Convection is the transfer of heat through which medium?

• A. Through a solid medium.
• B. Through liquids or gases.
• C. Through space by infrared rays.
• D. Friction or compression.

Answer: (B)

Convection is heat transfer through the bulk movement of a fluid. Liquids and gases can flow, so when part of the fluid is heated it becomes less dense and rises, while cooler fluid sinks, creating circulating currents that carry heat. That’s why boiling water shows convection and warm air rises in a room. In solids, heat moves mainly by conduction, not by the bulk flow of the material. In space there’s no medium, so heat travels by radiation, not convection. Friction or compression can raise temperature locally, but it doesn’t transfer heat through a fluid by bulk motion, so it isn’t convection.