P1 Energy and Electricity (1)

1. Radiation Thermal radiation is the transfer of heat energy. All objects emit and absorb radiation. The hotter an object the more energy it radiates. Different materials transfer heat at different rates. black surfaces emit more thermal radiation than white surfaces. white surfaces are poor absorbers of radiation compared to black surfaces. The rate at which an object transfers energy depends upon 1.surface area 2. material object is made from 3. Surface type it is touching 4. Temperature difference Convection is the transfer of heat energy in GASES and Liquids. This is because as they gain Energy particles move Faster spread out, become Lower density &rise. On cooling the particles lose energy, slow down, get closer together, become more dense & falls. Draw an arrow on the diagram to show the convection current. What are the 3 methods by which heat can be transferred: Conduction convection radiation purple crystals Conduction transfers heat energy in solids. Thermal conductors are good at transferring heat e.g metals due to free electrons & vibrating particles Thermal insulators are materials through which heat is not easily transferred e.g plastics, wood air vacuum because no free electrons, trapped air heat P1 Energy and Electricity (1) What can be done to reduce heat loss in the home? Roof insulation Cavity wall insulation Draught excluders Double glazing Name the non-renewable energy sources 1Coal 2Oil 3. Gas 4 Nuclear What energy changes are shown in the pictures: chemical to movement + heat + sound electrical to light + heat Name the different forms of energy: 1.Sound 2. Light 3.Thermal (heat) 4. Elastic potential 5.Gravitaional potential 6. chemical 7. Kinetic (movement) 8.electrical 9.nuclear Draw a sankey diagram to show the energy transfer in a 60J light bulb in which of 54 is wasted as heat: Efficiency= Useful Energy out Total energy in Calculate the efficiency of the light bulb (left). Efficiency = 6 = 0.1= 10% 60

2. power Rating (W) E= m x c x Θ J=kg x ‘C x J/kg ‘C Calculate the energy needed to heat up 2.5 kg water by 10 degrees. (Θ = 4200 J/kg ‘C) E= 2.5 x 10 x 4200 = 105 000 J = 105 kJ Total energy Transferred (J) When would insulation be called COST EFFECTIVE Pays for itself quickly (pay back time is quick) When would insulation be called EFFECTIVE? saves most per year Define specific heat capacity energy required to raise the temperature of a 1 kg mass by 1 ‘C time (s) x = What is the total energy in Joules used by 1.2kW microwave used for 5 minutes? E = P x t E = 1200 x (5 x 60) = 360 000 Joules = 360 kJ Energy (kWh)= Power (kW) x time (h) If electricity cost 14p per kilowatt hour, how much will it cost to cut a large lawn that takes 3 hours using a 2000 watt lawn mower? Energy =Power x time kWh= kW x h kWh = 2 x 3 = 6 kWh Cost = kWh x 14p = 6 x 14 = 84 p The different energy resources have different advantages and disadvantages summarize some of these in the table: P1 Energy and Electricity (2) In the national grid what is the role of step up and step down transformer?Step up transformers increase voltage before transmission on national grid to keep current low so temp remain cool to save energy (more efficient) Step down transformers reduce voltage (increase current) to make safe for use in homes. What renewable energy resources are there? Solar Geothermal Wave Tidal Wind Biomass (wood etc..) What things do you need to consider when choosing an energy resource Initial set up costs Running costs Pollution created Decommisioning costs Fill in the boxes to show the energy changes that occur at each stage in a power station: Boiler Chemical to movement Turbine Movement To movement Generator Kinetic To electrical Transformer Electrcial To electrical