# physics unit 1

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• Created by: haydn
• Created on: 20-12-12 13:25

## physics unit 1 heat radiation

• Heat energy can be transferred by radiation, conevection and conduction.
• Heat radiation is the transfer of heat energy by infared radiation
• Conduction and convection involve the transfer of energy by particles
• Conduction is the main form of heat transfer in solids
• Convection is the main form of heat transfer in liquids and gases
• IR can be emitted by solid, liquids and gases
• They can all absorb and emit IR as well
• The bigger the temperature difference between a body and its surroundings, the faster energy is transferred by heating.
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## physics unit 1 surface colour and texture (radiati

• Dark, matt surfaces surfaces absorb IR falling on them much better than light, shiny surfaces such as gloss white or silver. They also emit more as well.
• Light, shiny surfaces also reflect a lot of the IR falling on them.
• Vacuum flasks have shiny inner surfaces to keep heat in or out, depending on whether its storing hot or cold liquid.
• Solar hot water panels contain water pipes under a black surface.
• Radiation from the sun is absorbed to heat the water in the pipes
• This water can be used for washing or pumped to radiators.
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## physics unit 1 kinetic theory

• Solids - strong forces of attraction hold the particles close together. The particles don't have much energy so they can only vibrate about their fixed points.
• Liquids - there are weaker forces of attraction and can move over each other but are still close together. They have more energy than the particles in a solid. They move in random directions at low speeds.
• Gases - There are almost no forces of attraction and the particles have more energy than liquids and solids. They are free to move and travel in random directions at high speeds.
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## physics unit 1 conduction of heat

• Conduction of heat energy is the process where vibrating particles pass on their extra kinetic energy to neighbouring particles.
• This process is gradually continued through the solid and some of the kinetic energy or heat is passed all the way through.
• Usually conduction is faster in denser solids, because the particles are closer together and so will collide more often and pass energy between them.
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## physics unit 1 metals good conductors?

• Metals 'conduct' so well because the electrons are free to move inside the metal.
• At the hot end the electrons move faster and collide with other free electrons, transferring energy.
• Because the electrons can move freely, this is obviously a much faster way of transferring the energy through the metal than slowly passing it between jostling neighbouring atoms.
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## physics unit 1 covection

• Convection occurs when the more energetic particles move from the hotter region to the cooler region - and take their heat energy with them.
• Convection of Heat - liquids and gases only.
• Convection currents are all about changes in density.
• The radiator example, heating a room with a radiator relies on convection currents too.
• Hot, less dense air by the radiator rises and denser, cooler air flows to replace it.
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## physics unit 1 condensation and evaporation

• Condensation is when gas turns to liquid.
• When a gas cools, the particles in the gas slow down and lose kinetic energy.
• The attractive forces between the particles pull them closer together.
• Evaporation is when particles escape from a liquid.
• Particles can evaporate from a liquid at temperatures that are much lower than the liquids boiling point.
• The fastest particles are most likely to evaporate from the liquid
• The cooling effect can be really useful. As the water from the sweat on your skin evaporates, it cools you down.
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## physics unit 1 energy efficiency in the home

• payback time = intial cost divided by annual saving
• The most effective methods of insulation are ones that give you the biggest annual saving
• Eventually, the money you've saved on heating bills will equal the intial cost of putting in the insulation
• The most cost-effective methods tend to be cheapest
• They are cost-effective becuase they have a short payback time - this means the money you save covers the amount you paid really quickly.
• Heat transfers faster through materials with high U-values, so better the insulator the lower the U-value.
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## physics unit 1 energy transfer

• Electrical Energy - whenever a current flows
• Light Energy - from the Sun, light bulbs, etc
• Sound Energy - from the loudspeakers or anything noisy
• Kinetic/Movement Energy - anything that's moving has it
• Nuclear Energy - released only from nuclear reactions
• Thermal/Heat Energy - flows from hot objects to colder ones
• Gravitational Potential Energy - possessed by anything that can fall
• Elastic Potential Energy - stretched springs, elastic, rubber bands etc
• Chemical Energy - possessed by foods, fuels, batteries, etc
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## physics unit 1 conservation principle

• Energy can be transferred usefully from one form to another, stored or dissipated - but it can never be created or destroyed.
• Dissipated is a fancy way of saying the energy is spread out and lost.
• Energy is only useful when it can be converted from one form to another.
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## physics unit 1 energy sources & power stations

• A nuclear power station uses nuclear fission of uranium or plutonium producing the heat to make steam to drive turbines.
• Nuclear power stations take the longest time of all the power stations to start up. Natural gas power stations take the shortest time of all the fossil fuel power stations.
• A fossil fuel is burned to convert its stored chemical energy into heat energy
• The heat energy is used to heat water to produce steam
• The steam turns a turbine, converting heat energy into kinetic energy
• The turbine is connected to a generator, which transfers kinetic energy into electrical energy
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