What term describes heat transfer without an intervening medium?

The term that describes heat transfer without an intervening medium is radiation. Unlike conduction and convection, which require a material medium to transfer heat, radiation enables heat to be transferred through electromagnetic waves. This means that heat can be emitted from a source, such as the sun or a heating element, and travel through the vacuum of space or air without needing any physical substance to carry it.

Radiation is the primary method of heat transfer in spaces where no air or other materials are present, such as in outer space. This form of heat transfer is essential for understanding how heat from the sun warms the Earth or how infrared heaters operate to warm objects in a room directly without needing to heat the air in between.

The other terms relate to different methods of heat transfer, where conduction involves direct contact between materials, and convection requires fluid movement to transfer heat. Evaporation refers to the phase change of liquid to gas and is associated with cooling effects but not the direct transfer of heat in the same manner as radiation. Understanding these distinctions clarifies why radiation uniquely represents heat transfer without an intervening medium.