1. Mr. Lajos Papp The British International School, Budapest 2011/2012

2. UNITS seconds kilogramkg metrem metre/secondm/s metre/second 2 m/s 2 newtonN wattW jouleJ

4. Energy is measured in Joules and comes in many forms. Examples are: chemical (including food), nuclear, electrical, thermal (heat), light,

5. sound, potential (gravitational and elastic) kinetic energy. When one form of energy is changed into another form, we say that energy is transferred.

6. We can do useful things when energy is transferred. For example, if we want to light a room, we can transfer electrical energy into light energy. We can do this by switching on a light bulb. If we want to travel from one place to another, we can transfer chemical energy into kinetic energy. We can do this by getting on a bus.

7. The amount of energy does not increase or decrease during the transfer, it is only changed from one form into others. Energy cannot be created or destroyed. This is called "the conservation of energy„ (not the same as conserving energy). Not all of the energy is changed into the form we want (the useful form). Some energy is changed into other forms and is wasted (body heat).

8. Heat is transferred naturally from a substance with a higher temperature to a substance with a lower temperature. Heat can be transferred in three ways. 1.Conduction - by a substance which does not move (solids). 2.Convection - by a substance which moves (liquids and gases). 3.Radiation - infra-red radiation is exchanged between all substances.

9. Conduction Heat can be transferred by conduction only in solids. If one end of a solid is heated, the particles of the solid gain kinetic energy. This means that they move faster. In a solid the particles are held together by strong forces of attraction. The only way in which the particles can move is to vibrate forwards and backwards. When the solid is heated, the amount by which the particles vibrate is increased. This is what is meant by saying that the particles of the solid have gained kinetic energy.

10. The increase in energy (heat) is passed on to the next particle, which in turn starts to vibrate more. In non- metals the process is slow. It takes a long time for the particles to pass on their heat. Non-metals are not good conductors. They are good insulators.

11. Metals have ions which are surrounded by free electrons. These free electrons can travel quickly and easily throughout the structure. The electrons transfer the heat energy by colliding with other atoms and electrons in the metal.

12. Convection Heat can be transferred by convection in liquids and gases. Particles in the liquid or gas collide with a substance which has a high temperature and gain kinetic energy (heat). The particles move to a region which has substance at a lower temperature and transfer heat by colliding with the colder substance. In this way, the high temperature substance has heat taken away from it and gets colder. The low temperature substance has heat given to it and gets warmer.

13. The liquid or gas which transfers the heat can circulate round and round between the hot and cold regions. You may be asked to draw the direction of convection currents and explain why they move in this way. The picture below shows a radiator heating a room in a house.

15. The hot radiator transfers heat to the nearby air then air molecules collide with the radiator surface. The hot air near to the radiator expands and increases in volume. Hot air expands because the particles move further apart as they get hotter. This makes the density of the hot air decrease and it starts to rise upwards. The colder air above it gets pushed along to the right and then circulates as shown by the arrows.

16. The arrows show the convection currents. As the hot air moves around the room, it loses its heat by collision with the walls, ceiling and the objects in the room. Finally the colder air circulates near to the radiator where it is heated and the whole process repeats itself. The efficiency of convection can be improved by placing shiny metal foil behind the radiator.

17. Radiation Infra-red radiation (also called thermal radiation) transfers heat between all objects. Infra-red radiation is an electromagnetic wave and can travel through a vacuum. Heat from the Sun reaches us through the vacuum of space by travelling as infra-red radiation.

18. An object can absorb (take in), emit (give out) and reflect radiation. The hotter an object, the faster it will emit infra-red radiation. Hotter objects will emit infra- red radiation faster than they absorb it from colder objects around them. Colder objects will absorb infra- red radiation faster than they emit it to hotter objects around them. In this way heat is transferred from hotter to colder objects.

19. An object whose temperature does not change will emit infra-red radiation at the same rate as it is absorbed. Objects which are at the same temperature as each other will absorb, emit and reflect infra-red radiation at different rates depending on the type of surface which the object has. An object with a matt (dull) surface will absorb and emit infra-red radiation at a faster rate than an object with a shiny surface.

20. An object with a dark surface will absorb and emit infra-red radiation at a faster rate than an object with alight surface. Radiation is also reflected at the surface. Imagine a hot piece of metal which has a matt black surface and a shiny white surface. A thermometer is placed at the same distance from both surfaces.

21. The thermometer next to the matt black surface shows a higher temperature because it emits radiation at a faster rate. Heat leaves the metal more quickly through the matt black surface than the shiny white surface. When an amount of infra-red radiation falls on an object, some will be reflected and some will be absorbed. The greater the proportion of radiation which is reflected, the less will be absorbed.

