Page 1 What type of radiation transmits heat energy? Complete this sentence Hotter objects emit infrared radiation than cooler objects. What type of surfaces are good absorbers and good emitters of infrared radiation? What type of surfaces are poor absorbers and poor emitters of infrared radiation? What type of surfaces are good reflectors of infrared radiation? What can we say about the arrangement of particles (and kinetic energy) in solids? What can we say about the arrangement of particles (and kinetic energy) in liquids? What can we say about the arrangement of particles (and kinetic energy) in gases? Describe how heat energy can be transferred by conduction. Why are metals very good conductors of heat? Describe how heat energy can be transferred by convection. How is heat lost by evaporation and gained by condensation?
Page 2 Hotter objects emit more infrared radiation than cooler objects. Heat energy is transmitted by infra-red radiation. Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation. Dark, matt surfaces are good absorbers and good emitters of infrared radiation. In solids, the particles are close together and arranged in a regular pattern. The particles are not moving from place to place but they are vibrating. Particles have a small amount of kinetic energy. Light, shiny surfaces are good reflectors of infrared radiation. In gases, the particles are far apart. The particles are moving very rapidly from place to place. Particles have a very large amount of kinetic energy. In liquids, the particles are close together and not arranged in any pattern. The particles are moving from place to place. Particles have a large amount of kinetic energy. Metals are very good conductors of heat because they have free electrons which can move and transfer the heat energy. Conduction takes place best in solids because the particles are close together. If we heat the solid, the particles gain kinetic energy and vibrate more. This vibration is passed onto nearby particles causing them to vibrate, spreading the heat energy. When a liquid turns to a gas (evaporation) the particles gain kinetic energy. This energy is transferred from the surface, which cools down. When a gas turns to a liquid (condensation) the particles lose kinetic energy. This energy is transferred to the surface, which warms up. Convection takes place in liquids and gases. When they are heated, the particles move further apart. This causes the liquid/gas to become less dense and move up. Cooler regions sink to take their place. This is a convection current.
Page 3 Describe the factors that increase the rate of evaporation. Explain why animals in hot conditions usually have large ears and animals in cold conditions usually have small ears. What is meant by an insulator? Describe in terms of particles how these work. What does the U-value tell us about an insulator? What is meant by the specific heat capacity of a substance? Complete this sentence: Energy can neither be.. nor.. but it can be transferred. When energy is transferred, some is often wasted. What happens to wasted energy? How do we calculate the efficiency of a device? State the energy transfers taking place in a food mixer. Which energy transfers are wasted? How do we calculate the total amount of energy transferred by an appliance in a given time? How many kilowatt-hours are used by a heater with a power of 2kW running for 2 hours. What is meant by the payback time for different methods of home insulation?
Page 4 Heat is lost faster from objects with a large surface area. Animals in hot conditions have to lose body heat so they often have larger ears which increases their surface area helping to lose heat. Animals in cold conditions have to retain their body heat so they often have smaller ears which reduces their surface area, reducing heat loss. These conditions make evaporation faster: Warmer conditions Dry conditions (not humid) Windy conditions The U-value tells us the amount of heat energy that can pass through an insulator. Good insulators have a low U-value. Insulators reduce heat transfer. They have large gaps between particles so vibrations cannot easily pass between them. Energy can neither be created nor destroyed but it can be transferred. The specific heat capacity of a substance tells us the amount of energy required to change the temperature of 1kg of the substance by 1 o C. Efficiency = useful energy out x 100 total energy in The unit of efficiency is %. Remember that efficiency cannot be greater than 100%. Wasted energy is eventually transferred to heat, warming the surroundings. This energy is spread out and is less useful. E = P x t E = energy in Joules (or kilowatt-hours) P = power in Watts (or kilowatts) t = time in seconds (or hours) Electrical energy is transferred to kinetic energy, heat energy (wasted) and sound energy (wasted). Different methods of home insulation save different amounts of money in reducing energy use. The payback time tells us how long it takes to save enough money to pay for the cost of installation. A heater with a power of 2kW running for 2 hours uses a total of 4 kilowatt-hours.
