P2 - Energy transfer by heating

• Thermal conductivity


  Tells you how quickly energy is transferred throughg it by thermal conduction
• Factors that affect the heat loss from a building

  • The thickness of its walls and roof
  • The thermal conductivity of its walls and roof
• The thermal conductivity of the walls and roof of a house can be reduced by using thermal insulators
• Thermal insulator


  • A material which has a low thermal conductivity
  • The rate of energy transfer through an insulator is low
• The energy transfer throuhg a material depends on:

  • The material's thermal conductivity
  • The temperature difference between the two sides of the material
  • The thickness of the material
• When a substance is heated or cooled the temperature change depends on:

  • The substance's mass
  • The type of material
  • How much energy is transferred to it
• Specific heat capacity


  The amount of energy needed to raise the temperature of 1kg of the substance by 1 C
• Every type of material has a specific heat capacity
• change in thermal energy (J) = mass (kg) x specific heat capacity (J/kgC) x temperature change (C)
• Infrared radiation

  • Part of the electromagnetic spectrum
  • All objects emit and absorb infrared radiation
  • The higher the temperature of an object, the more infrared radiation it gives out in a given time
• For an object at a constant temperature:

  • Infrared radiation emitted = infrared radiation absorbed
  • Infrared radiation is emitted across a continuous range of wavelengths
• An object's temperature will increase if it absorbs infrared radiation at a higher rate than it emits it
• Black body


  • A theoretical object that absorbs 100% of the radiation that falls on it
  • A perfect black body would not reflect or transmit radiation, and would also be a perfect emitter of radiation
• The Greenhouse effect


  • Greenhouse gases absorb infrared radiation emitted by the surface of the Earth and precent it escaping into space
  • They then re-emit the infrared radiation back towards the surface of the Earth, increasing the Earth's temperature
  • Greenhouse gases in the Earth's atmosphere include water vapour, methane, and carbon dioxide