vacuum cuts out energy transfer by convection as well. |
| U-values | Compare different insulating materials if know U-value this is energy per second that passes one square metre of material when temperature difference across it is 1 degree celsius. Lower the U-value, the more effective the material as an insulator. |
| Solar heating panels | Heating water at home using electricity or gas can be expensive, solar heating panel uses solar energy to heat water. Panel is usually fitted on roof that faces south, making most of Sun's energy. Panel is flat box containing liquid-filled copper pipes with matt, black metal plate. Pipe are connected to a heat exchanger in a water storage tank in the house. Transparent cover on top of panel allows solar radiation through to heat the metal plate, insulating material under the plate stops energy being transferred through the back of panel. On sunny day the metal plate and copper pipes in box become hot, liquid pumped through pipes is heated when it passes through panel. Liquid may be water or solution containing anti freeze. The hot liquid passes through the heat exchanger and transfers energy to water in storage tank. |
| Payback time | solar heating panels save money as no fuel is needed to heat the water. Their expensive to buy and install. Payback time taken to recover the up front cost from saving on fuel bills. |
| Forms of energy: On the move | Cars, buses, planes and ships all use energy from fuels, carry own fuels electric trains use energy from fuel in power stations. Electricity transfers energy from power stations to train. Describe energy stored or transferred in different ways as forms of energy. Examples of forms of energy: - Chemical energy is energy stored in fuel (including food) this energy is released when chemical reactions take place. - Kinetic energy is energy of a moving object - Gravitational potential energy is energy of object due to position - Elastic potential energy is energy stored in spring object when we stretch or squash it - Electrical energy is energy transferred by electric current Energy may be transferred from one form to another, in torch battery pushes a current through the bulb which makes the bulb emit light and also gets hot. Show energy transfer using flow diagram: chemical energy in battery -> electrical energy -> light energy + energy heating surrounding |
| Conservation of energy: Funfair | Lots of energy transfers quickly happen, roller coaster gains gravitational potential energy when it climbs, roller coaster rolling downwards: GPE -> kinetic energy + sound + energy transfer by heating due to air resistance and friction. Energy transferred by heating is 'wasted' energy |
| Pendulum swinging | As moves towards the middle its gravitational potential energy is transferred to kinetic energy. As moves from middle its kinetic energy transfers back to gravitational potential energy. If air resistance on bob is very small, should find that bob reaches the same height on each side. |
| Conservation of energy | Scientists done lot of tests to find out if total energy after a transfer is same as energy before transfer. Conservation of energy no energy can be created or destroyed. |
| Bungee jumping | When rope is slack some of gravitational potential energy of bungee jumper is transferred to kinetic energy as jumper falls. Once slack in rope has been used up the rope slows the bungee jumper's fall. Most of gravitational potential energy and kinetic energy of jumper is transferred into elastic strain energy. After reaching the bottom the rope pulls the jumper back up, as jumper rises, most of elastic strain energy of the rope is transferred back to GPE and kinetic energy of jumper. Bungee jumper doesn't return to same starting height as some of initial GPE has been transferred to surroundings by heating as rope stretched then shortened again. |
| Useful energy | A machine transfers energy for a purpose, friction between moving parts of a machine causes parts to warm up so not all the energy supplied to a machine is usefully transferred, some energy is wasted. Useful energy: - Energy transferred to where it's wanted in the form wanted. Wasted energy: - energy thats not usefully transferred. |
| Disc brakes at work | When brakes applied, pads are pushed on disc of wheel, friction between pads and each of disc slows the wheel down. Some of kinetic energy of car is transferred to energy heating the disc pads and discs. |
| Spreading out | Wasted energy is dissipated to the surroundings: Ex. Gears of car get hot due to friction, when car is running, so energy transfers from gearbox to surrounding air. Useful energy eventually transfers to surroundings: Ex. Useful energy supplied to car wheels is transferred to energy heating the car tyres. Energy is then transferred to the road and surrounding air. Energy becomes less useful the more it spreads out. Ex. Hot water from cooling system of CHP (combined heat and power) power stations get used to heat nearby buildings. Energy supplied to heat the buildings will eventually be transferred to the surroundings. |
| Energy and efficiency | When lift object useful energy from muscles transferred to gravitational potential energy depending on weight and how high it's raised. Weight's measured in newtons (N), weight of 1kg object is 10N. Energy measured in joules (J), energy needed to lift 1N by a height of 1metre equal to 1 joule. Muscles get warm when used so they waste some energy. |
