Chapter Objectives and Summaries
for the Oxford University Press text by Walding, Rapkins and Rossiter:-
" NEW CENTURY Senior Physics - Concepts in Context "
CHAPTER 12 Heat transfer.
Knowledge of subject matter
- Identify and discuss how heat is transferred in given situations
- Distinguish between the methods of heat transfer: conduction, convection and radiation
- Identify and discuss why certain materials are good or bad at transferring heat
- The meaning of "Thermal Conductivity"
- Calculate the rate of heat flow in given situations
- Discuss methods of changing th rate of heat transfer to and from substances or structures
- Explain the green house effect in terms of heat transfer
- Solve problems involving heat transfer
- Collect and organise data on temperature transfer.
- Locate thermal data from tables.
- Design simple experiments to test the efficiency of heat transfer and its prevention.
COMPLEX REASONING PROCESSES
- Design a coherent strategy for complex 'real-world' problems related to heating and cooling.
- Select relevant data to confirm or refute theories about the efficiencies of various cooling measures.
CHAPTER 12 SUMMARY
- Conduction is the process where heat energy is transferred through a medium by the vibration to the particles of the medium.
- In conduction the particles of the medium do not travel with the heat flow.
- Conduction occurs better where the particles are in close contact. Metallic solids are the best conductors.
- Insulators are materials that have very low thermal conductivity.
- Materials that trap air are poor conductors, as air is a poor conductor of heat.
- The rate of heat energy flow through a material is given by the equation:-
R = k (T2 - T1).A/d
Where R is the rate of heat flow in Watts, k is the thermal conductivity in W.m-1 K-1, (T2 - T1) is the temperature difference on either side of the material in K, A is the surface area of the material in m2, and d is the thickness of the material in m.
- Convection is the process where heat energy is transferred through a medium by the movement of the particles of the medium. This movement of particles sets up convection currents.
- As convection requires the free movement of particles it is confined to liquids and gases.
- Radiation is the transfer of heat by means of electromagnetic waves, in particular, infra-red waves.
- The transfer of heat energy by radiation does not require a medium.
- White shiny materials can reflect radiation, while dark materials absorb radiation
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