<P> Infrared radiation in the spectral distribution of a black body is usually considered a form of heat, since it has an equivalent temperature and is associated with an entropy change per unit of thermal energy . However, "heat" is a technical term in physics and thermodynamics and is often confused with thermal energy . Any type of electromagnetic energy can be transformed into thermal energy in interaction with matter . Thus, any electromagnetic radiation can "heat" (in the sense of increase the thermal energy temperature of) a material, when it is absorbed . </P> <P> The inverse or time - reversed process of absorption is thermal radiation . Much of the thermal energy in matter consists of random motion of charged particles, and this energy can be radiated away from the matter . The resulting radiation may subsequently be absorbed by another piece of matter, with the deposited energy heating the material . </P> <P> The electromagnetic radiation in an opaque cavity at thermal equilibrium is effectively a form of thermal energy, having maximum radiation entropy . </P> <P> Bioelectromagnetics is the study of the interactions and effects of EM radiation on living organisms . The effects of electromagnetic radiation upon living cells, including those in humans, depends upon the radiation's power and frequency . For low - frequency radiation (radio waves to visible light) the best - understood effects are those due to radiation power alone, acting through heating when radiation is absorbed . For these thermal effects, frequency is important only as it affects penetration into the organism (for example, microwaves penetrate better than infrared). It is widely accepted that low frequency fields that are too weak to cause significant heating could not possibly have any biological effect . </P>

Which of the following types of radiation would be classified as electromagnetic