| Sankey diagrams | Can represent any energy transfer where energy is wasted, diagram is called Sankey diagram. Input energy = useful energy delivered + energy wasted Efficiency= useful energy transferred to device/ total energy supplied to device * 100% |
| Efficiency limits | No machine can be 100% efficient as can never get more energy from machine than we put in. |
| Improving efficiency | Problem - Friction between moving parts causes friction, solution - lubricate moving parts to reduce friction. Problem- Resistance of wire causes wire to get hot when current passes through, solution - in circuits use wires with as little electrical resistance as possible. Problem- air resistance causes energy transfer to surroundings, solution- streamline shapes of moving objects to reduce air resistance. Problem - sound created by machinery causes energy transfer to surroundings, solution - cut out noise ex. tighten loose parts to reduce vibration. |
| Electrical appliances | Transfer electricity energy into useful energy. Light bulb use useful energy from a filament, wasted energy is energy transferred from filament to surroundings |
| Clockwork radio | Trevor Baylis invented in 1990's when you turn handle wind up clockwork spring in radio. When spring unwinds turns a small electric generator in the radio. People in remote areas where there's no mains electricity can listen to radios without having to walk miles for replacement battery. But must constantly be turning spring |
| Choosing an eletrical appliance | These have many purposes each appliance is designed for a particular purpose rock musician at a concert you would need appliances that transfer sound of energy into electrical energy and then back to sound energy. Wouldn't want to produce lots of energy heating the appliance itself and surroundings |
| Electrical power | Energy we supply per second to a motor is the power supplied to it More powerful a motor is the faster it moves a particular load The more powerful an appliance the faster the rate at which it transfers energy. Measure power of an appliance in watts (W) or kilowatts (kW). A watt is a rate of energy transfer of 1 joule per second (J/s). Kilowatt is equal to 1000 watts ex. 1000 joules per second P=E/t P - power in watts, W E - energy transferred to appliance in joules, J t - time taken for energy to be transferred in seconds, s |
| Efficiency and power | For any appliance: - Useful power out (output energy) is useful energy per second transferred to it - Total power /input energy is energy per second supplied to it Efficiency = useful power in/ useful power out * 100% |
| Using electrical energy | For any appliance energy used depends on: - how long used for - power supplied to it Energy supplied to a 1kW appliance in one hour is 1 kilowatt-hour (kWh) E=P*t E- energy transferred in kilowatt-hour, kWh P - power in kilowatt, kW t - time taken for energy transferred in hours, h If you use joules: E- energy transferred in joules, J P - power in watts, W t - time taken for energy transferred in seconds, s |
| Paying for eletrical energy | Electricity meter in home measures how much electrical energy family uses. Records total energy supplied no matter how many appliances you all use. Gives a reading of number of kilowatt-hours (kWh) of energy supplied by mains. In most house someone reads meter every three months. Difference been two readings in number of kilowatt-hours supplied since last bill. Use kilowatt-hour to work out cost of electricity. Ex. Cost of 12p per kWh means each kilowatt-hour of electrical energy cost 12p. total cost = number of kWh used * cost per kWh |
| Cost effectiveness | Must ensure attain value for money when buying energy-saving appliances that do the same job. To compare cost effectiveness of different cost-cutting measures must consider: - capital cost: buying and installing item - environmental impacts ex: - removal or disposal of old equipment ex. used batteries - tax charges like carbon taxes of fossil fuels - other costs like loans |
| Payback time! | Householder aims to reduce energy losses from home, she compared loft insulation with cavity wall insulation in terms of payback time. - Loft insulation costs 200 pounds (-gloves and safety mask) would fit insulation herself. Could save 100 pounds a year on fuel bill, so payback time would be 2 years. - Cavity wall insulation for house costs 500 pounds and an additional 100 pounds to fit the insulation. Could save 200 pounds a year on fuel bill which would pay for itself in three years. |
| Lighting costs | Low energy bulbs use less electrical energy than filament bulbs, why UK has banned use of filament bulbs. Filament bulbs are only 20% efficient wasting energy as heat, halogen bulbs are 25% efficient getting hot, low energy compact fluorescent bulbs are 80% efficient though takes a few minutes for full brightness, and when disposed must be sealed in bag as contain mercury so they're toxic and low-energy light-emitting diodes are 90% efficient though are expensive to buy and not so bright. |
