Convection (Oxford AQA IGCSE Physics)
Revision Note
Convection
Convection is the main way that thermal energy is transferred through liquids and gases
Convection only occurs in fluids
Remember that fluids are gases or liquids
Convection cannot happen in solids
This is because convection requires the movement of particles
Particles are held in a fixed position in a solid
Descriptions of convection currents always need to refer to changes in temperature causing changes in density
A convection current can be created when temperature increases or decreases
When a liquid (or gas) is heated (for example by a radiator near the floor):
The molecules move apart, making the liquid/gas expand
This makes the hot liquid/gas less dense than its surroundings
The hot liquid/gas rises, and the cooler (surrounding) liquid/gas moves in to take its place
Eventually, the hot liquid/gas cools, contracts and sinks back down again
The resulting motion is called a convection current
Convection current from a fire
When a liquid (or gas) is cooled (for example by an A.C. unit high up on a wall):
The molecules move closer together, making the liquid/gas contract
This makes the cold liquid/gas more dense than the surroundings
The cold liquid/gas falls and warmer liquid or gas moves into the space created
The warmer liquid or gas gets cooled and also contracts and falls down
The resulting motion is called a convection current
An example of a convection current is when potassium permanganate is added to a beaker of water and heated
The purple potassium permanganate rises and falls, eventually making the entire beaker purple
Heating potassium permanganate
Examiner Tip
If a question on energy transfers mentions liquids or gases, the answer will probably be about convection.
Heat does not rise. The hot gas or liquid that rises due to the change in density when it is heated.
Last updated:
You've read 0 of your 10 free revision notes
Unlock more, it's free!
Did this page help you?