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Cambridge IGCSE Physics · 0625

Chapter 2: Thermal physics — Part 7

Topic 2.3.2 · Convection

Convection in liquids and gases

Convection is an important method of thermal energy transfer in fluids (liquids and gases). It cannot happen in a solid because the particles cannot flow.

When a fluid is heated it expands, becomes less dense, and rises. Cooler, denser fluid sinks to take its place. This circulating flow is a convection current.

Show it with potassium permanganate in heated water, or smoke over a heater / a paper-wheel above a candle.

Convection current in a liquid: heater at the bottom, warm less-dense fluid rising, cooler denser fluid sinking, forming a loop; similar loop in a room with a heater.
Diagram 1: Convection current in a liquid: heater at the bottom, warm less-dense fluid rising, cooler denser fluid sinking, forming a loop; similar loop in a room with a heater.

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