Convection — Explain

How does convection occur in liquids and gases, and how can it be demonstrated experimentally?

When part of a fluid is heated, its particles gain kinetic energy and move further apart, so that region expands and becomes less dense than the surrounding fluid. This warmer, less dense fluid rises, while cooler, denser fluid sinks to take its place, setting up a convection current that transfers heat through the fluid. This can be demonstrated by gently heating water containing a crystal of potassium permanganate from below with a Bunsen flame and observing purple streaks of coloured water rising and circulating; convection in air can be shown using a smoke box with a candle, observing smoke rising above the flame and circulating around the box.