The transfer of heat through the particles in a liquid or gas is called?

• A. Conduction
• B. Convection
• C. Radiation
• D. Condensation

Answer: (B)

Convection is the transfer of heat through the movement of fluid particles in liquids and gases. When part of the liquid or gas is heated, its particles move faster and spread apart, making that region less dense so it rises. Cooler, denser portions then sink, creating a circulating pattern that carries heat through the fluid. A common example is heating water in a pot: the hot bottom layer rises while cooler liquid moves down to take its place, forming convection currents that distribute heat. This differs from conduction, which relies on direct contact and vibrations of particles (more important in solids), and from radiation, which transfers heat by infrared waves and can occur without any medium. Condensation is a phase change, not a heat-transfer mechanism through a medium.