| Inside a power station | Almost all generated electricity is from power stations. In coal or oil fired power station and in most gas fired power stations the burning fuel heats water in a boiler which produces steam. The steam drives a turbine that turns an electrical generator. Coal, oil and gas are fossil fuels, which are fuels obtained from long-dead biological material. In some gas-fired power stations we burn natural gas directly in a gas turbine engine. This heats the air drawn into the engine, it produces a powerful jet of hot gases and air that drives the turbine. Gas-fired turbine can be switched on very quickly. |
| Biofuels | Can get methane gas from cows or animal manure and from sewage works, decaying rubbish and other sources. This can be used in small-scale gas-fired power stations - methane is a biofuel. A biofuel is any fuel obtained from living or recently living organisms like animal waste or wood chip. Other biofuels are ethanol (from feremented sugar cane), straw, nutsheels and woodchips. Biofuel is: - renewable as its biological source continues to exist and never dies out at species - carbon-neutral as in theory the carbon it takes in from the atmosphere as carbon dioxide can equal the amount released when it is burned. |
| Nuclear power | Each atom contains a positively charged nucleus surrounded by electrons. The atomic nucleus is composed of two types of particles: neutrons and protons. Atoms of the same element can have different number of neutrons in the nucleus. |
| How electricity is obtained from a nuclear power station | Fuel in a nuclear power station is uranium/ plutonium the uranium fuel is in sealed cans in the core of the reactor. The nucleus of the uranium atom is unstable and can split into two, energy is released when this happens. This process is called nuclear fission as there are lots of uranium atoms in the core it becomes very hot. Energy of the core is transferred by a liquid (called coolant) that is pumped through core. Coolant is very hot when it leaves the core, it flows through a pipe to a heat exchanger then back to reactor core. Energy of the coolant is used to turn water into steam in the heat exchanger, the steam drives turbines that turn electricity generators. |
| Wind power | This is carbon free as no fuel is required to produce electricity from this natural source and is renewable. A wind turbine is an electricity generator at the top of a narrow tower, the force of the wind drives the turbines blade around. This turns a generator, the power generated increases as wind speed increases. |
| Wave power | This is carbon free as no fuel is required to produce electricity from this natural source and is renewable. Wave generator uses waves to make floating generator move up and down, this motion turns the generator so it generates electricity. A cable between the generator and the shore delivers electricity to the grid system. Wave generators must be able to withstand storms and don't produce a constant supply of electricity. Also lots of cables (and buildings) are needed along the coast to connect the wave generator to the electricity grid. This can can spoil areas of the coastline, tidal flow patterns might also change, affecting habitats of marine life and birds. |
| Hydroelectric power | Can generate hydroelectricity when rainwater collected in a reservoir or water in a pumped storage scheme flows downhill. The flowing water drives turbines that turn electricity generators at the foot of the hill. |
| Tidal power | These trap water from each high tide behind a barrage, can then release the high tide into the sea through turbines in low tide. The turbines drive generators in the barrage. In Britain the Severn estuary is a promising site as the estuary rapidly becomes narrower as you move up river away from open sea. So it funnels the incoming tide and makes it higher. |
| Solar radiation | Transfers energy to you from the Sun, can cause you to become sunburnt but can use Sun's energy to generate electricity using solar cells. Can also use Sun's energy to heat water directly in solar heating panels. |
| Solar cells | These presently convert less than 10% of solar energy absorbed to electrical energy. We can connect them to make solar cell panels. They are useful when we only need small amounts of electricity ex. watches and calculators, or in remote places ex. small islands. They are expensive to buy even though running costs are 0. We need lots of them and plenty of sunshine to generate enough power to be useful. |
| Solar heating panel | This heats water that flows through it, this doesn't require sunshine to function |
| Solar power tower | This uses thousands of flat mirrors to reflect sunlight on to a large water tank at the top of a tower, the mirrors on the ground surround the base of the tower. - The water in the tank is turned to steam by the heating effect of the solar radiation directed at the water tank - Steam is piped down to lower levels where it turns a turbine which in turns a electricity generator. The mirrors are controlled by a computer so they track the Sun. |
| Geothermal energy | This comes from energy released by radioactive substances deep within the Earth. - Energy released by these radioactive substances heats the surrounding rock - By consequence energy is transferred by heating towards the Earth's surface. Can build geothermal power stations in volcanic areas or where there are hot rocks deep below the surface. Water gets pumped down to these rocks to produce steam, the steam produced drives a turbine at ground level. In some areas can directly heat buildings using geothermal energy directly heat flow from underground is called ground heat. This can be used to heat water in long lengths of underground pipes, the hot water is then pumped around the building, ground heat is used as underfloor heating in some 'eco-buildings'. |
