P1 Revision Cards

• Double glazing reduces energy loss by conduction. The gap between the two pieces of glass is filled with a gas or contains a vacuum.
  • Particles in a gas are far apart. It is very difficult to transfer energy. There are no particles in a vacuum so it is impossible to transfer energy by conduction.

• Loft insulation reduces energy loss by conduction and convection:
  • Warm air in the home rises.
  • Energy is transferred through the ceiling by conduction.
  • Air in the loft is warmed by the top of the ceiling and is trapped in the loft insulation.
  • Both sides of the ceiling are at the same temperature so no energy is transferred.
  • Without loft insulation, the warm air in the loft can move by convection and heat the roof tiles.
  • Energy is transferred to the outside by conduction.

• Cavity wall insulation reduces energy loss by conduction and convection:
  • The air in the foam is a good insuator.
  • The air cannot move by convection because it is trapped in the foam.
• Insulation blocks used to build new homes have shiney foil on both sides to reduce energy transfer by radiation.
  • Energy from the sun is reflected back to keep the home cool in summer.
  • Energy from the home is reflected back to keep the home warm in winter.

• Energy can be transferred by:
  • Conduction- due to the transfer of kinetic energy between particles.
  • Convection- a gas expands when it is heated. This makes it less dense so it rises. The unit of density is kg/m³ or g/cm³.
    • density = mass ÷ volume
  • Radiation does not need a material to transfer energy. Energy can be transferred through a vacuum.

efficiency = useful energy output (x 100%) ÷ total energy input

• Energy transformations can be shown by Sankey diagrams.
• Energy from the source (home) is lost to the sink (environment).
• Different types of insulation cost different amounts and save different amounts of energy.

Payback time = cost of insulation ÷ annual saving

• Everything that transfers energy will waste some of the energy as heat to surroundings.
• Buildings that are energy efficient are well insulated; little energy is lost to surroundings.
• Designers and architects have to make sure that as little energy as possible is wasted.