- This form of heat transfer occurs due to differences in temperature causing differences in density
- Commonly occurs in fluids (liquids and gases)
- By Archimedes Principle, if a material is less dense than the fluid it is suspended in (the material’s relative density less than 1), that material will float in the fluid due to the upthrust on the material being greater than its weight
- In convection, one fluid (the hotter portion) floats in another fluid (the cooler portion)
How it works
- When water is heated in a beaker, the water closest to the heat source (the water at the bottom of the beaker) is subjected to an increase in temperature
- This increase in temperature causes its volume to increase (heating causes expansion) and thus its density is lowered
- This heated fluid is thus lighter (less dense) than the rest of the water in the beaker and rises in it
- As it cools, its density increases and thus it will sink in the rest of the water
Convection in gases
- Hot air rises due to convection – the hotter air has a lower density compared to the surrounding air
- A sea breeze is when the wind blows from the ocean or surrounding body of water to the land due to the sun heating the land faster during the day (the land has a lower SHC than the water)
- A land breeze is the breeze which occurs due to the body of water being hotter than the land which is cooler at night
Video demonstration of convection:
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Factors affecting the rate of convection
- Exposed surface area
- Viscosity
- Density
- Conductivity (when conductivity is high, there is no need for convection)
- Acceleration due to gravity