AQA GCSE Physics - Paper 1 Study Guide Graded A

Energy Stores - 1) Elastic potential 2) Gravitational potential 3) Thermal 4) Electrostatic 5) Nuclear 6) Chemical 7) Kinetic 8) Magnetic 9) Light 10) Sound How is energy transferred? - 1) Mechanically - force doing work 2) Electrically - work done by moving charges 3) Heating/Radiation - light, sound How can work be done? - When a current flows or by a force moving an object Kinetic energy formula - E=1/2mv² Kinetic energy(J) = 0.5 x mass(kg) x speed²(m/s) Gravitational potential energy formula - E=mgh G.P.E(J) = mass(kg) x gravitational field strength (N/kg) x height (m) What happens when an object falls and there's no air resistance? - Energy lost from the g.p.e store = energy gained in the kinetic energy store What does air resistance do when acting against falling objects? - It causes some energy to be transferred to other energy stores e.g. the thermal energy stores of the object and the surroundings Elastic potential energy formula - E=1/2ke² E.P.E(J) = 0.5 x spring constant(N/m) x extension²(m) What is SHC? - The amount of energy needed to raise the temperature of 1kg of a substance by 1°C SHC formula - E=mcθ Change in thermal energy(J) = mass(kg) x SHC(J/kg/°C) x temperature change(°C) What is the conservation of energy principle? - Energy can be transferred usefully, or stored or dissipated (wasted energy), but can never be created or destroyed What is power? - The rate of energy transfer, or the rate of doing work What is 1W equal to? - 1J of energy transferred per second Power Equation 1 - E=Pt Energy transferred(J) = power(W) x time(s) Power Equation 2 - W=Pt Work done(J) = power(W) x time(s) What is conduction? - The process where vibrating particles transfer energy to neighbouring particles Energy is transferred to thermal stores of the object - this energy is shared across the kinetic energy stores What is thermal conductivity? - A measure of how quickly energy is transferred through a material via conduction What is convection? - Where energetic particles move away from hotter to cooler regions Energy is transferred to the thermal energy stores of the object and is shared across the kinetic stores What do radiators create? - Convection currents Convection currents - process - 1) Energy is transferred from the radiator to the nearby air particles by conduction 2) The air by the radiator becomes warmer and less dense as the particles move quicker 3) The warm air rises and displaces the cooler air, which is then heated by the radiator 4) The previously heated air transfers energy to the surroundings - the air cools, becomes denser and sinks What does lubrication do? - Reduce frictional forces What does insulation do? - Reduce the rate of energy transfer by heating Thermal insulation techniques - 1) Cavity walls - made up of an inner and outer wall with an air gap in the middle - the air gap reduces the amount of energy transferred by conduction through the walls 2) Cavity wall insulators - the air gap is filled with foam also reduces energy transfer by convection in the wall cavity 3) Loft insulation - reduces convection currents being created in lofts 4) Double-glazed windows - air gap between two sheets of glass that prevent energy transfer by conduction through the windows 5) Draught excluders - reduce energy transfers by convection around doors and windows How do you improve efficiency? - 1) Lubrication 2) Insulation 3) Making objects more streamlined Efficiency - energy transfer equation - Useful output energy transfer divided by total input energy transfer Efficiency - power equation - Useful power output divided by total power input Is any device 100% efficienct? - No Where is wasted energy usually transferred? - Thermal energy stores How do thick walls prevent energy losses through heating? - They're made from a material with a low thermal conductivity - the thicker the walls, the lower the thermal conductivity, the slower the rate of energy transfer What objects are usually 100% efficient? - Electric heaters - all the energy in the electrostatic energy stores is transferred to useful thermal energy stores Fossil fuels (coal, oil, natural gas) - Non-renewable Cause acid rain Cause global warming Reliable currently - they are finite, so they will run out eventually Coal mining ruins the landscape Oil spillages cause serious environmental problems Energy resources used for transport - Petrol and diesel from oil - non-renewable Coal (steam trains) - non-renewable Bio-fuels - renewable Energy resources used for heating - Natural gas - non-renewable Coal - non-renewable Electric heaters - non-renewable Geothermal - renewable Solar water heaters - renewable Bio-fuels - renewable Wind Power - Renewable Doesn't cause global warming