P1 Revision 2

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  • Created by: LBC0502
  • Created on: 14-06-14 12:18
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  • P1 Revision
    • Evaluating Energy Transfers
      • Appliances that need to transfer thermal energy: Kettle- (convection/electric). Toaster- (infrared radiation/electric). Oven- (convection/chemical). Dishwasher- (convection/electric). Hair dryer- (radiation/electric).
      • The Vacuum Flask: Stops the transfer of thermal energy by conduction and convection because there are no particles in the vacuum flask. The shiny surface reflects thermal radiation to prevent transfer in the flask. The silver coating reflects thermal energy back into the hot liquid. The plastic cap is a good insulating of thermal energy and prevents a convection current. There is also an outer layer of insulation. Parts of the vacuum flask: plastic cup, silver surfaces, double wall plastic container, plastic protective cover, sponge pad (protection), plastic spring, vacuum (contains no particles to prevent conduction/convection).
      • Examples of insulating materials: Wood, plastic, clothing (soft, thick fibres, overlap). One of the best insulators is trapped air. Trapped air is in between the fibres of loft insulation, bubble foam cavity wall insulation, duvets etc.
    • Evaporation and Condensation
      • Evaporation: Solids- Particles vibrate quicker when they gain more thermal energy and the solid expands. Liquids- Particles will gain energy and move faster and move faster and the bonds will break and the liquid will evaporate. Gas- Particles gain more energy and move faster and the gas expands.
      • Evaporation: Puddle dries up: The water molecules in the puddle gain thermal energy through infrared radiation from the sun and the water molecules in the puddle gain kinetic energy. The bonds weaken and eventually break and the water molecules escape the surface of the liquids. The liquid becomes less dense and rises and forms a gas.
      • Evaporation: Why do we feel cold when we get out of a swimming pool? The thermal energy transfers from the heat from our bodies (skin) to the water. The water particles gain kinetic energy and the particles move around quickly and have enough energy to break the bonds and the water evaporates into the air.
      • Condensation: Water particles with thermal energy and kinetic energy meets a cool object and the water particles lose thermal and kinetic energy and this makes the particles more dense and the particles fall and the water vapour condenses into a liquid (e.g water droplets on a mirror). The particles move close together into a liquid and slow down (form a bond).
    • What affects heat loss from an object?
      • When a substance gains thermal energy, the substance will expand. The particles stay the same size but the spaces between the particles increase. This causes the density of the substance to decrease.
      • Experiment: How does the volume of water affect how quickly it cools down?: Hot water is poured into three cans (small, medium, large). IV: surface area of cans. DV: The volume of water and temperature of water after 5 minutes. CV: Same starting temperature of volume of water. Conclusion: The larger the surface area of the can, the quicker the water will take to cool down/transfer thermal energy.
      • More area to transfer thermal energy from/large area to make contact with air. By decreasing the surface area and volume, the transfer of thermal energy is prevented.
      • Examples: Foxes have small ears, short legs, white fur. Small surface area: volume decreases transfer of thermal energy and white is a poor emitter of thermal energy. Ducks huddle together to decrease surface area and decrease the transfer of thermal energy.
    • Convection
      • Convection happens in liquids and gases (fluids) because they both can flow.
      • Convection current (gas): Particles in the gas gain thermal energy. They move faster and gain more kinetic energy. The particles spread out and the density of the gas decreases. The gas rises and thermal energy is transferred by the bulk movement of the gas. The particles start to lose kinetic energy and thermal energy when reaching the cooler region and the gas becomes more dense. The particles fall and replaces the gas which has risen and the convection current repeats.
      • Convection current (liquid): Particles in a liquid gain thermal energy and the particles gains kinetic energy and more faster. The particles spread out and the liquid expands. The density of the liquid decreases and the liquid rises. The particles start to lose kinetic energy and thermal energy and the liquid become more dense and falls and the convection current repeats.
      • Convection Current: Cool water warms then hot water cools.

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