IGCSE - Thermal Physics Revision

Convection

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Thermal energy can circulate around gases and liquids even though they are poor conductors of heat. This is because the particles in these states always carry a small amount of energy in the form of kinetic energy. Convection currents occur when pockets of cool matter sink, as they are less dense, whilst pockets of warm matter rise as they are denser.

Convection is the movement of molecules within fluids. It is one of the major methods of heat transfer. Convection occurs when liquids and gases circulate and carry thermal energy from one place to another.

Convection in a liquid

As the picture below shows, the bottom right of this beaker is being heated. This causes the water in that area to become warmer and less dense and as a result, it rises. At the same time, colder denser water sinks. This starts a circulating current also called a convection current. This convection current transfers energy to other parts of the beaker, this will continue until the thermal is spread evenly throughout the liquid.

Convection in Gases

Convection can also happen in gases. For example, the sun can heat the air making it rise while cooler air sinks. This causes a large convection current in the Earth’s atmosphere. These currents cause wind across all the continents and oceans.

Other examples of Convection

Convection also play significant roles in a larger extent on our planet:

Convection in the Oceans

Convection also affects the oceans as warm water that originates from the Equator normally goes towards the poles, while colder water originating from the poles normally goes towards the equator and gets warmed up.

Convection in the Mantle

Convection currents inside the mantle are thought to be the root of the plate tectonics theory.  Heat from the inner and outer core heat the lower portion of the mantle causing it to rise while the upper portion cools and sinks. This convection is very slow and one cycle can take millions of years to be complete.