Convection refers to heat transfer by which process?

• A. Movement of a fluid
• B. Radiation from a surface
• C. Direct contact with a solid
• D. Evaporation

Answer: (A)

Convection is heat transfer via the movement of a fluid. When a gas or liquid flows, it can carry thermal energy with it from warmer regions to cooler ones. In the body, this shows up as blood transporting heat from the core to the skin, or air moving across the skin or lungs to remove heat. This bulk fluid motion is what distinguishes convection from other modes.

Radiation is heat transfer through electromagnetic waves, not requiring a fluid medium. Direct contact with a solid describes conduction, where heat moves through solids (or stationary fluids) by molecular interactions. Evaporation involves latent heat loss as a liquid changes to vapor, not the bulk movement of a fluid.