| Fossil fuel problems | Burning coal, oil or gas produces greenhouse gases like carbon dioxide, releasing these to the atmosphere. These gases cause global warming, we get some of our electricity from oil-fired power stations, we use much more oil to produce fuels for transport. Burning fossil fuels can also produce sulfur dioxide the gas causes acid rain, we can remove sulfur from a fuel before burning it to stop acid rain. Ex. Natural gas has sulfur impurities removed before its used. Fossil fuels are nonrenewable we will use up all of the Earth's reserves of fossil fuels, we will then have to find alternative fuel sources. Oil and gas reserves could be used up in the next 50 years coal reserves will last much longer. Carbon capture and storage (CCS) could be used to stop carbon dioxide emissions into the atmosphere from fossil fuel power stations, old oil and gas fields could be used as storage. |
| Nuclear power advantages | Don't produce greenhouse gases, much more energy per each kilogram of uranium/plutonium fuel than from fossil fuels. |
| Nuclear power disadvantages | Fuel rods contain radioactive waste which must be stored safely for centuries. Nuclear reactors are safe in normal operation but an explosion at one could release large amounts of radioactive material over a large area like in Chernobyl in Ukraine, this would affect area for many years High decommissioning cost |
| Renewable energy sources and the environment - advantages | -Will never run out - Don't produce greenhouse gases or acid rain - Don't create radioactive waste products - Can be used where connection to National grid is uneconomic ex. solar cells can be used for road signs |
| Renewable energy sources and the environment - disadvantadges | - Wind turbines create whining noise which can upset nearby people and some consider aesthetically displeasing - Tidal barrages affect river estuaries and habitats of creatures and plants there - Hydroelectric schemes need large reservoirs of water, which can affect nearby plant and animal life, habitats often flooded to create dams - Solar cells would need to cover large areas to generate large amounts of power. |
| National Grid | This is how supplied electricity reaches your home, it's a network of cables and transformers that distributes electricity from power stations to homes and other buildings. The step-up transformers are used at power stations, the step-down transformers are used at substations near homes. National Grid voltage is 132,000 V or more as transmitting electricity at a high voltage reduces power loss, making the system more efficient. Power stations produce electricity at a voltage of 25,000 V, step-up transformers are used to step this voltage up to the grid voltage, step-down transformers are used at local substations to step the grid voltage down to 230V for use in homes and offices. |
| Power and grid voltage | Electrical power supplied to any appliance depends on the appliance's current and voltage. To supply certain amount of power we can lower the current if we raise the voltage. This is what step-up transformer does in the grid system. Step-up transformer raises the voltage so less current is needed to transfer the same amount of power, lower current passes through the grid cables, so energy losses due to the heating effect of the current are reduced to almost 0. We need to lower the voltage at the end of the grid cables before we can use mains electricity at home. Step-up transformers raise the voltage and lower the current Step-down transformers lower the voltage and raise the current |
| Underground or overhead | Lots of people object to electricity pylons, say they spoil the landscape affect their health. Electric currents produce electric currents and magnetic fields that might affect people. Underground cables would be more expensive much more difficult to repair and difficult to bury where they cross canals, rivers and roads. What's more overhead cables are high above the ground, underground cables might affect people more because the cables wouldn't be very deep. Plus undergound are closer to people as overhead underground are high above the ground. |
| Supply and demand | Demand for electricity varies during each day, also higher in winter than summer, electricity generators must match changes in demand. Power stations can't 'start up' instantly, the start up time depends on the type of power stations: Natural gas has shortest start up time, followed by oil, coal and with the longest start up time is nuclear power. Renewable energy sources are unreliable the amount of electricity they generate depends on the conditions: Hydroelectric upland reservoirs could run dry, wind/waves too weak on calm days, tidal - height of tide varies both on monthly and yearly cycle, solar - no solar energy at night and variable during day. |