22. An object with a matt or dark surface will be a poor reflector of infra-red radiation. An object with a shiny or light surface will be a good reflector of infra-red radiation. Shiny metal foil can be placed behind a radiator in a room to increase its efficiency. The foil reflects radiation back into the room which heats the air rather than heating the wall. This adds to the efficiency of convection in the room.

23. Something which slows down the rate of heat transfer is called an insulator. The word "insulator" is also used in electricity for a material which does not conduct. Heat insulation can take different forms depending on the type of heat transfer involved. We shall look at examples of heat insulation in buildings involving conduction, convection, radiation

24. We have seen that non-metals are good insulators. Examples of non-metals used as insulators include wood, glass and plastics (polymers). Gases are particularly good insulators if you can stop them moving. This prevents them transferring heat by convection. A layer of air is trapped by our clothing to keep us warm. The trapped air slows down the rate of heat loss by conduction from our bodies. The fur of animals also traps a layer of air to keep them warm. When the animal is cold, its fur stands up more to trap more air.

25. The same idea can be used to insulate buildings. Trapped air can be used in various ways to insulate buildings. Examples are loft insulation, hot water tank and pipe insulation, double glazing and cavity wall insulation.

26. Cavity wall insulation Many houses are built with "cavity walls" consisting of two rows of bricks. There is an outside wall and an inside wall with an air gap between them. The air can transfer heat across the gap by convection. Cavity wall insulation involves filling the gap with a polymer foam. The foam has air trapped inside it The foam replaces the air in the gap between the bricks. No heat can now be transferred by convection because the air has been replaced by foam. Conduction is very poor because both the polymer and the trapped air are good insulators.

28. Loft insulation The space between the roof and the ceiling is called the loft. Glass fibre is laid across the loft to reduce heat transfer out of the roof. Glass fibre traps air like woollen clothing. The glass fibre with trapped air is a very poor conductor which reduces heat transfer from the ceiling to the loft. The room in the house stays warmer for longer.

30. Hot water tank and pipe insulation Glass fibre can also be used to insulate a hot water tank and pipes. The fibre is put inside a cloth container and wrapped around the tank and pipes. This type of insulation is called lagging. The lagging may also have an inside shiny surface to reduce heat loss by radiation.

32. Double glazing Double glazing involves two layers of glass with a small air gap between them. It works as an insulator in much the same way as cavity wall and loft insulation. The air gap is too small to allow the air to circulate. This prevents heat transfer by convection. The trapped air is a very poor conductor which reduces heat loss through the window. The room in the house stays warmer for longer. Double glazing is a good barrier to sound and can help reduce unwanted noise.

34. All of the insulation methods in buildings that we have looked at so far use trapped air to reduce conduction. The air within the rooms in buildings will transfer heat to the outside by convection. This happens particularly where warm air leaves a building through gaps around doors and windows. These gaps can be sealed by using draught proofing. Draught proofing involves using plastic strips or foam around the edges of doors and windows to seal any gaps when the door or window is closed. This reduces heat loss by convection. The room in the house stays warmer for longer.

35. There are many types of process which transfer energy. The transfer of energy can be shown by a flow diagram (also called a Sankey diagram).

36. Efficiency is a measure of how well a device transfers energy into the form we want. efficiency (%) = (useful energy out ÷total energy in) x 100 or efficiency (%) = (useful power out ÷total power in) x 100

37. When energy is transferred, some of the energy turns into forms we don't want. This energy is called wasted energy. Wasted energy takes the form of heat and sometimes sound or light. During any energy transfer, some energy is changed into heat. The heat becomes spread out into the environment. This dispersed energy becomes increasingly difficult to use in future energy transfers. In the end, all energy is transferred into heat.

38. The thing which transfers energy from one form into another is called a device. Below are some examples of energy transfers of various devices. DeviceEnergy In Useful Energy Out Use EngineChemicalRotationalTransport BoilerChemicalHeatHeating, Bathing Electric heaterElectricalHeatHeating

39. DeviceEnergy In Useful Energy Out Use Light bulbElectricalLightLighting MotorElectricalRotational Clock, Fan, Pump, Transport TelevisionElectricalLight and Sound Education, Entertainment PianoKineticSoundMusic Power stationVariousElectrical Electricity Supply

40. An engine burns a hydrocarbon (petrol or diesel) which has come from a fossil fuel. The engine uses the released energy to rotate a steel shaft. The rotational energy is used to move the vehicle and to generate electricity for the vehicle's needs. The fossil fuel is called "chemical energy„ because energy is released during chemical reactions with oxygen. The fuel is burned.

