The latter will

• A. Penetrate deeper into tissue
• B. Emit radiation ranging from 1500-12,000 mu in wavelength
• C. Emit short wave infrared radiation
• D. Be less satisfactory to treat larger areas of the body

Answer: (C)

Infrared heating devices used in electrotherapy work by emitting energy in the near to short-wave infrared range. This radiation is absorbed mainly by superficial tissue, causing surface heating and a local increase in blood flow without deep penetration. That means the defining feature of these devices is emitting short wave infrared radiation.

Penetrating deeper into tissue would be more typical of other modalities that use different energy forms (like certain diathermy methods), and the wavelength range described in the other option corresponds to wavelengths outside what infrared devices used for superficial heating typically produce. While infrared heating is useful for heating smaller, superficial areas, the core idea here is the emission of short wave infrared radiation.