Physics: Thermal Energy Transfer

- Convection

- Conduction

- Evaporation

- Infra- red radiation

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Convection

Convection= the transfer of energy from particle to particle.                                              Particles move faster when they are hot and expand becoming less dense. Warm particles are less dense than cold particles meaning hot particles rise and cold particles sink.                                           The Vacuum Flask                                                                                                                                    The vacuum round the flask means that no heat can pass from particle to particle and through the sides, meaning the substance in the flask either stays hot or cold.                                                                     The Particles                                                                                                                                               The radiator heats the air causing it to rise and force the cold air down to be heated by the radiator which then in turn rises, cools and is re-heated.

(http://upload.wikimedia.org/wikipedia/commons/thumb/1/18/Vacuum_Dewar_Flask_Red.svg/100px-Vacuum_Dewar_Flask_Red.svg.png)  (http://t2.gstatic.com/images?q=tbn:ANd9GcTw-aZP8xdM0C9nRG3YJsSRDZRVL5ngAiFZ7kE0yL3Cs0dgd9GT)                                                  

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Conduction

Conduction= The transfer of energy through a substance without the substance itself moving.

At the hot end atoms vibrate with more kinetic energy (faster). Energy gradually passes along the bar.Non-metals, liquids & gases= poor conductors .Metals= v. good conductors because they have lots of free electrons that can move around.

Heat is transferred more quickly if:

- the conductor= shorter

- the conductor is bigger in cross- sectional area

- the temperature difference is greater.

 

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