41. Other examples of chemical energy are electrical cells and food. A cell (or battery) transfers chemical energy into electrical energy. Living organisms eat food and food is also called "chemical energy„ because energy is released during respiration. Respiration is the reaction of oxygen with glucose and is the reverse of photosynthesis. An engine will transfer some of the available chemical energy into rotational energy and some into heat.

42. We can calculate the efficiency of the engine using the equation efficiency (%) = (useful energy out ÷total energy in) x 100. If the available chemical energy is 270,000J and the rotational energy produced is 70,000J, then efficiency = (70,000÷ 270,000) x 100 = 25·9 %. A petrol engine has a typical efficiency of 20 to 30 %. A diesel engine has a typical efficiency of 30 to 40 %.

44. "Work done" is another way of saying "energy transferred". Work done = Energy transferred. W = E The equation which connects work, force and distance is Work done= Force x Distance moved W = F x d The equation can also be written as Energy = Force x Distance E = F x dUNITS!

45. If a car has a mass of 800 kg and moves with a velocity of 25m/s, what force is needed to stop the car in 50 metres? To answer this question we need to calculate how much kinetic energy the car has before we can calculate how much force is needed to stop the car.

46. Kinetic Energy = 0.5 x mass x velocity 2 = 0.5 x 800 x 25 2 = 0.5 x 800 x 625 = 250,000J. Energy = Force x Distance The equation can be rearranged to give Force= Energy ÷ Distance = 250,000 ÷ 50 = 5,000 N.

47. The equation which connects power and energy is: Power = Energy (Work done) ÷ Time taken P = W ∕ tUnits! Power is the rate at which energy is transferred. It is measured in Watts. 1 Watt = 1 Joule per second.

48. A motor lifts a15 kg mass by 3 metres in 8 seconds. What is the motor's power output? The motor has transferred rotational energy into gravitational potential energy. GPE = mass x gravity x height = 15 x 10 x 3 = 450 J Power = Energy ÷ Time = 450÷ 8 = 56.25 W

49. Gravitational potential energy to kinetic energy When an object with GPE starts to fall, its GPE is transferred into KE. The further the object falls, the less GPE it has and the more KE it has. When the object hits the ground, all of its GPE has been transferred into KE. Examples are a bouncing ball, a pendulum and a comet. If we look at the example of the 75 kg rock 4.0 metres above the ground, we can calculate that it has 3000J of GPE.

50. Using the equation for KE, we can calculate how fast it is travelling when it hits the ground. All of the rock's GPE has become KE, so the rock has 3000J of KE when it hits the ground. KE = ½ x m x v 2 3000= 0.5 x 75 x v 2 v 2 = 3000 ÷ (0.5 x 75) = 80 v= √80 = 8.94 m/s.

51. Since we now know how fast the rock was travelling, we can calculate how long it took to fall the 4.0 metres. Try it using the equation for acceleration. a = 10 m/s 2 (for gravity), v= 8.94 m/s, u = 0 (the answer is t = 0.894 seconds).

53. Power stations convert a primary energy resource into electrical energy. Electrical energy is called a secondary energy source. Electricity is a very useful form of energy because it can be used to do so many different things and it is easily transmitted over long distances.

54. The primary energy resources may be non-renewable (fossil fuels, nuclear power), or renewable (hydroelectric, tidal, wave, wind, wind, solar, geothermal, biomass). Non-renewable means that there is only a certain amount of the resource. Once it is used up, it cannot be replaced. Renewable means that the resource will not run out.

55. Fossil fuels Most of the electricity generated in the world today comes from power stations which burn fossil fuels. Fossil fuels are coal, oil and natural gas. The original source of the energy is the Sun. Plants use sunlight energy for photosynthesis. Coal is made from plant remains. Oil and natural gas are made from both plant and animal remains. Animals received their energy from eating plants. Natural gas causes the least pollution of the three fossil fuels.

56. Advantages 1. They give a large amount of energy from a small amount of fuel. 2. They are readily available. If you need more energy, you just burn more fuel. 3. They are relatively cheap.

57. Disadvantages 1. They are non-renewable. Once you burn them, they are gone. 2. They cause pollution. Burning a fossil fuel can produce carbon dioxide, sulfur dioxide and smoke. Carbon dioxide is a greenhouse gas and causes global warming. Sulfur dioxide causes acid rain. 3. They use water as a coolant and may return warm water into a river. This decreases the amount of dissolved oxygen in the river.

58. Nuclear power Nuclear power stations use the heat generated by fission of a fuel to boil water to make steam. The steam is used to turn a turbine to generate electricity.

