energy transfers

• describe how loft insulation reduces heat loss through the roof (4 mark)

  insulation is made of fibres which are poor conductors, which minimises heat loss by conduction

  air is trapped between fibres , preventing convection currents forming
• a factory chimney is used to expel hot gases from an industrial process. the base of the chimney is hotter than the top. describe how a convection current forms because of the temperature difference. (6 marks)


  the gas molecules are hot as they leave the industrial process, causing them to expand/move apart

  the gas becomes less dense and rises

  the cooler air takes place of the displaced gas

  gas at the top of the chimney cools , becoming more dense and falls

  repeated process is know as a convection current
• why is a black object that has been exposed to heat warmer than a white object

  black is a good absorber and emitter of heat

  black emits absorbed heat which results in it feeling warm to the touch

  white absorbs less heat from the sun and reflects more of it back to the surroundings
• describe the energy transfer when boiling a kettle


  transferred electrically/by heating

  thermal energy is increased in the water
• describe the energy transfer when a car breaks

  energy transferred mechanically- friction

  kinetic energy store decreases in the wheel

  thermal energy store increases in the breaks