thermal energy transfers Flashcards
thermal conduction
the transfer of thermal energy by the vibration of molecules
experiment to demonstrate conduction
Use small blobs of petroleum jelly to attach to paper clips along the copper rod. Secure the rod in the clamp and heat the other end. Watch what happens to the paper clips.
How does conduction work?
Atoms near the heat source vibrate more due to increased kinetic energy. These atoms collide with their neighbours and transfer thermal energy. Then the neighbours collide with their neighbours and the process continues until lack of energy.
Why are metals good conductors?
The delocalised electrons that are free to move can carry thermal energy and move along the metal.
convection
the transfer of thermal energy through a material by the movement of the material itself.
How do hot air balloons work?
The fire heats up the air going into the balloon, making the air expand, becoming less dense, making the balloon float up.
convection current
the transfer of thermal energy by the motion of a fluid
fluid
a substance that can flow
why does cold air sink?
air particles shrink and become more dense
why does hot air rise?
air particles expand and become less dense
infrared radiation
the transfer of thermal energy by waves and without a medium
How do thick curtains and draught excluders reduce heat loss?
Stops convection currents
How do lofts and underfloor insulating materials reduce heat loss
prevents conduction of thermal energy through floors and ceilings
How do double and triple glazing windows reduce heat loss
vacuum between glass panes cuts out losses or gains by conduction and convection
How do cavity walls reduce heat loss?
reduces thermal energy loss/gain by conduction
How does foam or rockwool in wall cavities reduce heat loss?
reduces convection
For an object to be at constant temperature what must happen?
it needs to transfer energy away from the object at the same rate it recieves energy
factors that effect the earths temperature
incoming radiation (from sun) and radiation emitted from the earth’s surface
everyday applications of conduction and convection
heating objects (pans) - conduction
heating a room (heaters) - convection
what effects the rate of emission of radiation?
the surface temperature - higher the temp, higher amount of radiation being emitted
the surface area - larger surface area, higher amount of radiation being emitted
