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Transfer of Thermal Energy

Revision Package
by

jiahui au

on 6 April 2011

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Transcript of Transfer of Thermal Energy

Transfer of Thermal Energy Heat transfer occurs from a region of HIGHER temperature to a region of LOWER temperature
Heat is a form of energy Conduction Convection Radiation Solid Liquid, Gas heated molecules gain energy, vibrate faster, bump into neighbouring molecules more often, hence transferring heat energy to neighbouring molecules Metals Non-metals conduct heat better because of the presence of free electrons poor conductors of heat due to molecular structure
molecules are further apart (especially gas) transfer of thermal energy by means of currents in a fluid

convection current is the movement of fluid caused by the change in density in various parts of the fluid transfer of thermal energy without any flow of material medium
through molecular vibration and electron diffusion Liquid & Gas requires bulk movement of fluid molecules (A) Land heats up faster than sea in the day, hence the air above land is hotter, expands and becomes less dense than the air above sea. The less dense air above air rises and the denser air sinks above sea.
(B) Land cools down faster than sea in the night, hence the air above land is cooler, contracts and becomes denser than the air above sea. The denser air above land sinks and the less dense air above sea rises. continual emission of thermal energy in the form of infrared waves
emitted from surface of all bodies
no medium required Rate of Transfer of Thermal Energy depends on... surface temperature surface area colour & texture of surface higher surface temperature, higher rate of radiation larger surface area, emit and absorb more radiation dull black
VS
shiny white Applications Conduction Convection Radiation Good Conductors cooking utensils made of good conductors of heat (stainless steel, aluminium) so that food cooks faster Poor Conductors Handles of cooking utensils and appliances made of poor conductors of heat so as to prevent our hands from being scalded
Woolen clothings to keep people warm on cold days Heating coil placed at the bottom of the kettle Air conditioner installed near ceiling of room Shiny surface of thermoflask to prevent heat loss due to radiation Q&A! Why does wool feel warm? Why do birds fluff up their feathers during winter? Why are houses painted white in hot countries? Why do astronauts wear shiny suits? How do thermal energy from the sun reach us? Why do we get goose pimples when we are cold? Why do people lie low or crawl on the floor when a fire breaks out?
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