59. Advantages of nuclear power 1. A large amount of energy is generated from a very small amount of fuel. 2. The fuel is readily available. If you need more energy, you just use more fuel. 3. Nuclear power does not produce carbon dioxide or sulfur dioxide and so does not contribute to global warming or acid rain.

60. Disadvantages 1. Poisonous waste is produced, highly radioactive. Disposal of this radioactive waste has not been safely achieved. Careless disposal of waste in the past has led to pollution of land, rivers and the ocean. 2. The power station is potentially dangerous to large areas of the planet. Despite reassurances from the nuclear industry that nuclear power is safe, serious accidents have happened and large areas have been contaminated with radioactivity.

61. 3. The power station is very expensive to build and to safely dismantle afterwards. When the costs are taken into account, the electricity produced by the power station is relatively expensive.

62. Hydroelectric power A large river which falls down a steep slope is suitable for generating hydroelectric power. The river is dammed at the top and the valley is flooded creating a large reservoir (lake) of water. The water is let out through turbines at the bottom of the dam. The turbines turn a generator which produces electricity.

63. Advantages 1. It is renewable. 2. It is readily available. If you need more energy, you just let out more water through the turbines. 3. It does not cause pollution. Disadvantages 1. Flooding the river valley will destroy the local habitat for many of the species which live there.

64. Tidal power The place where a river flows into the sea is called an estuary. A dam (called a barrage) is built across the estuary. The barrage has turbines in it. When the tide comes in, water flows through the turbines generating electricity. The water can be stored behind the barrage and then released out through the turbines as the tide goes out, again generating electricity.

65. Advantages 1. It is renewable. 2. It is reliable. The tide goes in and out twice a day. 3. It does not cause pollution. Disadvantages 1. It may not look as nice as the unspoiled river. 2. Boats may not be able to get past the barrage.

66. Wave power Wave power uses the rise and fall of the sea as waves approach the coast. A float on the water surface pushes air forwards and backwards through a turbine on the land, as the waves cause the float to rise and fall. The turbine generates electricity.

67. Advantages 1. It is renewable. 2. It does not cause pollution. Disadvantages 1. It is unreliable. When the wind drops, the waves get smaller and less electricity is generated. 2. An individual wave power machine does not generate very much electricity. You would need a lot of them to replace one fossil fuel power station. 3. The natural beauty of an area may be spoiled.

68. Wind power Wind power uses wind turbines which have their own generator built in. A wind turbine looks like a windmill with three blades. When the wind blows, the windmill rotates and the turbine generates electricity.

69. Advantages 1. It is renewable. 2. It does not cause pollution (except noise). Disadvantages 1. It is unreliable. When the wind drops, the turbine turns more slowly and less electricity is generated. 2. An individual wind turbine does not generate very much electricity. You would need a lot of them to replace one fossil fuel power station. 3. The natural beauty of an area may be spoiled.

70. Solar power Solar power can be used to generate electricity directly from sunlight or to heat air. In both systems the original source of the energy is the Sun. In a solar photo voltaic power system sunlight falls on to solar panels (solar cells) and generates direct current electricity. Small systems can use the electricity directly (for example solar cells can light roadside signs). Large systems can use the direct current to make hydrogen from water or have the direct current changed into alternating current using an inverter.

71. Advantages 1. It is renewable. 2. It does not cause pollution. Disadvantages 1. It does not work well when the sky is cloudy. It is does not work at night. 2. It is relatively expensive. The future cost is expected to fall with (i) higher levels of production (make more and they get cheaper) (ii) improved technology (more electricity from the same amount of sunlight). (iii) governments pay people to generate their own electricity.

72. Solar thermal tower The original source of the energy is the Sun. A solar thermal tower uses thermal radiation from sunlight to heat air beneath a glass cover. The hot air rises up a tall chimney (tower) which causes a decrease in pressure. More cold air is pushed in beneath the glass from the higher pressure in the atmosphere outside. The moving air is used to turn turbines and generate electricity.

74. Advantages 1. It is renewable. 2. It does not cause pollution. Disadvantages 1. A large solar tower takes up a large amount of land. The tower can be over 1000 m high and the heated area over 4,000,000 m 2.

75. Geothermal power Some countries have hot underground rocks close to the Earth's surface. Water is pumped down to the rocks through a pipeline and returns to the surface as steam through another pipe. The steam is then forced through a turbine which turns a generator.

76. Advantages 1. It is renewable. 2. It is reliable. 3. It does not cause pollution. Disadvantages 1. It is limited to being used in those parts of the world where hot rocks are near the surface.