| Meeting variable demand for electricity | - Using nuclear, coal and oil-fired power stations to provide constant amount of electricity (base load demand) - Using gas-fired power stations and pumped-storage schemes to meet daily variations in demand and extra demand in winter - Using renewable energy sources when demand is high and renewables are in operation (ex. use wind turbines in winter when wind speeds are suitable) - Using renewable energy sources when demand is low to store energy in pumped storage schemes |
| Nature of waves | Use waves to transfer information and we can use them to transfer energy can use information transferred by waves in communication ex. mobile phone or radio. Different types of waves: - sound waves, water waves, waves on springs and ropes and seismic waves produced by earthquakes. These are examples of mechanical waves which are vibrations that travel through a medium (substance). - Light waves, radio waves and microwaves are electromagnetic waves which can travel through a medium at the same speed of 300,000 kilometres per second. |
| Transverse waves | When vibrate perpendicular to direction which waves are moving, the waves on a rope are called transverse wave as vibrations are from up to down or side to side, all electromagnetic waves are transverse waves. Vibrations of a transverse wave are perpendicular to the direction in which the waves transfer energy. These oscillate as the move repeatedly between two positions. |
| Longitudinal waves | When one end of slinky is pushed in and out repeatedly vibrations travel along the spring. Vibrations are parallel to the direction which the waves transfer energy along the spring. Waves that travel in this way are called longitudinal waves. Sound waves are longitudinal waves when an object vibrates in air it makes the air around it vibrate as it pushes and pulls on the air. Vibrations (compressions - coils pushed together and rarefaction - coils moving apart) which travel through the air are sound waves. Vibrations are along the direction in which wave travels. Vibrations of longitudinal waves are parallel to direction in which waves are travelling. Hence mechanical waves can be transverse or longitudinal. |
| Measuring waves | Must measure waves if want to find out how much energy or information they carry. The crests or peak are at the top of the wave, the troughs are at the bottom, they are equally spread. The amplitude of waves is the height of the wave crest or depth of wave trough from the middle - position of rest. The larger the amplitude the more energy the wave carry. Wavelength of waves is distance from one wave crest to next crest, its one complete wave. |
| Frequency | The number of wave crests passing a fixed point each second is the frequency of a wave. Unit of frequency is hertz (Hz), one wave crest passing each second is a frequency of 1 Hz. |
| Wave speed | Ripple tank is used to study water waves in controlled conditions can make straight by moving a ruler up and down on the water surface in a ripple tank. Straight waves are called plane waves the waves all move at the same speed and keep the distance apart. Speed of waves is distance travelled by a wave crest or a wave trough each second. Ex. sound waves in air travel at a speed of 340m/s, in five seconds sound waves travel a distance of 1700m. For waves of a constant frequency speed of waves depends on frequency and wavelength: wave speed (m/s) (v) = frequency (Hz) (f) * wavelength (m) (lambda) |
| Plane mirror | Produces normal image of object, this is a perfectly flat mirror, can see exact mirror image. |
| Law of relfection | Use light rays to show direction of light waves are moving in. Perpendicular line to mirror is normal, angle of incidence is angle between incident ray and ray, angle of reflection is angle between reflected ray and normal. For any light ray reflected by a plane mirror: angle of incidence = angle of reflection |
| Image formation by a plane mirror | Ray diagram shows path of two light rays from a point object that reflects off the mirror, the image an object at equal distances from the mirror. |
| Real and virtual images | Image formed on a virtual image is virtual, upright, and laterally inverted. A virtual image cannot be projected on to a screen like movie images in movies. An image on a screen is described as a real image because it's formed by focusing light rays onto the screen. |
| Refraction | Changing the direction of light is refraction. This is a property of all waves, glass plate placed is submerged in a ripple tank, waves are slower in shallow water than deep water. If waves are not parallel to boundary, they change direction when they cross the boundary: - towards the normal when they cross from deep to shallow water - away from the normal when they cross from shallow to deep water |
| Refraction rules | Light ray: - Changes direction towards normal when travels from air to glass, angle of refraction (r) is smaller than the angle of incidence (i). - Changes direction away from the normal when travels from glass to air angle of refraction (r) is greater than the angle of incidence (i). These are measured between the ray and normal. |
| Refraction by prism | When narrow beam of white light passes through a triangular glass prism, the beam comes out of the prism in a different direction to incident ray and is split into colours of spectrum. White light contains all colours of spectrum each colour of light is refracted slightly differently so prism splits light into colours. |
