Thermal energy transfer

Nature of science:

Simple and complex modelling: The kinetic theory of gases is a simple mathematical model that produces a good approximation of the behaviour of real gases. Scientists are also attempting to model the Earth’s climate, which is a far more complex system. Advances in data availability and the ability to include more processes in the models together with continued testing and scientific debate on the various models will improve the ability to predict climate change more accurately. (1.12)

• 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

• The concern over the possible impact of climate change has resulted in an abundance of international press coverage, many political discussions within and between nations, and the consideration of people, corporations, and the environment when deciding on future plans for our planet. IB graduates should be aware of the science behind many of these scenarios.

Theory of knowledge:

• The debate about global warming illustrates the difficulties that arise when scientists cannot always agree on the interpretation of the data, especially as the solution would involve large-scale action through international government cooperation. When scientists disagree, how do we decide between competing theories?

• 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.

Data booklet reference:

• Climate models and the variation in detail/processes included
• Environmental chemistry (see Chemistry option topic C)
• Climate change (see Biology sub-topic 4.4 and Environmental systems and societies topics 5 and 6)
• The normal distribution curve is explored in Mathematical studies SL sub-topic 4.1

Aims:

• Aim 4: this topic gives students the opportunity to understand the wide range of scientific analysis behind climate change issues
• Aim 6: simulations of energy exchange in the Earth surface–atmosphere system
• Aim 8: while science has the ability to analyse and possibly help solve climate change issues, students should be aware of the impact of science on the initiation of conditions that allowed climate change due to human contributions to occur. Students should also be aware of the way science can be used to promote the interests of one side of the debate on climate change (or, conversely, to hinder debate).