CONVECTION

THERMAL ENERGY-CONVECTION

convection is the transfer of thermal energy by means of currents in a fluid(liquid or gas)

• convection requires the movement of particles
  
• thus this process can only take place in liquid/gas


• and not solids,because the particles in solids are not able to move about freely
  
• convection current = hot fluid rise, cold fluid sinks (change in density)


• when a fluid is heated, its density decreases due to the increase of volume
  
• heated fluid therefore rises


• cooler part of the liquid has a greater density now,thus sinks downwards
  
  

convection in liquids

* liquid is heated

*the density of the heated liquid decreases because the liquid expands

*the density of the cooler part of the liquid is now greater then the heated part of the liquid

*therfore,the heated liquid rises and the cooler liquid sinks

convection in gas

*air is heated

*the density of the heated air decreases

*the density of the cooled part of the air is now
greater then the density of the heated air

*the heated air rises and the cold air sinks

*thus,creating a current which cost the spiral to spin

(sea breezes and land breezes are examples of convection currents)