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Essential idea: For simplified modelling purposes the Earth can be treated as a black-body radiator and the atmosphere treated as a grey-body.
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)
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.
Data booklet reference:
International-mindedness:
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?
Utilization:
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).
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)
Vocab Lists / Quizlets:
Vocab Lists / Quizlets:
Thermal Resources:
Thermal Resources:
Vocab Lists / Quizlets:
Vocab Lists / Quizlets:
2016_Topic_8.2_Sample_Exam_Problems.pdfThermal Energy Problem Solving
Video Resources
Andy Masley Playlist
Louis Wong Topic 8 Playlist
Conduction:
Conduction:
Thermal energy (heat) will transfer from one place to another if there is a difference in temperature. Conduction can be visualised as the result of collisions of molecules. As one end of the object is heated, the molecules there move faster. As they collide with their slow moving neighbours they transfer some of their energy. So energy is transferred by molecular collisions along the object as shown in the gif to the left.
Using the highly technical 'Heat Conduction' device to the right we were able to see that the BRASS conducted heat the fastest.
Most people have convection heaters within their house/apartment. While the heater is placed near the wall the entire room is warmed the convection of heat by the mixing of molecules.
Convection is a process where heat is transferred by the mass movement of molecules from one place to another, and often over large distances.
Liquids and gases are typically warmed by the process of convection. As the substance is heated, its density decreases causing it to rise and then is replaced by colder more dense material.
Like a candle in a tube...(or wind)
Radiation:
Radiation:
Whereas conduction and convection require matter, heat can be transferred by radiation across empty space. Radiation consists of electromagnetic waves. Radiation from the Sun for example consists of visible light plus other wavelengths that the eye cannot see including infrared radiation which is responsible for heating the Earth.
The rate at which an object radiates energy (the power) is found using the following equation known as the Stefan-Boltzmann law.
A is the surface area of the object and T is the surface temperature. The Stefan-Boltzmann constant σ is 5.67 x 10-8 W m-2 K-4. Black surfaces emit radiation best while white and shiny surfaces emit radiation least. This is represented by the emissivity e in the equation. A perfect emitter of radiation (i.e. an ideal black body) has an emissivity of 1. A poor emitter of radiation has an emissivity closer to 0. The temperature is measured in degrees Kelvin. Conversion from Celsius to Kelvin below.
The left side is painted white, where as the right side is unpainted copper.
The left side is a 'matte' black finish, where as the right side is a 'gloss' finish paint.
By varying the voltage (J/q) we were able to change the color quality of the light.
The wavelength at the peak of the spectrum is related to the absolute temperature of the hot filament by the following equation known as Wien's Law.
From the graph of intensity against wavelength, determine the wavelength of the peak of the spectrum and calculate the temperature of the hot filament at the four different voltages.
The data to the left is from 4 different voltages. Using the information within the graph, determine the temperature of using the equation below.
An explanation of where the equation came from: Thermal Radiation (use the drop down links to read more)
We can see from the chart at the right the relationship amongst wavelength (λ), Frequency (f), and temperature (T).
For the peak wavelength of 483 nm.
A good summary.
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