week- 9 presentation 1 conduction of heat 1. lesson objectives: i. understand heat transfer ii....
TRANSCRIPT
Lesson Objectives:
i. Understand Heat transfer
ii. Understand Conduction and carryout an experiment
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Comparing Materials
Materials have certain PROPERTIES which make them USEFUL
We need to be able to describe and compare the properties of a material and say why its used for a job. We use certain materials for certain jobs…
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Conductors and Insulators of Heat1. Some Materials let Heat pass
through them Easily1) These materials are called
THERMAL CONDUCTORS2) METALS are good THERMAL
CONDUCTORS3) Because heat passes through
them quickly – metal normally feels COLD
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Some Materials Do Not let Heat pass through them
1) Materials that do not let heat pass through them are called THERMAL INSULATORS.
Wooden handle
Oven glove
thermals
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2) Plastic, cork, wood and fabrics are good THERMAL INSULATORS
3) Thermal insulators are good for keeping heat OUT as well as IN
ThermosDoes both
Polystyrene cup – keeps heat in
Fridge – keeps heat out
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Heat Transfer
Heat travels from a region of higher temperature to a region of lower temperature.
This process is carried out by Conduction Convection Radiation
When thermal equilibrium is reached in all regions, there is no net heat transfer. 20
Conduction
Conduction is the process in which heat is transferred through a medium (solid) from one particle to the next.
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Conduction
Heat travels at different speed through different materials.
wood did not drop copper 14 s steel 73 s aluminium 16 s
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Conduction Good heat conductors have high heat
conductivity, e.g. Copper and Silver. Generally, all substances can conduct
heat, But some are exceptionally bad conductors e.g. air and gases or non-metals.
Poorest Conductor – Vacuum Poor Conductors are also called
Insulators.23
Insulation of Heat Conduction
To reduce heat conduction, insulators are used.
The poorest conductors are used as heat insulators where applicable.
Insulation is found in the walls of the home, on heating pipes and air-con pipes (pipe lagging),
Winter clothing or the sweater that you wear
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Fibreglass Insulation Glass is a poor conductor. Fibreglass
uses this property. Layers are placed between walls to
reduce heat conducted into the house in summer or conducted out of the house in winter.
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