Convection is characterized by which statement?

• A. A medium such as air or water moves across the body, creating temperature variations.
• B. Direct contact heat transfer between two solids.
• C. Radiant energy transfer without contact.
• D. Cryotherapy cooling effect on skin.

Answer: (A)

Convection involves heat transfer through a moving fluid. When air or water flows across the body, it carries heat with it, creating temperature changes on the body's surface. This movement can be natural, due to density differences from heating and cooling, or forced, like when a fan or pump drives the fluid. That makes the statement about a moving medium such as air or water across the body the best description of convection.

Conduction, by contrast, is heat transfer through direct contact between solids. Radiation is heat transfer via electromagnetic waves without needing contact. The cryotherapy option describes a cooling effect that is often due to conduction (contact with a cold surface) or could involve convection if air movement is involved, but it does not define convection itself.