Continuation of Physics term 1 year 10

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  • Physics
    • Condensation
      • When a gas cools the particles slow down & lose kinetic energy. The attractive forces pull them closer together. If the temp. gets cold enough & the particles close enough then condensation will take place turning the gas into a liquid.
      • The rate will be faster if the temp. of the gas is lower so that more particles will slow down enough to clump together & form liquid droplets. Also if the temp. of the surface the gas touches is lower. If the density is higher the forces between the particles will be stronger.
        • Fewer particles will have enough energy to overcome these forces & so will instead clump together. Airflow is less & then the concentration of the substance in the air will be higher, so the rate of condensation will be greater.
    • Evaporation
      • This is when particles escape from a liquid.
      • Particles can evaporate from a liquid at temps that are much lower than the liquids boiling point.
      • Particles near the surface of a liquid escape to become gas particles if they are travelling in the right direction, are fast enough to overcome the attractive forces of other particles in the liquid.
      • The fastest particles most likely will evaporate & then the average speed/kinetic energy of remaining particles decreases. This means that the temp. of the liquid falls & cools.
      • Rate of evaporation is higher when the temp. is higher therefore more particles will have more energy to escape. If density is lower then the forces will be weaker so that the particles can overcome them. Also if the surface area is larger more particles will be nearer to the surface. If airflow over the liquid is greater the lower the concentration of an evaporating substance in the air it's evaporating into. A greater airflow means air above the liquid is replaced more quickly, so the concentration in the air will be lower.
    • Heat Transfer
      • Rate of heat transfer is affected by: 1) radiated from the surface of the object. 2) A larger surface area. 3) Volume ( smaller volume of object will cool more quickly. 4) Type of material(conductor or insulator).
    • Energy Efficiency in the home
      • Payback time= Initial Cost/ annual saving.
        • Types of heat  transfer are: Cavity Wall Insulation- reduces convection, conduction & radiation. Loft Insulation- reduces conduction & convection. Draught Proofing- reduces convection. Hot Water Tank Jacket- reduces conduction & radiation. Thick Curtains- reduces conduction & radiation.
      • Most effective methods of insulation are the 1's that give you the most saving & that equal the initial cost to give you the most profit in the smallest payback time.
        • The most cost effective methods tend to be the cheapest. This is when they have a short payback time.
      • U values show how fast heat can transfer through a material. The better the insulator the lower the U value.


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