Which mode of heat transfer requires a material medium?

• A. Conduction
• B. Radiation
• C. Convection
• D. All modes require a medium

Answer: (A)

Conduction is the transfer of heat through direct interactions between particles within a material. It requires a material medium because energy moves by collisions and vibrations from one molecule or atom to its neighbors (and, in metals, by free electrons). If there’s no matter at all, such as in a vacuum, conduction can’t occur.

Radiation, by contrast, travels as electromagnetic waves and can happen across empty space, so it doesn’t require a medium. Convection involves the bulk movement of a fluid, which is also a material medium, but the defining feature here is that conduction relies on those particle interactions within matter to transfer energy.