| Diffraction | This is the spreading of waves when they pass through a gap or move past an obstacle, the waves pass through the gap or past the edges of the obstacle can spread out. The effect is most noticeable if the wavelength of the waves is similar to width of gap. The wider the gap the less the waves spread out the narrower the gap the more the waves spread out |
| Diffraction details | Diffraction of light is important in optical instrument, Hubble space station orbiting around Earth focusing mirror is 2.4m in diameter. When used astronomers can attain separate images of objects which are far too close to be seen separately using a narrower telescope, little diffraction occurs when light passes through the Hubble Space Telescope because so wide, so images are clear and detailed. Diffraction of ultrasonic waves is important factor in design of ultrasound scanner. Ultrasonic waves are sound waves at frequencies above range of human ear, ultrasonic wave can be made of a baby in a womb. Ultrasonic waves spread out from a hand-held transmitter and then reflect from tissue boundaries inside the womb. If transmitter is too narrow, waves spread too much and image is not very clear. |
| Signal problems | People in hilly areas have poor TV reception, signal from TV transmitter mast is carried by radio waves. If hills between a TV receiver and transmitter mast, signal may not receive the transmitter. Radio waves passing top of hill are diffracted by hill but don't spread enough beyond the hill. |
| Investigating sound waves | Any object vibrating in air makes air near object vibrate, layer of air make layers of air further away vibrate. Vibrating object pushes and pulls repeatedly on the air, which sends out vibrations of air in waves of compression and rarefaction. When waves reach ear make eardrums vibrate in and out so you can hear sound by consequence. Vibrations travelling through air are sound waves, waves are longitudinal as air particles vibrate along direction the waves transfer energy. Can use loudspeaker to produce sound waves by passing alternating current through it. Our hearing is between 20Hz to 20000Hz this decreases as you get older so older people can't hear frequencies at higher end of range. |
| Relfection of sound | An echo is reflection of sound - If walls are covered with soft fabric, fabric will absorb sound instead of reflecting it so no echoes will be heard. - If wall surface is uneven echoes won't be heard as the reflected sound is 'broken up' and scattered Reflection best occurs in a large hall or gallery (spacious) which has bare smooth walls. |
| Refraction of sound | Sound travels through air at speed of 340m/s the warmer the air is the greater the speed of sound. At night you can hear sound a long way from it's source, as sound waves refract back to ground instead of travelling away from ground. Refraction takes place at boundaries between layers of air at different temperatures. In daytime, sound refracts upwards, not downwards as air near ground is warmer than air higher up. |
| Musical sounds | Music notes are easy to listen to because their rhythmic, sound waves change smoothly and wave pattern repeats itself regularly. Noise consists of sound waves that vary in frequency without any pattern. Increasing the loudness of a sound increases the amplitude of the waves. Increasing the frequency of the waves (number of waves per second) increases it's pitch which makes more waves appear on the screen. |
| Musical instruments | When play instrument create sound waves by making instrument and inside it vibrate. Each cycle of vibrations make vibrations stronger at certain frequencies. Say instrument resonates at these frequencies. As instrument and air inside strongly vibrate at these frequencies when played, hear recognisable notes of sound from instrument. - Wind instrument like flutes designed so air inside resonates while played, can make air in empty bottle resonate by blowing across the top gently. - String instrument like guitar produces sound when strings vibrate, vibrating strings make surface of instrument vibrate and produce sound waves in the air. In acoustic guitar air inside hollow body of guitar (sound box) vibrates too. - Percussion instrument like drum vibrates and produces sound when struck. |
| Electromagnetic spectrum | Electromagnetic waves are electric and magnetic disturbances that transfer energy from one place to another. Electromagnetic waves don't transfer matter, energy transfer depends on wavelength of waves, why waves of different length have different effects. The spectrum is continuous frequencies and wavelengths at the boundaries are approximate as different parts of spectrum aren't precisely defined. Long-wave radio waves have a wavelength can be as long as 10km X-rays and gamma rays have wavelength as short of millionth of a millionth of a millimetre! |
| Speed of electromagnetic waves | All electromagnetic waves travel at speed of 300 million m/s through space or in a vacuum. This is the distance wave travels per second, can link speed of waves to their frequency and wavelength using wave speed equation: v (wave speed in metres per second, m/s) =f (frequency in hertz, Hz) *h (wavelength in metres, m) |
| Energy and frequency | Wave speed equation shows us the shorter the wavelength of waves the higher the frequency is. Energy of waves increases as frequency increases, energy and frequency of waves therefore increases from radio waves to gamma rays as wavelength decreases. |
