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O-Level Thermal Processes
What the O-Level syllabus expects for Thermal Processes, and how to practise it.
What the syllabus expects
- Understand that heating transfers energy from a hotter region to a cooler one until the two reach thermal equilibrium.
- Describe conduction in solids at the microscopic level, via vibrating atoms/molecules and moving electrons.
- Describe how convection happens in fluids through changes in density.
- Explain that electromagnetic radiation transfers energy without needing a material medium, and that a body's rate of radiative energy transfer depends on its surface colour and texture, its surface temperature, and its surface area.
- Apply the ideas of conduction, convection and radiation to everyday situations.
How it's examined
Questions on this topic most often ask you to explain, name, suggest. About 5% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (3 marks)
A hot-water shower uses a heating element sitting inside a tank filled with hot water. (e) Suggest two changes you could make to the outside of the tank to cut down heat loss. For each, name the type of heat transfer being reduced and explain how your change lowers the heat flow out of the tank.
Show the worked answer
Change 1: Give the outside of the tank a shiny/silvered (or white) surface. This reduces heat loss by radiation, because shiny, light-coloured surfaces are poor emitters of infra-red radiation, so less thermal energy is radiated away. Change 2: Wrap the tank in an insulating lagging/jacket (e.g. foam or fibreglass). This reduces heat loss by conduction, because the lagging is a poor conductor (traps air) and so slows the flow of thermal energy through the tank wall to the surroundings.
More O-Level Pure Physics topics
Physical Quantities, Units and Measurement · Kinematics · Dynamics · Turning Effects of Forces · Pressure · Energy · all of O-Level Pure Physics