P2

• Thermal conductivity tells you how fast energy is transmitted through thermal conduction
• Insulating buildings:

  • factors that affect rate of heat loss from a building include thickness and thermal conductivity of walls and roof
• lower thermal conductivity = lower rate of heat loss
• thermal conductivity can be reduced by thermal insulators - these are materials with low rate of energy transfer
• • energy transfer per second depends on:
  • material’s thermal conductivity
  • temp difference between 2 sides of material
  • thickness of material
• Specific heat capacity:

  • amount of energy needed to raise the temp of 1kg of substance by 1°C
  • change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg°C) x temp change (°C)
• Infrared radiation:

  • part of the electromagnetic spectrum
  • all objects absorb and emit it
  • higher temp of object, more infrared radiation
• Infrared radiation:

  • good absorber is also good emitter
  • object’s temp will increase if it absorbs infrared radiation at a higher rate than it emits it
  • infrared emitted = infrared absorbed
  • infrared is emitted across continuous range of wave lengths
• Black bodies:

  • theoretical object that absorbs 100% of radiation that falls on it
  • perfect black body wouldn’t reflect or transmit any radiation; would also be a perfect emitter of radiation
• • greenhouse gases absorb infrared radiation emitted by surface of Earth and prevent it escaping to space
  • then re-emit it back to Earth’s surface, increasing Earth’s temp
• greenhouse gases include CO2, water vapour and methane
• human activities such as burning fossil fuels, deforestation, and livestock farming increase amount of greenhouse gases
• REQUIRED PRACTICAL for Measuring Specific Heat Capacity:

  • use scale to measure mass of metal block
  • connect the immersion heater to a 12 volt supply
  • put heater into central hole of metal block
  • put thermometer into smaller hole
  • switch on power supply
  • take the temperature measurement every 2 minutes for 20 minutes, or until block reaches 50°C
  • replace block with water in suitable container
  • measure temp. rise of water when same amount of energy supplied to it by the heater
  • results should show that metal block heats up faster than water
• REQUIRED PRACTICAL of different materials as insulators:

  • using identical cans or beakers of hot water
  • wrap each material around the beaker/can
  • use thermometer to measure temp. after a fixed time
  • compare temp. between beginning and after fixed time between the materials to determine which is the best insulator
  • CVs = start temp. of water and volume of water