| Light and colour | Light from lamp and sun is white light as all the colours of visible spectrum is in it. Wavelength increases across spectrum as go from violet to red. See colour of spectrum when look at rainbow, and glass prism, photographers must know how shades and colours of light affect photographs they take. 1. In film camera: Light is focused by camera lens onto a light sensitive, film then needs to be developed to see image of the objects that were photographed. 2. In digital camera: Light is focused by lens onto a sensor, consists of thousands of tiny light-sensitive cells called pixels, each pixel gives a dot of the image. Image can be seen on a smart screen at back of camera. When photograph is taken image is stored electronically on memory card |
| Infrared radiation | All objects emit infrared radiation - Hotter an object is more infrared radiation it emits - Infrared radiation is absorbed by skin damages or kills skin cells as it heats up the cells |
| Infrared devices | - Optical fibres in communication use infrared radiation instead of light as infrared radiation is absorbed less than light in glass fibres. - Remote control handsets for TV and video equipment transit signals carried by infrared radiation, when you press a button on a handset sends of sequences of infrared pulses. - Infrared scanners used in medicine to detect 'hot spots' on body surface, hot areas can be mean underlying tissue is unhealthy - Can use infrared cameras to see people and animals in dark. |
| Microwaves | Microwaves lie between radio and infrared radiation in electromagnetic spectrum, called 'microwaves' as have shorter wavelength than radio waves. Use microwaves for communication, ex. Satellite TV as can pass through atmosphere and reach satellites above Earth. Also use them to beam signals from one place to another as microwaves don't spread as much as radio waves. Microwaves and radio waves used to carry mobile phone signals. |
| Radio waves | Their frequency ranges from 300,000Hz to 3000 million Hz (where microwaves frequencies begin). Radio waves are longer in wavelength and lower in frequency than microwaves. Use radio waves to carry radio, TV and mobile phone signals. Can also use radio waves instead of computers to connect a computer to other devices like printers or a mouse. Ex. bluetooth enabled devices can communicate with each other over range of 10 metres. No cables are needed- just Bluetooth radio in each device and necessary software. Such wireless connections work at frequencies of about 24,000 Hz and operate at low power. Bluetooth was set up by electronics manufacturers who realised they need to agree on the radio frequencies to be used for common software. |
| Radio communications | Radio waves are emitted from an aerial when we apply an alternating voltage to the aerial. Frequency of radio waves is produced is the same as the frequency of the alternating current. When radio waves pass over a receiver aerial they cause tiny alternating current voltage in the aerial. The frequency of the alternating voltage is the same as the frequency of the radio received. The aerial is connected to a loudspeaker. The alternating voltage from the aerial is used to make the loudspeaker send out sound waves. The radio and microwave spectrum is divided into bands of different wavelength ranges as the shorter the wavelength of the waves: - the more information it can carry - shorter their range ( due to increasing absorption by the atmosphere) - less they spread out ( as diffract less) |
| Radio wavelengths | Microwaves and radio waves of different wavelength used for different purposes, ex: - Microwaves - used for satellite phones and TV links and satellite TV broadcasting as microwaves can travel between satellites in space and the ground also they spread out less than radio waves do so the signal doesn't weaken as much. - Radio waves of wavelengths less than one metre - used for TV broadcasting from TV masts as they can carry more information than longer radio waves. - Radio waves of wavelengths from about 1m to 100m are used by local radio stations (and emergency services) as their range is limited area around transmitter - Radio waves of wavelengths greater than about 100m used by national and international radio stations as they have a much longer range than shorter wavelength radio waves. |
| Mobile phone radiation | Mobile phone sends from your phone, the signal is picked up by a local mobile phone mast and is sent through the phone network to the other phone. The return signal goes through the phone network back to the mobile phone mast near you and then onto you. Signals to and from your local mast are carried by radio waves at different frequencies. Radio waves to and from mobile phone have wavelength of about 30cm radio waves at this wavelength aren't quite in microwave range but have similar heating effect to microwaves so usually referred to as microwaves. |
| Is mobile phone radiation dangerous | Radiation much weaker than microwave oven but when mobile phone very close to brain. Some scientists think the radiation may affect the brain. As children have thinner skulls than adults their brains might be affected more by mobile phone radiation. UK government published in May 2000 recommended use of mobile phones by children should be limited. |
