Thermal energy transfer

Understandings:

• Conduction, convection and thermal radiation
• Black-body radiation
• Albedo and emissivity
• The solar constant
• The greenhouse effect
• Energy balance in the Earth surface–atmosphere system

Applications and skills:

• Sketching and interpreting graphs showing the variation of intensity with wavelength for bodies emitting thermal radiation at different temperatures
• Solving problems involving the Stefan–Boltzmann law and Wien’s displacement law
• Describing the effects of the Earth’s atmosphere on the mean surface temperature
• Solving problems involving albedo, emissivity, solar constant and the Earth’s average temperature

Guidance:

• Discussion of conduction and convection will be qualitative only
• Discussion of conduction is limited to intermolecular and electron collisions
• Discussion of convection is limited to simple gas or liquid transfer via density differences
• The absorption of infrared radiation by greenhouse gases should be described in terms of the molecular energy levels and the subsequent emission of radiation in all directions
• The greenhouse gases to be considered are CH4, H2O, CO2 and N2O. It is sufficient for students to know that each has both natural and man-made origins.
• Earth’s albedo varies daily and is dependent on season (cloud formations) and latitude. The global annual mean albedo will be taken to be 0.3 (30%) for Earth.