Radiation in thermotherapy refers to movement of radiant energy through air from a warmer to a cooler source.

• A. Movement of radiant energy through air from a warmer to a cooler source
• B. Heat exchange by direct contact between objects
• C. Circulation of heated fluid
• D. Internal heat generation within tissue by electricity

Answer: (A)

Radiation is heat transfer through electromagnetic waves, moving energy from a warmer source to a cooler one without needing to touch. Saying that energy moves through air from a warmer to a cooler source fits this idea exactly, since the heat travels across space or air to reach the cooler tissue, as seen with infrared heat in thermotherapy. In contrast, conduction is heat transfer by direct contact between objects, convection involves heat carried by circulating fluids, and internal heat generation refers to heat produced inside tissue itself (not transferred from another object). So the statement correctly describes radiation.