Convection is best described as what?

• A. Currents in a fluid caused by uneven heating
• B. Molecular interactions at contact point
• C. Heat transfer through a vacuum
• D. Radiation of energy from a light source

Answer: (A)

Convection is heat transfer through the bulk movement of a fluid driven by buoyancy forces from temperature-induced density differences. When a part of the fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks to take its place, creating circulating currents that move heat with the fluid. This is why warm air circulates in a cabin or why coolant flows through a radiator. The other descriptions refer to conduction (heat transfer by direct molecular contact, typically in solids) and radiation (energy transfer by electromagnetic waves, which can occur without a medium). So the best description is currents in a fluid caused by uneven heating.