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- conduction is the transfer of heat two objects in contact and - there is a temperature difference between them how does conduction take place in metals? solid metals - in contact with a hot object - silver, copper, steel, iron..., - molecules vibrate strongly at hot end - they have more kinetic energy - attractive forces between molecules cause neighbouring molecules to vibrate too - kinetic energy passes on from hot end to cold end - the process is very slow and not effective what are common uses of conductors? - making cooking utensils - heat sinks for computers or hi-fi system, - conduction is the transfer of heat two objects in contact and - there is a temperature difference between them how does conduction take place in solid non-metals? solid non-metals - in contact with a hot object - plastic, glass, wool, styrofoam, trapped air, wood..., vibration of molecules how does molecular vibration transfer energy? - molecules vibrate strongly at hot end - they have more kinetic energy - attractive forces between molecules cause neighbouring molecules to vibrate too - kinetic energy passes on from hot end to cold end - the process is very slow and not effective, only vibration of molecules how does molecular vibration transfer energy? - molecules vibrate strongly at hot end - they have more kinetic energy - attractive forces between molecules cause neighbouring molecules to vibrate too - kinetic energy passes on from hot end to cold end - the process is very slow and not effective - thus non-metals are good insulators of heat, solid non-metals - in contact with a hot object - plastic, glass, wool, styrofoam, trapped air, wood... how does energy transfer take place? only vibration of molecules, - convection is the transfer of heat by movement of heated liquids or gases how does convection take place? - heated liquid or gas expands - volume increases but mass is unchanged - becomes less dense - rises upward - cold liquid or gas is denser - sinks downward - convection current is set up - heat is transferred away from hot region to cold region, diffusion of free electrons how does free electrons transfer energy? - free electrons move at high speed at hot end - they have high kinetic energy - they collide with slow moving electrons - kinetic energy is transferred during collisions - the process is fast & very effective - it is about 1000 times faster than molecular vibration - thus metals are good conductors of heat, - radiation is the transfer of heat by electromagnetic waves what affects the rate of absorption or emission of radiation? - dull & rough black surfaces are good absorbers and emitters of radiation - shiny & smooth white surfaces are poor absorbers and poor emitters ( good reflectors) of radiation, conduction what does conduction mean? - conduction is the transfer of heat two objects in contact and - there is a temperature difference between them, Transfer of thermal energy (Heat) what are the processes involved? conduction, Transfer of thermal energy (Heat) what are the processes involved? convection, Transfer of thermal energy (Heat) what are the processes involved? radiation, radiation what does radiation mean? - radiation is the transfer of heat by electromagnetic waves, - molecules vibrate strongly at hot end - they have more kinetic energy - attractive forces between molecules cause neighbouring molecules to vibrate too - kinetic energy passes on from hot end to cold end - the process is very slow and not effective - thus non-metals are good insulators of heat what are common uses of insulators? - handles of cooking utensils - roof of building - lagging materials for heater or boiler or hot water system - wall materials for building, - dull & rough black surfaces are good absorbers and emitters of radiation - shiny & smooth white surfaces are poor absorbers and poor emitters ( good reflectors) of radiation what are everyday examples or uses of radiation? - cooling fins at the back of a fridge is painted black so that heat can be removed from the fridge at fast rate by radiation - solar panel on the roof top are painted black to absorb radiation at optimum rate - glass wall in thermos-flask are silvered to reduce heat loss by radiation, - heated liquid or gas expands - volume increases but mass is unchanged - becomes less dense - rises upward - cold liquid or gas is denser - sinks downward - convection current is set up - heat is transferred away from hot region to cold region what are everyday examples of convection? - land breeze and sea breeze - air-conditioner is installed at ceiling - freezer is at the top of a fridge - heating coil in kettle is at the bottom, - land breeze and sea breeze - air-conditioner is installed at ceiling - freezer is at the top of a fridge - heating coil in kettle is at the bottom how to reduce convection loss? Thermos flask - vacuum between glass walls prevents convection from taking place Refrigerator - Freezer is placed on top so that cold air sinks and warm air rises to the top - convection current is set up to ensure uniform cooling, solid metals - in contact with a hot object - silver, copper, steel, iron... how does energy transfer take place? vibration of molecules, solid metals - in contact with a hot object - silver, copper, steel, iron... how does energy transfer take place? diffusion of free electrons, convection what does convection mean? - convection is the transfer of heat by movement of heated liquids or gases