What term describes heat transferred by the movement of heated liquids or gases?

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

Answer: (A)

Convection is heat transfer through the movement of a heated fluid, whether liquid or gas. When part of the fluid is warmed, it becomes less dense and rises, while cooler fluid flows in to replace it, creating circulating currents that transport heat. This is why hot air and smoke from a fire rise and spread with air currents in a room. Forced convection uses devices like fans to move the fluid and speed up heat transfer.

The other terms describe different mechanisms: conduction is heat transfer through direct contact or stationary matter, radiation is energy transfer by electromagnetic waves from a hot surface, and evaporation is a phase change process where liquid becomes vapor—not the general movement-driven transfer of heat in a fluid.