How is radiation defined in the context of heat transfer?

Radiation in the context of heat transfer refers to the process whereby heat energy is emitted in the form of electromagnetic waves, particularly infrared radiation, and can be absorbed by other surfaces. This mode of heat transfer does not require a medium, meaning it can occur through a vacuum, and is particularly significant in situations involving warm and cool surfaces.

Option B accurately captures this concept, as it describes the transfer of heat from warm surfaces to cooler ones. Surfaces that are warmer radiate heat energy, which can then be absorbed by cooler surfaces nearby, leading to a change in temperature of those surfaces.

The other options encompass different modes of heat transfer. The first describes conduction, which involves heat being transferred through solid materials when there is a temperature gradient. The third option refers to convection, where heat is carried by the movement of air or fluid, commonly in the context of heating or cooling within a given space. The fourth option suggests the process of absorption of heat by cool surfaces, which can occur but lacks the active transfer mechanism highlighted by the correct definition of radiation.