GCSE Physics

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  1. in an iron rod the particles vibrate . If one end of an iron rod is heated , the vibrating particles transfer energy to the neighbouring particles which are not vibrating so violently . What is this process called
  2. an electric immersion heater is put at the bottom of a large tank of water . the water next to the heater becomes warm . What will happen to the warmed water next to the heater ? Give a reason for your answer
    • the water next to the hater is warm
    • the particles expand
    • the warm water particles becomes less dense
    • the less dense water particles rise through the colder regions
    • the colder regions replace the warmer regions which have just risen
    • once the warm water particles have reached the surface the particles have become more dense and cool
    • the water particles sink and reach the heater
    • the process is restarted
  3. A) in a liquid , some of the particles have enough kinetic energy to escape from the surface . This process happens even when the liquid is below its boiling point . what is this process called ?
    B) how will this affect the temperature of the liquid left in the container
    • A) evapouration
    • B) the temperature will be cooler
  4. explain why the boiler is below the hot water tank
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    because due to convection currents hot water particles rise
  5. why is heat energy transferred from hot water in the tank to the surrounding air
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    due to conduction through the sides of the tank
  6. how may heat loss from the water tabk be reduced
    • by covering the outside of the tank in foam or insulating material , which contains trapped air
    • or
    • by covering the tank with foil , but make sure the shiny side is facing inwards , this will reflect any heat that tries tos escape the tank back into the tank
  7. the diagram shows part of a solar water heater . Water circulating through the solar panel is heated by the sun .
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    a) complete the following sentence . Heat energy si transfered from the sun to the solar panel by
    b) the pipe inside the solar panel is black why ?
    c) there is a leyer of expanded polystrene behind the black pipe why ?
    d) a silvered surface is used at the back of a solar panel why ?
    • a) radiation
    • b) because black surfaces are good absorbers of radiation , so will absorb as much of the suns energy as possible
    • c) because polystrene contiand trapped air so is a good insulator of heat
    • d) because silvered surfaces are good refelectors of thermal radiation , so will reflect any escaping heat back into the solar panel
  8. the bigger the temperature difference between an objects and its surroundings , the .... the rate at which thermal energy is transfered
  9. under similar conditions different materials transfer thermal energy at different rates , the rate at which an object transfers thermal energy depends on
    • the external temperature (the cooler is surroundings , the faster it cools )
    • the surface are of the object ( a large suraface area cools fast)
    • the colour of the object
    • the material
  10. a heat sink is a term for :
    something that transfers heat generated within a solid material to air or a liquid . heat sinks are used to remove unwanted heat from a device to keep it from overheating .
  11. examples of heat sinks are (3)
    • the heat exchangers used in refrigeration
    • air conditioning systems
    • the cooling fins on a motorbike engine
  12. two people are in the sea , they both come out one gets dried and the other doesnt , the one who didnt dry shivers explain why
    this is because the sea is colder than us , so the sea water on us makes our body temperature lower as our body transfers heat energy to the sea because hot obejects transfer heat energy to cooler objects
  13. much of the heat energy we use to warm our houses is lost to the atmosphere . heat energy is lost through (4)
    the roof , walls , windows and the floor
  14. describe cavity wall insulation and how it reduces heat transfer
    the space between the double wall is filled with fiberglass . this contains a lot of trapped air which is a good insulator , this reduces convection and radiation across the gap
  15. describe loft insulation and how it reduces heat transfer
    a thick layer of fiberglass wool id laid out across the whole loft floor , the fiberglass contians a lot of trapped air which is a good insulator , this reduces heat transfer by radiation and conduction
  16. describe double glazing and how it reduces heat transfer
    two layer of glass are used at a window trapping a layer of air between them . air is a very good insulator reduces heat transfer by radiation and the narrow column stops convection currents from forming easily , this method also reduces heat transfer by conduction as gases are poor condcutors of heat
  17. describe draught profing and how it reduces heat tarnsfer
    strips of foam and plastic are placed around doors and windows , this stops draughts of cold air blowing in , meaning the reduces heat loss due to convection
  18. describe hot water tank jacket and how it reduces heat transfer
    lagging such as fribre glass wool is places around the hot water cylinder , this contains a lot of trapped air which is a good insulator , this reduces heat transfer by radiation , convection and conduction
  19. describe how carpets reduce heat loss
    they are usually made of wool or a wool mixture which again contain a lot of trapped air and so reduces heat loss by conduction through the floor
  20. on a winters day , this is how thermal energy escapes from a house
    heat escapes beacause of heat lost in one hour
    roof 6MJ
    windows 8MJ
    walls 12 MJ
    floor 4MJ
    draughts and air changes 20MJ

    a) what is the total loss of heat from the house in one hour
    b) what percentage of heat is lost through the windows
    • a) 50
    • b) 8/50 * 100 = 16%

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GCSE Physics
2012-04-03 09:57:11


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