Describe the mechanism of heat transfer by convection in liquids and gases.
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1. Consider liquid being heated in a vessel from below.
2. The liquid at the bottom of the vessel is heated first and consequently its density decreases i.e., liquid molecules at the bottom are separated farther apart.
3. These hot molecules have high kinetic energy and rise upward to cold region while the molecules from cold region come down to take their place.
4. Thus, each molecule at the bottom gets heated and rises then cool and descends.
5. This action sets up the flow of liquid molecules called convection currents.
6. The convection currents transfer heat to the entire mass of liquid via actual physical movement of the liquid molecules.
7. Similar process takes place in case of a gas.