Which form of heat transfer requires a medium to occur?

Heat transfer can occur in different ways, and the correct option highlights that both convection and conduction require a medium for the transfer of heat.

Convection involves the movement of fluids – liquids or gases – where warmer regions of a liquid or gas rise while cooler parts sink, creating a circulation pattern that transfers heat. This process is dependent on the presence of a fluid medium, as the actual movement of the molecules carries the thermal energy from one place to another.

Conduction, on the other hand, occurs in solids when heat is transferred through direct contact between molecules. In this case, the vibrating particles of the heated material transfer energy to neighboring particles. Like convection, conduction also requires a medium—in this case, a solid—through which heat can be transferred.

Radiation, however, is distinct in that it does not require any medium to transfer heat. It can occur through the vacuum of space, as it involves the transfer of energy through electromagnetic waves.

Therefore, the correct answer encompasses both convection and conduction, as they indeed depend on a medium to facilitate the transfer of heat.