| Mobile phone hazards | Some findings by different scientists: - Short-term memory of volunteers using a mobile phone was found to be unaffected by whether the phone was on or off. Brains of rats exposed to microwaves found to respond less to electrical impulses than brains of unexposed rats. Mice exposed to microwaves by scientists developed more cancer than unexposed mice, other scientists were unable to confirm results. Survey of mobile phone users in Norway and Sweden found experienced the headaches and fatigues. No control group of people who didn't use mobile phone were surveyed - no conclusions can be made can be affect of other factors. |
| Optical fibre communication | These are very thin glass fibres. Use them to transit signals carried by light or infrared radiation, light ray's can't escape from fibre. When reach surface of the fibre they are reflected back into the fibre. In comparison with radio and microwaves: - Optical fibres can carry much more information as light has much smaller wavelength than radio waves so can carry more pulses of waves. - Optical fibres are more secure as the signals stay in the fibre. Total internal reflection occurs in an optical fibre. |
| Doppler effect | This is the change of observed wavelength (and frequency) of waves due to motion of source of waves. Christian Doppler discovered effect 1842 using sound waves, demonstrated by using open railway carriage filled with trumpeters, spectators had to listen to the pitch of the trumpets as sped past. |
| Red-shift | Can found out lot of stars and galaxies by studying light from them, can use a prism to split the light into a spectrum. Wavelength of light increases across the spectrum from blue to red can tell its spectrum if a star or galaxy is moving towards or away from us, as: Light waves are stretched out if star or galaxy is moving away from us. Wavelength of waves is increased, call this red-shift as spectrum of light is shifted towards the red part of the spectrum. Lightwaves are squashed together if the star and galaxy is moving towards us, wavelength of the waves are reduced, call this blue-shift as the spectrum of light is shifted towards the blue part of the spectrum. Dark spectral lines caused by absorption of lines by certain atoms like hydrogen that make up star or galaxy. Position of lines tells us if there is a shift and if so whether red-shift or a blue-shift. The bigger the shift the more the waves are squashed together or stretched out so the faster the galaxy must be moving towards or away from us. Faster a star or galaxy is moving (relative to us) the bigger the shift. |
| Expanding universe | 1929 Edwin Hubble discovered: 1. Light from distant galaxies was red-shifted 2. The further galaxy is from us the bigger the red-shift is Concluded that: Distant galaxies are moving away from us ( receding) Greater the distance a galaxy is from us the greater the speed is at which it is moving away from us (speed of recession). As have no special place in universe means whole universe is expanding. |
| Big bang | Big bang theory put forward to explain expanding universe: Universe is expanding after suddenly exploding in Big Bang from very small initial point. Space, time and matter were created in the Big Bang. Alternative theory was Steady State theory scientists said galaxies being pushed apart thought caused by matter entering universe through 'white holes' ( opposite of black holes), until 1965 most people supported this theory. |
| Evidence for big bang | Scientists worked out if universe began in Big Bang there should have been high-energy electromagnetic radiation produced. Radiation would have stretched as universe expanded and become lower-energy radiation. In 1965 first detected microwaves coming from every direction in space, existence of cosmic background radiation can only be explained by Big Bang theory. Cosmic background radiation isn't perfectly evenly spread as scientists thought it would be. Model of early universe needed to be developed further by gathering evidence and producing theories to explain this 'unevenness' in early universe. |
| Cosmic background radiation | -Created by high-energy gamma radiation just after Big Bang. - It has been travelling through space since then. - As universe has expanded it stretched out to longer and longer wavelengths and is now microwave radiation Has been mapped out using microwave detectors on the ground and on satellites. |
| Future of universe | Dependant on density of universe to whether it will expand forever of force of gravity between them stop them from moving away from each other. If density of universe is less than certain amount will expand forever stars will die out and everything else in the universe - Big Yawn. If density of universe more than certain amount will stop expanding and reverse - Big Crunch. Recent observation suggest galaxies accelerating away from us have been checked and confirmed by other astronomers - reliable. So astronomers concluded expansion of universe is accelerating - Big yawn. Discovery distant galaxy are accelerating is puzzling scientists think an unknown energy 'dark energy' must be causing accelerating motion. Gravity can't be used to explain 'dark energy' as it is an attractive force so acts against outward motion away from each other. |
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