Page 5 How do we calculate the payback time? Loft insulation costs 200 to install and saves 100 each year. Calculate the payback time. Complete: In some power stations, water is heated and turned to.. This drives a.. connected to a.. generating electricity. What is meant by geothermal energy? When can small-scale electrical production be useful (eg solar cells). What is meant by carboncapture and storage? electricity by burning fossil fuels. State three examples of fossil fuels? Which elements are used to generate electricity in nuclear power stations? electricity by nuclear power. electricity by solar power. electricity by wind power.
Page 6 Payback time = 2 years. Payback time = cost of installation saving per year Geothermal energy is available in volcanic areas. Hot water and steam rise to the surface. The steam is used to drive turbines, generating electricity. In some power stations, water is heated and turned to steam. This drives a turbine connected to a generator generating electricity. Carbon dioxide (eg from power stations) is trapped and stored so it does not enter the atmosphere. This can be done in old oil and gas fields e.g. under the North Sea. Small-scale electrical production can be useful when it is not economical to connect to the National Grid, for example roadside signs. Fossil fuels include: Coal Oil Gas Very reliable, generating lots of electricity when we need it. Relatively cheap Non-renewable. Fossil fuels are running out. Produces carbon dioxide which leads to global warming. Very reliable, generating lots of electricity when we need it. Expensive to build and decommission Potentially dangerous. If an accident occurs, radioactive materials could be released. Nuclear power stations use uranium or plutonium. Renewable. Will not run out. Unreliable. Will not generate electricity on days when there is little wind. Wind turbines contribute to visual pollution. Renewable. Will not run out. Unreliable. Will not generate electricity on very cloudy days or at night.
Page 7 What is meant by the startup time for a power station? Which fossil fuel power stations have the shortest startup time? Why are nuclear power stations so expensive? electricity by hydroelectric power. electricity by wave and tidal power. How can we match the supply of electricity to the demand for electricity? How does a pumped-storage system help us to manage the changing demand for electricity? What are the advantages and disadvantages of overhead power lines and underground power cables? electricity by burning biofuels. What is meant by the National Grid? What does a step-up transformer do in the National Grid? What does a step-down transformer do in the National Grid? Why is electricity transmitted at extremely high voltages through power cables from power stations?
Page 8 Nuclear power stations are very expensive to build and decommission (dismantle at the end of their useful life). The startup time is the time taken to produce electricity when a power station is switched on. Gas-fired power stations have the shortest startup time, followed by oil. Coal has the longest startup time. Renewable. Will not run out. Only useful in certain countries (for example the UK). Tidal power destroys habitats e.g. birds. Renewable. Will not run out. Only useful in certain countries (those with lots of fast-flowing rivers). Dams destroy habitats by flooding. In pumped storage, when electricity demand is low (eg at night), electricity is used to pump water uphill into a reservoir. This stores energy as gravitational potential energy. When demand is higher, the water is allowed to flow downhill through turbines generating electricity. Electricity demand changes during the day (for example very low at night). Power stations cannot easily be turned on and off and electricity cannot easily be stored. We need large power stations (eg nuclear) to provide the base-load and then gas-fired power stations which can be turned on and off as demand changes. Biofuels include wood-chippings from the timber industry and methane gas from landfills. These are renewable and relatively cheap. Although carbon dioxide is released, in some cases (eg wood), this was taken in by the growing plants. Overhead power lines are cheaper to install and easier to maintain/repair. However, they can be affected by weather and can be a hazard e.g. to low-flying aircraft. They also cause visual pollution (pylons are unattractive). Underground power cables are expensive to install and repair. However, they are not affected by weather and are not hazardous in most cases. A step-up transformer increases the voltage of the electricity supply from the power station before it is transmitted through power cables. The National Grid is a system of transformers and power cables. Increasing the voltage means that we can transmit electricity at a lower current. A lower current reduces the energy lost as heat as the electricity passes through the cables. A step-down transformer decreases the voltage of the electricity supply from the power cables before passing to peoples homes.