Which statement correctly contrasts conduction and convection?

• A. Conduction involves direct contact between surfaces.
• B. Convection involves movement of heated particles through a medium.
• C. Conduction involves movement of heated particles through a medium.
• D. Convection involves direct contact between surfaces.

Answer: (A)

Heat transfer by conduction relies on direct contact between surfaces, where energy moves from the hotter to the cooler surface through molecular interactions at the boundary. Convection, by contrast, requires a moving fluid (air or liquid) in which the heated portion circulates and carries energy with the moving particles. The statement that conduction involves direct contact between surfaces captures the essential contrast: conduction transfers heat through contact, while convection transfers heat through the movement of a fluid rather than just contact. In therapy, this helps distinguish modalities like a heat pack or paraffin (conduction) from a system where heated air or circulating water moves around and transfers heat (convection). The other choices either describe convection or misstate what conduction does, so they don’t highlight the contrast as clearly.